[Five-ring analogs of nifedipine. 3. Synthesis and reactions of 1,4-dihydropyridines with 4-(4-nitro-5-imidazolyl)-substituents].

In the Hantzsch pyridine synthesis the 4-nitro-5-imidazolylcarbaldehydes 4 react with methyl 3-aminocrotonate or 3-aminocrotononitrile in acetic acid to yield the 1,4-dihydropyridines (DHP) 5 and 6. The corresponding pyridines 7 and 8 are obtained by oxidation with cerium(IV) or chromium(VI), respectively. Reduction of the nitro group in 7 with iron in acetic acid leads to the lactames 9, while from 8a the imidazolylamine 10 is isolated. Compound 8a reacts with dithionite to yield the cyclic amidine 11. Irradiation of the DHP 5 and 6b with UV-A light affords the 4-nitroso-5-imidazolyl-pyridines 12 and 13. The half wave potentials E1/2 of the DHP 5 were determined by anodic oxidation using difference pulse voltammetry (DPV); nifedipine was used as reference substance. The DHP 5 inhibit the growth of Staphylococcus aureus in the platelet diffusion test.