Antimicrobial diterpenes from the stem bark of Mitrephora celebica.

Four diterpenes were isolated from the stem bark of Mitrephora celebica through bioassay-guided fractionation. Ent-trachyloban-19-oic acid (1) and ent-kaur-16-en-19-oic acid (2) were identified as the compounds responsible for the antimicrobial activity of the plant against methicillin-resistant Staphylococcus aureus and Mycobacterium smegmatis. 8(14),15-pimaradien-18-oic acid (3) and 7,15-pimaradien-18-oic acid (4) were isolated from the same fraction and were inactive against the microorganisms.