Structures of Steroidal Saponins from the Tubers of Brodiaea californica and Their Inhibitory Activity on Tumor Promoter-Induced Phospholipid Metabolism.

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Abstract
Phytochemical examination of the fresh tubers of Brodiaea californica resulted in the isolation of four new steroidal saponins. Their structures were determined, by extensive spectral analysis including two-dimensional (2D) NMR spectroscopy and acid-catalyzed hydrolysis, to be (25S)-spirost-5-ene-1 beta,3 beta-diol [(25S)-ryscogenin] 1-O-[O-beta-D-glucopyranosyl-(1-->3)-O-alpha-L-rhamnopyranosyl-(1-->2)- beta-D-glucopyranoside] (1), (25S)-ruscogenin 1-O-[O-beta-D-glucopyranosyl-(1-->3)-O-alpha-L-rhamnopyranosyl-(1-->2)-O -[beta-D-xylopyranosyl-(1-->3)]-beta-D-glucopyranoside] (2), the C-20 and C-22 isomer of 2 (3) and the 6'-O-acetyl derivative of 2 (4), respectively. The conformations of the tetrasaccharide moiety of 2 and 4 were inspected through molecular mechanics and molecular dynamics calculation studies, showing that the acetyl group attached to C-6 of the inner glucose was near the C-21 methyl of the aglycon in the calculated preferred conformation of 4, which must cause the downfield shift of 21-Me by 0.07 ppm in comparing the 1H-NMR of 4 with that of 2. The inhibitory activity of the isolated saponins on 12-O-tetradecanoylphorbor-13-acetate (TPA)-stimulated 32P-incorporation into phospholipids of HeLa cells was evaluated to identify new antitumor-promoter compounds.

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