EXTRACTION AND CHROMATOGRAPHIC ISOLATION OF CERTAIN CHEMICAL CONSTITUENTS OF TWO ALLIUM SPECIES AND THEIR EVALUATION AS ANTIOXIDANT AND CYTOTOXIC AGENTS

Abstract

- The present study was designated to find out antioxidant and cytotoxic agents from plant origin as well as chromatographic isolation of the most active extracts. Therefore, preliminary antioxidant activity of each defatted methanolic extract of six Allium species was carried out. The results revealed that methanolic extracts of A. cepa (ssp. red onion) and A. porrum exhibited high antioxidant and cytotoxic activities. - Fractionation of each defatted methanolic extract of A. cepa and A. porrum using different organic solvents such as CHCl3, EtOAc and n-BuOH was carried out and the antioxidant and the cytotoxic activities of these fractions were evaluated. Also, the phenolic and flavonoid contents of these fractions were determined. The results revealed that the ethyl acetate and butanolic fractions have high activity in both plants whereas A. cepa was the most active and there a high correlation between the phenolic content and their antioxidant activity. - Owing to the high antioxidant and cytotoxic activities of the ethyl acetate and butanolic fractions derived from the defatted methanolic extracts of A. cepa (red onion ), each fraction was submitted to chromatographic separation process to identify their chemical constituents . -Firstly, each of ethyl acetate and butanolic fraction was separately submitted to silica gel column chromatography. Certain fractions could be purified by using sephadex LH20 columns, TLC and PC whereas fraction IV from ethyl acetate column and fraction II from butanolic column showed complex mixture, therefore the two fractions (IV and II) were submitted to HPLC analysis. - Four compounds were isolated from A. cepa (red onion ) ethyl acetate fraction and their structure were elucidated as kaempferol (1), quercetin (2) isorhamentin (3) and isorhamentin-4`-O-β- D-glucopyranoside (4) and two compounds from the butanolic fractions, their structures were elucidated as α -D-glucopyranose (5), β-D-glucopyranosyl- α- D-glucopyranoside (6). - HPLC-DAD and HPLC-ESI-MS/MS analysis of mixed fractions resulted from ethyl acetate columns revealed that presence of five phenolic acids, one flavane, five flavonol and two flavones derivatives. - HPLC-DAD and HPLC-ESI-MS/MS analysis of the mixed fractions resulted from the butanolic column revealed the presence of five flavonols, five anthocyanidin and seven steroidal saponins compounds.