Ring transformation reactions of C-nucleosides: Facile synthesis of pyrazolo[1,5-a]pyrimidine and pyrazolo[1,5-a]triazine C-nucleosides

1,3-Dimethyluracil ( 1 ), a versatile synthon for the synthesis of various heterocycles, reacted readily with 3-aminopyrazoles 2 in sodium ethoxide to give pyrazolo[1,5-a]pyrimidines 3 . Under similar conditions, 3-aminopyrazole C-nucleosides 4 and the synthon 1 gave a mixture of pyrazolo[1,5-a]pyrimidine C-nucleosides, which was separated on a silica gel column. Attempts to remove the protecting groups yielded pyranose derivative 10 . Another synthon 1,3-dimethyl-5-azauracil and 3-aminopyrazoles 12 gave pyrazolo[1,5-a]triazines 13 . In a similar reaction with 3-aminopyrazole C-nucleosides 4 gave the corresponding pyrazolo[1,5-a]-triazine C-nucleosides 14 and 15 .     

Recent synthetic methodologies for pyrazolo[1,5-a]pyrimidine

The development of new synthetic routes towards pyrazolo[1,5-a]pyrimidines for their biological and medicinal exploration is an attractive area for researchers. This review focuses on various synthetic routes developed in the last decade for the synthesis of differently substituted pyrazolo[1,5-a]pyrimidines by a broad range of organic reactions by means of 5-aminopyrazole as a precursor.     

Synthesis of some new purine-related compounds: Regioselective one-pot synthesis of new tetrazolo[1,5-a]pyrimidine,pyrazolo[1,5-a]pyrimidine and pyrimido[1,6-a]pyrimidine derivatives

An easy and efficient route for the synthesis of some tetrazolo[1,5-a]-, pyrazolo[1,5-a]- and pyrimido[1,6-a] pyrimidine derivatives was described through the reaction of sodium salts of formyl ketones with 5-aminotetrazole, 5-aminopyrazole derivatives and 6-aminothiouracil, respectively. The antimicrobial screening of some derivatives of the prepared compounds has been achieved, and it exhibited a moderate activity against the tested microorganisms.     

Solvent-free combinatorial synthesis of tetrazolo[1,5-a]thiopyrano[3,4-d]pyrimidine derivatives

A series of novel tetrazolo[1,5-a]thiopyrano[3,4-d]pyrimidine derivatives were synthesized by reaction of aryl aldehyde, 2H-thiopyran-3,5(4H,6H)-dione, and 5-aminotetrazole under solvent-free conditions. The features of this procedure are mild reaction conditions, high yields, and operational simplicity.     

Synthesis of new substituted pyrazolo[1,5-a]-pyrimidines and pyrazolo[1,5-a]1,3,5-triazines

5-Substituted 3-amino-1H-pyrazole-4-carbonitriles 2a-d react with appropriate biselectrophilic reagents in the presence of (TEA) to give the substitution products pyrazolo[1,5-a]pyrimidines 4a-d, 6a-d and pyrazolo[1,5-a ]1,3,5-triazines 8a-d. Compounds 6a and 8a react with secondary amines to 10a-c and 11a-c. Treatment of 2a with malonodinitrile results in the substituted pyrazolo-[1,5-a]pyrimidine 16. Condensation of 2a, 2c and 2d with ethyli-dene-malodintriles leads to racemic dihydro-pyrazolo[1,5-a] pyr-imidines 18a-e. Reaction of diene 20 with the heterodienophile 21 leads to formation of Diels-Alder adduct 22.     

The synthesis of 7,8-dihydroimidazo[1,2-e]pyrazolo[1,5-a]-1,3,5-triazines, 8,9-dihydro-7H-pyrimido[1,2-e]pyrazolo[1,5-a]-1,3,5-triazines and 7,8,9,10-tetrahydro[1,3]diazepino[1,2-e]pyrazolo[1,5-a]triazines

Cyclic hydrazino amidines were converted to the corresponding aminopyrazolyl derivatives. Ring closure between the amino groups of pyrazoline moieties and NH groups of cyclic amidines afforded the following ring systems: 7,8-Dihydroimidazo[1,2-e]pyrazolo[1,5-a]-1,3,5-triazines, 8,9-dihydro-7H-pyrimido[1,2-e]pyrazolo[1,5-a]-1,3,5-triazines and 7,8,9,10-tetrahydro[1,3]diazepino[1,2-e]pyrazolo[1,5-a]-1,3,5-triazines.     

