Cryptobuchanosides A–G: seven previously undescribed triterpene glycosides from Cryptolepis buchananii R.Br. ex Roem. and Schult. with nitric oxide production inhibition activity

Abstract

In this study, nine triterpene glycosides including seven previously undescribed compounds (1–7), were isolated from leaves of Cryptolepis buchananii R.Br. ex Roem. and Schult. using various chromatographic methods. The chemical structures of the compounds were elucidated to be 3-O-β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranosyluncargenin C 28-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-glucopyranosyl ester (1), 3-O-β-d-glucopyranosyl-(1 → 2)-β-d-glucopyranosyluncargenin C 28-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-glucopyranosyl ester (2), 3-O-β-d-glucopyranosyl-(1 → 2)-β-d-glucopyranosyluncargenin C 28-O-β-d-glucopyranosyl-(1 → 4)-α-l-rhamnopyranosyl-(1 → 2)-β-d-glucopyranosyl ester (3), 3-O-β-d-glucopyranosyl-(1 → 2)-β-d-glucopyranosylhederagenin 28-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-glucopyranosyl ester (4), 3-O-β-d-glucopyranosylarjunolic acid 28-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-glucopyranosyl ester (5), 3-O-β-d-glucopyranosyl-(1 → 2)-β- d-glucopyranosyl-6β,23-dihydroxyursolic acid 28-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-glucopyranosyl ester (6), 3-O-β-d-glucopyranosyl-6β,23-dihydroxyursolic acid 28-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-glucopyranosyl ester (7), asiatic acid 28-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-glucopyranosyl ester (8), and 3-O-β-d-glucopyranosylasiatic acid 28-O-α-l-rhamnopyranosyl-(1 → 2)-β-d-glucopyranosyl ester (9), through infrared, high-resolution electrospray ionization mass spectrometry, one- and two-dimensional nuclear magnetic resonance spectral analyses. The isolates inhibited nitric oxide production in lipopolysaccharide-activated RAW 264.7 cells, with half-maximal inhibitory concentration (IC₅₀) values of 18.8–58.5 µM, compared to the positive control compound, dexamethasone, which exhibited an IC₅₀ of 14.1 µM.

Graphical abstract