New Pyrazolo-Pyrimidines

United States Patent ‘Office- 3 ,098,075 Patented July 16, 1963 1 . 3,098,075 ’ ’ NEW PYRAZOLO-PYRIMIDINES Jean Druey, Riehen, Paul Schmidt, Therwil, and Kurt Eichenberger, Basel, Switzerland, assignors to Ciba Cor- poration, a corporation of Delaware No Drawing. Filed May 26, 1959, Ser. No. 815,825 Claims priority, application Switzerland Feb. 10, 1956 ’ 24 Claims. (Cl. 260-—256.4) This invention relates to new pyrazolo-pyrimidines and a process for their preparation. , More particularly, the invention concerns hydro-pyrazolo(3,4-d)pyrimidines having the nucleus of the formula 4 N5 6 2N \§, \§;/ which contain in at least oneof the positions 4 and 6 an oxo group and are alkylated, oxyalkylated, e.g. oxyeth- ylated or cycloalkylated at at least one ring nitrogen atom, their tautomeric forms and salts thereof. The alkyl radi- cals in the new compounds are preferably of low molecu- lar weight; such groups are e.g. methyl, ethyl, straight- chain or branched propyl, butyl, amyl or hexyl, cyclo- pentyl or cyclohexyl. Methyl and isopropylradicals are particularly advantageous. Apart from the alkyl radicals at at least one ring nitrogen atom and the oxo (hydroxy) group in at least one of the positions 4 and 6, these com- pounds may be further substituted, for example, at one of the nitrogen atoms and/or in 4- or =6-position. The 4- or . 6-position may for instance be occupied by a free or etheri- fied hydroxyl or mercapto group, for example such a group etherified with a lower alkanol, such as methanol, ethanol or propanol, or a free or lower a1ky1ated,,e.g. methyl- ated or ethylated amino group or halogen, such as chlo- _rine, bromine or iodine. A ring nitrogen atom may carry for example, an aminoalkyl radical, such as a_dilower al- kyl-amino-lower alkyl e.g. dimethyl-, diethyl or dipropyl- amino-ethyl or propyl radical, but more especially a lower alkyl group, such as methyl, ethyl or isopropyl. The new compounds have valuable pharmacological properties, especially a caffein-like action, and can be used as medicaments with stimulating and diuretic activity and as intermediate products for the manufacture of medica- ments having such activity. Especially valuable as diure- tics are hydropyrazolo(3,4-d)pyrimidines havingthe nu- cleus of the formula ' 4 N5 3! p, N N/ which contain in at least one of the positions 4.and 6 an oxo group and which are lower alkylated or oxyalkylated or cycloalkylated at at least two ring nitrogen atoms, and _ also their tautomeric forms. . Preferred are the compounds of the formula 0 R’—N/l\ 4 - I Q} Ill. 0 I R/—N °=LN‘ ii.” it 10 15 I. 20: 25 30 35 40 45 50 60 65 70 2 ‘u’ R,—_N/\ L\N/\N ‘R and I . ‘ O R'—N —— 04, fill in which R—R” stand for hydrogen or lower alkyl pro- vided that at least two of the ring nitrogen atoms are lower alkylated. Of outstanding usefulness among these compounds are the 2,5,7-trimethyl-4,6—dioxo-4,5,6,7-tetrahydro-pyrazolo- (3,4.-d)pyrimidine, the 1,5—dimethyl-4-oxo-4,5-dihydro- ‘pyrazo1o(‘3,4-d)-pyrimidine, and above all the l-isopro- pyl-4,-6 - dioxo - 5,7 - dimethyl - 4,5,6,7 - tetrahydro - pyr- azo1o(3,4-d) pyrimidine. The above-mentioned new compounds are obtained by reacting together a 3—aminopyrazolo-4-carboxylic acid ‘ester or amide with -urea, isocyanates, thiourea, guanidine, formamide, or, if an amide is used, also an organic acid _‘anhydride whereby the corresponding new 4-hydroxy- pyrazo1o(3,4—d)pyrimidines are formed, which unless they already have alkyl radicals at at least one ring nitrogen atom, are N -alkylated. If alkyl- or cycloalkylisocyanates are used there may be formed carbamyl-ureas, which can be ring closed to the 5-substituted 4,6-dioxo-4,5,6,7w-tetra- hydro-pyrazolo(3,4-d)pyrimidines by treatment .with al- kaline agents. The 3-aminopyrazole-4-carboxylic acid esters or amides may be N-unsubstituted or substituted, for example, by lower alkyl radicals. In the preparation of the new compounds, therefore, such 3-amino-pyrazole-4-carboxylic acid esters or amides may be used as starting materials that the desired final products are directly obtained. Alternatively, there may first be formed a pyrazolo-pyrimidine lacking the desired substituents and these substituents may be introduced or formed subsequently. Thus, substituents convertible into an oxo group in the 6-position may be so converted, or a 'pyrazolo-pyrimidine formed, which is not alkylated at at least one ring nitrogen atom, may be treated with a reac- tive ester of a lower alkanol, especially of methanol, for example with a lower alkyl halide or di-lower alkyl sul- fate, one or more of the ring nitrogen atoms being alkyl- atedhdepending on the reaction conditions employed. At the same time other alkylatable groups that may be pres- ent, such as.e.g. mercapto or amino group, can also be alkylated. The condensation" of the aminopyrazoles to form the pyrazolo-pyrimidines is advantageously carried out at a temperature above 100° C., if desired, in the presence of a diluent and/or a condensing agent under atmospheric or superatmospheric pressure. Substituents present in the compounds so obtained may be converted in the usual manner into other substituents or may be exchanged for hydrogen atoms provided that the final products still contain an alkyl, oxyalkyl or cyclo- alkyl - group at -at least one ring nitrogen atom and con- tain an oxo group in at least one of the 4- and 6-position. Thus hydroxyl or mercapto groups -may be etherified or esterified, for example alkylated, e.g. methylated, for ex- ample, by treatment with the corresponding lower alkyl halides or sulfates, or may be exchanged for halogen atoms such as chlorine or bromine for example by treat- 3,093,075 3 ment with halides or phosphoric acid. Hydroxyl groups may be exchanged for sulfur atoms for example by treat- ment with phosphorus pentasulfide. Free or etherified mercapto groups can be exchanged for amino or hydroxyl groups for example by reaction with ammonia, primary or secondary amines or hydrolyzing agents, respectively, halogen atoms can be exchanged for hydroxyl groups or etherified hydroxyl or mercapto groups or for amino or hydrazino groups or hydrogen by reaction with hydrolyz- ing agents, alcohols, mercapt-ans, amines, hydrazines or appropriate hydrogenating agents, respectively. It is also possible to introduce additional substituents. Non-alk- ylated ring nitrogen atoms, for example, can be substituted in any -desired manner, above -all by aminoalkyl radicals, such as the dimethylaminoethyl radical, or alkyl radicals. These subsequent reactions may be carried out in any order and combination. A preferred embodiment of the above subsequent re- action consists in exchanging in a 6-hydroxy-5-a1kyl-4- oxo-4,5-dihydro-pyrazolo(3,4-d)pyrimidine the hydroxyl group for a halogen atom in the customary manner. This is performed, for example, by treatment with a phosphoric acid halide, such as phosphorus oxychloride or pentachlo- ride or pentabromide. The thus obtained 5-alkyl-6-halo- gen-4-oxo - 4,5 - dihydro-pyr‘azole(3,4 - d)pyrimidines are new. They may bear substituents of any kind in the pyrazole ring. In particular, they are substituted at one of the two nitrogen atoms of the pyrazole ring by a lower alkyl group, e.g. methyl or isopropyl. The alkyl radical in the 5-position is more especially of a lower character, such as for example a methyl or ethyl group, and the halogen atom in 6-position preferably chlorine or bromine. The new compounds have valuable properties. They have an antibacterial and antimycotic activity. More par- ticularly they have a coronary dilatating elfect. They can therefore be used as medicaments or disinfectants. 8 Especially valuable 6-halogen compounds are 2,5-di- methyl-4-oxo-6-chloro-4,5-dihydro-pyrazolo(3,4-d)pyrimi- dine, 2-isopropyl-4-oxo-5 - methyl-6-chloro-4,5 - dihydro- pyrazolo(3,4-d)pyrirr1idine, 1-isopropyl-4-oxo - 5 - ethyl-6- chloro-4,5-dihydro - pyrazolo(3,4—d)pyrimidine and 1-iso- propyl-4-oxo-5 - methyl-6 - chloro-4,5 - dihydro-pyrazolo- (3,4-d)pyrimidine. Owing to the reactivity of the halogen atom they are also important intermediates for the manufacture of me- dicaments. Thus they can be convertedinto 6-alkoxy com- pounds by exchanging the halogen atom in the customary manner. This is preferably carried out by treatment with an alkanol, advantageously in the presence of a strongly basic condensing agent, more especially one which is ca- pable of forming salts with the alkanol, or with already formed alkanolates, such as alkali alkanolates or alkaline earth alkanolates. As condensing agents there come into consideration more especially alkali metals or alkaline earth meta-ls, their amides, hydrides, alcoholates or hydro- carbon compounds. The reaction is carried out in the usual manner in the presence or absence of a -diluent, preferably at a raised temperature. The 5-alkyl-6 - alkoxy - 4 - oxo - 4,5 — dihydro-pyrazolo (3,4-d)pyrimidines so obtained are new. They can be substituted in any way in the pyrazole ring. In particu- lar, they carry a lower alkyl group, for example methyl or isopropyl, at one of the two nitrogen atoms of the pyrazole ring. The alkyl radical in the 5-position is more especially of a lower character, such as a methyl or ethyl group. The radical in the 6-position is particularly a lower alkoxy group, such as a methoxy group. The new compounds have valuable pharmacological properties. They exhibit a coronary dilatating and di- uretic activity and can be used as medicaments. Especially valuable are 1,5-dimethyl-4-oxo-6-methoxy- 4,5-dihydro-pyrazolo(3,4-d)pyrimidine, 1-isopropy1-4-oxo- 5-methyl.