Isopimarane diterpenoids from Aeollanthus rydingianus and their antimicrobial activity.

Four acyloxy-isopimarane derivatives along with two known isopimarane diterpenoids, the flavone cirsimaritin and the sterols beta-sitosterol and stigmasterol were isolated from the aerial parts of Aeollanthus rydingianus. The structures of the compounds were established on the basis of spectroscopic analysis and chemical evidence. The isolated substances were screened for antimicrobial activity against Gram-positive and Gram-negative bacteria and a yeast strain. 19-Acetoxy-7,15-isopimaradien-3beta-ol and 7,15-isopimaradien-19-ol showed minimum inhibitory concentration (MIC) values of 3.90-15.62 microg/ml for Staphylococcus aureus and of 7.81microg/ml for Enterococcus hirae.