α-glucosidase inhibitors from the stems of thunbergia laurifolia

Abstract

Alpha-glucosidase inhibitory assay-guided isolation of Thunbergia laurifolia L. stems yielded a new compound named 5-acetoxyfuranonapthoquinone (1) along with nineteen known compounds (2-20). The structure of the isolated compounds was elucidated by the analysis of multiple spectroscopic data as well as by comparison with the previous reports. The isolated compounds were evaluated for α-glucosidase inhibition. Syringaresinol (6), rosmarinic acid (11), 1,2,8-trihydroxyxanthone (17), and isojacareubin (18) showed the most potent inhibitory activity among isolated compounds. Kinetic study indicated that syringaresinol (6), 1,2,8-trihydroxyxanthone (17), and isojacareubin (18) could inhibit the maltase and sucrase function by non-competitive, and rosmarinic acid (11) was identified as a non-competitive inhibitor against maltase and a mixed manner inhibitor against sucrase.