Antibacterial terpenes from the oleo-resin of Commiphora molmol (Engl.)

Two octanordammaranes, mansumbinone (1) and 3,4‐seco ‐mansumbinoic acid (2), and two sesquiterpenes, β ‐elemene (3) and T‐cadinol (4) have been isolated from the oleo‐resin of Commiphora molmol (Engl.). The structures of these compounds were established unambiguously by a series of 1D and 2D‐NMR analyses. We have also unambiguously assigned all 1H and 13C NMR resonances for 2 and revised its 13C data. The crude extract of the oleo‐resin of C. molmol displayed potentiation of ciprofloxacin and tetracycline against S. aureus , several Salmonella enterica serovar Typhimurium strains and two K. pneumoniae strains. The antibacterial activity of terpenes 1–4 was determined against a number of Staphylococcus aureus strains: SA1199B, ATCC25923, XU212, RN4220 and EMRSA15 and minimum inhibitory concentration (MIC) values were found to be in the range of 4–256 µg/ml. The highest activity was observed by the seco ‐A‐ring octanordammarane 2 with an MIC of 4 µg/ml against SA1199B, a multidrug‐resistant strain which over‐expresses the NorA efflux transporter, the major characterized antibiotic pump in this species. This activity compared favorably to the antibiotic norfloxacin with an MIC of 32 µg/ml. Compound 2 also displayed weak potentiation of ciprofloxacin and tetracycline activity against strains of Salmonella enterica serovar Typhimurium SL1344 and L10.