-6-methoxy-4,5 - dihydro-pyrazolo(3,4—d)pyrimi- dine, 1-1sopropyl-4-oxo-5-ethyl-6-methoxy - 4,5 - dihydro. U! 10 15 20 25 30 40 45 50 55 60 70 75 4 pyrazolo(3,4-d)pyrimidine, 2-isopropyl-4-oxo-5-methyl-6- methoxy-pyrazolo(3,4-d)pyrimidine and 2,5-dirnethyl-4- oxo-6—methoxy-4,5-dihydro-pyrazolo ( 3,4—d ) pyrimidine. Depending on the substituents present in the final prod- ucts they can be converted into salts. I-f they contain free hydroxyl, mercapto or carboxyl groups, metal salts, such as alkali metal, alkaline earth metal, or ammonium salts, can be made, for example, by dissolving the prod- ucts in appropriate alkaline solutions. Compounds of basic character, such as those having basic substituents, form therapeutically useful acid addition salts with ap- propriate inorganic or organic acids. As salt-forming acids there may be used, for example, hydrohalic acid, sulfuric acid-, phosphoric acids, nitric acid or perchloric acid; aliphatic, alicyclic, aromatic or heterocyclic carbox- ylic or sulfonic acids, such as formic acid, acetic acid, propionic acid, oxalic acid, succinic acid, glycollic acid, lactic acid, malic acid, tartaric ‘acid, citric acid, ascorbic acid, oxymaleic acid, dihydroxymaleic acid, pyroracemic acid; phenyl-acetic acid, benzoic acid, para-aminobenzoic acid, anthranilic acid, para-hydroxybenzoic acid, salicylic acid or para-aminosalicylic -acid; methane sulfonic acid, ethane sulfonic acid; toluene sulfonic acids, naphthalene sulfonic acids or sulfanilic acid; and methionine, trypto- phane, lysine or arginine. In the process of the invention there are advantageously used starting materials which lead to the formation of the pyrazolo-pyrimidines stated above to be especially valuable. The 3—aminopyrazoles used as starting materials and containing in the 4-position an esterified carboxyl group or the amide group can be obtained, for example, by re- acting a substituted or unsubstituted a-cyano-;3-oxo-pro- pionic acid ester or nitrile or an enol-ether, acetal or mercaptal thereof, with a hydrazine. The latter is un- substituted or mono-substituted, e.g. by an alkyl or cy- cloalkyl radical. As functional derivatives of oc-cyano-B- oxo-propionic acid there are advantageously used enol ethers of oz-cyano-13-ox-o-propionic acid esters or nitriles, for example, ethoxy-methylene-cyanoacetic acid ethyl ester. The condensation to form the pyrazoles proceeds mi-ld conditions, in part at room temperature and exo- tthermically. It is -also possible to work at a higher tem- perature and in the presence of a condensing agent, for example, an .acid, -advantageously the reactants are re- acted together in the presence of a diluent, such as an alcohol, -toluene or chloroform. A nitrile group in the resulting 3-amino-pyrazoles in which the substituent of the hydrazine, if any, is in the 2-position may be hy- drolyzed to the amide group in the usual manner. The preparation of the starting materials is furthermore dis- closed in our copending application Serial No. 637,897, now Patent No. 2,965,643, and No. 637,898, now Pat- ent No. 2,868,803, both filed February 4, 1957. 1-alkyl- 3-amino-pyrazoles of the above kind are obtained in the manner, however using a hydrazine which besides the desired substituent contains at the other nitrogen a sub- stituent capable of being split off by hydrolysis. This substituent is then split off from the open chain inter- mediate forrned whereupon usually under the condition of the hydrolysis, ring closure occurs. The pyrazolo-pyrimidines described above, and their salts, or mixtures of these compounds can be used as dis- infectants, stimulants, or diuretics e.g. in the form of pharmaceutical preparations. These preparations con- tain the aforesaid compounds in admixture with a phar- maceutical organic or inorganic carrier sutiable for en- teral, parenteral or topical administration. As carriers there are used substances that do not react with the afore- said compounds, for example, gelatine, lactose, starches, magnesium stearate, talc, vegetable oil, benzyl alcohols, gums, polyalkylene glycols, cholesterol or another car- rier known for medicaments. The pharmaceutical prepa- rations may be made up, for example, in the form of tablets, dragees or in liquid form as solutions, suspensions or emulsions. If desired, they may be sterilized and/ or may contain auxiliary substances, such as preserving, 3,098,075 5 stabilizing, wetting or emulsifying agents. They may contain other therapeutically valuable substances. The preparations can be made by the usual methods. This is a continuation-in-pant of copending application Ser. No. 775,344, filed November 21, 1958, by Jean Durey and Paul Schmidt, and now abandoned, which is a con- tinuation-in-part of application Ser. No. 718,438, filed March 3, 1958, by Jean Durey and Paul Schmidt, and now abandoned, which itself is a continuation-in-pant of application Ser. No. 637,896, filed February 4,, 1957, by Jean Druey and Paul Schmidt, and now abandoned. The following examples illustrate the invention; the quantities, unless given in grams or cc., -are given in parts by weight. Example 1 50 grams of 3-amino-4-carbethoxy—pyrazole and 100 grams of urea are mixed together well and heated for 40 minutes in a bath at 200° C. The melt is then extracted with 400 cc. of a hot 1 N-s-olufion of caustic soda, the mixture is filtered to remove a small amount of undis- solved material, and the filtrate is rendered acid with glacial acetic acid, and the wh-ite precipitate so formed is filtered off with suction. There is obtained 4,6-dihy- droxy-pyrazolo(3,4-d) pyrimidine in the form of white crystals, which do not melt even -at 300° C. A solution of 15.2 grams of 4,6-dihydroxy-pyrazolo (3,4-d)pyrimidin-e in 200 cc. of a 2 N-solution of caustic soda is slowly mixed, while stirring, with 42 grams of di- methyl sulfate. The whole is then stirred for 20 hours at room temperature, and the solution is extracted with a large quantity of chloroform. The residue obtained by evaporating the chloroform solution is recrystallized from boiling water. There is obtained 2,5,7-trimethyl-4,6- dioxo-4,5,6,7—tetrahydropyrazolo(3,4-d)pyrimidine of the formula 0 ll HaC——N 0% N—CH3 N/\N/ la. in the form of white crystals melting at 195—196° C. The 3-amino-4—carbethoxy-pyrazole used as starting material can be prepared as follows: 8.5 grams of ethoxy-methylene-cyanacetic acid ethyl ester are introduced into 50 cc. of alcohol. The solution is then mixed with 2.5 cc. of hydrazine and the whole is boiled for 6 hours under reflux. The whole is evapo- rated to dryness in vacuo and crystallized from a small amount of water. 3-amino-4-carbethoxy-pyrazole is ob- tained in the form of while crystals melting at 102- 103 ° C. The 2,5,7 — trimethyl-4,6-dioxo-4,5,6,7-tetrahydro-pyra- »zolo(3,4-d)pyrimidine can be used as medicament with caifein-like stimulating activity, e.g. in the form of dragees having the following composition: . Milograms 2,5,7—trimethyl-4,6-dioxo-4,5,6,7-tetrahydro-pyrazolo 3,4-d)pyrimidine ____________________ __'__..__ 100 Lactose ___________________________________ __ 86 Acrosit Compositum _________________________ -_ 30 Wheat starch _______________________________ __ 82 Arrowroot ____________________________ ..i._-__ 35 Magnesium stearate _________________________ __ 2 Talc _____________________________________ _- 15 350 The dragees are prepared in the usual manner. ‘Example 2 A mixture of 25 grams of 3-amino-4-carbethoxy-pyin azole and 50 grams of thiourea is heated for one hours in .a bath at 200° C. The melt is then taken up on 400 cc. of 2 N-solution of caustic soda and acidified with C1 10 15 20 25 30 35 40 45 50 55 60 65 740 75 .10 hours at room temperature. 6 glacial acetic acid, whereupon 4—hydr'oxy-6—mercapto-pyr- az,olo(3,4~d)Pyrimi:d-ine precipitates as white crystals, which do not melt even at 300° C. _ 16.8 grams of 4-hydroxy-6-mercapto-pyrazolo(3,4-d)- pyrimidine are dissolved in 200 cc. of a 2 N-solution of caustic soda, and the solution is slowly mixed, while stirring, with 42 grams of dimethyl sulfate. The whole is stirred for 20 hours at room temperature and then extracted with a large quantity of chloroform. The chloroform solution is evaporated and the -residue consists of a mixture of two compounds, of which one is sparingly soluble in ethyl acetate and is recrystallized from a large quantity of alcohol. 