[Studies on PAF antagonistic bicyclo(3,2,1) octanoid neolignans from Piper kadsura].

As a continuation of our previous report dealing with the structures of novel neolignans from Piper kadsura (Choisy) Ohwi, two other new bicyclo(3,2,1) octanoid neolignans, named kadsurenin K and kadsurenin L, were isolated. On the basis of spectral analysis and chemical derivatization, their structures were established as 7R,8R,3'R,5'R-delta 8'-3,5'-dimethoxy-4-hydroxy-2',3',4',5'-tetrahydro-2', 4'-oxo-7.3',8.5'-neolignan and 7R, 8R, 3'S, 4'R, 5'R-delta 8'-3,4,5'- trimethoxy-4'-acetoxy-2',3',4',5'-tetrahydro-2'-oxo-7.3', 8.5'-neolignan respectively. Kadsurenin B and kadsurenin C were known compounds. In 3H-PAF receptor binding assay, kadsurenin B, C, K and L demonstrated significant PAF-antagonistic activity.