Synthesis of α-(aminomethylene)-9H-purine-6-acetic acid derivatives

α-(Aminornethylene)-9H-purine-6-acetamide ( 3a ) and the corresponding ethyl acetate 9 have been synthesized by catalytic hydrogenation of 6-cyanomethylenepurine derivatives 2 and 7 which were obtained by the substitution of 6-chloropurine derivatives with α-cyanoacetamide and ethyl cyanoacetate, respectively. Substitution of α-(aminomethylene)-9-(tetrahydrofuran)-9H-purine-6-acetamide ( 3b ) with amines gave the corresponding N-alkyl- and N-arylamines 5 , which were treated with acid to give N-substituted α-(aminomethylene)-9H-purine-6-acetamides 6 . Substitution of 9 with amines gave the corresponding N-alkyl- and N-aryl substituted amines 10 .     

The synthesis of 6-C-substituted 9-methoxymethylpurine derivatives

6-Cyanomethylene ( 2 ), which was prepared via 1 by substitution with malononitrile, has been catalytically hydrogenated to the α-(aminomethylene)-9-(methoxymethyl)-9H-purine-6-acetonitrile ( 3 ) in good yield using N,N-dimethylformamide-benzene as solvent over Pd-C under medium pressure. Intermediate 3 was derived to aldehyde 5 by hydrolysis with acid or base. Substitution of 3 with amines gave the corresponding alkylamines 6 and 7 . Reaction of 3 with hydrazine and acetamidine hydrochloride gave pyrazole derivative 8 and pyrimidine derivative 9 , respectively.     

Ring closure of 1-[4-(imidazol-1-yl)phenyl]-3-phenyl-2-propen-1-one derivatives to potential biologically active compounds

1-[4-(Imidazol-1-yl)phenyl]-3-phenyl-2-propen-1-one 1 reacted with acetone cyanohydrin, ethyl phenylacetate and cyanoacetamide to give the adducts 2, 8 and 10 respectively. Action of hydrazine hydrate on both the γ-ketonitrile 2 and the corresponding γ-ketoacid 4 led to pyridazine derivatives 3 and 5 . 4,5-Dihydropyridazinone 5 was dehydrogenated by the action of bromine in acetic acid to give pyridazinone 6 . Cyclization of acid 8 in acetic medium resulted in α-pyrone 9 . Cyanopentanamide 10 was converted with hydrochloric acid into δ-ketoacid 13 which led to α-pyrone 14 via an intramolecular dehydration. Refluxing 10 in the presence of acetic acid and ammonium acetate gave 3,4-dihydropyridone 11 which was dehydrogenated to produce pyridone 12 .     

Synthesis and tautomerism of ethyl 2-(2-benzothiazolyl)-2-(6-purinyl)acetate and related compounds

Reaction of 6-chloro-9H-(2-tetrahydropyranyl)purine ( 2d ) with the sodium salt of ethyl benzothiazole-2-ace-tate ( 1 ) in dimethylformamide effects condensation of the two compounds (with loss of sodium chloride) to give the corresponding ethyl diarylacetate 4 (35%), present largely as an enol chelate tautomer. Isolated as a by-product is 6-(2-aminophenyl-1-thio)-9H-(2-tetrahydropyranyl)-purine (4%), formed via opening of the thiazole ring. Removal of the tetrahydropyranyl protective group from 4 occurs by treatment with p-toluenesulfonic acid in aqueous ethanol to produce ethyl benzothiazole-2-(6-purinyl)acetate (80%), existent largely as two enol chelate isomers. Spectral data for the various products are presented. An attempt to use 6-chloro-9-acetyl-9H-purine in place of 2d in the first reaction gives acetylation of 1 instead of condensation.     

