Mammalian multidrug resistance lipopentasaccharide inhibitors from Ipomoea alba seeds

As part of an ongoing project to identify inhibitors of multidrug efflux pumps, three new resin glycosides, albinosides I-III (1-3), were isolated from a CHCl(3)-soluble extract from the seeds of moon vine (Ipomoea alba). Their structures were established through NMR spectroscopy and mass spectrometry as partially acylated branched pentasaccharides derived from three new glycosidic acids, named albinosinic acids A-C (4-6). The same oligosaccharide core formed by two D-quinovose, one D-glucose, and two L-rhamnose units was linked to either convolvulinolic or jalapinolic acid for 1 and 3, respectively. They were partially esterified with (2R,3R)-3-hydroxy-2-methylbutanoic, acetic, or 2-methyl-2-butenoic acid. Compound 2 has two D-quinovose and three L-rhamnose units, linked to convolvulinolic acid, and its esterifying residues were characterized as two units of 2-methyl-2-butenoic acid. The aglycone lactonization site was located at C-2 of the terminal rhamnose unit (Rha) for 1, at C-3 of the terminal rhamnose unit (Rha') for 2, and at C-3 of the second saccharide unit (Glc) for 3. Reversal of multidrug resistance by this class of plant metabolites was also evaluated in vinblastine-resistant human breast carcinoma cells (MCF-7/Vin). The noncytotoxic compound 3 exerted the strongest potentiation effect of vinblastine susceptibility to over 2140-fold, while a moderate activity was observed for 1 (3.1-fold) and 2 (2.6-fold) at a concentration of 25 μg/mL.