Inhibitory effect of dalbergioidin isolated from the trunk of Lespedeza cyrtobotrya on melanin biosynthesis

Tyrosinase is a key enzyme for melanin biosynthesis, and hyperpigmentation disorders are associated with abnormal accumulation of melanin pigments, which can be reduced by treatment with depigmenting agents. The methanol extract of Lespedeza cyrtobotrya MIQ showed inhibitory activity against mushroom tyrosinase. The active compound was purified from the methanol extract of L cyrtobotrya, followed by several chromatographic methods, and identified as dalbergioidin (DBG) by spectroscopic methods. The results showed that DBG exhibited tyrosinase inhibitory activity with an IC50 of 20 mM. The kinetic analysis tyrosinase inhibition revealed that DBG acted as noncompetitive inhibitor. In addition, DBG showed a melanin biosynthesis inhibition zone in the culture plate of Streptomyces bikiniensis that has commonly been used as an indicator organism. Furthermore, 27 mM DBG decreased more than 50% of melanin contents on the pigmentation using immortalized mouse melanocyte, melan-a cell.