New saponins from the roots of Tocoyena formosa (Rubiaceae)

Abstract

Tocoyena formosa (Cham. et Sch.) K. Schun, popularly known as „genipapo do campo“, is a small ornamental tree that grows spontaneously in Brazilian Cerrado, a floristically and physiognomically diverse savanna vegetation [1]. In earlier communications, the isolation of iridoids from the leaves and stems of Tocoyenna formosa with antifungal properties, as well as the known triterpene saponin (3-O-β-D-glucopyranosyl-28-O-β-D-glucopyranosyl quinovic acid) has been reported [2,3]. In continuation of our studies with species of Rubiaceae family, the n-butanol soluble fraction of the ethanolic extract of the roots of T. formosa was chromatographed over Sephadex LH-20 and HPLC to yield five other triterpenoid saponins. Their structures were determined using a combination of homo- and heteronuclear 2D NMR techniques and HRESIMS and were established as 3-O-β-D-glucopyranosyl-(28→1)- β-D-glucopyranosyl quinovic acid (1) 3-O-β-D-glucopyranosyl-(2→1)-α-L-rhaminopyranosyl-(28→1)-β-D-glucopyranosyl quinovic acid (2), 3-O-β-D-glucopyranosyl-(2→1)-α-L-rhamnopyranosyl-(28→1)-β-D-glucopyranosyl chincolic acid (3), 3-O-β-D-glucopyranosyl-(1→4)-α-L-rhamnopyranosyl-(28→1)-β-D-glucopyranosyl quinovic acid (4) and 3-O-β-D-glucopyranosyl-(2→1)-α-L-rhamnopyranosyl-(28→1)-β-D-glucopyranosyl pomolic acid (5).