Biotransformations of 4-Methyl umbelliferone derivatives - Fungal mediated O-dealkylations

Abstract Fungal mediated/ catalyzed O-dealkylations are known to occur either through a hydroxyl transfer from water or hydroxylation of the carbon adjacent to the ether oxygen. Hence, it becomes imperative that the substrates chosen should not only differ as their alcohols(primary, secondary or benzylic), but, also in their oxidation potentials. Five derivatives of 4-methyl umbelliferone (7-hydroxy 4-methyl coumarin) namely, 7-methoxy, 7-ethoxy, 7-butoxy,7-o- benzyloxy and 7-acetoxy, were chosen for the study of biotransformation with Aspergillus niger . 100% transformation (O-dealkylation) occurred in 7-o-ethyl 4-methyl umbelliferone, 96% in 7-o-acetyl, 75% in 7-o-butyl, 73% in 7-o-methyl and 54% in 7-o-benzyl 4-methyl umbelliferone. No transformation was observed in 4-methyl coumarin. It is obvious from the percentage yields of the transformed products (o-dealkylated products) that this procedure is synthetically viable. The above study also provides an insight into the biochemical mechanism of fungal mediated o-dealkylations.