Structures and Biological Activities of Plant Glycosides: Cholestane Glycosides from Ornithogalum Saundersiae, O. Thyrsoides and Galtonia Candicans, and Their Cytotoxic and Antitumor Activities

Systematic phytochemical screening of higher pants using a cytotoxicity-guided fractionation procedure resulted in the isolation from the bulbs of Ornithogalum saundersiae (Liliaceae) an acylated cholestane diglycoside, 17α-hydroxy-16β-[(O-(2-O-p-methoxybenzoyl-β-D-xylopyranosyl)-(1→3)-2-O-acetyl-α-L-arabinopyranosyl)oxy]cholest-5-en-22-one, tentatively named OSW-1. In vitro cytotoxic and in vivo antitumor screening of OSW-1 revealed that it is a possible candidate as a novel anticancer agent. Furthermore, more than 20 OSW-1-related compounds were isolated, not only from the bulbs of O. saundersiae, but also from those of O. thyrsoides and Galtonia candicans, which are taxonomically related to O. saundersiae. In vitro cytotoxic evaluation of all the isolated compounds and their semi-synthetic analogues allowed the structure-activity relationships of the OSW-1 derivatives to be established. In addition, these three plants were found to produce a series of novel cholestane glycosides with a new rearranged side-chain moiety, 24(23→22)abeo-cholestane, some of which showed potent cytotoxic activity against HL-60 leukemia cells.

The chemistry and biological activity of the Hyacinthaceae

The Hyacinthaceae (sensu APGII), with approximately 900 species in about 70 genera, can be divided into three main subfamilies, the Hyacinthoideae, the Urgineoideae and the Ornithogaloideae, with a small fourth subfamily the Oziroëoideae, restricted to South America. The plants included in this family have long been used in traditional medicine for a wide range of medicinal applications. This, together with some significant toxicity to livestock has led to the chemical composition of many of the species being investigated. The compounds found are, for the most part, subfamily-restricted, with homoisoflavanones and spirocyclic nortriterpenoids characterising the Hyacinthoideae, bufadienolides characterising the Urgineoideae, and cardenolides and steroidal glycosides characterising the Ornithogaloideae. The phytochemical profiles of 38 genera of the Hyacinthaceae will be discussed as well as any biological activity associated with both crude extracts and compounds isolated. The Hyacinthaceae of southern Africa were last reviewed in 2000 (T. S. Pohl, N. R. Crouch and D. A. Mulholland, Curr. Org. Chem., 2000, 4, 1287-1324; ref. 1); the current contribution considers the family at a global level.