2,5—dirnethyl-6-methylmercapto-4- oxo-4,5—dihydro-pyrazolo(3,4-d)pyrimidine of the formula 0 I H3C—N N—CH3 HaCS— kN/ is obtained as white crystals melting at 203—204° C. Example 3 7.5 grams of 3-amino-4-carbethoxy-pyrazole are mixed with 30 cc. of formamide, and the mixture is then heated for 8 hours in a bath at 190—20~0=° C. The whole in then allowed to cool, whereupon a grey crystalline precipitate is -formed, and the latter is filtered ofi with suction. The precipitate is dissolved in dilute caustic soda solution, the solution is agitated with charcoal and adjusted to a pH value of 3-4 . with 2 N-hydrochloric acid, whereupon a white precipitate is formed, and the latter is crystallized from a large quantity of boiling water. The 4-hydroxy-pyrazolo(3,4-d)pyrimidine is obtained in the form of white crystals which do not melt even at 350° C. 14 grams of 4-hydroxy-pyrazolo(3,4-d)pyrimidine -are introduced into 150 cc. of a 2 N-solution of caustic soda. The solution is slowly mixed, while stirring, with 30 grams of dimethyl sulfate, and the whole is further stirred -for The solution is then extracted several times with a large quantity of chloro- form, -and the combined residues, obtained by evaporating the chloroform solution, are crystallized from a large amount of boiling alcohol. There are obtained two com- pounds, none of which is sparingly soluble in alcohol -and melts at 287-289“ C., and the other of which dis- solves easily in alcohol -and melts at 181-182“ C. The latter compound -is 1,5-dimethyl-4-oxo-4,5-dihydro-pyr- ‘:azole(3,4-d)pyrimidine of the formula . 0 ll IE[aC—N Ki N \N N/ (EH3 and the first 2,5-dimethyl-4-‘oxo-4,5-dihydro-pyrazolo- (3,4-d)pyrimidine of the formula 0 ll CH3-—N/\T“-‘T?’ Q N—CHa \N/ Example 4 15 .2 grams of the 4,6 - dihydroxy - py-razolo(3,4 - d) pyrimidine obtainable as indicated in Example 1 -are dis- solved in 110 cc. of 2 N-caustic soda solution. In the course of 4 hours, 25 grams of dimethylsulfate are added dropwise to the resulting solution and stirring is continued at room temperature -for 6 hours. The alkaline solution is then extracted with a large quantity of chloroform, the trimethyl derivative formed as by-product passing into the chloroform phase. The aqueous solution is given ao9ao75 ? a pH of 4, whereupon a white crystalline precipitate is formed which is distilled in caustic soda solution and then precipitated with glacial acetic acid. The resulting precipitate is crystallized seve-ral times from boiling water to obtain 4,6-dioxo-5,7-dimethyl-4,5,6,7-tetral1ydro—pyr— azolo(3,4-d)pyrimidine of the formula l x”\ H3C———N O_ N N/\N/ I H OH: in the form of white crystals of melting point 280° C. Example 5 15 grams of 4,6-dihydroxy-pyrazolo(3,4-d)pyrimidine and 50 grams of pulverized phosphorus pentasulfide are introduced into 800 cc. of pyridine and the mixture is heated for 6 hours in a bath have a temperature of 130° C. The pyridine is expelled under reduced pressure, the resinous residue mixture with 600 cc. of ice-water, the whole allowed to stand at room temperature for half an hour, and then heated on the water bath for 2 hours. After cooling, the precipitate is filtered off with suction. It is dissolved while hot in dilute caustic soda solution, treated with animal «charcoal, precipitated «by means of 2 N-acetic acid, filtered with suction, and washed with water and alcohol. In this manner there is obtained 4-mercapto- 6-hydroxy-pyrazolo(3,4-d) pyrimidine in the «form of crys- tals which do not melt even at 300° C. A solution of 12.6 grams of 4-mercapto-6-hydroxy- pyrazolo(3,4—d) pyrimidine in 150 cc. of 2 N-caustic soda solution is mixed in the course of 2 hours with 31.5 grams of dimethyl sulfate. Stirring of the mixture is continued for 6 hours at room temperature and the alkaline solution is then extracted from a large quantity of chloroform. The residue is recrystallized from a small quantity of alcohol to obtain 2,7-dimethyl-4-methyl- rnercapto-6-oxo-6,7-dihydropyrazolo(3,4-d) pyrimidine of the formula OH; in the form of yellowish crystals of melting point 216- 218“ C. Example 6 A ‘solution of 10 ‘grams of the 2,7-dime-thyl-4-methyh mercapto-6-oxo-6,7-dihydro-pyrazolo(3,4-d) pyrimidine in 80 cc. of concentrated hydrochloric acid is boiled for 3 hours. It is then allowed to cool and filtered with suc- tion to separate the white precipitate. The latter is then recrystallized from -dilute alcohol. There is obtained 2,7- dimethyl-4,6-dioxo-4,5,6,7 - tetrahydro-pyrazolo(3,4-d) py- rimidine of the formula 0 I HN 04 I ‘-0... N/\\N/ (IJH; in the form of white crystals melting at 325—‘327° C. Example 7 10 grams of the 2,7-dimethyl-4-methylmercapto-6-oxo- 6,7-dihydno-pyrazo1~o(3,4-d)pyrirnidine obtainable accord- ing to Example 5 and 100 cc. of liquid ammonia are heated at 100° C. for 6 hours in a sealed tube. The grey Cl 10 20 30 40 60 75 8 crystals obtained after evaporation of the ammonia are recrystallized from alcohol and 2,7—.dimethyl-4-amino-6- oxo-6,7-dihydro-pyrazolo(3,4-d) pyrimidine of the formula CH3 obtained in the form of white crystals which do not melt even -at 320° C. When this substance is treated with alcoholic hydro- chloric acid there is obtained its -monochloro hydrate which melts at 312° C. with decomposition. In similar manner other salts, such as the sulfate, perchlorate, nitrate or methane sulfonate can be obtained. Example‘ 8 A solution of 8 grams of the 2,5-dimethyl-6-methyl- mercapto-4-oxo-4,5 - dihydro-pyrazolo(3,4-d)pyrimidine obtained according t-o Example 2 in 70 cc. of concentrated hydrochloric acid is heated to the boil for '3 hours. After cooling, the resulting white precipitate is separated by filtering with suction. It is crystallized from dilute alcohol and there is obtained 2,5-dimethyl-4,6-dioxo-4,5,6,7-tetra- hydro-pyrazolo(3,4-d) pyrimidine of the formula in the form of white crystals which do not melt even at 330° C. Example 9 In a sealed tu-be, 8 grams of the 2,5-dimethyl-6-methyl- mercapto-4-oxo-4,5 - dihydro-py'razolo'(3,4-d)pyrimidine obtainable according to Example 2 and 80 cc. of liquid ammonia -are heated to 20 hours at 100° C. The am- monia is expelled and the residue crystallized from a large quantity of alcohol. There is obtained the 2,5-di- methyl - 6 - amino-4-oxo-4,5-dihydropyrazolo(3,4-d)py- rimidine of the formula 0 ll H3C-—N _ N—CH3 H2N \N/LN/ in the form of white crystals which do not melt even at 320° C. When this substance is treated with alcoholic hydro- chloric -acid there is obtained its monohydrochloride which melts at 298° C. with decomposition. Example 10 9 grams of the 4,6-dioxo-5,7-dimethyl-4,5,6,7«tetrahy- dro-pyrazolo(3,4-d)pyrimidine described in Example 4 ‘are introduced into a solution of 1.3 grams of sodium in 200 cc. of ‘alcohol, and the suspension stirred for 1 hour at room temperature. 6 ‘grams of chlorethyldimethyl- amine are then admixed and the whole ‘boiled for 10 hours while stirring. The reaction mixture is then evaporated in vacuo. The residue is mixed with 100 cc. of 1 N- caustic soda solution and extracted with chloroform. By recrystallization of the residue from petroleum ether there is obtained the 2-(,8-di-methylaminoethyl)-4,6-dioxo-5,7- dimethyl-4,5,6,7-tetrahydro-pyrazolo(3,4-d)pyrimidine in the form of white crystals of melting point 126—127° C. Example I] 10 grams of 2-isopropyl-3-amino-4-carbamyl-pyrazole and 20 grams of urea are mixed thoroughly and heated 3,093,075 9 for 1 hour in a bath having a nternperature of 200° C. The hot melt is then introduced into 15 0 cc. of 1 N-caustic soda solution, treated with animal icharcoal, and filtered with suction. The filtrate is given a pH of 3 with hydro- chloric acid, whereupon white crystals precipitate. By re- crystallization of the precipitate from water there is ob- tained 1-isopnopyl-4,6-dihydroxy~pyrazolo( 3,4-d) pyrimi- dine of the formula on I N/\N/ (En 0&3 \OH3 in the form of white crystals of melting point 286-287“ C. (with decomposition). The 2-iso-propyl-3-amino-4-carbamylpyrazole used as starting material can be prepared as follows: A solution of 48:8 parts of ethoxymethylene-maloni- trile in 500 parts by volume of alcohol is mixed with 30 grams of isopropyl hydrazine. The mixture is then heated to the boil for 10 hours, evaporated to dryness under reduced pressure, and the residue crystallized from a large quantity of isopropyl ether. 2—isop=ropyl-3-amino- ’4-cyano-pyrazole is obtained -in this manner in the form of white crystals of melting point 94-95“ C. 10 grams of the compound thus obtained are mixed -with 200 cc. of 2 N-caustic soda solution and 100 cc. of alcohol, and the solution boiled for :3 hours. The alcohol is evapo- rated under reduced pressure, the reaction mass allowed to cool, and the precipitate separated by filtering with suction. The precipitate is recrystallized from alcohol. There is obtained 2-isopropyl-3-amino-4-carbamyl-pyn azole in the form of white crystals of melting point 215- 216° C. Example 12 A solution of 10 ‘grams of the 1-isopropyl-4,6-dihy- droxy-pyrazolo(3,4-d)pyrimidine described in Example 11 in 75 cc. of 2 N-caustic soda solution is mixed slowly, .while being stirred, with 14 grams of dimethyl sulfate. The reaction mass is allowed to stand overnight and ex- ‘ tracted with chloroform in the morning. The chloro- form residue is recrystallized from alcohol to obtain 1- isopropyl - 4,6 - dioxo - 5,7 - dimethyl - 4,5,6,7 - tetra- hydro-pyrazolo(3,4-d)pyrimidine of the formula 0 I H30-N 1. ll- 0.. 