Synthesis of 3H-pyrazol-3-one derivatives containing a 9H-thioxanthene ring

2,4-Dihydro-5-methyl-2-phenyl-4-(9H-thioxanthen-9-yl)-3H-pyrazol-3-one ( 3 ) was prepared by condensing 9H-thioxanthen-9-ol ( 1 ) with 2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-one ( 2 ), or by cyclizing ethyl α-acetyl-9H-thioxanthene-9-acetate ( 4 ) with phenylhydrazine. 2,4-Dihydro-5-methyl-2-phenyl-4-(9H-thioxan- then-9-yl)-3H-pyrazol-3-one 10,10-dioxide ( 8 ) was prepared by cyclizing ethyl α-acetyl-9H-thioxanthene-9-acetate 10,10-dioxide ( 7 ) with phenylhydrazine. Compound 8 was also obtained by oxidizing 3 with hydrogen peroxide in acetic acid. 5-Amino-2,4-dihydro-2-phenyl-4(9H-thioxanthen-9-yl)-3H-pyrazol-3-one ( 10 ) was obtained by condensing 1 with 5-amino-2,4-dihydro-2-phenyl-3H-pyrazol-3-one ( 9 ).     

Synthesis of 1,8-, 1,6- and 3,6-dichloro-9H-thioxanthen-9-ones

Cyclization of 2-chloro-6-[(3-chlorophenyl)thio]benzoic acid ( 2 ) gave a mixture of 1,8-, 3 , and 1,6-dichloro-9H-thioxanthen-9-ones 4 . The mixture was converted to 1,8-diamino- 7 , and 1-amino-6-chloro-9H-thioxanthen-9-ones 8 , from which 3 and 4 were prepared separately, respectively. From a mixture of 4 and 3,6-dichloro-9H-thioxanthen-9-one ( 11 ) obtained by cyclizing 4-chloro-2-[(3-chlorophenyl)thio]benzoic acid ( 10 ) was separated 11 by conversion of 4 to 8 .     

Synthesis of nucleoside analogs of 1,4-oxathiane, 1,4-dithiane,and 1,4-dioxane

The two regioisomers 6-chloro-9-(1, 4-oxathian-3-yl)-9H-purine ( 5 ) and 6-chloro-9-(1,4-oxathian-2-yl)-9H-purine ( 6 ) were obtained when 3-acetoxy-1,4-oxathiane ( 3 ) was subjected to the acid-catalyzed fusion procedure; compound 3 was prepared by a Pummerer reaction with 1,4-oxathiane 4-oxide ( 2 ). The nucleoside analog 6 could he converted into the adenine derivative 7 and 9-(1,4-oxathian-2-yl)-9H-purine-6(1H)thione ( 8 ). The following nucleoside analogs have also been synthesized: 6-chloro-9-(1,4-dithian-2-yl)-9H-purine ( 13 ), 9-(1,4-dithian-2-yl)adenine ( 14 ), 9-(1,4-dithian-2-yl)-9H-purine-6(1H)thione ( 15 ), and 6-chloro-9-(1,4-dioxan-2-yl)-9H-purine ( 18 ).     

Photochemistry synthesis. Part 1: Syntheses of xanthine derivatives by photolysis of 1-(5′-oxohexyl)-3,7-dimethyl-3,7-dihydro-1H-purine-2,6-dione (pentoxifylline): an ambident chromophore

We investigated the use of photochemistry to make novel derivatives of pentoxifylline. Under conditions that favour singlet excited states, we obtained 1-allyl-3,7-dimethyl-3,7-dihydro-1H-purine-2,6-dione, (R^∗,R^∗)-(±)-1-{[2-hydroxy-2-methylcyclobutyl]methyl}-3,7-dimethyl-3,7-dihydro-1H-purine-2,6-dione and 1-(5-hydroxyhexyl)-3,7-dimethyl-3,7-dihydro-1H-purine-2,6-dione. Naphthalene or molecular oxygen increases the yields and triplet sensitisers (acetophenone, benzophenone and acetone) decrease the yields. Efficient intramolecular triplet energy transfer from the carbonyl to the xanthine moiety allows the carbonyl moiety to react from a singlet excited state only. In solvents with an α-hydroxyalkyl hydrogen under conditions that favour triplet excited states, we obtained 8-substituted pentoxifylline derivatives: 8-(1-hydroxy-1-methylethyl)-3,7-dimethyl-1-(5-oxohexyl)-3,7-dihydro-1H-purine-2,6-dione in isopropanol, 8-(1-hydroxymethyl)-3,7-dimethyl-1-(5-oxo-hexyl)-3,7-dihydro-1H-purine-2,6-dione in methanol and 8-(1-hydroxyethyl)-3,7-dimethyl-1-(5-oxohexyl)-3,7-dihydro-1H-purine-2,6-dione in ethanol. The xanthine moiety reacts from a triplet state via a radical mechanism and yields are considerably improved by the addition of catalytic amounts of di-tert-butyl peroxide.     

