Synthesis and Antimicrobial Activity of Novel Piperidinyl Tetrahydrothieno[2,3-c]isoquinolines and Related Heterocycles

A novel series of 1-amino-2-substituted-5-piperidinyl-6,7,8,9-tertahydrothieno[2,3- c ]isoquinolines ( 4a-e ) was synthesized upon treatment of 4-cyano-1-piperidinyl-5,6,7,8-tetrahydroisoquinline-3(2 H )-thione ( 2 ) with α-halo carbonyl compounds such as chloroacetone, ethyl chloroacetate, 2-bromoacetophenone, chloroacetamide, and chloroacetanilide. Construction the pyrrolyl ring associated with the thienotetrahydroisoquinoline moiety was achieved by treatment of compounds 4a , b with 2,5-dimethoxytertahydrofuran in acetic acid. 1-Pyrrolyl-2-substituted-thieno[2,3- c ]isoquinolines 5a and 5b which in turn were used as multipurpose precursors for synthesis of other new heterocycles. Assignments of the chemical structures of the respectively synthesized thienotetrahydroisoquinolines and their derivatives were established on the bases of elemental and spectral techniques (Fourier transform infrared, 1 H NMR, 13 C NMR, and mass spectroscopy). Furthermore, certain compounds were screened for their antimicrobial activity which revealed promising activities against various pathogenic strains of bacteria and fungi.