Biotransformation of coumarins by Cunninghamella elegans

Microbial biotransformation of coumarin (I) was undertaken using a battery of twenty five microorganisms. Among them, the fungus Cunninghamella elegans NRRL 1392 was the sole microbe that efficiently metabolized coumarin (I) into umbelliferone (II), 3, 4-dihydrocoumarin (V) and transcinnamic acid (VI). Umbelliferone was also biotransformed into 6, 7-dihydroxycoumarin (aesculetin, VII) and p-coumaric acid (VIII). On the other hand, warfarin (III) was biotransformed into 4`-hydroxywarfarin (IX) and also dicoumarol (IV) was transformed into 4-hydroxycoumarin (X) by the same microorganism. The structures of the metabolites were established using only one property and spectroscopic techniques including melting points, 1H NMR, 13C NMR and mass spectroscopy. The cytotoxic effect of coumarin substrates and their metabolites was also investigated. Key words: Biotransformation, coumarins, Cunninghamella elegans, cytotoxic.