Antibacterial proanthocyanidins isolated from the Australian medicinal plant, Planchonia careya (F. Muell.) R. Knuth (Lecythidaceae)
One of the many plants traditionally used for wound healing by the indigenous peoples of northeastern Australia is Planchonia careya (F. Muell) R. Knuth. Based on this knowledge, investigation was carried out into the antibacterial activity of the leaf extracts of this species. The chemical constituents responsible for the observed activity were then isolated.
The plate-hole diffusion method was used to evaluate the antibacterial activity of the crude aqueous and methanol extracts against a range of Gram positive and Gram negative bacteria. Based on these assays, HPLC-piloted activity-guided fractionation was carried out to isolate the active compounds from the crude aqueous extract. Separation was performed using XAD-16 media, followed by a 20µm grade Chromatorex® C18 column with a 10% methanol/ water mobile phase. The active fractions from these columns were separated further with Sephadex LH-20 gel in methanol, and final isolation was attained using an Alltima Preparative C18 (5µm) column in a 5% methanol/ water mobile phase.
Elucidation of the isolated active compounds was achieved by UV, 1-D NMR (1H, 13C), and 2-D NMR (COSY, HSQC, HMBC) techniques. This analysis yielded (+)-gallocatechin and the prodelphinidin, gallocatechin-(4α-8)-gallocatechin. The structures were confirmed by reference to previously reported NMR spectra of these compounds (1, 2). Further examination of the UV profiles of other active fractions and of the crude methanol extract suggests that the minor active constituents of P. careya are also of the flavonoid class. The isolation of these known antibacterial compounds confirms the traditional use of P. careya in wound healing.
References: 1. Sun, D., et al. (1987), Phytochem. 26: 1825–1829. 2. Cai, Y., et al. (1991), Phytochem. 30: 2033–2040.