Thiophene as a structural element of physiologically active compounds. 19. The synthesis of substituted (6H-thieno[2,3-bpyrrol-4-yl)phenylmethanones

The synthesis of 4-Methoxyphenyl-[5-methyl-6-(2-(4-morpholinyl)-ethyl)-6H-thieno[2,3- b]pyrrol-4-yl)phenylmethanone (1), a thiophene analogue of the analgesic Pravadoline B, is described. Starting with the acetylprotected thienylhydrazine 2b compound 7 was obtained in a Fischer-analogue cyclication in two steps. Use of the BOC-protected thienylhydrazine 2a yielded the pyrazol 5. Alkylation of 7 with N-(2-Chloroethyl)morpholine gave the target compound 1. In the acetylcholine-writhing-test in mice as well as in the acetic acid-writhing-test in rats 1 showed a significant lower antinociceptive activity than Pravadolin (B).