Three Novel Constituents from Curculigo capitulata and Revision of C-2 Stereochemistry in Nyasicoside

Abstract

Continuing study of the constituents of the rhizomes of Curculigocapitulata provided three novel compounds, including two norlignan glucosides, curcapicycloside (2) and (1S,2R)-O-methylnyasicoside (3), and a phenanthrofuran, curcapital (9). The former two compounds were characterized as their tetra-O-methyl derivatives. Compound 2 possesses a glucosyl-fused skeleton with 1R,2R configuration. Biogenetic consideration led to a revision of the previously assigned 2S configuration of nyasicoside (1) to 2R, which was confirmed by NOE studies of the acetonide of its tetra-O-methyl derivative. The 2R configuration in tetra-O-methyl-1-O-methyl curculigine (7a) and isocurculigine (8a) was also established by chemical correlation of the former with (1R,2R)-tetra-O-methyl-1-O-methylnyasicoside (10a). Curcapital (9) represents the first natural product having a phenanthro[9,10,b]furan skeleton.