Syntheses of 6-Amino-1-(β-D-ribofuranosyl)-1H-pyrazolo[3,4-d]-1,3-oxazin-4-one,an isostere of oxanosine,and the guanosine analog 6-amino-1-(β-d-ribofuranosyl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one via ring closure of pyrazole-5-thioureido intermediates

6-Amino-1-(β-D-ribofuranosyl)-1H-pyrazolo[3,4-d]-1,3-oxazin-4-one ( 4 ), an isostere of the nucleoside antibiotic oxanosine has been synthesized from ethyl 5-amino-1-(2,3-O-isopropylidene-β-D-ribofuranosyl)pyrazole-4-carboxylate ( 6 ). Treatment of 6 with ethoxycarbonyl isothiocyanate in acetone gave the 5-thioureido derivative 7 , which on methylation with methyl iodide afforded ethyl 1-(2,3-O-isopropylidene-β-D-ribofuranosyl)-5-[(N'-ethoxycarbonyl-S-methylisothiocarbamoyl)amino]pyrazole-4-carboxylate ( 8 ). Ring closure of 8 under alkaline media furnished 6-amino-1-(2,3-O-isopropylidene-β-D-ribofuranosyl)-1H-pyrazolo[3,4-d]-1,3-oxazin-4-one ( 10 ), which on deisopropylidenation afforded 4 in good yield. 6-Amino-1-(β-D-ribofuranosyl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one ( 5 ) has also been synthesized from the AICA riboside congener 5-amino-1-(2,3-O-isopropylidene-β-D-ribofuranosyl)pyrazole-4-carboxamide ( 12 ). Treatment of 12 with benzoyl isothiocyanate, and subsequent methylation of the reaction product with methyl iodide gave 1-(2,3-O-isopropylidene-β-D-ribofuranosyl)-5-[(N'-benzoyl-S-methylisothiocarbamoyl)amino]pyrazole-4-carboxamide ( 15 ). Base mediated cyclization of 15 gave 6-amino-1-(2,3-O-isopropylidene-β-D-ribofuranosyl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one ( 14 ). Deisopropylidenation of 14 with aqueous trifluoroacetic acid afforded 5 in good yield. Compound 4 was devoid of any significant antiviral or antitumor activity in culture.     

Synthesis of certain pyrazolo[3,4-d]pyrimidin-3-one nucleosides

Synthesis of the pyrazolo[3,4-d]pyrimidin-3-one congeners of guanosine, adenosine and inosine is described. Glycosylation of 3-methoxy-6-methylthio-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one ( 13 ) with 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose ( 16 ) in the presence of boron trifluoride etherate gave 3-methoxy-6-methylthio-1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)pyrazolo[3,4-d]pyrimidin-4(5H)-one ( 17 ) which, after successive treatments with 3-chloroperoxybenzoic acid and methanolic ammonia, afforded 6-amino-3-methoxy-1-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidin-4(5H)one ( 18 ). The guanosine analog, 6-amino-1-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidine-3,4(2H,5H)-dione ( 21 ), was made by sodium iodide-chlorotrimethylsilane treatment of 6-amino-3-methoxy-1-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)pyrazolo[3,4-d]pyrimidin-4(5H)one ( 19 ), followed by sugar deprotection. Treatment of the adenine analog, 4-amino-1H-pyrazolo[3,4-d]pyrimidin-3(2H)-one ( 11 ), according to the high temperature glycosylation procedure yielded a mixture of N-1 and N-2 ribosyl-attached isomers. Deprotection of the individual isomers afforded 4-amino-3-hydroxy-1-βribofuranosylpyrazolo-[3,4-d]pyrimidine ( 26 ) and 4-amino-2-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidin-3(7H)-one ( 27 ). The structures of 26 and 27 were established by single crystal X-ray diffraction analysis. The inosine analog, 1-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidine-3,4(2H,5H)-dione ( 28 ), was synthesized enzymatically by direct ribosylation of 1H-pyrazolo[3,4-d]pyrimidine-3,4(2H,5H)-dione ( 8 ) with ribose-1-phosphate in the presence of purine nucleoside phosphorylase, and also by deamination of 26 with adenosine deaminase.     