Optimization of pyrazolo[1,5-a]pyrimidine based compounds with pyridine scaffold: Synthesis,biological evaluation and molecular modeling study

BackgroundPyrazolopyrimidine heterocycle and its isosteres represent the main scaffold for many pharmacologically active drugs including anti-inflammatory agents. The COX-2 inhibitors are the principal gate for the design of new safe and potent anti-inflammatory agents.MethodsNovel derivatives of pyrazolo[1,5-a] pyrimidines were synthesized and screened in vivo and in vitro for their anti-inflammatory potential.ResultsWithin the constructed compounds, compound 11 was the most active compound on IL-6 and TNF-α (percentage inhibition = 80 and 89%, respectively). In addition, compound 12 displayed the most inhibitory effect towards COX-2 (IC₅₀ = 1.11 µM), whereas compound 11 recorded the highest COX-2 selectivity (S.I = 8.97). The target derivatives 11–14 displayed good edema inhibitory potential (46–68%) and compound 11 was the most potent candidate (ED₅₀ = 35 mg/kg). Additionally, the most potent sPLA2-V inhibitors were compounds 11 and 13 (IC₅₀ = 1 and 1.7 µM respectively). Regarding activity towards 15-LOX, derivative 12 was the most active compound with IC₅₀ = 5.6 µM revealing higher inhibitory activity than nor-dihydroguaiaretic acid (IC₅₀ = 8.5 µM). To confirm the anti-inflammatory potential of the target derivatives, molecular modeling was performed inside COX-2 and 15-LOX active sites.ConclusionDisplay discoveries increment the plausibility that these pyrazolo[1,5-a]pyrimidines might act as a beginning point for the improvement of anti-inflammatory agents.     

Reactivity of 7-(2-dimethylaminovinyl)pyrazolo[1,5-a]pyrimidines: Synthesis of pyrazolo[1,5-a]pyrido[3,4-e]pyrimidine derivatives as potential benzodiazepine receptor ligands. 2

A series of pyrazolo[1,5-a]pyrido[3,4-e]pyrimidin-6-ones was obtained by reaction of ammonium acetate with ethyl 7-dimethylaminovinylpyrazolo[1,5-a]pyrimidine-6-carboxylates and these had been prepared from ethyl 7-methylpyrazolo[1,5-a]pyrimidine-6-carboxylates by reaction with dimethylformamide dimethylacetal. Under these conditions the compounds bearing a 2-hydroxy group were also O-alkylated. During the preparation of the ethyl 2-hydroxy-7-methyl-3-phenylpyrazolo[1,5-a]pyrimidine-6-carboxylate the corresponding 5-methyl isomer was isolated and identified.     

Reactivity of 7-(2-dimethylaminovinyl)pyrazolo[1,5-a]pyrimidines: Synthesis of pyrazolo[1,5-a]pyrido[3,4-e]pyrimidine derivatives as potential benzodiazepine receptor ligands. 1

A series of 7-methylpyrazolo[1,5-a]pyrimidines were reacted with dimethylformamide dimethylacetal to give the corresponding dimethylaminovinyl derivatives. These were reacted with ammonium acetate affording, through a ring closure, a number of 6-methylpyrazolo[1,5-a]pyrido[3,4-e]pyrimidines bearing various substituents on the pyrazole ring. The 6-acetyl-2-hydroxy-7-methylpyrazolo[1,5-a]pyrimidine was used as starting material for obtaining some O-alkyl derivatives. Catalytic transfer hydrogenation of 2-benzyloxy-6-methylpyrazolo[1,5-a]pyrido[3,4-e]pyrimidine led to the 2-hydroxy derivative.     

