ABSTRACT
In our antioxidant screening of some Vietnamese plant extracts, the CHCl3-soluble fraction from Calotropis gigantea (L.) W.T.Aiton flowers showed moderate DPPH free radical scavenging activity with an IC50 value of 55.8 µg/mL. Thus, a further phytochemical study was carried out to obtain five alkaloids, including a new ß-carboline-type alkaloid, caloside H (1). These known compounds were identified as 5-hydroxy-(2-methoxymethyl)pyridine (2), nicotinic acid (3), p-(acetylamino)phenol (4), and thymine (5). These structures were determined based on the NMR spectroscopic analysis. In antioxidant assay, caloside H at concentration of 100 µM showed DPPH radical scavenging capacity with a percentage of inhibition of 40.2%. In addition, a plausible biosynthetic pathway for the formation of caloside H was proposed based on the Schiff base formation and Mannich-like reaction.
ABSTRACT
Bioactivity-guided isolation of the CHCl3-soluble fraction of the stems of Salacia chinensis L. (Celastraceae) was carried out to obtain a new 7',9-epoxylignan (1) and three 7,9':7',9-diepoxylignans (2-4). The absolute configuration of 1 was elucidated based on NMR and ECD spectroscopic data interpretation. All isolated lignans showed intermediate α-glucosidase inhibitory activity with the IC50 values ranging from 28.5 to 85.6 µM.
