By fusing methyl picolinate with phenacyl bromides, the corresponding phenacyl salts were obtained, cyclization of which in acetic anhydride led to previously undescribed 3-aryl-1H-pyrido[2,1-c][1,4]oxazinium bromides. Reduction of the quaternary salts of methyl picolinate followed by acid hydrolysis leads to the alkaloid DL-baikiain.

The reaction of ethyl pyridine-2-ylcarbamate with phenacyl bromides in acetonitrile gave 2-aryl-1-(ethoxycarbonyl)-2-hydroxy-2-phenyl-2,3-dihydro-1H-imidazo[1,2-a]pyridine-4-ium bromides which were con­­verted into 2-arylimidazo[1,2-a]pyridines by heating in acetic anhydride, followed by treatment with potassium carbonate.

The reaction of nicotinic acid ethyl ester with phenacyl bromides containing electron-donating substituents in the benzene ring afforded the corresponding quaternary pyridinium salts which were reduced with sodium tetrahydridoborate to ethyl 1-(2-aryl-2-hydroxyethyl)-1,2,5,6-tetrahydropyridine-3-carboxylates, and acid hydrolysis of the latter involved cleavage of the exocyclic C–N bond with the formation of guvacine in 76–93% yield. Analogous imidazo[4,5-c]pyridine and β-carboline derivatives containing a guvacine fragment were synthesized following a similar reaction sequence.

Readily available 4-methyl-3-nitrobenzenesulfonic acid and 2-methyl-5-nitrophenol were used to develop two alternative approaches to the synthesis of 2-methoxy-4-(methylsulfanyl)benzoic acid in total yields of 17% and 37%, respectively. The synthesis starting from 2-methyl-5-nitrophenol is more process-oriented and can be used in the resynthesis of Sulmazole and Isomazole.

Isonicotinic acid ethyl ester reacted with substituted phenacyl bromides to give the corresponding quaternary salts which were reduced with sodium tetrahydridoborate to ethyl 1-(2-aryl-2-hydroxyethyl)-1,2,3,6- tetrahydropyridine-4-carboxylates. The presence of an electron-donating substituent in the benzene ring of the latter is a necessary condition for their acid hydrolysis with cleavage of the C–N bond and formation of isoguvacine. Analogous derivatives with electron-withdrawing substituents are not converted to isoguvacine under similar conditions.

Treatment of 5-amino-1,3-dialkyl-2,3-dihydro-1 H -imidazo[4,5- b ]pyridin-2-ones with sodium nitrite in aqueous HCl gave 1,3-dialkyl-1 H -imidazo[4,5- b ]pyridine-2,5(3 H ,4 H )-diones which were nitrated with potassium nitrate in sulfuric acid to 6-nitro derivatives, and the latter underwent recyclization into 4-amino-1,3-dialkyl-5-(1 H -pyrazol-5-yl)-2,3-dihydro-1 H -imidazol-2-ones by the action of hydrazine hydrate.

Oxidative dehydrogenation of 1-aryl(hetaryl)-1,2,3,4-tetrahydro-9Н-β-carboline-3-carboxylic acids derivatives with dimethyl sulfoxide leads to the formation of 1-aryl(hetaryl)-9Н-β-carbolines. Simultaneously with the dehydrogenation decarboxylation occurs. At the oxidation with dimethyl sulfoxide of methyl 1-aryl (hetaryl)-1,2,3,4-tetrahydro-9Н-β-carboline-3-carboxylicates methyl 1-aryl(hetaryl)-9Н-β-carboline-3-carboxylates formed whose hydrolysis afforded the corresponding 1-aryl(hetaryl)-9Н-β-carboline-3-carboxylic acids.

Computer simulation at the PM7 level of theory of the structures of imidazo[4,5-c]pyridine derivatives (deaza analogs of purines) and their complexes with Aurora kinase A (AURKA) indicated prospects for their use as potential AURKA inhibitors in the treatment of oncological diseases. A number of new compounds of the selected imidazo[4,5-c]pyridine series, for which the highest inhibitory activity against AURKA was predicted, were synthesized in high yields for further biological testing.

A series of 4-(4-dimethylaminophenyl)pyridine derivatives were synthesized and tested for antimicrobial activity. 4-(4-Dimethylaminophenyl)-1-phenacylpyridinium bromide and 4-(4-dimethylaminophenyl)-1-dimethylcarbamoylpyridinium chloride were highly active against M. luteum and C. tenuis test cultures.

Reaction of allylthiocarbamoyl fragment of N-allylthioureas with excess bromine or iodine leads to the formation of 5-halomethyldihydrothiazole ring as confirms the dehydroiodination of the 5-(5-iodomethyl-4,5-dihydro-1,3-thiazol-2-yl)-4-phenyl-4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine with the formation of a 5-methylthiazole ring. The reaction of allylthiourea with hydrochloric acid affords a 5-methyldihydrothiazole ring.

