Muscarinic receptor binding activity of polyoxygenated flavones from Melicope subunifoliolata.

Abstract The bark extract of Melicope subunifoliolata (Stapf) T.G. Hartley showed competitive muscarinic receptor binding activity. Six polymethoxyflavones [melibentin (1) ; melisimplexin (3) ; 3,3′,4′,5,7-pentamethoxyflavone (4) ; meliternatin (5) ; 3,5,8-trimethoxy-3′,4′,6,7-bismethylenedioxyflavone (6) ; and isokanugin (7) ] and one furanocoumarin [5-methoxy-8-geranyloxypsoralen (2) ] were isolated from the bark extract. Compounds 2 and 6 were isolated for the first time from M. subunifoliolata . The methoxyflavones (compounds 1 , 3 , 4 , 5 , 6 , and 7 ) show moderate inhibition in a muscarinic receptor binding assay, while the furanocoumarin (compound 2 ) is inactive. The potency of the methoxyflavones to inhibit [ 3 H]NMS-muscarinic receptor binding is influenced by the position and number of methoxy substitution. The results suggest these compounds are probably muscarinic modulators, agonists or partial agonists/antagonists.