Humupulusones A and B, Two Skeletally Novel Acylphloroglucinol Derivatives from Humulus lupulus

Two novel acylphloroglucinol derivatives, humupulusones A and B (1 and 2), were isolated from Humulus lupulus. Compound 1, a pair of enantiomers (1a/1b), is the first acylphloroglucinol derivative with a bicyclo[2.2.2] carbon skeleton possessing a novel 5/6/6/5/5 ring system. Humupulusone B (2), a pair of hemiacetal tautomers, features a highly rearranged 5/6/5-fused tricyclic scaffold. Moreover, 1a and 2 exhibited significant inhibitory effects on LPS-induced NO production in BV-2 cells with IC50 values of 13.55 and 16.09 μM, respectively.