Stytontriterpenes A−C, three unusual oleanane-derived triterpenoids from the resin of Styrax tonkinensis as potential immunosuppressive agents in atherosclerosis

Three unusual oleanane-derived triterpenoids, stytontriterpenes A-C (1-3), were isolated from the resin of Styrax tonkinensis together with an oleanane-lactone (stytontriterpene D, 4). Their structures and absolute configurations were characterised using a combination of spectroscopic analysis, electronic circular dichroism, and theoretical calculations. 1 and 2 belong to nor-oleanane with rare spiro D/E rings and 3 contains one infrequent C32 scaffold. 1 considerably suppressed the number of adhered leukemic monocytes (THP-1) to human umbilical vein endothelial cells and attenuated the upregulations of mRNA and protein levels of intracellular adhesion molecule-1 and vascular cell adhesion molecule-1 at 5 μM, suggesting that 1 might be a promising anti-vascular inflammatory chemical for atherosclerosis therapy. Plausible biosynthetic pathways for 1-4 are also proposed.