Triterpenoid saponins from a cytotoxic root extract of Sideroxylon foetidissimum subsp gaumeri

Evaluation of the cytotoxicity of an ethanolic root extract of Sideroxylon foetidissimum subsp. gaumeri (Sapotaceae) revealed activity against the murine macrophage-like cell line RAW 264.7. Systematic bioassay-guided fractionation of this extract gave an active saponin-containing fraction from which four saponins were isolated. Use of 1D (H-1, C-13, DEPT135) and 2D (COSY, TOCSY, HSQC, and HMBC) NMR, mass spectrometry and sugar analysis gave their structures as 3-O-(beta-D-glucopyranosyl-(1 -> 6)-beta-D-glucopyranosyl)-28-O-(alpha-L-rhamnopyranosyl-(1 -> 3)[beta-D-xylopyranosyl-(1 -> 4)]-beta-D-xylopyranosyl-(1 -> 4)-alpha-L-rhamnopyranosyl-(1 -> 2)-alpha-L-arabinopyranosyl)-16 alpha-hydroxyprotobassic acid, 3-O-beta-D-glucopyranosyl-28-O-(alpha-L-rhamnopyranosyl-(1 -> 3)[beta-D-xylopyranosyl-(1 -> 4)]-beta-D-xylopyranosyl-(1 -> 4)-alpha-L-rhamnopyranosyl-(1 -> 2)-alpha-L-arabinopyranosyl)-16 alpha-hydroxyprotobassic acid, 3-O-(beta-D-glucopyranosyl-(1 -> 6)-beta-D-glucopyranosyl)-28-O-(alpha-L-rhamnopyranosyl-(1 -> 3)-beta-D-xylopyranosyl-(1 -> 4)[beta-D-apiofuranosyl-(1 -> 3)]-alpha-L-rhamnopyranosyl-(1 -> 2)-alpha-L-arabinopyranosyl)-16 alpha-hydroxyprotobassic acid, and the known compound, 3-O-beta-D-glucopyranosyl-28-O-(alpha-L-rhamnopyranosyl-(1 -> 3)[beta-D-xylopyranosyl-(1 -> 4)]-beta-D-xylopyranosyl-(1 -> 4)-alpha-L-rhamnopyranosyl-(1 -> 2)-alpha-L-arabinopyranosyl)-protobassic acid. Two further saponins were obtained from the same fraction, but as a 5:4 mixture comprising 3-O-(beta-D-glucopyranosyl)-28-O-(alpha-L-rhamnopyranosyl-(1 -> 3)-beta-D-xylopyranosyl-(1 -> 4)[beta-D-apiofuranosyl-(1 -> 3)]-alpha-L-rhamnopyranosyl-(1 -> 2)-alpha-L-arabinopyranosyl)-16 alpha-hydroxyprotobassic acid and 3-O-(beta-D-apiofuranosyl-(1 -> 3)-beta-D-glucopyranosyl)-28-O-(alpha-L-rhamnopyranosyl-(1 -> 3)[beta-D-xylopyranosyl-(1 -> 4)]-beta-D-xylopyranosyl-(1 -> 4)-alpha-L-rhamnopyranosyl-(1 -> 2)-alpha-L-arabinopyranosyl)-16 alpha-hydroxyprotobassic acid, respectively. This showed greater cytotoxicity (IC50 = 11.9 +/- 1.5 mu g/ml) towards RAW 264.7 cells than the original extract (IC50 = 39.5 +/- 4.1 mu g/ml), and the saponin-containing fraction derived from it (IC50 = 33.7 +/- 6.2 mu g/ml). (C) 2009 Elsevier Ltd. All rights reserved.