Photodimerization of heteroaryl chalcones: comparative antimicrobial activities of chalcones and their photoproducts

摘要

The heterocyclic analogues of chalcones were synthesized by Claisen Schmidt reaction of (a) benzaldehyde with 2-acetylfurane, 2-acetylpyrrole and 2-acetylthiophene and (b) acetophenone with furfural, thiophene-2-carbalde-hyde and pyrrole-2-carbaldehyde. The photolysis of class (a) and (b) chalcones under UV lamp gave different products. The stereoselective photodimerization of l-(furane-2-yl)-3-phenylprop-2-en-l-one (1), 3-phenyl-l-(lH-pyrrole-2-yl)-prop-2-en-l-one (2) gave beta-truxinic type dimers, (3,4-diphenylcyclobutane-l,2-diyl)bis (furane-2-yl metha-none) (7), (3,4-diphenylcyclobutane-l,2-diyl)bis ((lH-pyrrol-2-yl) methanone) (8) by syn head-to-head coupling whereas 3-phenyl-l-(thiophen-2-yl)-prop-2-en-l-one (3) gave delta-tru-xinic type dimers, (3,4-diphenylcyclobutane-l,2-diyl)bis (thiophen-2-yl methanone) (9) by anti head-to-head coupling. The photolytic products of 3-(furane-2-yl)-l-phenylprop-2-en-l-one(4), l-phenyl-3-(thiophen-2-yl)-prop-2-en-l-one (5) and l-phenyl-3-(lH-pyrrole-2-yl)- prop-2-en-l-one (6) were identified as corresponding l,6-di(furane-2-yl)-3,4-diphenyl-hexa-l,5-diene-3,4-diol (10), 3,4-diphenyl-l,6-di(thiophen-2-yl)hexa-l,5-diene-3,4-diol (11) and 3,4-diphenyl-l,6-di (lH-pyrrol-2-yl)hexa-l,5-diene-3,4-diol (12) pinacol dimers. The antibacterial and antifungal activity of the precursor chalcones and the dimeric products showed antimicrobial activities of different extents with respect to individual compounds. In general, photolysis of heteroaryl chalcones causes the depletion of antimicrobial activity.