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.     

Reaction of N1,N2-diarylacetamidines with (2,4,7-trinitro-9H-fluoren-9-ylidene)propanedinitriles

Novel spiro[fluorene-9,4′-(1′,2′,3′,4′-tetrahydropyridine)]-5′-carbonitriles 6a-c have been obtained from the reaction of N¹,N²-diarylacetamidines 1a-c with (2,4,7-trinitro-9H-fluoren-9-ylidene)propanedinitrile ( 2 ) in ethyl acetate solutions at ambient temperature for 6a,b or under reflux for 6c , respectively.     

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.     

Steroid derivatives of purine-6(1H)-thione (1a-c)

The products obtained as a result of the alkylation of purine-6(1H)-thione, and 6-alkylthiopurines with steroidal-21-(p-bromobenzenesullonates) (H) and 3-methoxy-16α-bromoestra-1,3,5 (10)-tricne-17-one (IV) is reported. The ratio of 9-alkylated to 7-alkylated purine in the alkylation of 6-methylthiopurine (VI) is presented. The use of the S-diphenylmethylprotecling group in the syntheses of sensitive 9-steroidal-9H-purine-6(1H)-thiones is discussed.     

Synthesis of 2-(β-D-ribofuranosyl)pyrimidines,A new class of C-nucleosides

A new C-glycosyl precursor for C-nucleoside synthesis, 2,5-anhydroallonamidine hydrochloride ( 4 ) was prepared and utilized in a Traube type synthesis to prepare 2-(β-D-ribofuranosyl)pyrimidines, a new class of C-nucleosides. The anomeric configuration of 4 was confirmed by single-crystal X-ray analysis. Reaction of 4 with ethyl acetoacetate gave 6-methyl-2-(β-D-ribofuranosyl)pyrimidin-4-(1H)-one ( 5 ). Reaction of 4 with diethyl sodio oxaloacetate gave 2-(β-D-ribofuranosyl)pyrimidin-6(1H)-oxo-4-carboxylic acid ( 6 ). Esterification of 6 with ethanolic hydrogen-chloride gave the corresponding ester 7 which when treated with ethanolic ammonia gave 2-(β-D-ribofuranosyl)pyrimidin-6(1H)-oxo-4-carboxamide ( 8 ). Condensation of 2,5-anhydroallonamidine hydrochloride ( 4 ) with ethyl 4-(dimethylamino)-2-oxo-3-butenoate ( 9 ), gave ethyl 2-(β-D-ribofuranosyl)pyrimidine-4-carboxylate ( 10 ). Treatment of 10 with ethanolic ammonia gave 2-(β-D-ribofuranosyl)pyrimidine-4-carboxamide ( 11 ). Single-crystal X-ray analysis confirmed the β-anomeric configuration of 11. Acetylation of 11 followed by treatment with phosphorus pentasulfide and subsequent deprotection with sodium methoxide gave 2-(β-D-ribofuranosyl)pyrimidine-4-thiocarboxamide ( 14 ). Dehydration of the acetylated amide 12 with phosphorous oxychloride provided 2-(β-D-ribofuranosyl)pyrimidine-4-carbonitrile ( 15 ). Treatment of 15 with sodium ethoxide gave ethyl 2-(β-D-ribofuranosyl)pyrimidine-4-carboximidate ( 16 ), which was converted to 2-(β-D-ribofuranosyl)pyrimidine-4-carboxamidine hydrochloride ( 17 ) by treatment with ethanolic ammonia and ammonium chloride. Treatment of 16 with hydroxylamine yielded 2-(β-D-ribofuranosyl)pyrimidine-4-N-hydroxycarboxamidine ( 18 ). Treatment of 2-(β-D-ribofuranosyl)pyrimidine-4-carboxamide ( 11 ) with phosphorus oxychloride gave the corresponding 5′-phosphate, 19 , Coupling of 19 with AMP using the carbonyldiimidazole activation procedure gave the corresponding NAD analog, 2-(β-D-ribofuranosyl)pyrimidine-4-carboxamide-(5′ ? 5′)-adenosine pyrophosphate ( 20 ).     

