Isoprenylated phenolic compounds with tyrosinase inhibition from Morus nigra

A new isoprenylated sanggenon-type flavanone, nigrasin K (1), together with three known analogs (2–4) and five known Diels–Alder adducts (5–9), were isolated from the twigs of Morus nigra. Their structures were elucidated by spectroscopic methods. Sanggenon M (2), chalcomoracin (5), sorocein H (6), kuwanon J (7), sanggenon C (8), and sanggenon O (9) showed significant inhibitory effects on mushroom tyrosinase.