31113 bH(0H3)z in the form of white crystals melting at 141-142° C. Example 13 19.7 grams of 2-isopropyl-4-carbethoxy-3-amino-pyraz- ole are heated -with 50 cc. of formamide for 4 hours in a bath of 2»00‘—21()° C. After cooling, the reaction mix- ture is taken up in 2 N—caustic soda solution, treated with ‘animal charcoal, and precipitated by adjusting the pH to 3 with 2 N-hydrochloric acid. l-isopropyl-4-hydroxy- pyrazolo(3,4-d)pyrin1idi-ne of a formula (|)H in \ Cfia CH3 10 15 20 25 30 35 40 50 60 65 70 #5 "C. 10 is obtained in the form of crystals of melting point 197- 198” C. The 2-isopropyl-4-carbethoxy-3-amino-pyrazole used as starting material can be prepared as follows: 8.2 grams of isopropyl hydrazine are introduced into a solution of 16.9 grams of ethoxymethylenecyano-acetic acid ethyl ester in 100 cc. of alcohol and boiled for 12 hours. The reaction mass is then evaporated to dryness and the residue distilled in vacuo. 2-isopropyl-3-amino- 4-carebethoxy-pyrazole passes over at 164—166° C. un- der a pressure of 10 mm. and solidifies in crystalline form in the receiver. The colorless crystals obtained melt at 46—48° C. Example 14 9 grams of 5,7-dimethyl-4,5,6,7-tetrahydro-4,6-dioxo- pyrazolo(3,4-d)pyrimidine are introduced into a solution of 1.2 grams of sodium in 200 cc. of anhydrous ethyl alcohol. The reaction mixture is stirred for 1 hour at room temperature. 7 grams of chlorethyldiethylamine are then added and the whole heated to the boil for 10 hours while stirring. After cooling, the precipitated salt is removed by filtering with suction and the filtrate evapo- rated to dryness. The residue, is mixed with 20 cc. of 3 N-caustic soda solution and extracted -with a large quantity of chloroform. -By distilling olf the chloroform and recrystal-lizing the residue from isopropyl ether there is obtained the 2-(13-diethylaminoethyl)-S,7-dimethyl-4,6- dioxo—4,5,6,7 - tetrahydro-pyrazolo(3,4 - d) pyrimidine of melting point v85—87° C. Example 15 9 grams of 1-isopropyl—4-hydroxy-pyrazolo(3,4-d) py- rimidine are dissolved in 40 cc. of 2 N—caustic soda solu- tion and mixed slowly, while being agitated, with 8 grams of dimethyl sulfate. A white product precipitates and is separated by filtration with suction. By recrystalliza- tion from water there is obtained 1-isopropyl-5—m'ethyl- 4-oxo - 4,5 - dihydroxypyrazolo(3,4 - d) pyrimidine in the form of white crystals melting at 162—163° C. Example 16 10 grams of 2-methyl-3-amino-4-carbamyl-pyrazole and 20 grams of urea are thoroughly mixed and heated for 3 hours in a bath of 200° C. The hot melt is then poured into 150 cc. of 1 N-caustic soda solution, treated with animal charcoal, and filtered with suction. The filtrate is given a pH of 3 with hydrochloric acid whereupon white crystals separate. By recrystallization of the pre- cipitate from a large amount of Water, the 1-methyl-4,6- dihydroxy-ptyrazolo(3,4-d)pyrimidine is obtained in the form of white crystals which do not melt when heated to 300° C. 7.5 grams of dimethyl sulfate are added dropwise to a solution of 4.2 grams of 1-methyl-4,6-dihydroxy-pyra- zolo(3,4-d) pyrimidine in 30 cc. of 3 N—caustic soda solu- tion, and stirring continued for 10 hours. The pH is then adjusted to 9 with 2 N-caustic soda solution, which oper-a- tion is followed by extraction with chloroform. The chlo- reform residue is recrystallized from much alcohol. 1,5, 7 - trimethyl-4,6-dioxo-4,5,6,7-tetrahydropyrazolo(3,4-d)- pyrimidine is thus obtained in the form of white crystals of melting point 230—231° C. The 2-methyl-3-a-mino-4-carbamyl-pyrazole used as starting material can be obtained as follows: A solution of 40 gvams of ethoxymethylene-malonitrile -in 400 cc. of ethanol is mixed with 27 grams of methyl hydrazine. The mixture -is -boiled for 10 hours, allowed to cool, and the precipitated product separated by filtra- tion. 2—methyl-3-amino-4-cyano-pyrazole is thus obtained in the form _of white crystals of melting point 2l9—220° 10 grams of this compound are mixed with 200 cc. of 2 N-caustic soda solution and 100 cc. of ethanol, and the solution boiled for 3 hours. The ethanol is evaporated under reduced pressure, the reaction mass allowed to cool, 3,098,075 11 and the precipitate separated by filtration with suction. The product is recrystallized from ethanol. There is thus obtained 2-methyl-3-amino-4-carbamyl—pyrazole in the form of white crystals of melting point 232-234“ C. Example 17 A mixture of 17.5 parts of 3-amino-4—pyrazole-carbox- amide (obtainable by -condensation of ethoxymethylene- malonitrile with hydrazine and hydrolysis of the 3-amino- 4—cyano-pyrazole with concentrated sulfuric acid) and 35 parts of urea is heated at 160-180“ C. for 90 minutes and then cooled. The solid fusion product is washed with water. 13 parts of the unpurified 4,6—dihydroxy-pyra- zolo(3,4-d)pyrirnidine thus obtained are dissolved -in 50 parts of 10% aqueous sodium hydroxide solution and 100 parts of water by heating. The solution is then brought to about 40° C. and treated with 90 parts of 95% ethanol and 28.6 parts of bromoethane «and the mixture is refluxed for one day. Then, at 2 hour intervals, 5 portions each of 17 parts of bromoethane and 22 parts of 10% sodium hydroxide are added. The reaction mixture is taken al- most to dryness and the resulting residue is exhaustively extracted with chloroform. The chloroform extract is dried over anhydrous sodium sulfate, stirred with activated carbon, filtered and taken to dryness under vacuum. The residue is taken up in a solution containing 7 parts of benzene to 3 parts of petroleum ether and applied to a chromatography column containing 500 parts of alumina. Elution of the column with benzene yields first in impurity and later the 2,5,7-triethyl-4,6-dioxo-4,5,~6,7-tetrahydro- pyrazolo(3,4-d)pyrimidine. ecrystallized from dilute ethanol the compound melts at about 118—120° C. The chromatography column described above is further de- veloped with benzene solutions containing increasing con- centrations of ethyl acetate. Elution with a 50% solu- tion of ethyl acetate in benzene yields 5,7-diethyl-4,6-di- oxo - 4,5,6,7-tetrahydropyrazolo(3,4-d)pyrimidine which, crystallized from water, melts at about 205-207“ C. The amount of this fraction can be increased by decreasing the amount of bromoethane in the alkylation procedure. «Example 18 A solution of 2.3 grams of sodium in 40 cc. of abso- lute ethanol is added to a solution of 15.05 grams of cyclo- hexylhydrazine hydrochloride in 50 cc. of absolute etha- nol. 16.9 grams of ethoxy-methylene-cyanoacetic acid ethyl ester, dissolved in 20 cc. of ethanol are added to the reaction solution, and the whole is heated for 10 hours at the boil. After cooling the mixture, the precipitated sodium chloride is filtered off with suction, and the fil- trate is evaporated to dryness. The crystalline residue is triturated with water and filtered with suction. There is obtained 2-cyclohexyl-3-amino-4-carbethoxy—pyrazole melting at 112-114" C. After being recrystallized from petroleum ether the melting point of the product rises to 115-116° C. 20 grams of 2-cyclohexyl-3-amino-4-carbethoxypyrazole are heated with 50 grams of formamide for 6 hours in a bath having a temperature of 200—2l0° C. After cooling the mixture, 1-cyclohexyl-4-hydroxy-pyrazolo(3,4-d)-py- rimidine crystallizes out. It melts lat 245—246° C. Example 19 16.9 grams of ethoxy-methylene-cyanoacetic acid ethyl ester and 8.8 grams of secondary-butyl-hydrazine are heated in 100 cc. of absolute ethanol for 10 hours at the boil. The mixture is then evaporated in vacuo, and the residue is distilled in vacuo. 2-(secondary-butyl)-3-ami- no-4-carbethoxy-pyrazole boils under 0.09 mm. pressure at 105-107“ C. 10.5 grams of 2-(secondary-butyl)-3-amino-4-carbeth- oxy-pyrazole -are heated with 25 cc. of formamide for 6 hours at 200—210° C. The reaction solution is cooled to 0° C. and there is obtained crystalline 1-(secondary- CI 10 20 30 40 45 50 55 60 65 70 75 12 butyl)-4-hydroxy-pyrazolo(3,4-d)pyrimidine of the for- mula OH I C / Ha /I-‘-‘l C C2H5 melting at 174—175° C. Example 20 86 -grams of unethyl-isopropyl ketone are added to a solution of 50 grams of hydrazine hydrate in 500 cc. of 2 N-hydrochloric acid with stirring and ice-cooling. Hydro- genation is then carried out at room temperature and 19 atmosphere gauge pressure with 2 grams of platinum oxide -as catalyst. Within an hour 22.4 liters of hydrogen are taken up, which corresponds to one mol of H2. The catalyst is filtered oif with suction, the reaction mixture is evaporated to dryness under reduced pressure and 500 cc. of concentrated sodium hydroxide solution are added to the -residue, 3-hydrazino-2-.methy1-butane separating in the -form of oil. For the purpose of purification the oil separated in the separating funnel is distilled. 3-hy- drazino-2-methyl-butane passes over at 39—44° C. under 11 of pressure. 