Studies on inhibitors of skin tumor promotion, IX. Neolignans from Magnolia officinalis.

Three neolignans, known as magnolol [1], honokiol [2] and the new monoterpenylmagnolol [3], were isolated from the bark of Magnolia officinalis as inhibitors of Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). The structure of 3 was determined from 2D nmr spectral data and difference nOe experiments. The MeOH extract of this plant and magnolol exhibited remarkable inhibitory effects on mouse skin tumor promotion in an in vivo two stage carcinogenesis test. This investigation indicates that these neolignans and the extract might be valuable antitumor promoters.