Purification and identification of antibacterial compounds from Euclea crispa subsp. crispa (Ebenaceae) leaves

Abstract

The isolation, purification and identification of antibacterial compounds from Euclea crispa subsp. crispa reported here, is a continuation of earlier work. Most of the antimicrobial activity was located in an ethyl acetate fraction obtained by means of liquid–liquid extraction. Subsequent purification of this fraction, by means of multiple preparative thin layer chromatography using different solvent systems, revealed the presence of essential oils, bitter principles and saponins, all terpenoid derivatives, as well as alkaloids and phenolic compounds. A terpenoid that tested positive for bitter principles and for saponins, and possessed a steroidlike structure, was isolated and purified from the ethyl acetate fraction. This compound was active against the Gram-negative Moraxella catarrhalis. Also isolated from the ethyl acetate fraction, and showing antimicrobial activity as individual compounds, were five flavonoids identified as catechin, epicatechin, gallocatechin, hyperoside and quercitrin. Of these epicatechin and hyperoside were most active in inhibiting the growth of M. catarrhalis (−), Streptococcus pneumoniae (+) and Haemophilus influenza (−). The isolated flavonoids seemed, in general, to have less activity than the entire ethyl acetate fraction, suggesting that these compounds function in synergy.