Identification of gymnopilin A10 as an antibacterial agent in Gymnopilus mushrooms and discovery of gymnoprenol B13 from the fruiting bodies of G. orientispectabilis
摘要
Gymnopilus orientispectabilis, a bitter and hallucinogenic mushroom found in East Asia, contains polyisoprenepolyol ester gymnopilins as active constituents. Detection of antibacterial activity against a solanaceous plant pathogen, Ralstonia solanacearum SUPP1541, prompted fractionation of an extract of this mushroom, which specified a mixture of gymnopilins responsible for the activity. Evaluation of antibacterial activity of purified gymnopilins A10 and A11, their deacylated metabolites gymnoprenols A10 and A11, and gymnopilene, a terminally desaturated derivative of gymnoprenol B10, all obtained from G. aeruginosus, revealed gymnopilin A10 to be active but the rest were not active at 200 μg/disk. Meanwhile, a new polyisoprenepolyol, gymnoprenol B13 (1), along with three known congeners, gymnoprenols B10, B11, and B12, was discovered from a fraction eluting faster than the active fraction in HPLC. The planar structure of 1 was determined by NMR and MS/MS fragmentation analysis. Consistent with the above observation, the four gymnoprenol B congeners were not antagonistic to R. solanacearum. The present study discovered antibacterial activity of a polyisoprenepolyol-class metabolite against R. solanacearum and revealed the importance of both the 3-hydroxy-3-methylglutaryl unit and a specific length of the polyisoprenyl chain or composition of hydroxylation in gymnopilin A10 for its activity.