Simple 1,4-benzoquinones with antibacterial activity from stems and leaves of Gunnera perpensa

From the dichloromethane extract of the leaves and stems of Gunnera perpensa two new, simple 1,4-benzoquinones and a known benzopyran-6-ol were isolated. From the methanol extract phytol was obtained. The two benzoquinones, 2-methyl-6-(-3-methyl-2-butenyl)benzo-1,4-quinone (1) and 3-hydroxy-2-methyl-5-(3-methyl-2-butenyl)benzo-1,4-quinone (2) and the benzopyran, 6-hydroxy-8-methyl-2,2-dimethyl-2H-benzopyran (3) were examined for antimicrobial properties together with the crude stem, leaf and root extracts. Minimum inhibitory concentration (MIC) assays were used to quantify antimicrobial activity and the MIC values for the crude extracts of stems, roots and leaves ranged between 100 microg and >16 mg/ml against the eight microorganisms investigated. Compound 1 showed significant antimicrobial activity with the most sensitive organism being Staphylococcus epidermidis with an MIC of 9.8 microg/ml. For compound 2, no activity was noted. Compound 3 exhibited good activity against the yeasts Cryptococcus neoformans (75 microg/ml) and Candida albicans (37.5 microg/ml).