Aromatization of 4-aryl(hetaryl)tetrahydroimidazo[4,5- c ]pyridine-6-carboxylic acids and their lithium salts by the action of dimethyl sulfoxide has been revealed for the first time. Heating of these compounds in DMSO for 5–7 h at 90–95°C leads to the formation of 4-aryl(hetaryl)imidazo[4,5- c ]pyridine derivatives as a result of dehydrogenation and decarboxylation. Heating of the corresponding lithium salts generated in situ (DMSO, 90–95°C, 3–5 h) affords difficultly accessible 4-aryl(hetaryl)imidazo[4,5- c ]pyridine-6-carboxylic acids.

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1,3-Dialkyl-5-amino-1,3-dihydro-2 H -imidazo[4,5- b ]pyridin-2-ones reacted with acetylacetone to give the corresponding 4-(1,3-dialkyl-2-oxo-1,3-dihydro-2 H -imidazo[4,5- b ]pyridin-5-ylamino)pent-3-en-2-ones which underwent intramolecular cyclization to 1,3-dialkyl-5,7-dimethyl-1,3-dihydro-2 H -imidazo[4,5- b ]-[1,8]naphthyridin-2-ones on heating in polyphosphoric acid or diphenyl ether. Analogous reaction of 1,3-dialkyl-5-amino-1,3-dihydro-2 H -imidazo[4,5- b ]pyridin-2-ones with ethyl acetoacetate led to the formation of ethyl 3-(1,3-dialkyl-2-oxo-1,3-dihydro-2 H -imidazo[4,5- b ]pyridin-5-ylamino)but-2-enoates whose cyclization afforded 1,3-dialkyl-8-hydroxy-7-methyl-1,3-dihydro-2 H -imidazo[5,4- b ][1,8]naphthyridin-2-ones.

Nitration of 2,3-dihydro-1 H -imidazo[4,5- b ]pyridin-2-one gave its 5-nitro derivative which was subjected to alkylation with dimethyl sulfate, diethyl sulfate, and benzyl(dimethyl)phenylammonium chloride. The resulting 1,3-dimethyl-, 1,3-diethyl-, and 1,3-dibenzyl-5-nitro-2,3-dihydro-1 H -imidazo[4,5- b ]pyridin-2-ones were reduced to the corresponding 1,3-dialkyl-5-amino-2,3-dihydro-1 H -imidazo[4,5- b ]pyridin-2-ones, and the latter reacted with itaconic acid to produce 1-(1,3-dialkyl-2-oxo-2,3-dihydro-1 H -imidazo[4,5- b ]pyridin-5-yl)-5-oxopyrrolidine-3-carboxylic acids. 1-(2-Oxo-2,3-dihydro-1 H -imidazo[4,5- b ]pyridin-5-yl)-5-oxopyrrolidine-3-carboxylic acid was obtained by analogous reaction with 5-amino-2,3-dihydro-1 H -imidazo[4,5- b ]-pyridin-2-one.

2-Chloropyridine-3,4-diamine reacted with hetarenecarboxylic acids (pyridine-2-, pyridine-3-, and pyridine-4-carboxylic acids and 6-oxo-1,6-dihydropyridazine-3-carboxylic acid) in polyphosphoric acid at 160–170°C to give the corresponding 2-hetarylimidazo[4,5- c ]pyridin-4-ones. Nitration of the latter with a mixture of concentrated nitric and sulfuric acids led to the formation of 2-hetaryl-7-nitroimidazo[4,5- c ]pyridin-4-ones which were converted into 2-hetaryl-7-methylimidazo[4,5- d ]pyridazin-4-ones by the action of hydrazine hydrate at 140–150°C.

Nitration of 1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-one and its N-methyl derivatives at 0–5°C and 60°C gives 5-nitro-and 5,6-dinitro-1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-ones, respectively. The latter can also be obtained by nitration of 5-mononitro derivatives under similar conditions. The nitration of 6-chloro-and 6-bromo-1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-ones and their N-methyl-substituted analogs leads to the formation of the corresponding 6-chloro(bromo)-5-nitro compounds. The same products are formed in the nitration of 5,6-dichloro-and 5,6-dibromo-1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-ones. In this case, the process involves replacement of the halogen atom in position 5 of the pyridine fragment by nitro group. The nitration of 6-bromo-5-methyl-1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-one is accompanied by oxidation of the 5-methyl group to carboxy.

Reactions of 2-hydrazino-substituted 1-methylbenzimidazole, benzothiazole, and benzoxazole with azobenzene at 160–180°C resulted in hydrazino group elimination and formation of the corresponding 2-H-benzazoles. Under similar conditions the 2-deuterohydrazinobenzazoles prepared from 2-hydrazinobenzazoles and heavy water were converted into 2-deuterobenzazoles.

1-and 3-Substituted imidazo[4,5-b]pyridin-2-ones were synthesized by heating equimolar amounts of 3-amino-2-chloropyridine or 2-chloro-3-methylaminopyridine, urea, and the corresponding arylamine at 150–210°C. The reaction of 3-amino-2-chloropyridine with urea and p-phenylenediamine or p,p′-diaminobiphenyl at a ratio of 2:2:1 under analogous conditions gave 1,4-bis-(2-oxoimidazo[4,5-b]pyridin-3-yl)benzene or 1,4-bis(2-oxoimidazo[4,5-b]pyridin-3-yl)biphenyl, respectively.