1H and 13C NMR study of copteroside E derivatives

Abstract

The triterpenoid saponin copteroside E (1) was isolated from the flowers and leaves of Verbesina suncho. Detailed 1H and 13C NMR assignment of its acetyl derivatives 2 and 3 was achieved by 2D NMR techniques including COSY, TOCSY, NOESY, HMQC and HMBC. The presence of a glucuronolactone moiety in 2 is supported by the calculated vs observed 1H–1H coupling constants. Molecular mechanics calculations on 1 were useful for understanding the formation of glucuronolactone 2 and decaacetate 3.