New glycocerebrosides from the trunk of Tabernaemontana contorta Stapf. (Apocynaceae) and their antibacterial activity

Phytochemical investigation of the trunk of Tabernaemontana contorta Stapf. led to the isolation and identification of two new glycocerebrosides, tabernamides A (1) and B (2), together with three known compounds: 2 alpha,3 alpha,23-trihydroxyursa-12,20(30)-dien-28-oic acid (3), 2 alpha,3 beta, 23-trihydroxyursa-12,5(6)-dien-28-oic acid (4), and tombozine (5). All these compounds have been isolated for the first time from this plant. Their structures were established by UV, IR, HR-ESIMS, 1D, and 2D experiments, and by comparison of our data with the literature values. The antibacterial activities of the extract and the compounds were evaluated. Compounds 1-3 exhibited significant antibacterial activities against Escherichia coli (ATCC 25922), with MIC values of 1.5 mu g/mL, 1.7 mu g/mL, and 1.3 mu g/mL, respectively (Standard drug: ofloxacin, MIC = 0.14 mu g/mL). The chemotaxonomic significance of these compounds is also discussed.