Identification and characterization of organic and glycosidic acids in the crude resin glycoside fraction of Ipomoea lacunosa seeds

Resin glycosides are commonly found in plants belonging to the Convolvulaceae family. Ipomoea lacunosa L. (Convolvulaceae) is an herbaceous vine native to the United States. The resin glycosides of this plant have not been studied in detail. In this study, the components of the crude resin glycoside fraction extracted from the seeds of I. lacunosa are characterized. Alkaline hydrolysis of the crude resin glycoside fraction obtained from methanolic extract of the seeds yielded three organic acids, namely, 2S-methylbutyric, (E)-2-methylbut-2-enoic, and 2R-methyl-3R-hydroxybutyric acids, and a glycosidic acid fraction. Acidic hydrolysis of the glycosidic acid fraction yielded hydroxyl fatty acid components, including 7S-hydroxydecanoic, 11S-hydroxytetradecanoic, 11S-hydroxyhexadecanoic, 3S,11S-dihydroxytetradecanoic, 3S,11S-dihydroxyhexadecanoic, and 3S,12S-dihydroxyhexadecanoic acids, as well as monosaccharide components, including d-glucose, d-quinovose, d-fucose, and l-rhamnose. Trimethylsilyldiazomethane-hexane treatment of the glycosidic acid fraction further yielded eleven previously undescribed glycosidic acid methyl esters and two known glycosidic acid methyl esters. The structures of the obtained compounds were characterized using various spectral techniques. Four of the undescribed compounds were hexaglycosides, five were heptaglycosides, and two were octaglycosides. The aglycone of these compounds was either methyl 11S-hydroxytetradecanoate, methyl 3S,11S-dihydroxytetradecanoate, or methyl 3S,11S-dihydroxyhexadecanoate. Among the undescribed compounds identified, eight contained novel glycans, and three were rare bisdesmosides with sugar linkages at the C-3 and C-11 positions of methyl 3S,11S-dihydroxytetradecanoate.

Isolation and structural characterization of eight new resin glycosides, calyhedins XVI-XXIII, from the rhizomes of Calystegia hederacea

Biological effects attributed to resin glycosides, including cytotoxicity against cancer cells and antibacterial, multidrug resistance-modulating, and antiviral activities have been documented. Penta-glycosides composed of calysolic acid A or calyhedic acid A, which are glycosidic acid components of the crude resin glycoside fraction of Calystegia hederacea, have not yet been isolated from this plant. In this study, eight new resin glycosides, termed calyhedins XVI (1)-XXIII (8), were isolated from the rhizomes of C. hederacea. Compounds 1-8 are penta- or hexa-glycosides with macrolactone structures, and their sugar moieties are partially acylated by five organic acids, including 2S-methylbutyric, (E)-2-methylbut-2-enoic, and 2R-methyl-3R-hydroxybutyric acids. Compounds 1-5 are the first identified macrocyclic resin glycosides with five monosaccharides obtained from this plant, and 2 and 4 are the first to be characterized as containing calyhedic acid A as the glycosidic acid component. Compounds 1-8 were of the four following macrolactone types: one with a 22-membered ring (5), another with a 23-membered ring (6-8), the third with a 27-membered ring (1, 3), and the fourth with a 28-membered ring (2, 4). Compounds 2-8 exhibited cytotoxic activity against HL-60 human promyelocytic leukemia cells comparable to that of the positive control, cisplatin.

Five new resin glycosides, calyhedins XI-XV, from Calystegia hederacea

Calystegia hederacea Wall. (Convolvulaceae) is a perennial herbaceous vine that grows widely in India and East Asia. All parts of this plant are used to treat various disorders such as menoxenia and gonorrhea. Four new resin glycosides, calyhedins XI (1)-XIV (4), were isolated from the rhizomes of C. hederacea. A new glycoside, calyhedin XV (5), was isolated from its leaves and stems. Alkaline hydrolysis of 1 and 2 furnished a new glycosidic acid, calyhedic acid G (1a), from 1 and a new acid, calyhedic acid H (2a), from 2 along with 2S-methylbutyric acid and 2R-methyl-3R-hydroxybutyric (2R,3R-nilic) acid. The structures of 1-5, 1a, and 2a were determined using MS and NMR spectral analyses. Compounds 1a and 2a had the same sugar moiety, β-D-glucopyranosyl-(1 → 6)-O-β-D-glucopyranosyl-(1 → 6)-O-β-D-glucopyranosyl-(1 → 3)-[O-β-D-glucopyranosyl-(1 → 3)-O-α-L-rhamnopyranosyl-(1 → 2)]-O-β-D-glucopyranosyl-(1 → 2)-β-D-fucopyranose, while their aglycones were 11S-dihydroxyhexadecanoic acid and 12S-dihydroxyhexadecanoic acid, respectively. These compounds are the first glycosidic acids, with fucose as the monosaccharide component obtained from the resin glycosides of C. hederacea. Compounds 1-5, comprising either 1a or 2a, were heptaglycosides with macrolactone structures, and their sugar moieties were partially acylated with 5 mol of organic acids comprising 2S-methylbutyric, (E)-2-methylbut-2-enoic, and 2R,3R-nilic acids. Compounds 1 and 5 had 22-membered rings, while 2-4 had 28-membered rings. In addition, 1 and 5 exhibited cytotoxic activity against HL-60 human promyelocytic leukemia cells, comparable to that of the positive control cisplatin.