Synthesis of pyrazolo[3,4‐b]pyridines and attachment of amino acids and carbohydrate as linkers

Synthesis of novel pyrazolo[3,4‐b]pyridines has been achieved successfully by sequence of Gould ‐ Jacobs reaction between 5‐aminopyrazole and diethylethoxymethylenemalonate in good yield. Further the pyrazolo[3,4‐b]pyridines were converted into succinimidoyl active esters which are then replaced by biological samples such as amino acids and carbohydrate in slightly aqueous medium.     

New one‐ pot synthesis of pyrazolo[3,4‐c]pyridazine and isoxazolo‐[5,4‐b]pyridine derivatives from potassium cyanoacetahydroxamate

The reaction of potassium cyanoacetohydroxamate 1 with ethyl 2‐aryl‐hydrazono‐3‐oxobutyrates 2 gave the unexpected pyrazolo[3,4‐c]pyridazines 7 and isoxazolo[5,4‐b]pyridines 10 via a one‐pot reaction. A mechanistic proof is suggested to account for the products.     

Regioselective three‐component synthesis of novel indeno[1,2‐b]‐pyrazolo[4,3‐e]pyridines‐fused derivatives of 4‐azafluorenone alkaloid

New fused indeno[1,2‐b]pyridine derivatives have been prepared in a multicomponent reaction from benzaldehydes, indanedione and the appropriate aminoheteroaryl compound. The simple methodology permitted the syntheses of a series of indeno[1,2‐b]pyrazolo[4,3‐e]pyridines 4 from 5‐aminopyrazol 1 and modulated by the corresponding benzaldehyde 2 .     

The first synthesis of furazano[3,4‐b][1,6]naphthyridines

Reaction of 6‐acetyl‐7‐aminofurazano[3,4‐b]pyridines with DMFDMA afforded N,N‐dimethylformamidines that were cyclized to the novel furazan‐fused [1,6]naphthyridine system by treatment with sodium methylate in good yield. The tricyclic system is characterized by X‐ray crystallography.     

A green and efficient synthesis of furo[3,4‐e]pyrazolo[3,4‐b]‐pyridine derivatives in water under microwave irradiation without catalyst

A series of furo[3,4‐e]pyrazolo[3,4‐b]pyridine analogues of podophylloxin were synthesized via three‐component reactions of aldehydes, 3‐methyl‐1‐phenyl‐1H‐pyrazol‐5‐amine and tetronic acid in water under microwave irradiation without catalyst. This efficient synthesis not only offers an economical and green synthetic strategy to this class of significant compounds but also enriches the investigations on microwave‐assisted synthesis in water.     

Synthesis of pyrazolo[3,4‐b]pyridines using ammonium acetate as green reagent in multi‐component reactions

Several new pyrazolo[3,4‐b]pyridine derivatives were synthesized by one pot cyclocondensation of the components; 5‐amino‐3‐aryl‐1H‐phenylpyrazoles, p‐substituted benzoylacetonitriles and some aldehydes. The condensations were most effective by using ammonium acetate as the base catalyst; triethylamine was also studied as a catalyst.     

An efficient synthesis of new class of pyrazolo[3,4‐b]pyridine‐6‐one derivatives by a novel cascade reaction

A novel cascade reaction of 4‐arylidene‐2‐phenyl‐1,3‐oxazol‐5(4H)‐one with 3‐methyl‐1‐phenyl‐1H‐pyrazol‐5‐amine was described and a number of new pyrazolo[3,4‐b]pyridine‐6‐one derivatives were synthesized. This new protocol has the advantages of shorter time, higher yields, and lower cost as well as easier operation.     

An alternate approach for the synthesis of 2‐substituted‐arylimidazo[4,5‐b]pyridines and their anti‐bacterial activity

An alternate method for the convenient preparation of the imidazo[4,5‐b]pyridines from 2,3‐pyridinediamine and 2‐aryl‐3(1)‐benzoxazine‐4H‐one has been illustrated. The mechanistic pathway for the formation of the product 4 has been proposed. All the compounds prepared herein were screened for their anti‐ bacterial properties.     

An efficient microwave‐assisted synthesis furo[3,4‐b]‐[4,7] phenanthroline and indeno[2,1‐b][4,7]phenanthroline derivatives in water

A series of furo[3,4‐b][4,7]phenanthroline and indeno[2,1‐b][4,7]phenanthroline derivatives were synthesized via a three‐component reaction of aromatic aldehydes, 6‐aminoquinoline and either tetronic acid or 1,3‐indanedione in water, under microwave irradiation without use of any catalyst. This green procedure offers several advantages including operational simplicity, clean reaction, and increased safety for small‐scale high‐speed synthesis.     

Quinolone analogues 9. Synthesis of 7‐methylsulfanyl‐ and 7‐methanesulfonylpyridazino[3,4‐b]quinoxalin‐4(1H)‐ones

The reaction of 7‐chloro‐1‐methylpyridazino[3,4‐b]quinoxalin‐4(1H)‐ones 3a‐5a with sodium methylthiolate gave 1‐methyl‐7‐methylsulfanylpyridazino[3,4‐b]quinoxalin‐4(1H)‐ones 8a‐c , whose reaction with m‐chloroperbenzoic acid afforded the 7‐methanesulfonyl‐1‐methylpyridazino[3,4‐b]‐quinoxalin‐4(1H)‐ones 9a‐c , respectively. The above substituent change at the 7‐position resulted in the activity alteration to microorganisms.     