[f]-Fused purine-2,6-diones: Synthesis of new [1,3,5]- and [1,3,6]-thiadiazepino-[3,2-f]-purine ring systems

Summary 6-Phenyl-1,3-dimethyl-2,4-dioxo-1,2,3,4,8,9-hexahydro-[1,3,5]-thiadiazepino-[3,2-f]-purine (5) was obtained by a three-step synthesis from 8-mercapto-1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione (1) and 2-(benzoylamino)-ethyl chloride (2)via 8-(benzoylaminoethylthio)-1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione (3) and its chloromido derivative4. The analogous 9-phenyl-1,3-dimethyl-2,4-dioxo-1,2,3,4,6,7-hexahydro-[1,3,6]-thiadiazepino-[3,2-f]-purine (7) was synthesized either from compound1 and N-(2-chloroethyl)-benzimido chloridevia N-(chloroethyl)-S-(1,3-dimethyl-2,4-dioxo-1,2,3,4-tetrahydro-7H-purin-8-yl)-benzothioimide (6), or alternatively from 7-(2-benzoylaminoethyl)-8-bromo-1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione (9), its 8-mercapto derivative10 and the corresponding chloroimido compound11 being the intermediates.Part of this paper was presented as a preliminary report at the Congress of Czech and Slovak Chemical Societies, Olomouc, Czech Republic, September 13–16, 1993     

Synthesis of new phosphorylated analogs of nucleotides containing adenine and ethylidene-1,1-bisphosphoryl moieties

Reaction of adenine and 9-[2-(1,3-dioxolan-2-yl)ethyl]-9H-purine-6-amine with ethylidene-1,1-bisphosphonates resulted in the formation of new purine bases containing ethylidene-1,1-bisphosphoryl groups.

     

Synthesis and comparative study of reactivities of δ-lactone,estor group and oxazinone ring in coumarin derivatives towards carbon or nitrogen nucleophiles

Condensation of methyl 7-methylcoumarin-4-acetate ( 2 ) with primary amines and with anthranilic acid gave 7-methyl-2-oxo-N-aryl-2H-[1]-benzopyran-4-acetamide ( 4a—d ) and (7), respectively. Compound 7 underwent cyclization to give 2-(7-methyl-2-oxo-2H-[1]-benzopyran-4-yl)-methyl-4H-3,1-benzoxazin-4-one ( 3 ). The reaction of 3 with aromatic amines gave the corresponding quinazolone derivatives 5 which tautomerises to the thermodynamically more stable isomer 6 , whereas its reaction with Grignard reagents and aromatic aldehydes gave 8a, 8b , and 9a, 9b , respectively.     

Synthesis and optical behaviors of 2-(9-phenanthrenyl)-, 2-(9-anthryl)-, and 2-(1-pyrenyl)-1-alkylimidazole homologues

Eight 2-(9-phenanthrenyl)-, 2-(9-anthryl)- and 2-(1-pyrenyl)-1-alkyl-benzimidazole compounds, three 2-(9-anthryl)-1-alkylphenanthroimidazole compounds and five 4,5-diphenyl-1-alkyl-2-(9-anthryl)imidazole compounds were synthesized by alkylation reactions of the corresponding benzimidazole, phenanthroimidazole or imidazole compounds. 2-(10-Bromo-9-anthryl)-1-alkyl-benzimidazole compounds were prepared by bromination reaction of 2-(9-anthryl)-1-alkylbenzimidazole compounds. All the synthesized compounds were characterized by elemental analysis, ¹H NMR, ¹³C NMR, MS or HRMS; their absorption coefficients (), maximum absorption λ_amax, fluorescence emission maximum λ_em, Stokes shifts and fluorescence quantum yields (Φ_F) in ethyl acetate were determined; their fluorescent lifetimes (T₁ and T₂) were measured in ethyl acetate and in solid state, respectively. The crystal structure of 2-(9-anthryl)-1-n-butyl-4,5-diphenylimidazole (12a) was determined to be triclinic, space group P-1 types, using single crystal X-ray crystallography technique. The results showed that these compounds exhibited moderate fluorescence-emission abilities and higher solubility in most organic solvents than their corresponding starting materials. The relationships between the optical behaviors and structures for these compounds were discussed.     