A facile synthesis of certain 4- and 4,5-disubstituted 1-β-d-ribofuranosylpyrazoles

A number of pyrazole ribonucleosides, structurally related to AICA riboside and ribavirin have been prepared and evaluated for their biological activity in vitro. Deisopropylidenation of 5-amino-1-(2,3-O-isopropylidene-β-D-ribofuranosyl)pyrazole-4-carbonitrile ( 6 ) with aqueous trifluoroacetic acid gave 5-amino-1-(β-D-ribofuranosyl)pyrazole-4-carbonitrile ( 7 ). Conventional transformation of the carbonitrile function of 7 gave the AICA riboside congener ( 2 ) and related 5-amino-1-(β-D-ribofuranosyl)-pyrazoles ( 8–10 ). Acetylation of 7 at low temperature gave the versatile intermediate 5-amino-1-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)pyrazole-4-carbonitrile ( 15 ). Non-aqueous diazotization of 15 with isoamylnitrite in dibromomethane or diiodomethane gave the corresponding C₅-bromo 13 and C₅-iodo 16 derivatives. Compounds 13 and 16 were subsequently transformed into 5-bromo-1-(β-D-ribofuranosyl)pyrazole-4-carboxamide ( 11 ) and the 5-iodo analog 25 . However, a similar nonaqueous diazotization of 15 in dichloromethane afforded the deaminated product 1-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)pyrazole-4-carbonitrile ( 22 ). Treatment of 22 with ammonium hydroxide/hydrogen peroxide gave the ribavirin congener 1-(β-D-ribofuranosyl)pyrazole-4-carboxamide ( 18 ). Similar treatment of 22 with hydrogen sulfide in pyridine or hydroxylamine in ethanol gave the 4-thiocarboxamide 19 and 4-carboxamidoxime 20 derivatives, respectively. Catalytic hydrogenation of 20 afforded 1[β-D-ribofuranosyl)pyrazole-4-carboxamidine ( 21 ). These pyrazole nucleosides are devoid of any significant antiviral or antitumor activity in vitro.     

Synthesis of 8-amino-9-β-D-ribofuranosylpurin-6-thione and related 6-substituted-8-aminopurine nucleosides

Acetylation of 8-amino-9-β-D-ribofuranosylpurin-6-one (III), followed by chlorination of the tetraacetyl derivative 8-acetamido-9-(2,3,5-tri-O-aeetyl-β-D-ribofuranosyl)purin-6-one (IV) with phosphorus oxychloride yielded 8-aeetamido-6-ehloro-9-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)-purine (V). The 6-chloro substitutent of V was readily displaced with thiourea to give, after treatment with sodium methoxide 8-acetamido-9-β-D-ribofuranosylpurine-6-thione (VIII). Chlorination of 8-bromo-9-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)purin-6-one (IX) yielded 6,8-dichloro-9-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)purine (X), which underwent nucleophilic displacement with ethanolic ammonia selectively in the 8 position. The resulting 8-amino-6-chloro-9-β-D-ribofuranosylpurine (VII) was converted to 8-amino-9-β-D-ribofuranosylpurine-6-thione (I), 8-amino-6-methylthio-9-β-D-ribofuranosylpurine (II), and to 8-amino-6-hydrazino-9-β-D-ribofuranosylpurine (XI).     

Synthesis of 2-(β-D-ribofuranosyl)[1,3,5]triazines

The synthesis of the first [1,3,5]triazine carbon linked nucleosides are reported. 4-Amino-6-(β-D-ribofuranosyl)[1,3,5]triazin-2(1H)-one ( 8 ), an analog of 5-azacytidine and pseudoisocytidine was prepared. 2,5-Anhydro-D-allonamidine hydrochloride ( 3 ) was condensed with dimethyl cyanoiminodithiocarbonate ( 4 ) to give 4-methylthio-6-(β-D-ribofuranosyl)[1,3,5]triazin-2-amine ( 5 ). Compound 5 was reacted with m-chloroperbenzoic acid to give 4-methylsulfinyl-6-(β-D-ribofuranosyl)[1,3,5]triazin-2-amine ( 6 ). Displacement of the methyl sulfinyl with the appropriate nucleophile gave 6-(β-D-ribofuranosyl)[1,3,5]triazine-2,4-diamine ( 7 ), 4-amino-6-(β-D-ribofuranosyl)[1,3,5]triazin-2(1H)-one ( 8 ), and 4-amino-6-(β-D-ribofuranosyl)[1,3,5]triazine-2(1H)-thione ( 9 ). Dethiation of compound 5 with Raney nickel gave 4-(β-D-ribofuranosyl)[1,3,5]triazin-2-amine ( 10 ). The crystal structure of 7 was determined by single crystal X-ray.     