21 grams of 3-hydrazino-Znmethyl-butane are added to a solution of 24.4 -grams of ethoxy-methylene-malonic wacid-dinitrile in 250 cc. of ethanol. The reaction mix- ture is heated under reflux for 12 hours, allowed to cool and the precipitate filtered with suction. After recrystal- lization from ethanol there is obtained 2-[3’—methyl-butyl- (2) ]-3-amino-4-cyano-pyrazole in the form of white crys- tals melting at 167—168° C. 200 cc. of 2 N-sodium hydroxide solution and 100 cc. ‘of alcohol are added to 18 grams of 2-[3’—methyl-butyl- (2’)]-3-amino-4-cyano-pyrazole and the solution heated at the boil for 3 hours. The alcohol is evaporated under reduced pressure, -the reaction mixture allowed to cool and the precipitate suction-filtered. The latter is -recrystallized from alcohol and there is obtained 2-[3’—methyl-butyl- (2’)]-3-amino-4-carbamyl-pyrazole in the form of white crystals melting at 227-—228° C. 10 grams of 2-[3’-methyl-butyl-(2')]-3-amino-4-car- bavmyl-pyrazole are heated with 30 grams of formamide for 5 hours in a bath at 200—210° C. After cooling, 1- [3' - methyl-butyl-(2') ]4-hydroxy-pyrazolo(3,4-d)pyrimi- dine of the formula (')H N l. k\N‘N/ I CH3——C—CII(CI~I;)2 11 crystallizes; the product melts at 190—192° C. Example 2] 344 grams of diethyl ketone are added to a solution of 200 grams of hydrazine hydrate in 528 cc. of 7.57 N- hydrochloric acid with stirring and ice-cooling. After adding 270 cc. of ethanol the whole is stirred for 30 minutes. Hydrogenation is carried out at room tempera- ture and under 130 atmospheres gauge pressure with 2 grams of platinum oxide as catalyst. Within 15 minutes the quantity of hydrogen calculated for 4 mols, 89.6 liters, is taken up. The catalyst is suction-filtered, the filtrate is adjusted to pH 4 with 2 N-hydrochloric acid and the solu- tion is concentrated under reduced pressure until crystal- lization sets -in. 500 cc. of concentrated sodium hydroxide solution are added with ice-cooling. Solid sodium hy- 3,098,075 13 droxide is added until isopentylhydrazine separates as an oil. The oil is decanted oif, dried over sodium hydroxide and distilled. Pentyl-3-hydrazine passes over between 102 and 109°C. 84.5 grams of ethoxymethylene cyanacetic acid ethyl ester and 51 grams of pentyl-3-hydrazine are heated to the boil in 500 cc. of absolute alcohol for 10 hours. The whole is evaporated under -reduced pressure and the . residue distilled in vacuo. 2-pentyl-(3’)-3-amino-4-can bethoxy—pyrazole boils at 175° C. under 11 mm. of pres- su-re. 22.5 grams of 2-pentyl-(3')-3-amino-4~carbethoxy-pyra- zole are heated in 50 cc. of formamide at 200—210° C. for 10 hours. After cooling, the reaction product is ex- tracted with methylene chloride. The methylene chloride solution is washed twice with water and then evaporated. The resulting residue is dissolved in 2 N-sodium hydroxide solution. By acidifying with 2 N-hydrochloric acid there is obtained l-pentyl-(3')-4-hydroxy-pyrazolo(3,4-d)py- rimidine of the formula (1)11 N K. N 1lq/ CH / \ 0 2H5 0 2H5 melting at 140‘—l41° C. On recrystallization from a mix- ture of ether and petroleum ether the melting point is raised to 142—143° C. Example 22 336 grams of cyclopentanone are added to a solution of 200 grams of -hydrazine hydrate in 572 cc. of 7 N-hydro- chloric acid with stirring and ice-cooling. Hydrogenation is carried out at room temperature under 100 atmospheres gauge pressure with 2 grams of platinum oxide as cata- lyst. Within an hour -the quantity of hydrogen calculated for 4 mols. 89.6 liters, is taken up. The catalyst is filtered oil with suction, the filtrate is adjusted to pH 4 with 2 N- hydrochloric -acid and the solution evaporated in vacuo until crystallization sets in. 500 »cc. of concentrated so- dium hydroxide .sol-ution are then added with ice-cooling. Solid sodium hydroxide are then added until cyclopentyl hydrazine separates as an oil. The latter distils at 60- 65” C. under 11 mm. of pressure. 67.6 grams of ethoxymethylene cyanacetic acid ethyl ester and 40 grams of cyclopentyl hydrazine are boiled under reflux in 400 cc. of absolute alcohol for 10 hours. The solution is evaporated in vacuo and the residue dis- tilled in high vacuum. 2-cyclopentyl-3-amino-4-carbeth- oxy-pyrazole boils at 152° C. under 0.15 mm. of pressure. The melting point of the compound is 64—66° C. 22.3 grams of 2-cyclopentyl-3-amino-4-carbethoxy-pyra- zole are heated in 50 cc. of formamide at 200‘-210° C. for 10 hours. After cooling, the precipitated crystals are suc- tion-filtered, dissolved in 1 N-sodium hydroxide solution, filtered and the filtrate acidified with 2 N-hydrochloric acid to pH 4, whereby 1-cyclopenty1-4-hydroxy-pyrazolo (3,4-d)pyrimidine melting at 225-226“ C. separates. Example 23 392 grams of cyclohexanone are added to a solution of 200 grams of hydrazine hydrate in 572 cc. of 7 N-hy- . drochloric acid with stirring and ice-cooling. Hydrogena- tion is then carried out at room temperature and under 100 .atmospheres gauge pressure with 2 grams of platinum oxide as catalyst. Within 30 minutes the quantity of hy- drogen calculated for 4 mols, 8-9.6 liters, is taken up. 1000 cc. of ethyl alcohol are added in order to dissolve the precipitated crystals. The catalyst is then filtered oif 10 15 20 25 30 35 40 45 50 455 60 65 170 75 14 with suction, the filtrate is adjusted to pH 4 and evap- orated in vacuo until crystallization sets in. After cool- ing, the precipitated crystals are filtered and the filtrate mixed with 500 cc. of concentrated sodium hydroxide solu- tion with ice-cooling. Solid «sodium hydroxide is then added until cyclohexylhydrazines separates as an oil. The latter distils at 77—80° under 12 mm. of pressure. The resulting distillate is reacted immediately with alcoholic hydro-chloric acid into the hydrochloride; melting point 112—113‘’ C. ' 150.5 grams of cyclohexyl-hydrazine hydrochloride are dissolved in 500 cc. of ethyl alcohol and a solution of 23 grams of sodium in 400 cc. of ethyl alcohol is added with stirring to a solution of 122 grams of ethoxymethylene malonic acid dinitrile, the temperature rising to about 45° C. The mixture is then heated -at the boil for 10 hours, allowed to cool -and the precipitated sodium chloride fil- tered off. The filtrate is evaporated to dryness in vacuo. The residue is dissolved in 200 cc. of ethyl alcohol, filtered and the solution poured into 1400 cc. "of water with stir- ring, 2-cyclohexyl-3-amino-4-cyanopyrazole which melts -at 124—126° C., precipitating in the form of crystals. 5 7 ‘grams of 2-cyclohexyl-3-amino—4—cyano-pyrazole are boiled under reflux -for 21/2 hours in 230 cc. of absolute alcohol and 230 cc. of 2 N-sodium hydroxide solution. After cooling, the crystals are suction-filtered. There is obtained 2-cyclo-hexyl-3-amino-pyr-azole-4-carboxylic acid amide melting at 267-268° C. 30 grams ‘of 2-cyclohexyl-3-amino-pyrazole-4-carbox- ylic acid amide are heated at 200° C. for 11/2 hours with 60 grams of urea. After cooling, 1 N-sodium hydroxide is added to the reaction product, a small quantity of un- dissolved matter is filtered off, and the filtrate acidified with 5 N-hydrochloric acid, whereupon a precipitate sep- arates. The latter is taken up in dimethyl-formamide, filtered and allowed to crystalline out. There is obtained 1 - cyclohexyl-4:6-dihydroxy-pyrazolo(3,4-d)pyrimidine melting at 330° C. with decomposition. Example 24 75 grams of 2-secondary buty-l-3-amino-4-cyano-pyra- zole are boiled under reflux for 21/2 hours in 750 cc. of absolute -alcohol and 1500 of 2 N-sodium hydroxide solu- tion. The solution is then concentrated to a volume of about 1000 cc. in vacuo at a temperature of 50° C. and then cooled to 0° C. The separated crystals are filtered off. There is obtained 2-secondary butyl-3-a.-mino-pyra- zole-4-carboxylic acid amide melting at 19‘8—l99° C. 60 grams of 2-secondary butyl-3-amino-pyrazole-4- car- hoxylic -acid amide are heated at 200° C. for 11/2 hours with 120 grams of urea. After cooling, 2.5 N-sodium v hydrox-ide solution is added to the react-ion product, any undissolved material is filtered off and the filtrate acidified to a pH value of 3 with hydrochloric acid of 27% strength, whereupon crystals separate. The latter are dissolved in alcohol, the solution is filtered, the filtrate evaporated and water added, whereupon crystallization sets in. There is obtained 1-secondary butyl-4:6-dihy- droxy-pyrazolo(3,4-d)pyrimidine melting at 225-227” C. Example 25 A solution of 11.6 grams of N1-isopropyl-N2-acetyh hydrazine and 17 grams of ethoxymethylene-cyanacetic acid ester, in 250 cc. of ethanol is boiled for 12 hours under reflux. The ethanol is then evaporated in vacuo, 150 cc. of 8 N-alcoholic hydrochloric acid are added to the oily residue containing [3-(N2-acety1-N1-isopropyl-hy- drazino)-on-cyano»acry1.ic acid ethyl ester, and the whole is boiled under reflux for 2 hours. The mixture is again evaporated in vacuo, the residue is taken up in 2 N- aqueous hydro—chloric acid, the solution is filtered to re- ’ move undissolved material, and its pH value is adjusted to 8 to 9 with caustic soda solution. The mixture is then ex- tracted with chloroform and the residue obtained by evap- orating chloroform is recrystallized from cyclohexane. 