A new ent-clerodane diterpene from Detarium microcarpum Guill. & Perr. and its protective potential for osteoporosis.

A new clerodane diterpene, named 6α-hydroxy-3,13E-clerodien-15-oic acid (1), together with a known clerodane diterpene (2), four known labdane diterpenes (3-6), a triterpenoid (7), a known steroid (8), and two benzenoid compounds (9 and 10) were isolated from Detarium microcarpum Guill. & Perr. The structures of all obtained compounds were determined by chemical properties and spectroscopic evidence, accompanied by comparisons with data in the literature. Electronic circular dichroism (ECD) was performed for compounds 1-4 to confirm the absolute configuration. Compounds 1-3 and 8-10 were evaluated for the protective effect on osteoblasts. Compound 1 was observed to increase the proliferation of dexamethasone (DEX)-treated MC3T3-E1 cells significantly at 1 μM, which was comparable with the positive control geniposide at 10 μM. The results were further confirmed by flow cytometry analysis. In addition, compound 1 increased the level of alkaline phosphatase (ALP) and mineralization in osteoblasts inhibited by DEX. Moreover, Compound 9 (vanillic acid) showed a pronounced inhibition (IC50 6.5 ± 0.6 μM) on reactive oxygen species (ROS) production, and 10 (4-O-methyl gallic acid) showed a good inhibition with IC50 as 103.3 ± 2.2 μM, compared with the standard drug ibuprofen (IC50 54.2 ± 9.2 μM). Besides, compounds 1-3 and 8-10 were non-cytotoxic against MCF-7, NCI-H460, Hela, and BJ cell lines.