Synthesis of certain exocyclic thiazole nucleosides related to tiazofurin. Formation of a unique acycloaminonucleoside

Several thiazole nucleosides structurally related to tiazofurin (1) and ARPP (2) were prepared, in order to determine whether these nucleosides had enhanced antitumor/antiviral activities. Ring closure of 1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)thiourea (4) with ethyl bromopyruvate (5a) gave ethyl 2-(2,3,5-tri-O-benzoyl-β-D-ribofuranosylamino)thiazole-4-carboxylate (6a) . Treatment of 6a with sodium methoxide furnished methyl 2-(β-D-ribopyranosylamino)thiazole-4-carboxylate (9) . Ammonolysis of the corresponding methyl ester of 6a gave a unique acycloaminonucleoside 2-[(1R, 2R, 3R, 4R)(1-benzamido-2,3,4,5-tetrahydroxypentane)amino]-thiazole-4-carboxamide (7a) . Direct glycosylation of the sodium salt of ethyl 2-mercaptothiazole-4-carboxylate (12) with 2,3,5-tri-O-benzoyl-D-ribofuranosyl bromide (11) gave the protected nucleoside 10 , which on ammonolysis provided 2-(β-D-ribofuranosylthio)thiazole-4-carboxamide (3b) . Similar glycosylation of 12 with 2-deoxy-3,5-di-O-p-toluoyl-α-D-erythro-pentofuranosyl chloride (13) , followed by ammonolysis gave 2-(2-deoxy-β-D-ribofuranosylthio)thiazole-4-carboxamide (3c) . The structural assignments of 3b, 7a , and 9 were made by single-crystal X-ray analysis and their hydrogen bonding characteristics have been studied. These compounds are devoid of any significant antiviral/antitumor activity in vitro.     

Synthesis of 4,6-disubstituted-7-β-D-ribofuranosyl- and arabinofuranosylpyrazolo[3,4-d]pyrimidines and certain related ribonucleosides

Several disubstituted pyrazolo[3,4-d]pyrimidine, pyrazolo[1,5-a]pyrimidine and thiazolo[4,5-d]pyrimidine ribonucleosides have been prepared as congeners of uridine and cytidine. Glycosylation of the trimethylsilyl (TMS) derivative of pyrazolo[3,4-d]pyrimidine-4,6(1H,5H,7H)-dione ( 4 ) with 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose ( 5 ) in the presence of TMS triflate afforded 7-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)pyrazolo-[3,4-d]pyrimidine-4,6(1H,5H)-dione ( 6 ). Debenzoylation of 6 gave the uridine analog 7-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidine-4,6(1H,5H)-dione ( 3 ), identical with 7-ribofuranosyloxoallopurinol reported earlier. Thiation of 6 gave 7 , which on debenzoylation afforded 7-β-D-ribofuranosyl-6-oxopyrazolo[3,4-d]pyrimidine-4(1H,5H)-thione ( 8 ). Ammonolysis of 7 at elevated temperature gave a low yield of the cytidine analog 4-amino-7-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidin-6(1H)-one ( 11 ). Chlorination of 6 , followed by ammonolysis, furnished an alternate route to 11 . A similar glycosylation of TMS-4 with 2,3,5-tri-O-benzyl-α-D-arabinofuranosyl chloride ( 12 ) gave mainly the N7-glycosylated product 13 , which on debenzylation provided 7-β-D-arabinofuranosylpyrazolo[3,4-d]pyrimidine-4,6(1H,5H)-dione ( 14 ). 4-Amino-7-β-D-arabinofuranosyl-pyrazolo[3,4-d]pyrimidin-6(1H)-one ( 19 ) was prepared from 13 via the C4-pyridinium chloride intermediate 17 . Condensation of the TMS derivatives of 7-hydroxy- ( 20 ) or 7-aminopyrazolo[1,5-a]pyrimidin-5(4H)-one ( 23 ) with 5 in the presence of TMS triflate gave the corresponding blocked nucleosides 21 and 24 , respectively, which on deprotection afforded 7-hydroxy- 22 and 7-amino-4-β-D-ribofuranosylpyrazolo[1,5-a]pyrimidin-5-one ( 25 ), respectively. Similarly, starting either from 2-chloro ( 26 ) or 2-aminothiazolo[4,5-d]pyrimidine-5,7-(4H,6H)-dione ( 29 ), 2-amino-4-β-D-ribofuranosylthiazolo[4,5-d]pyrimidine-5,7(6H)-dione ( 28 ) has been prepared. The structure of 25 was confirmed by single crystal X-ray diffraction studies.     