3,098,075 1 5 There is obtained 1-isopropyl-3-amino-4-carbethoxy-pyra- zole of the formula CzH5O O C-1 CH3 / H2N_\ N—CH \N/ \CH3 in the form of white crystals melting at 72—73° C. 19.7 grams of 1-isopropyl-3-amino-4-carbethoxy-pyra- zole and 30 grams of urea are thoroughly mixed together and heated for 2 hours in a bath at 200° C. The hot melt is then introduced into 150 cc. of 1 N-solution of caustic soda, and the mixture is treated with animal charcoal and filtered with suction. The filtrate is -given a pH value of 1-2 with hydrochloric acid, whereupon a white product precipitates. The latter is crystallized vfrorn a large quan- tity of water, and there is obtained 2-isopropyl-4:6-dihy- droxy-pyrazolo(3,4-d)pyrimidine melting at 280—282‘’ C. 2.8 grams of dimethyl sulfate are slowly added while stirring, to a solution of 1.9 grams of 2-isopropyl-4:6-di- hydroxypyrazolo(3,4-d)pyrimidir1e in 15 cc. of a 2 N- solution -of caustic soda. The whole is allo-wed to stand overnight and the precipitate that is formed is filtered off with suction. The latter is recrystallized from a large quantity of petroleum ether, and in this manner there is obtained 2-isopropyl-4,6-dioxo-5,7-dimethyl-4,5,6,7-tetra- hydro—pyrazolo(3,4-.d)pyrimidine of the formula 0 ll CH3—-N ~* /0113 0% \ N—CH 1,‘7/ N/ \OH3 CH3 in the -form of white crystals melting, at 182—l84° C. Example 26 3 grams of 1-ethyl-3-amino-4-carbethoxy-pyrazole, dis- solved in 25 cc. of benzene are heated with 5.17 cc. of ethyl isocyanate and 0.5 cc. of triethylamine in a closed tube for 10 hours at 100° C. By evaporating the reaction solution, there is obtained crude crystalline N-[1-ethyl-4- carbethoxypyrazolyl - ( 3)] - N’ - ethyl - N’ - ethyl - car- bamyl-urea of the formula C 2H5— O 0 (Pi CzH5HN—O C-N— o C—HN—L\ /N—C2H5 N $.11, The crude product, which melts at 83—84° C. after re- ' crystallization from a mixture of ether and petroleum ether may be used as such for carrying out the follow- ing ring closure: 1 gram of the crude N-[1-ethyl-4-carbethoxy-pyrazolyl- (3)]-N’-ethyl-N’—ethylcarbamyl-urea is boiled under re- flux in 10 cc. of a 2 N-solution of caustic soda for 7 minutes under reflux. After being cooled the aqueous solution is extracted with ether and adjusted to a pH value of 5 with 2 N-acetic acid, whereby 2:5-diethyl-4:6- dioxo - 4,5,6,7 — tetrahydro-pyrazolo-(3,4-d)pyrimidine of the formula 0 ll CgH5——N 0% N—C2H5 \N/\N/ I-I precipitates ‘out, melting at 257—258° C. Example 27 10.9 grams of ‘1-isopropyl-3-amino-4‘-carbethoxy-pyraz- ole are heated in 85 cc. of benzene with 12.6 grams of methyl isocyanate and :1.66 cc. of triethylarnine at 100° C. for 10 hours in a closed tube. The reaction solution Cl 10 15 30 ‘40 14> C1 C7! CI 60 65 70 16 is evaporated to yield an oily residue, which consists sub- stantially of N-[1-isopropyl-4-carbethoxy-pyrazolyl(3)]- N’-methyl—N’-methylcarbamyl urea of the formula C2H5O OC—i' CH3 / /N413 N 0 113 CH3—-IIN—0 C—lTI—0 C-—I'IN—\ CH3 6.1 grams of this crude product are mixed with 60 cc. of a 2 N-solution of caustic soda and the whole is boiled under reflux for 12 minutes. The aqueous reaction solu- tion is extracted with ether, and the aqueous solution is acidified with 2 ~N-acetic acid to a pH value of 4.5, where- upon 2-isopropyl-4,6-dioxo-5-methyl - 4,5,6,7 - tetrahydro- pyrazolo(3,4-d)pyrin1idine of the formula 0 ll /\ om—N *7‘ cm / 0% /L )I—CI\I 11} N om melting at 232—233° C. precipitates. The 1-alkyvl-pyrazoles used in the above example and in Example 26 can be obtained as follows: 8 grams of N1-isopropyl-N2-benzylidene-hydrazine and 8 grams of ethoxy-methylene-cyanacetic acid ethyl ester are heated in 50 cc. of benzene for 10 hours at 80° C. After the solvent has been removed in vaeuo, the residue is recrystallized from ethanol. There is obtained ,8-(NT rbenzylidene-N1-is opropyl-hydrazino ) -at-cyano-acrylic ‘acid ethyl ester in the form of yellow prisms melting at 118- l20° C. 4 grams of [3-(N2-benzylidene-N1—isopropyl-hydrazino)- oz-cyano-acrylic acid ethyl ester are boiled for 2 hours with 10 N-alcoholic hydrochloric acid; the alcohol is then re- moved by distillation in vacuo. The residue is taken up in 200 cc. of 2 N-hydrochloric «acid and the solution ex- tracted with ether. After separating the aqueous solution, the latter is rendered alkaline by adding 2 N-sodium hy- droxide solution. The separated base is extracted with ether. After drying and evaporating the ether, 1-iso- propyl-3—arnino-4-carbethoxy-pyrazole of the formula CzH5O O C- H2N—L \N/ CH; / N—CII \ CH3 remains which recrystallizes from cyclohexrane in the form of white lamellae melting at 72—73° C. In a similar manner 1-ethyl-3-amino-4-carbethoxy- pyrazole boiling at 111° C. under 0.06 mm. of pressure can be obtained. Example 28 19.7 grams of 1-isopropyl-3-amino-4-carbethoxy-pyra- zole are heated in 50 cc. of formamide for 5 hours in a bath having a temperature of 200—210° C. After cooling, the crystalline precipitate is suction-filtered and crystal- lized from "boiling ethyl alcohol for the purpose of purifi- cation. 2 - isopropyl-4-hydro~xy-pyrazolo(3,4 - d)pyrimi- dine is obtained in the form of crystals melting at 229—230° C. Example 29 4.5 grams of 2-isopropyl - 4 - hydroxy-pyrazolo(4,4-d) pyrimidine are added to 20 cc. of 2 N-sodium hydroxide solution. 4 grams of dimethyl sulfate are slowly added to the solution with stirring and the whole is stirred for 2 hours at room temperature. The precipitate is suction- filtered and crystallized from benzene. 2-isopropyl-4-oxo- 5-methyl-4,5—dihydro - pyrazolo(3,4 - -d)pyrimidine is ob- tained in the form of «white crystals melting at 209-210° C. Example 30 3 grams of 1-ethyl-3-amino-4-carbethoxy-pyrazole are 3,093,075 17 dissolved in 7 cc. of formamide and heated for 10 hours at 200—220° C. in an oil bath. The crystals which separate on cooling are suction-filtered, washed with ether and re- crystallized from -alcohol. 2-ethy1- 4 - hydroxy-pyrazolo (3,4-d)pyrimidine is obtained melting at 235-237“ C. Example 31 A mixture of 5 grams of 1-methyl-3-amino-4-carbeth oxy—pyrazole and 4 grams of urea is heated for 10 hours at 170° C. The reaction product is dissolved in 20 cc. of warm 2 N-sodium hydroxide solution. On adding dilute hydrochloric acid to the alkaline solution, 2-methyl-4,6- dihydroxy -pyrazolo(3,4 - «d)«pyrimidine precipitates. It melts at >360° C. Example 32 5 grams of dimethyl sulfate are added in portions to a solution of 5 -grams of 2-methyl-4,6-dihydroxy-pyrazolo (3,4-d)pyrimidine in 20 cc. of 2 N-sodium hydroxide solu- tion at room temperature. After 30 minutes the aqueous solution is extracted with chloroform. The residue re- maining «after drying and evaporating the chloroform ex- tract is -recrystallized from benzene. 2,5,7-trimethyl-4,6- dioxo-4,5 ,6,7-tetrahydropwyrazolo( 3,4 - d)pyrimidine melt- ing at 195—'196° C. is obtained. Example 33 5 grams of 1-methyl-3—amino-4-carbethoxy-pyrazole and 4 grams of thiourea are heated for 10 hours at 170° C. The reaction product is dissolved in 20 cc. of 2 N-sodium hydroxide solution. After filtering through active char- coal and adding dilute hydrochl-oric acid, 2-methyl-4-hy- droxy—6—mercapto - pyrazolo(3,4 — d) pyrimidine is precipi- tated melting -at >360” C. Example 34 In a sealed tube, 20 g; of 1-methyl-3-amino-4-carbeth- oxy-pyrazole in 85 cc. of benzene are heated at 100° C. for 10 hours with 10 g. of methylisocyanate. When the reaction solution has cooled, the crystals which have sepa- rated are filtered off with suction. There is obtained in this manner the N—(1-methyl-4-carbethoxy—7~nyrazolyl)- N’-methyl urea of the formula C2H5—OOC—:=:' CHa—NH——C-—NH N—°H3 ('3 of melting point 119° C. 21 g. -of the afore-described substituted urea are heated at 90° C. for 30 minutes in 20cc. of 5 N-caustic soda solu- tion. When the reaction solution has cooled, the pH is adjusted to 1 with 2 N-hydrochloric acid, after which the 2,5-dimethyl-4,6-dioxo-4,5,6,7 - tetrahydro - pyrazolo(3,4— d)pyrimidine separates in the form of white crystals of melting point 342-344° C. The 1-methyl-3-amino-4 - carbethoxy - pyrazole used as starting material is obtained as (follows: A solution of 65 grams of N1—methyl—N2-benzylidene- hydrazine and 85 grams of ethoxy-methylene-cyano-acetic acid ethyl ester in 500 cc. of benzene is boiled under re- flux for 10 hours. A precipitate is formed which is fil- tered and recrystallized from ethanol. ;3-(N2-benzylidene- N1-methyl-hydrazino)-at-cyano—acrylic acid ethyl ester in the form of faintly yellow crystals melting at 155-15 6° C. is obtained. 