Synthesis of new chromeno[4,3,2‐de]quinazolin‐2‐ones, ‐quinazolines and ‐pyrrolo[2,1‐b]quinazolines

The total synthesis of chromeno[4,3,2‐de]quinazolin‐2‐ones, ‐quinazolines and ‐pyrrolo[2,1‐b]quinazolines from easily prepared 4‐methoxy‐1‐nitro‐9H‐xanthen‐9‐one is reported. These compounds, in which a 1,3‐diazine ring is fused to the xanthene scaffold, were obtained with good overall yields in very few steps.     

Studies with S‐alkylpyrimidine: New route for the synthesis derivatives of isoxazol,pyrazolo[1,5‐a]pyrimidine,pyridazine, pyridine,thieno[2,3‐b]pyridine and thiophene of potential anti‐HIV

Derivatives of thiophene, thieno[2,3‐b]pyridine, pyridine, isoxazol, pyrazolo[1,5‐a]pyridine, pyridazine linked with s‐pyrimidine derivative have been synthesized and tested for antimicrobial and antifungal activities. The structure of the newly synthesized compounds have been established on the basis of their analytical and spectral data.     

Design and synthesis of new and significative bifunctional compounds containing two pyrazolo[3,4‐b]pyridine nucleis through multicomponent reaction under microwave irradiation

A series of new and significative bifunctional compounds containing two pyrazolo[3,4‐b]pyridine moieties has been synthesized through a rapid one‐pot three‐component reaction of dialdehyde, 5‐amino‐3‐methyl‐1‐phenylpyrazole and active methylene compounds in glycol under microwave irradiation without catalyst. The method has the advantages of good yield (85‐98%), short route and reaction time (45‐300s), wide reaction scope and easy work‐up procedure.     

Facile routes to 1,2,4‐triazolo[3,4‐b][1,3,4]thiadiazines and 1,2,4‐triazino[3,4‐b][1,3,4]thiadiazine by heteropolyacides

Cyclization of 4‐amino‐6‐methyl‐3‐propargylmercapto‐1,2,4‐triazine‐5‐one 3 and 4‐amino‐3‐propargyl mercapto‐1,2,4‐triazole derivatives 6 were afforded 1,2,4‐triazino[3,4‐b][1,3,4]thiadiazines 4 and 1,2,4‐triazolo[3,4‐b][1,3,4]thiadiazines 7 in presence of heteropolyacids, H₁₄[NaP₅W₂₉MoO₁₁₀] and H₆P₂W₁₈O₆₀ in high yields. Among used heteropoly acids, the yields were higher with H₁₄‐P₅Mo, caused to their high acid strengths.     

Synthesis of 4‐amino‐5,6,7,8‐tetrahydrothieno[2,3‐b]quinolin‐5‐ol derivatives

This paper describes the synthesis of 4‐amino‐5,6,7,8‐tetrahydrothieno[2,3‐b]quinolin‐5‐ol derivatives ( 3a‐h ) and 4‐amino‐5,6,7,8‐tetrahydrothieno[2,3‐b]quinoline ( 8a ) in good yield by three‐step procedures starting from 2‐aminothiophene‐3‐carbonitrile and 5‐substituted cyclohexane‐1,3‐dione.     

Synthesis and antifungal activity of novel 3,6‐diaryl‐5H‐[1,2,4]triazolo[4,3‐b][1,2,4]triazepines

5‐Aryl‐3,4‐diamino‐1,2,4‐triazoles 5 on treatment with β‐chlorocinnamaldehydes 7 in the presence of catalytic amount of p‐TsOH and N,N‐dimethylformamide as an energy transfer medium under microwave irradiation and as solvent with oil‐bath heating at 80 °C affords novel 3,6‐diaryl‐5H‐[1,2,4]triazolo[4,3‐b]‐1,2,4]triazepines 8 . The structures of the synthesized compounds were established on the basis of ¹H NMR, IR, mass spectral data and elemental analysis.     

Synthesis and reactivity of 1‐amino‐4‐methyl‐3,4‐dihydro‐5H‐pyrazolo[3′,4′:4,5]pyrimido[1,6‐a]benzoimidazolo‐5‐one

Pyrimido[2“,1”:5′,6′]pyrazolo[3′,4′:4,5]‐pyrimido[1,6‐a]benzoimidazoloe‐2,8(1H,7H)‐diones, and [1,2,4]‐triazino‐[3“,4”:5′,6′]pyrazolo[3′,4′:4,5]pyrimido[1,6‐a]benzimidazol‐8(7H)‐ones were synthesized in a good yields via 1‐amino‐4‐methyl‐3,4‐dihydro‐5H‐pyrazolo[3′,4′:4,5]pyrimido[1,6‐a]benzoimidazolo‐5‐one and the appropriate active methylene compounds. Structures of the newly synthesized compounds were elucidated on the basis of elemental analyses, spectral data, and alternative synthesis methods whenever possible.     

Phase transfer catalyzed synthesis of 3‐methyl‐4h‐pyrazolo[3,4‐d]isoxazole from 3,5‐dimethyl‐4‐isoxazolyldiazonium tetrafluoroborate

Reaction of 3,5‐dimethyl‐4‐isoxazolyl‐diazonium tetrafluoroborate ( 2 ) with two equivalents of potassium acetate and five mole percent of 18‐crown‐6 in ethanol‐free chloroform produce 3‐methyl‐4H‐pyrazolo[3,4‐d]isoxazole ( 3 ) in good to excellent yield. Pyrazole ( 3 ) was subjected to acylation/aroylation to afford the corresponding 4‐N‐acetyl/aroyl derivatives by reaction with CH₃COCl/ArCOCl in Et₃N.     

Synthesis of substituted amino‐cycloalkyl[b]thieno‐[3,2‐e]pyridines

An efficient two respectively three steps procedure for the synthesis of cycloalkyl[b]thieno[3,2‐e]‐pyridine amines was developed and in general good to very good yields were obtained.