Synthesis of ribonucleosides of 4(5)-cyano-5(4)-methylimidazole and related 4-substituted-5-methylimidazole ribosides

4-Cyano-1-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)-5-methylimidazole ( 4 ) and its corresponding 5-cyano-4-methyl substituted isomer ( 5 ) have been obtained by ribosylation of 4(5)-cyano-5(4)-methylimidazole ( 3 ) via the mercuric cyanide method or by ribosylation of the trimethylsilyl derivative of 3 . Treatment of 4 with methanolic ammonia, ammonium chloride in liquid ammonia and potassium hydrosulfide provided 4-cyano-1-β-D-ribofuranosyl-5-methylimidazole ( 6 ), 1-β-D-ribofuranosyl-5-methylimidazole-4-carboxamide ( 2 ) and 1-β-D-ribofuranosyl-5-methylimidazole-4-thiocarboxamide ( 11 ) respectively. Reaction of 6 with hydroxylamine afforded the corresponding 4-carboxamidoxime substituted nucleoside ( 13 ) which on catalytic reduction in the presence of ammonium chloride, was transformed into 1-β-D-ribofuranosyl-5-methylimidazole-4-carboxamidine ( 14 ) as hydrochloride salt.     

Synthesis of 1-(2-hydroxyphenyl)-2,4-imidazolidinedione derivatives through cyclic transformations of ethyl 2-oxo-3(2H)-benzoxazoleacetate derivatives

A series of ethyl 2-oxo-3(2H)-benzoxazoleacetate derivatives 2 have been synthesized. By reaction with ammonia, primary amines or hydrazine, these compounds 2 were transformed into 1-(2-hydroxyphenyl)-2,4-imidazolidinedione derivatives 4, 5 and 6 , respectively. Some of these new hydantoins 4 , treated with phosphorus oxychloride, gave 3H-2-oxoimidazo[2,1-b]benzoxazole derivatives 9 . Ethyl 2-oxo-3(2H)-benzoxazolepropionate ( 10 ) was prepared by a Michaël reaction of ethyl acrylate with 2-benzoxazolone ( 1a ). With 10 , no cyclic transformation was observed in the presence of ammonia or alkylamine.     

Synthesis of 5,8-dihydro-5-oxo-2-(3- or 4-pyridinyl)-pyrido[2,3-d]pyrimidine-6-carboxylic acids and the reinvestigation of the thermal cyclization of diethyl (2-hydroxy-4-pyrimidinyl)amino-methylenemalonate

Diethyl [2-(3- or 4-pyridinyl)-4-pyrimidinyl]aminomethylenemalonates 5 prepared by the reaction between 2-(3- or 4-pyridinyl)-4-pyrimidinamines 3 and diethyl ethoxymethylenemalonate ( 4 ) were thermally cyclized to afford ethyl 5,8-dihydro-5-oxo-2-(3- or 4-pyridinyl)pyrido[2,3-d]pyrimidine-6-carboxylates 6 . The later were alkylated with ethyl iodide and then saponified to give 5,8-dihydro-8-ethyl-5-oxo-2-(3- or 4-pyridinyl)pyrido-[2,3-d]pyrimidine-6-carboxylic acids 2 . Thermal cyclization of diethyl (2-hydroxy-4-pyrimidinyl)amino-methylenemalonate ( 8 ) gave ethyl 1,6-dihydro-4,6-dioxo-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate ( 10 ) instead of ethyl 5,8-dihydro-2-hydroxy-5-oxopyrido[2,3-d]pyrimidine-6-carboxylate ( 9 ) as previously claimed.     

