Isolation of a new quinic acid derivative and its antibacterial modulating activity

Background and the purpose of the study: The species Hymenocrater calycinus, belongs to the plant family Lamiaceae and grows wildly in the north-east of Iran. Previously, the antimicrobial activity of the plant extracts was reported. In the present study, the bioactivity-guided fractionation of the methanol extract of H. calycinus and the combination effects of the isolated compound with cell wall active agents against S. aureus and E. coli was investigated.Methods: Column and thin layer chromatographic methods were used for isolation and purification and spectroscopic data (MS, 1H- and 13C-NMR, HMQC, HMBC and 1H-1H COSY) were employed for identification of the compound isolated from the extract. A disk diffusion method was used to determine the antibacterial activity of the isolated compound against S. aureus and E. coli in comparison with 7 different antibiotics.Results: The isolated compound 1 was identified as 3-(3, 4- dihydroxyphenyl) lactic acid 2-O-quinic acid. Compound 1 (500 μg/disc) enhanced antibacterial effect of ampicillin, ciprofloxacin, vancomycin and cefepime against S. aureus and activated the effects of ampicillin and vancomycin against E. coli.Conclusion: Results showed that the compound 1 was not active against both tested strains at any concentration below 1 mg/disk, and as a result the enhancing effect of the compound could be due its association with antibiotics.