MR566A and MR566B, new melanin synthesis inhibitors produced by Trichoderma harzianum I. : taxonomy, fermentation, isolation and biological activities

Abstract

New melanin synthesis inhibitors (MR566A and B) and six related known isocyanocyclopentenes were isolated from the fermentation broth of Trichoderma harzianum. The IC50 values of MR566A and B against mushroom tyrosinase were 1.72 and 47 μM, respectively. They inhibited melanin biosynthesis in B16 melanoma cells with MIC values of 0.1 and 2.2 μM, respectively. Also isolated from the same culture extract of T. harzianum was a new oxazole (MR93B), which showed no inhibitory activity against mushroom tyrosinase at a concentration of 1,000 μg/ml.