Reactions of 3,4-Dichloro-N-R-maleimides with Substituted 2-Thiouracils

Reactions of 3,4-dichloro-N-R-maleimides with substituted thiouracils at 40°C gave a 1:1 mixture of isomers of pyrrolothiazolopyrimidinetriones. Under conditions of thermodynamic control (100°C, 5 h) only pyrrolo[3',4':4,5]thiazolo[3,2-a]pyrimidine-4,6,8-triones were formed, hydrolysis of which followed by decarboxylation gave 5-oxo-5H-thiazolo[3,2-a]pyrimidine-2-carboxamide. The structure of N²-phenyl-6-methyl-5-oxo-5H-thiazolo[3,2-a]pyrimidine-2-carboxamide was confirmed by X-ray crystallography. Analogous cyclization of 3,4-dichloro-N-R-maleimides with 2-thioxoquinazol-4-one also gave a mixture of two isomers which were successfully separated by fractional crystallization.     

Synthesis of certain 3-alkoxy-1-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidines structurally related to adenosine,inosine and guanosine

Several 3-alkoxysubstituted pyrazolo[3,4-d]pyrimidine ribonucleosides structurally related to adenosine, inosine and guanosine have been prepared by the direct glycosylation of preformed aglycon precursor containing a 3-alkoxy substituent. Ring closure of 5(3)-amino-3(5)-ethoxypyrazole-4-carboxamide ( 6b ) with either formamide or potassium ethyl xanthate gave 3-ethoxyallopurinol ( 7b ) and 3-ethoxy-6-thioxopyrazolo[3,4-d]-pyrimidin-4(5H,7H)-one ( 10 ), respectively. Methylation of 10 gave the corresponding 6-methylthio derivative 15 . Similar ring annulation of 5(3)-methoxypyrazole-4-carboxamide ( 6a ) with formamide afforded 3-methoxyallopurinol ( 7a ). Treatment of 5(3)-amino-3(5)-methoxypyrazole-4-carbonitrile ( 5a ) with formamidine acetate furnished 4-amino-3-methoxypyrazolo[3,4-d]pyrimidine ( 4 ). High-temperature glycosylation of 7b with 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose in the presence of boron trifluoride etherate gave a 2:1 mixture of N-1 and N-2 glycosyl blocked nucleosides 11b and 13b . Deprotection of 11b and 13b with sodium methoxide gave 3-ethoxy-1-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidin-4(5H)-one ( 12b ) and the corresponding N-2 glycosyl isomer 14b , respectively. Similar glycosylation of either 4 or 7a , and subsequent debenzoylation gave exclusively 4-amino-3-methoxy-1-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidine ( 9 ) and 3-methoxy-1-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidin-4-(5H)-one ( 12a ), respectively. The structural assignment of 12a was made on the basis of single-crystal X-ray analysis. Application of this general glycosylation procedure to 15 gave the corresponding N-1 glycosyl derivative 16 as the sole product, which on debenzoylation afforded 3-ethoxy-6-(methylthio)-1-(3-D-ribofuranosylpyrazolo[3,4-d]pyrimidin-4(5H)-one ( 17 ). Oxidation of 16 and subsequent ammonolysis furnished the guanosine analog 6-arnino-3-ethoxy-1-β-D-ribofuranosylpyrazolo[3,4-d]-pyrimidin-4(5H)-one ( 19 ). Similarly, starting from 3-methoxy-4,6-bis(methylthio)pyrazolo[3,4-d]pyrimidine ( 20 ), 6-amino-3-methoxy-1-β-D-ribofuranosylpyrazolo[3,4-d]pyrimidin-4(5H)-one ( 23 ) was prepared.     

Synthesis of 1-(β-D-ribofuranosyl)indol-3-acetic acid

By condensation of ethyl indolin-3-acetate ( 4 ) and 2,3,5-tri-O-benzoylribofuranosyl-1-acetate ( 5 ), ethyl 1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)indolin-3-acetate ( 6 ) was obtained in good yield. The indoline nucleoside 6 was aromatized to ethyl 1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)indol-3-acetate ( 7 ) with DDQ. The treatment of the indole nucleoside with barium hydroxide and methanol gave the methyl ester 8 , which was further treated in water to give the desired 1-(β-D-ribofuranosyl)indol-3-acetic acid ( 9 ).     