About the synthesis of [1,2]diazepinoindole derivatives from ethyl 2-(1-methylindole)acetate, 2-indole and 3-indoleacetohydrazones

The Vilsmeier-Haack reaction with ethyl 2-(1-methylindole)acetate and N,N-Dimethylamides/phosphorus oxychloride gave (65–85%) of ethyl 2-(3-acyl-1-methylindole)acetates 2 , which when boiled with hydrazine yielded about 90% of 4,5-dihydro-6-methyl-4-oxo-3H[1,2]diazepino[5,6-b]indoles 3. The attempted cyclization of 2-(1-methylindole)acetohydrazones 6 with acyl (acetyl and benzoyl) chlorides/triethylamine, to [1,2]diazepino[5,6-b]indole derivatives was fruitless and the bis(acyl)hydrazones 9 were obtained. Several transformations of 9 are reported. Similarly, the attempted cyclization of 3-indoleacetohydrazones 14 with acetyl chloride/triethylamine to [1,2]diazepino[4,5-b]indole derivatives was also fruitless and the bis(acyl)hydrazones 16 were again obtained.     

Synthesis of 9-(2-fluorobenzyl)-6-methylamino-9H-purine

Synthesis of 9-(2-fluorobenzyl)-6-methylamino-9H-purine ( 1 ) from nine different precursors is reported. Compound 1 was prepared by methylamination of 6-chloro-9-(2-fluorobenzyl)-9H-purine ( 4 ), by alkylation of 6-methylaminepurine ( 5 ) or form 9-(2-fluorobenzyl)-1-methyladeninium iodide ( 8 ) via the Dimroth rearrangement. Selective 2-step methylation of 6-aminopurine 6 was accomplished by hydride reduction of 6-formamidopurine 9 , 6-dimethylaminomethyleneaminopurine 10 or 6-phenylthiomethyl purine 11 to give 1. Compound 1 was also prepared by dethiation or reductive dechlorination of 2-methylthiopurine 16 or 8-chloropurine 19 , respectively, or by hydrolysis of 6-N-methylformamidopurine 12 , which was prepared from 6-dimethylaminopurine 13 by selective oxidation.     

3-(Dimethylamino)-2,2-dimethyl-2H-azirin als α-Aminoisobuttersäure(Aib)-Äquivalent: Cyclische Depsipeptide durch direkte Amid-Cyclisierung

3-(Dimethylamino)-2,2-dimethyl-2H,-azirine as an α-Aminoisobutyric-Acid (Aib) Equivalent: Cyclic Depsipeptides via Direct Amid Cyclization In MeCN at room temperature, 3-(dimethylamino)-2,2-dimethyl-2H-azirine ( 1 ) and α-hydroxycarboxylic acids react to give diamides of type 8 (Scheme 3). Selective cleavage of the terminal N,N-dimethylcarboxamide group in MeCN/H₂O leads to the corresponding carboxylic acids 13 (Scheme 4). In toluene/Ph SH , phenyl thioesters of type 11 are formed (see also Scheme 5). Starting with diamides 8 , the formation of morpholin-2,5- diones 10 has been achieved either by direct amide cyclization via intermediate 1,3-oxazol-5(4H)-ones 9 or via base-catalyzed cyclization of the phenyl thioesters 11 (Scheme 3). Reaction of carboxylic acids with 1 , followed by selective amide hydrolysis, has been used for the construction of peptides from α-hydroxy carboxylic acids and repetitive α-aminoisobutyric-acid (Aib) units (Scheme 4). Cyclization of 14a, 17a , and 20a with HCI in toluene at 100° gave the 9-, 12-, and 15-membered cyclic depsipeptides 15, 18 , and 21 , respectively.