Antibacterial and Antimycobacterial Lignans and Flavonoids from Larrea tridentata

Three lignans and four flavonoids were isolated and characterized from Larrea tridentata and compounds were tested against 16 bacterial species/strains. Results showed that: dihydroguaiaretic acid (1) had activity towards methicillin resistant (MR) Staphylococcus aureus (minimum inhibitory concentration (MIC) 50 µg/mL) and multidrug‐resistant (MDR) strains of Mycobacterium tuberculosis (MIC 12.5–50 µg/mL); 4‐epi‐larreatricin (2) was active against Enterobacter cloacae (MIC 12.5 µg/mL), as well as sensitive (MIC 50 µg/mL) and MDR strains of M. tuberculosis (MIC 25 µg/mL). 3′‐Demethoxy‐6‐O‐demethylisoguaiacin (3) displayed activity against sensitive and resistant S. aureus (MIC 25 µg/mL), Enterococcus faecalis (MIC 12.5 µg/mL), Escherichia coli (MIC 50 µg/mL), E. cloacae (MIC 12.5 µg/mL) and MDR strains of M. tuberculosis (MIC 12.5 µg/mL). 5,4′‐Dihydroxy‐3,7,8,3′‐tetramethoxyflavone (4) and 5,4′‐dihydroxy‐3,7,8‐trimethoxyflavone (5) were active against M. tuberculosis MDR strains having MIC values of 25 and 25–50 µg/mL, respectively, while 5,4′‐dihydroxy‐7‐methoxyflavone (6) was active against S. aureus (MIC 50 µg/mL) and E. faecalis (MIC 50 µg/mL). We concluded that lignan 3 is the main compound responsible for the antibacterial activity of L. tridentata. Lignans 1 and 2 as well as flavonoid 6 contribute with some degree of antibacterial activity. On the other hand, compounds 1, 2, 3, 4 and 5 contributed to the antimycobacterial activity found in L. tridentata. Copyright © 2012 John Wiley & Sons, Ltd.