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Abstract
A phytotoxic compound was identified in methanolic extracts of pigeonpea leaves. Results of fractionation of methanolic extracts to acidic, basic, and neutral compounds revealed that the acidic fraction exerted a strong inhibitory activity on lettuce radicle elongation. Further purification of the acidic fraction by preparative silica gel TLC showed that the one fraction inhibited lettuce germination completely. Analysis of the biological active fraction by HPLC enabled to detect a single peak with maximum UV absorption at 258 nm.
The phytotoxic compound was crystallized from methanolic extracts of fresh leaves (5 kg) with subsequent purification by silica gel column chromatography after extraction of the acidic compounds. The structure of the isolated phytotoxic compound analyzed by MS and NMR was found to correspond to 3-hydroxy-5-methoxystilbene-2-carboxylic acid that inhibited the lettuce radicle elongation by about 80% at the concentration of 500 μmol L-1. The possible role of the phytotoxic compound identified in pigeonpea leaves was discussed in relation to allelopathy.