A synthesis of 6-functionalized 7-unsubstituted- and 7-methyl[1,2,4]azolo[1,5-a]pyrimidine derivatives

6-Functionalized 7-R-4,7-dihydro[1,2,4]azolo[1,5-a]pyrimidines (R?=?H or Me) were synthesized by Biginelli-like reaction of formaldehyde or acetaldehyde, aminoazoles, and corresponding β-dicarbonyl precursor. Alkylation of the obtained compounds proceeds smoothly at position 4, while oxidation leads to 7-R-[1,2,4]azolo[1,5-a]pyrimidines formation. 6-Ethoxycarbonyl derivatives could be reduced to the corresponding alcohols by LiAlH₄ and hydrolyzed to the acids.     

Aryl-substituted 6,7-dihydropyrazolo[1,5-a]pyrimidine

We have studied the reaction of 5-amino-3-phenylpyrazole with chalcones which takes place with the formation of arylsubstituted forms of dihydropyrazolo[1,5-a]pyrimidine and have discussed a possible mechanism for the reaction. Dehydrogenation of the compounds prepared has been effected using N-bromosucciniimide.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 962–965, July, 1988.     

A new general synthesis of functionally substituted pyrazolo[1,5-a]pyrimidines

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Transition-metal-switchable divergent synthesis of nitrile-containing pyrazolo[1,5-a]pyridines and indolizines

Palladium-catalyzed oxidative formal [4 + 1] annulation of pyridine-substituted acrylonitriles toward divergent fused N-heterocycles synthesis is reported. The heterodifunctionalization reaction with Cu(OAc)₂ and urea as the nitrogen source accesses to nitrile-substituted pyrazolo[1,5-a]pyridines in moderate to good yields, while the homodifunctionalization reaction with FeBr₃ leads to synthesis of nitrile-substituted indolizines in excellent yields.     

α,β-Unsaturated nitriles in heterocyclic synthesis: Synthesis of some new pyrazolo[1,5-a]pyrimidine derivatives

3-Antipyrinyl-5-aminopyrazole (1) reacted with acrylonitrile to afford 5-amino-1--cyanoethyl-3-antipyrinylpyrazole (2). Compound2 could also be obtained from the reaction of -cyanoethylhydrazine (3) and compound4.2 was readily cyclized into 2-antipyrinyl-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrimidin-5-one (5) by acetic-hydrochloric acid.5 could be also obtained from the reaction of1 and methyl acrylate. The reaction of1 and cinnamonitrile derivatives7 a–e resulted in the formation of pyrazolo[1,5-a]pyrimidine derivatives9,11 and12.

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,-Ungesättigte Nitrile in der Heterocyclen-Synthese: Synthese einiger neuer Pyrazolo[1,5-a]pyrimidin-Derivate

Zusammenfassung 3-Antipyrinyl-5-aminopyrazol (1) reagierte mit Acrylnitril zu 5-Amino-1--cyanoethyl-3-antipyrinylpyrazol (2).2 konnte ebenfalls aus der Reaktion von -Cyanethylhydrazin (3) und Verbindung4 erhalten werden.2 wurde mittels Essigsäure-Salzsäure glatt zu 2-Antipyrinyl-4,5,6,7-tetrahydropyrazolo[1,5-a]-pyrimidin-5-on (5) cyclisiert.5 konnte auch aus der Reaktion von1 mit Methylacrylat erhalten werden. Die Reaktion von1 mit Zimtsäurenitrilderivaten7 a–e ergab die Pyrazolo[1,5-a]pyrimidin-Derivate9,11 und12.

     

Anti-cancer activities of pyrazolo[1,5-a]indole derivatives

The structure activity relationship (SAR) in the anti-cancer activities of pyrazolo[1,5-a]indole derivatives was investigated, and the following conclusions were obtained: 1) N(1)-quaternarization is essential for anti-cancer activity, 2) the size and polarity of the 2-substituent is crucial for in vitro activity which allows further investigation in an in vivo test, 3) the effect of the 4-substituent on the activity is minor compared with the other two factors.