Abstract
The methanol-soluble extract from the root of Ipomoea tyrianthina was studied in order to isolate compounds with activity on the central nervous system and vasorelaxant effects. Chromatographic methods were used to isolate and purify seven new glycolipids (2-8). The structures of compounds 1-8 were elucidated by a combination of NMR spectroscopy and mass spectrometry. Tyrianthinoic acid (1) is a glycosidic acid composed of a linear pentasaccharide core bonded to a 11-hydroxyhexadecanoic acid. The structure of tyrianthinic acids III (2), IV (3), and V (4) consists of a partially acylated tyrianthinoic acid. Tyrianthinic acid VI (8) is a tetrasaccharide core bonded to a jalapinolic acid, acylated by a 2-methyl-3-hydroxybutanoic acid. Tyrianthins C (5), D (6), and E (7) are ester-type heterodimers of scammonic acid A with different acylating residues in the two monomeric units. The macrolactonization site was located at C-3 of the rhamnose unit. The position of the ester linkage for monomeric unit B on the macrocyclic unit A was established at C-4 of the terminal quinovose. Compounds 5-7 increased the sleeping time induced by pentobarbital and the release of gamma-aminobutyric acid in brain cortex. In addition, compounds 5-7 showed significant in vitro relaxant effects on aortic rat rings, in endothelium- and concentration-dependent manners.
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