The synthesis of certain 8-cyano-2,4-disubstituted-imidazo[1,5-a] pyrimidines

A number of imidazo[1,5-a]pyrimidine-8-carboxamides were synthesized by reacting various β-dicarbonyl compounds with 5(4)-aminoimidazole-4(5)carboxamide (AICA, 1 ), the non-ribosylated form of AICAR, a key intermediate in the metabolic pathway of purine biosynthesis. Cyclization of 1 with ethylacetoacetate yielded 2-methylimidazo[1,5-a]pyrimidin-1H-4-one-8-carboxamide ( 2 ). The treatment of 2 with phosphorus oxychloride gave 4-chloro-8-cyano-2-methylimidazo[1,5-a]pyrimidine ( 3 ). Various nucleophiles displaced the 4-chloro substituent of 3 under mild conditions. However, the 4-methylthio group of 8-cyano-2-methyl-4-methylthioimidazo[1,5-a)pyrimidine ( 8a ) was also displaced under very mild conditions. Even more strangely, the 4-diethylamino group of 8-cyano-4-diethylamino-2-methylimidazo[1,5-a]pyrimidine ( 5a ) was displaced by ammonia to give 4-amino-8-cyano-2-methylimidazo[1,5-a]pyrimidine ( 7 ).     

Synthesis of 8-amino-4-methylthio-6-methyl-2-(β-D-ribofuranosyl)-2,6-dihydro-1,2,3,5,6,7-hexaazaacenaphthylene and an unusual reductive ring-opening of the 1,2,3,5,6,7-hexaazaacenaphthylene ring system

The tricyclic nucleoside 8-amino-4-methylthio-6-methyl-2-(β-D-ribofuranosyl)-1,2,3,5,6,7-hexaazaacenaphthylene ( 3 ) was synthesized from 3-cyano-4,6-bis(methylthio)-1-(β-D-ribofuranosyl)pyrazolo[3,4-d]pyrimidine ( 1 ). Attempts to synthesize 8-amino-6-methyl-2-(β-D-ribofuranosyl)-1H-2,6-dihydro-1,2,3,5,6,7-hexaazaacenaphthylene ( 5 ) ([an aza analog of 6-amino-4-methyl-8-(β-D-ribofuranosyl)-1,3,4,5,8-pentaazaacenaphthylene (TCN)], which is a potent antitumor agent), by the treatment of 3 with Raney nickel did not afford the desired aza analog of TCN. Instead, it was established that a reductive cleavage of the pyridazine moiety of 3 had occurred to give 4-methylamino-6-methylthio-1-(β-D-ribofuranosyl)-1H-pyrazolo[3,4-d]pyrimidine-3-carboxamidine ( 6 ). Assuming that solubility was a problem in the reductive step, the isopropylidene derivative of 3 , 8-amino-6-methyl-4-methylthio-2-(2,3-O-isopropylidene-β-D-ribofuranosyl)-2,6-dihydro-1,2,3,5,6,7-hexaazaacenaphthylene ( 8 ), was treated with Raney nickel, only to observe that a similar reductive ring cleavage of 8 had occurred to afford 4-methylamino-6-methylthio-1-(2,3-O-isopropylidene-β-D-ribofuranosyl)-1H-pyrazolo[3,4-d]pyrimidine-3-carboxamidine ( 10 ) and 4-methylamino-1-(2,3-O-isopropylidene-β-D-ribofuranosyl)-1H-pyrazolo[3,4-d]pyrimidine-3-carboxamidine ( 11 ). Structural assignments for all products were established by physico-chemical procedures.     

Chemical conversion of uridine to 8,5′-O-cyclo-3-deazaguanosine

Treatment of 1-(2,3-O-isopropy lidene-β-D-ribofuranosyl)-2-oxo-4-imidazoline-4-carboxylic acid methyl ester with formaldehyde gave the 5-hydroxymethyl derivative which, after aeetylalion, gave the 5-eyanomelhyl derivative by treatment with tetra-n-butylammonium cyanide. The 2,5′-O-cyclo derivative of the 5-cyanomethylimidazole-4-carboxylate was converted to the title compound by treatment with ammonia. The present sequence of reactions furnished the chemical conversion of uridine to a 3-deazaguanosine via the imidazole nucleoside as the intermediate.     