80 grams of B-(N2-benzylidene-N1-methyl-hydrazino)- on-cyano-acrylic acid ethyl ester are boiled under reflux for 2 hours with 10 N-alcoholic hydrochloric acid. The sol- vent is removed by ‘distillation in vacuo. The residue is taken up in 200 cc. of 2 N-‘hydrochloric acid and the acid solution extracted with ether. After separating the aque- ous layer it is rendered alkaline by adding 2 N-sodium hy- droxide solution. The precipitated -base is extracted sev- eral times with ether. A-fter separating, drying and evap- orating the ether extract, the residue is distilled at 130° LU! 10 15 20 25 30 35 40 45 50 55 60 65 70 7_5 ‘ 18 C. -under 0.01 mm. of pressure, 1—methyl-3-arnino-4-car- lbethoxy-pyrazole of the formula C2H50 O C I N—CH H2N—LN/ 3 melting at 92-93‘ C. is obtained. Example 35 19.7 grams of 2-isopropyl-3-amino-4-carbethoxy-pyraz- ole, dissolved in 150 cc. of benzene, are heated with 28.4 grams of ethyl isocyanate and 3 cc. of triethylamine for 10 hours at 100° C. in -a closed tube. Upon evap- orating the reaction solution there is obtained crude crystalline N- [2-isopropyl - 4 - carbethoxy-pyrazolyl-( 3 ) ] - N’-ethyl-N-ethylcarbamyl—urea of the formula C2Hs0OC --H 02H5HN—O o—N—o oHN:m N e. N” 2 5 bn Céa \CH3 The crude product, which melts at 129—l30° C. after recrystallization from ether, may be used directly for ring closure in the following manner: 16 grams of crude N- [2-isopropyl-4-carb ethoxy-pyrazolyl- (3 ) ] -N’ - ethyl-N’- ethy-lcarbamyl-urea are mixed with 1360 cc. of a 2 N-solu- tion of caustic soda, and the whole is boiled under reflux for 8 minutes in an oil bath having a temperature of 150° C. After -being cooled, the reaction solution is given a pH value of 4.5 by the addition of 2 N-acetic acid, where- upon 1-isopropyl - 4,6 - dioxo-5-ethyl-4,5,6,7-tetrahydro- pyrazolo(3,4-d)pyrimidine precipitates. It melts at 202- 204” C. — When the 2-isopropyl-3-amino-4-carbethoxy-pyrazole is reacted in the above manner with only one molecular proportion of ethyl cyanate, there -is obtained an inter- mediate product from which, after distilling off the start- ing material at 127° CI under 0.99 mm. pressure, N-[2- isopropyl-4-carbethoxy-pyrazolyl-(3 ) ]-N’—ethyl-urea melt- ing at 129—130° C. (after crystallization from a mixture of ether and petroleum ether), can be isolated. It can be subjected to ring closure in the manner described above. Example 36 13.8 grams of 2-isopropyl-3-amino-4-carbethoxy~pyraz- ole are heated in 105 cc. of benzene with 16 grams of methyl isocyanate and 2.1 cc. of triethylamine in a closed tube for 10 hours at 100° C. By evaporating the reac- tion solution, there is obtained crude crystalline N-[2-iso- propyl-4-carbethoxy-pyrazolyl- ( 3 ) ]-N’-methyl-N’—methyl- ca.-rbamyl-urea of the formula C2H5OOC CH3—HN——O C——lIT—O O—HN ' N CH3 4) / . CH3 CH3 The crude product,'which melts at 145—146° C. after recrystallization from alcohol, can be used directly for ring closure as follows: 5 grams of crude N-[2-isopropyl-4-carbethoxy-pyraz- olyl-(3)]-N’-methyl-N’-methylcarbamyl-urea are boiled under reflux for 7 minutes in 50 cc. of a 2 N-solution of caustic soda. The reaction solution is extracted with ether and adjusted to a pH value of 4.5 with 2 N-acetic acid, whereupon 1-isopropyl-4,6-dioxo-5-methyl-4,5,6,7- tetrahydro-pyrazolo(3,4-d) -pyrimidine precipitates. It melts at 235-236” C. Example 37 3.64 grams of 2-methyl-3-amino-4-carbethoxy-pyrazole, dissolved in 32 cc. of benzene, are heated with 4.92 grams /m \z 3,098,075 19 of methyl isocyanate and 0.7 cc. of triethylamine in a closed tube for 10 hours at 100° C. By evaporating the reaction solution there is obtained crude crystalline N-[2- methyl - 4 - carbethoxy-pyrazolyl — (3)] - N’-methyl-N5 methylcarbamyl-urea of the formula C2H50 O C -'——T| OHa—HN——O C—N—O C—HN N I N/ CH3 l on. The crude product, which melts at 148-149“ C. after recrystallization from -alcohol, can be used directly for the subsequent ring closure as follows: 1 gram of crude N-[2-methyl-4-carbethoxy-pyrazolyl- (3)]-N’-methyl-N’-methylcarbamyl-urea are boiled under reflux in 10 cc. of a 2 N-solution of caustic soda for 7 minutes. The aqueous reaction ‘solution is extracted with ether and then adjusted to a pH value of 5 with 2 N-acetic acid, whereupon 1,5-dimethyl-4,6-dioxo-4,5,6,7- tetrahydropyrazolo(3,4 -d)pyrimidine precipitates. It melts at 297—298° C. Example 38 5 grams of 1-methyl-3-amino-4-carbethoxy-pyrazole are heated with 15 cc. of formamide for 10 hours at 190° C. After cooling to room temperature the precipitate is filtered and recrystallized from water. 2-methyl-4-hy- droxy—pyrazolo(3,4-d)pyrimidine is obtained in the form of white crystals melting at 193 ° C. Example 39 A solution of 5 grams of ethyl-isocyanate and 10 grams of 1-methyl-3—amino-4-carbethoxy-pyrazole in 50 cc. of benzene is heated at 100° C. in an autoclave for 6 hours. After evaporating the solvent in vacuo, a solid residue remains which is recrystallized from ether-cyclo- hexane. N-ethy1- N’ - (1 - methyl-4-carbethoxy-3-pyraz- olyl)-urea of the formula C2H5—O 0 (PF __ __ _ _ N-CH; O2Hs EN 00 HN \N/ is -obtained in the form of prisms melting at 112° C. 15 grams of this urea are heated at 90° C. in 100 cc. of 5 N-sodium hydroxide solution for 1 hour. The solu- tion is filtered, and by adding 2 N-hydrochloric acid 2- methyl - 5 - ethyl-4,6—dioxo - 4,5,6,7 - tetrahydro-pyrazolo- (3,4-d) pyrimidine of the formula i C 2H5—I‘l/\ T‘ 0 J N— C H3 —\E/ w/ precipitates. After recrystallization from water the com- pound melts at 303 ° C. Example 40 60 cc. of phosphorus oxychloride are added to 3 grams of 1,5 - dimethyl - 4,6-dioxo-4,5,6,7-tetrahydropyrazolo [3,4-djpyramidine and boiled under reflux. After about 3 hours the substance is in solution, and boiling under reflux is continued for another 5 hours. The reaction solution is evaporated at a water jet pump at a tempera- ture of about 60° C. The residue is poured on to ice, the pH is adjusted -to 10 with 2 N-sodium hydroxide solu- tion, and extraction is carried out with chloroform. The chloroform solution is evaporated and the residue is re- crystallized fr-om ether. There is obtained 1,5-dimethy1- 10 15 20 30 4.0 45 50 55 60 65 70 75 20 4-oxo-6-chloro-4,5 — dihydro-pyrazolo[3,4-d] pyrimidine of the formula 0 ll CH3-N /\ ..lN N $113 melting at 177—178° C. Example 41 60 cc. of phosphorus oxychloride are added to 4 grams of 1-isorpropyl-4,6-diox-o-5 - methyl-4,5,6,7 - tetrahydro- pyrazolo(3,4-d)pyrimidine and heated for 8 hours at the boil. After about 1 hour the substance is in solution. For -the purpose of working up, the reaction solution is concentrated in vacuo at a maximum temperature of 50° C. The residue is poured on to ice, the pH is adjusted to 10 with 2 N-sodium hydroxide solution, and extrac- tion is carried out with ample ether. From the evapo- rated ether solution there is obtained 1-isopropyl-4-oxo- 5-methyl-6-chlor-o-4,5 - dihydro - pyrazolo(3,4-d) pyrimi- dine of the formula 0 H CH3-N /\ I OH /\ CH3 CH3 melting at 100-101 ° C. After recrystallization from petroleum ether the melting point is raised to 103—104° C. Example 42 4 grams of 1-isopropyl-5-ethyl-4,6-dioxo-4,5,6,7-tetra- hydro-pyrazolo(3,4-d-)pyrimidine are boiled under reflux with 25 cc. of phosphorus oxychloride for 8 hours. For the purpose of working up, the reaction solution is evapo- rated in vacuo at a temperature of 60° C. at the most. The residue is poured on to ice, the pH is adjusted to 10 with 2 N-sodium hydroxide solution, and extraction is carried out with ether. From the evaporated ether solu- tion there is obtained 1-isopropyl-4-oxo-5-ethyl-6-chloro- 4,5-dihydro-pyrazolo-(3,4-d)pyrimidine of the formula 0 C2H5—I\I/l\’.""] o1—h\NiN/N /it CH3 CH3 melting at 64—650° C. After recrystallization from pe- troleum ether, the melting point rises to 65—66° C. Example 43 4 grams of 2-isopropyl-4,6-dioxo-5-methyl-4,5,6,7-tetra- hydro-pyrazolo(3,4-d)pyrimidine are heated at the boil with 50 cc. of phosphorus oxy-chloride. After two hours the substance dissolves, and boiling is continued for an- other 6 hours. The reaction solution is evaporated in vacuo at a maximum temperature of 50° C. The solu- tion is then adjusted to pH=l0 with cooling and ex- tracted with ample ether. From the evaporated ether solution there is obtained 2-isopropyl-4-oxo-5-methyl-6- 3,093,075 21 chloro - 4,5 - dihydro-pyrazolo(3,4-d)pyrimidine of the formula ‘T CH3—N ‘: CH3 mi lee \N/W wt. melting at 14S~150° C. After recrystallization from other the substance melts at 150-151” C. Example 44 4 grams of 2,5»dimethyl-4,6-wdioxo-4,5,6,7-tetrahydro- .pyrazolo(3,4-d)pyrimidine are boiled under reflux with 130 cc. of phosphorus oxyohloride for 19 hours. After cooling, the undissolved starting material is separated off and the filtrate evaporated. The residue -is poured on to ice, rendered alkaline with 2 N-sodium hydroxide solu- tion and extracted with chloroform. From the evapo- rated chloroform solution there is obtained by recrystal- lization from acetone 2,5-dimethyl-4-oxo-6-chloro-4,5- «dihydro-pyrazolo(3,4-d)pyri.m.idine melting at 199—200° C. Example 45 A methylate solution, prepared -from 2.67 grams of sodium in 85 cc. of methanol, is added to 2.3 grams of 1,5 - dimethyl-4=oxo-6-chloro-4,5-dihydro-pyrazolo(3,4- d)pyrirnidine, and the whole is boiled for 1 hour under reflux. The mixture is then evaporated to 30 cc., water is added and -the solution is extracted with chloroform. The residue obtained from the evaporated chloroform solution is recrystallized