Ursane and tirucallane-type triterpenes of Boswellia rivae oleo-gum resin.

Two new ursane-type triterpenes characterized as 3-oxo-24-acetoxy-11α-hydroxy-urs-12-ene (1) and methyl 3α-acetoxy-11α-methoxy-urs-12-en-24-oate (2), together with known compounds 3-11, were isolated from Boswellia rivae oleo-gum resin exudate. Their structural elucidation was accomplished using physical, chemical, and spectroscopic methods. The compounds exhibited weak to moderate antibacterial activities against some Gram-positive and Gram-negative bacteria.