Steroidal saponins from Asparagus africanus

The structures of two new monodesmosidic spirostanosides and a new bisdesmosidic furostanol glycoside isolated from the roots of Asparagus africanus Lam. (Liliaceae) have been elucidated as (25R)-3 beta-hydroxy-5 beta-spirostan-12-one 3-O-{beta-D-glucopyranosyl-(1-->2)-[alpha-1-arabinopyranosyl-(1--> 6)]-beta- D-glucopyranoside} (1), (25R)-5 beta-spirostan-3 beta-ol 3-O-{beta-D-glucopyranosyl-(1-->2)-[alpha-L-arabinopyranosyl-(1--> 6)]-beta- D-glucopyranoside} (2) and 26-O-beta-D-glucopyranosyl]-22 alpha-methoxy-(25R)-furostan-3 beta,26-diol 3-O-{beta-D-glucopyranosyl-(1-->2)-[beta-D-glucopyranoside} (3), respectively, by the combined use of one and two dimensional NMR experiments. The complete 13C and 1H assignments of the peracetyl spirostanosides and the furostanol oligoside were derived. The interconversions between the methoxyl and hydroxyl group at C-22 of the furostanol glycoside was investigated and the genuine furostanol oligoside of A. africanus appears to be the hydroxyl type based on the comparative study of the methanol, pyridine and dioxane extracts.