from a mixture of ether and pe- troleum ether. There is thus obtained 1,5-dimethyl-4- oxo — 6 — metlioxy-4,5—dil1ydro-pyrazolo(3,4-d)pyrimidine of the formula 0 ll CH3-I\T/\|—TII\I CH3O \\N N/ $3. melting at 160-161° C. Example 46 To 2.26 grams of 1-isopropyl-4-oxo-5-methy1-6-ch1oro- 4,5-dihydro-pyrazolo(3,4-d)pyrimidine there is ‘added a sodium methylate solution prepared from 75 cc. of meth- anol and 2.3 grams of sodium, and the whole is boiled under reflux for 1 hour. The reaction solution is concen- trated -to 25 cc., diluted with water and extracted with ample chloroform. The residue obtained from the evapo- rated chloroform solution is recrystallized from a mixture of ether and petroleum ether with the addition of a little alcohol. There is obtained 1-isopropyl-4-oxo-5-methyl-6- metlroxy-4,5-dihydro-pyrazolo(3,4 - d)-pyrimidine of the formula 0 I CH3—N W. N/ /5? CH3 CHaO— \N CH3 melting at 158—159° C. Example 47 To 2.4 grams of 1-isopropy1-4-oxo-5-ethyl-6-chloro-4,5- dihydro-pyrazolo(3,4-d)pyrimidine there is added a so- dium methylate solution prepared from 75 cc. of methanol and 2.3 grams of sodium, and the whole is boiled under reflux for 1 hour. The reaction solution is concentrated 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 22 to about 25 cc., diluted with water and extracted with chloroform. The residue obtained from the evaporated 'chl-orofo-rm solution is recrystallized from petroleum ether. There is obtained 1-isopropyl-4-oxo-5-ethyl-6- methoxy-4,5-dihydropyrazolo(3,4-d)pyrimidine of the formula 0 II C 2H5-N \z=J CH30— \N 0-2 /13: / CH3 CH3 melting at 107.5—108.5° C. Example 48 To 2 grams of 2-isopropyl-4-oxo-5-methyl-6-chloro 4,5-dihydro-pyrazolo(3,4-d)pyrirnidine there is added a sodium methylate solution prepared from 2.04 grams of sodium in 65 cc. of methanol, and the whole is boiled for 1 hour under reflux. The reaction solution is con- centrated to about 25 cc., diluted with water and extracted with much chloroform. The residue from the evapo- rated chloroform solution is recrystallized from acetone- -petroleum ether. There is obtained 2-isopropyl-4-oxo-5- methyl-6-methoxy-pyrazolo(3,4-d)pyrimidine of the for- mula melting at 192-193“ C. Example 49 0.8 gram of 2.5-dimethyl-4-oxo-6-chloro-4,5-dihydro- pyrazolo(3,4-d)pyrimidine is boiled under reflux for 1 hour with a solution of 0.93 gram of sodium in 30 cc. of methanol. The reaction solution is concentrated, diluted with Water and extracted with chloroform. From the evaporated chloroform solution there is obtained 2,5- dimethyl - 4 — oxo - 6 - methoxy - 4,5 - dihydro - pyra- zolo(3,4-d)pyrimidine which crystallizes from acetone; M.P.=176—177° C. Example 50 20 grams of diethyl sulfate are added to a solution of 8 grams of 2-methyl-4,6-dioxo-4,5,6,7-tetrahydro-pyra- zolo(3,4—d)pyrimidine in 60 cc. of 2 N-sodium hydroxide solution, and the whole is stirred while being heated at 95° C. for 4 hours. On cooling, a precipitate is formed which is filtered off and recrystallized from ethanol. There is obtained the 2-methyl-7-ethyl-4,6-dioxo—4,5,6,7- tetrahydropyrazolo(3,4-d)pyrimidine in the form of crys- tals of melting point 255° C. Example 51 A mixture of 10 grams of 1-([3-hydroxy-ethyl)-3-amino- 4-oarbethoxy-pyrazole -and 20 grams of urea is heated at 180° C. for 6 hours. The solid reaction product is dissolved in 2 N-sodium hydroxide solution, filtered, and the filtrate is given a pH of 1 by adding 2 N-sodium hydroxide solution. On prolonged standing, the 2-(,B- hydroxy —ethyl) - 4,6 - dihydroxy - pyrazolo( 3,4 — d)py- rimidine separates out. For purification, it is recrystallized from water. Its melting point is at 292° C. Example 52 10 grams of 1-(/3-hydroxy-ethyl)-3-amino-4-carbeth- oxy—pyrazole «are heated at 160° C. for 4 hours with 30 cc. of formamide. A crystalline precipitate forms Which, for purification, is sublirned at 200° C. under a 5,098,075 23 pressure of 0.05 mm. In this manner there is obtained 2 — (2 - hydroxy - ethyl) - 4 - hydroxy - pyraz0lo(3,4-d) pyrimidine in the form of white crystals melting at 269° C. Example 53 A suspension of 10 grams of ethylhydrazine-oxalate in 1310 cc. of absolute alcohol is added to 11.25 grams of ethoxy-methylene-cyanacetic ester, dissolved in 30 cc. of absolute alcohol, -and the mixture boiled under reflux while being stirred for 10 hours. After cooling, the re- action solution is filtered and the filtrate evaporated. The residue is mixed with 2 N-sodium hydroxide solution and extracted several times with ether. The ethereal solution is evaporated and the residue subjected to fractional distil- lation under a high vacuum. There is obtained in this manner the 2-ethyl-3-amino-4-carbethoxy-pyrazole which under a pressure of 0.6 mm. boils at 120—121° C. 18.3 grams of 2-ethyl-3-amino-4-carbethoxy-pyrazole and 50 cc. of formamide are heated under a current of nitrogen for 10 hours in an oil bath having a temperature of 200-—2l0° C. Part of the formamide is then evapo- rated and the reaction mass allowed to cool. The crystals that separate are filtered oif, dissolved in 2 N-sodium hy- droxide solution, and filtered after the addition of active carbon. The filtrate is given a pH of 3,5 with 5 N-hydro- chloric acid, after which the 1-ethyl-4-hydroxy-pyrazolo (3,4-d) pyrimidine separates in the form of white crystals of melting point 236—237° C. What is claimed is: II. A member of the group consisting of 4,S,6,7-tetra- hydro-pyrazolo(3,4-d)pyrimidines of the formulae: B1 II R2-N /\ I I R41! and . R4 wherein R is a member selected from the group consisting of hydrogen, lower alkyl, hydroxy-lower alkyl, di—lower alkylamino-lower alkyl and cyclo-lower alkyl -and R2 and R4 are members selected from the group consisting of lower alkyl, hydroxy: lower alkyl, di—lower alkylamino-. lower alkyl and cyclo-lower alkyl and R1 and R2 «are members of the group consisting of oxo, imino and thiono, but at least one of these stands for oxo, and their thera- peutically useful acid addition salts. 2. A member of the group consisting of dihydro- pyrazolo(3,4-d) pyrimidines of the formulae: R1 I R-2~—N R:—L l N \N I?I/ R fir /\ R2—N 10 20 30 40 60 65 70 75 It i” R: R and Rs I N ._ _ ——R R“\N/ \N/ in and their tautomeric forms, wherein R is a member selected from the group consisting of lower alkyl, hydro- gen, hydroxy-lower alkyl, di—lower alkylamino-lower alkyl and cyclo-lower alkyl, and R2 is a member selected from the group consisting of lower alkyl, hydroxy-lower alkyl, di—lower -alkylamino—lower alkyl and cyclo-lower alkyl, and R1 is .a member selected from the group consisting of oxo, imino and thiono, and R3 is a member of the group consisting of hydroxy, amino, mercapto, lower alkoxy, lower alkylamino and lower alkylmercapto but at least one of R1 and R3 is a member selected from the group consisting of oxo and hydroxy, .and their therapeutically useful acid addition salts. 3. A member of the group consisting of pyrazolo(3,4- d) pyrimidines of the formulae R1 I N I N Br‘ \N N/ I R and R1 I N —” R2_ N——R ‘N/\‘N/ and their tautomeric forms, wherein R is a member selected from the group consisting of lower alkyl, lower hydroxy-alkyl, lower dialkylamino-lower alkyl and cyclo- lower alkyl and R1 and R2 are members selected from the group consisting of hydroxy, amino, mercapto, lower alkoxy, lower ralkylamino and lower alkylmercapto but ‘at least one of these radicals is hydroxy, and their thera- peutically useful acid addition salts. 4. 1 - R-5-R2-4,6-dioxo-4,5,6,7—tetrahydro-pyraz0lo-(3, 4-d)pyrimidine, wherein R and R2 are lower alkyl having together -at least 3 carbon atoms. 5. 1 - methyl - 5-R2-4,6-dioxo-4,5,6,7—tetrahydro-pyra- zolo(3,4-d)pyrimidine, wherein R2 is lower alkyl. 6. 2 - methyl - 5-R2-4,6—dioxo-4,5,6,7-tetrahydro-pyra: zolo(3,4—d) pyrimidine, wherein R2 is lower alkyl. 7. 1 - methyl - 5-R2—7-R4-4,6-dioxo-4,5,6,7-tetrahydro- pyrazolo(3,4-d)pyrimidine, wherein R2 and R4 are lower alkyl. 8. 2 - methyl - 5-R2-7-R1-4,6-dioxo-4,5,6,7-tetrahydro- pyrazolo(3,4-d) pyrimidine, wherein R2 and R1 are lower alkyl. 9. 1 - isopropyl - 5-R2-4,6-dioxo-4,5,6,7-tetrahydropyra- zolo(3,4-d) pyrimidine, wherein R2 is lower alkyl. 10. 1 - R1 - 5 - R2 - 4,6 - dioxo - 4,5,6,7 - tetrahydro- pyrazolo-(3,4-d)pyrimidine, wherein R1 and R2 are lower ‘alkyl, R1 and R2 together having at least 3 carbon atoms. 11. 4,6 - dihyvdroxy - pyrazolo(3,4 - d)pyrimidine N- substituted in the pyrazole nucleus by lower alkyl. 12. 5 - lower alkyl - 6 - halogeno - 4 - oxo - 4,5 - dihy- 3,098,075 25 dro-pyrazolo(3,4~d) pyrimidine N-substituted in the pyr- vazole nucleus by lower alkyl. 13. Snlower alky-1-6-lower alkoxy—4-oxo—4,5«dihydro- pyrazo1o(3,4-d)pyrimidine N-substituted in the pyrazole nucleus -by lower »alkyl. 14. 5 - R2 - 4,6 - rdioxo — 4,5,6,7 - tetrahydro - pyraz- o1o(3,4—d)pyrimivdine, wherein R2 is lower alkyl, and which is N-substituted in the pyrazole ring -by lower alkyl. 15. 1,5,7—trimethyl-4,6-dioxo-4,5,6,7-tetrahydropyraz- olo(3,4-d)pyrimidine. 16. 2,5,7-trimethyl-4,6~dioxo-4,5,6,7-tetrahywdropyraz- olo(3,4~d)pyri.midine. 17. 1-isopropyl-5,7-dimethyl—4,6-dioXo-4,5,6,7—teti