Inhibitory effect of diarylheptanoids on nitric oxide production in activated murine macrophages

Thirteen novel diarylheptanoids bearing a chalcone or a flavanone moiety (1-13), a new curcumin derivative, 1,2-dihydrobis(de-O-methyl)curcumin (14), and two known flavonoids (15 and 16) isolated from the seeds of Alpinia blepharocalyx K. Schum. were tested for their inhibitory effects on nitric oxide (NO) production in lipopolysaccharide (LPS)-activated murine macrophages J774.1 in vitro. All the tested compounds inhibited NO production in a concentration-dependent manner (IC₅₀=36-568 μM). Among the compounds examined, blepharocalyxin B (13) was the most potent inhibitor of NO production (IC₅₀=36 μM). Analysis of the structure activity relationship among these novel diarylheptanoids led to the conclusion that the position of attachment of a chalcone or a flavanone to a diarylheptanoid does not affect their inhibitory potency although their presence in association causes a substantial enhancement of the inhibitory activity. Moreover, a conjugated double bond in a chalcone moiety potentiated the inhibitory activity. On the other hand, hexamethoxydeoxycalyxin A (17) and pentamethoxycalyxin B (18), a methylated product of calyxin A (1) and an epimeric mixture of calyxin B, showed greatly reduced activity suggesting that phenolic hydroxyl groups are involved in the inhibitory activity.