Monoterpenes from Paeonia albiflora and their inhibitory activity on nitric oxide production by lipopolysaccharide-activated microglia.

Eleven new monoterpenes, paeonidangenin (1), paeonidanin A (2), paeonidanin B (3), paeonidanin C (4), paeonidanin D (5), paeonidanin E (6), paeoniflorone (7), 4-O-methylbenzoylpaeoniflorin (8), 4-O-methylgalloylpaeoniflorin (9), 4-O-methyldebenzoylpaeoniflorin (10), and 4-O-methylalbiflorin (11), were isolated from the 60% ethanol extract of the roots of Paeonia albiflora. Their structures were determined primarily on the basis of 1D and 2D NMR techniques and MS studies. Paeonidanins D (5) and E (6) are unprecedented examples of “cage-like” monoterpene dimers. The inhibitory effects of the isolated compounds on nitric oxide production by lipopolysaccharide (LPS)-activated N9 microglia were evaluated.