Polyoxygenated Stigmastane-Type Steroids from the Whole Plant of Vernonia glabra (Steetz) Vatke (Asteraceae) and Their Antibacterial and Antioxidant Activities

Six hitherto unreported polyoxygenated stigmastane-type steroids, vernoglabrosterols A and B (1 and 2), and vernoglabrosides A-D (3-6), along with two known analogues (7 and 8), were isolated from the ethanolic extract of the whole plant of Vernonia glabra (Steetz) Vatke (Asteraceae). Their structural elucidation was achieved by analysis of spectroscopic and spectrometric data, X-ray crystallography, as well as comparison to data reported in the literature. Compounds 3, 5, and 6 displayed significant DPPH scavenging activity, with IC₅₀ values of 2.49, 4.26, and 4.53 μg/mL, respectively. All of the tested compounds showed significant activities as judged by the FRAP assay compared to l-ascorbic acid. This is the first report of polyoxygenated stigmastane-type steroids C-6/C-7 oxygenated and 24,28-diol from the genus Vernonia.