Antifungal jujubogenin saponins from Colubrina retusa

Antifungal assay-guided isolation of the 95% ethanol extract of the stems o f Colubrina retusa yielded jujubogenin 3-O-alpha-L-arabinofuranosyl(1-->2)- [beta-D-glucopyranosyl (1-->3)]-alpha-L-arabinopyranoside (1), which showed modest growth-inhibitory effects against Candida albicans, Cryptococcus ne oformans, and Aspergillus fumigatus (MICs, 50 mu g/mL). In addition, two ne w minor saponins, jujubogenin 3-O-alpha-L-arabinofuranosyl(1-->2)-[2-O-(tra ns,cis)p-coumaryol-beta-D-glucopyranosyl(-->3)]-alpha-L-arabinopyranoside ( 2), and jujubogenin 3-O-(5-O-malonyl)-alpha-L-arabinofuranosyl (1-->2)-[bet a-D-glucopyranosyl(1-->3)]-alpha-L-arabinopyranoside (3), were obtained. Sa ponin 2 was marginally active against only C, neoformans, with a MIC of 50 mu g/mL, while 3 was inactive. NMR spectroscopy was used extensively for th e structure determination of these compounds. The previously reported ambig uity of the NMR assignments of jujubogenin saponins for carbons -26 to -29 was clarified by a comprehensive analysis of the NMR spectra of 1.