Synthesis of 5,6,7,8-tetrahydro-5-oxopyrido[2,3-d]pyrimidine-6-carbonitriles and -6-carboxylic acid esters

Dieckmann ring closure reactions of 4-[(2-cyanoethyl)substituted amino]-2-phenyl-5-pyrimidinecarboxylates (Ha-f) afforded several 5,6,7,8-tetrahydro-5-oxo-2-phenylpyrido[2,3-d]pyrimidine-6- carbonitriles (IIIa-f). The open-chain intermediates (IIa-f) were prepared by dechloroamination of 5-carbethoxy-4-chloro-2-phenylpyrimidine (1a) with several 3-substituted amino- propionitriles. Alkylation of the sodium salt of 5,6,7,8-tetrahydro-8-methyl-5-oxo-2-phenyl-pyrido[2,3-d]pyrimidine-6- carbonitrile (IIIa) with methyl iodide in DMF resulted in methylation at C-6 to afford IV. Tosylation of IIIa in pyridine gave the corresponding tosyl ester (V) of the enolic form. Oxidative dehydrogenation at the 6,7-position resulted when IIIa reacted with thionyl chloride, affording 5,8-dihydro-8-methyl-5-oxo-2-phenylpyrido[2,3-d]pyrimidine-6- carbonitrile (VII). Dechloroamination of la or 5-carbethoxy-4-chloro-2-methylthiopyrimidine (Ib) with ethyl 3-ethylaminopropionate followed by Dieckmann cyclization of the resulting open-chain intermediates gave the corresponding ethyl 5,6,7,8-tetrahydro-5-oxopyrido[2,3-d]pyrimidine-6-carboxylates IX'a and IX'b, respectively. These exist predominately in the enol form and undergo alkylation and oxidation reactions similar to IIIa.     

The synthesis and PMR study of certain 3-substituted 2-(β-D-Ribofuranosyl)indazoles

The synthesis of 3-cyano-2-(β-D-ribofuranosyl)indazole (4) has been accomplished by a condensation of N-trimethylsilyl-3-cyanoindazole (1) with 2,3,5-tri-O-aeetyl-D-ribofuranosyl bromide (2) followed by subsequent deacetylation. The reactivity of the 3-cyano group was demonstrated by the conversion of 4 to 2-(β-D-ribofuranosyl)indazole-3-carboxamide (5) and 2-(β-D-ribofuranosyl)indazole-3-thiocarboxamide (6). The site of ribosylation and the assignment of anomeric configuration for 4 is discussed. The magnetic anisotropy effect of the exocyclic group at C3 on the anomeric proton as determined by pmr spectroscopy is discussed.     

Synthesis of 8-methyl-2-azainosine and related nucleosides

The synthesis of 6-methyl-7-(β-D-ribofuranosyl)imidazo[4,5-d]-v-triazin-4-one (8-methyl-2-azainosine ( 2) ) and 6-methyl-7-(β-D-glucopyranosyl)imidazo[4,5-d]-v-triazin-4-one ( 5 ) by diazotization of 5-amino-1-(β-D-ribofuranosyl)-2-methylimidazole-4-carboxamide ( 1 ) and diazotization of 5-amino-1-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-2-methylimidazole-4-carboxamide ( 3 ), followed by deacetylation of the resulting compound 4 , is described. The preparation of 6-methyl-5-(β-D-ribofuranosyl)imidazo[4,5-d]-v-triazin-4-one ( 10 ) and 6-methyl-5-(β-D-glucopyranosyl)imidazo[4,5-d]-v-triazin-4-one ( 11 ) by glycosylation of 6-methylimidazo[4,5-d]-v-triazin-4-one (8-methyl-2-azahypoxanthine, ( 7) ) is also described. Structural assignments were made on basis of analytical and ¹H-nmr and uv spectral data.     

Nucleosides CV. Synthesis of the 8-((β-D-ribofuranosyl)pyrazolo[1,5-a]-1,3,5-triazine isosteres of adenosine and inosine

Reaction of ethyl N-cyanoformimidate ( 3 ) and of ethyl N-carbelhoxyformimidate ( 5 ) with 3-aminopyrazole ( 2 ) gave 4-amino- and 4-oxo-3H-pyrazolo[1,5-a]-1,3,5-triazine ( 4 and 7 ), respectively. Reaction of 3-amino-4-(2,3-O-isopropylidene-5-O-trityl-β-D-ribofuranosyl)pyrazole ( 8 ) with the same reagents similarly gave the blocked 4-amino-8-ribosyl- and 4-oxo-3H-8-ribosyl-pyrazolo[ 1,5-a]-1,3,5-triazine ( 9 and 15 ), respectively. Deblocking in acid finally afforded the unblocked products 10 (an isostere of adenosine and formycin) and 16 (an isostere of inosine and formycin B). The corresponding derivatives in the a series were made by identical procedures for confirming all structural assignments. Preliminary in vitro testing results of 10 are included.