Neoflavonoids and related constituents from Nepalese propolis and their nitric oxide production inhibitory activity

A methanolic extract of Nepalese propolis yielded 10 new open-chain neoflavonoids (1-10), a new chalcone (11), and eight previously reported compounds (12-19). Their structures were determined on the basis of spectroscopic data and chemical conversion. The isolated compounds other than 5, 8, and 16 showed dose-dependent inhibitory activities on nitric oxide production in lipopolysaccharide-activated macrophage-like J774.1 cells and were more active than a positive control, N-G-monomethyl-L-arginine (IC50, 27.1 mu M). The most potent activities, of 6 and 7 (IC50, 0.5 mu M), were greater than another positive control, caffeic acid phenethyl ester (IC50, 4.8 mu M).