Antimicrobial diterpenoids from Rosmarinus officinalis

Three new diterpenoids, 12,16-epoxy-11-hydroxy-17(15 → 16)-abeo-abieta-8,11,13-trien-7-one (1), 7,12-dihydroxy abieta-6,8,10(5),11,13-quien-20-oic acid 1,20-lactone (2), labda-5(10),13(E)-dien-15-ol (11), one new natural product (2E,6E)-3,7-dimethyl-9-[(1S,6R)-1,2,6-trimethylcyclohex-2-enyl]nona-2,6-dien-1-ol (16) and thirteen known compounds were isolated and elucidated from the excellent antimicrobial active fractions of Rosmarinus officinalis ethanol extract. The structures of the isolated compounds were determined by spectral data analysis and combined with literature reports. Among them, monocyclic diterpenoids (16 and 17) were discovered from rosemary for the first time. All isolated compounds were tested for antimicrobial activity against four strains (B. subtilis, S. aureus, P. aeruginosa, and Fusarium spp.), with six compounds showing very strong inhibitory activity against B. subtilis and four compounds showing strong inhibitory activity against P. aeruginosa.