Identification of some antibacterial constituents of New Zealand manuka honey

Abstract

Some components responsible for the exceptionally high antibacterial activity of manuka honey were isolated by testing fractions of the honey for activity against Staphylococcus aureus. An ethanol-ether extract of the honey was separated by preparative-layer chromatography and the fractions thus obtained were assessed for antibacterial activity. One fairly homogeneous fraction was identified as methyl 3,5-dimethoxy-4-hydroxybenzoate (methyl syringate, 1b). Combined gas chromatography-mass spectroscopy indicated the presence of this compound in some of the other antibacterial fractions together with methyl 3,4,5-trimethoxybenzoate (1c) and 3,4,5-trimethoxybenzoic acid (1a). Authentic specimens of 3,5-dimethoxy-4-hydroxybenzoic acid (syringic acid, 1d) and 3,4,5-trimethoxybenzoic acid (1a) and their methyl esters were tested against S. aureus. The acids and, to a lesser extent, methyl syringate were found to possess significant antibacterial activity.