Phytochemical Investigation Of Aloe Secundiflora For Antiplasmodial And Antimicrobial Activity

Abstract

The stems of Aloe secundiflora was exhaustively extracted by percolation in CH2Ch-MeOH (1: 1) at room temperature. The extract showed significant antiplasmodial activity against the chloroquine-resistant (W2) strain of Plasmodium falciparum with an ICso value of 2.09±0.43 ug/rnl. The extract was subjected to chromatographic separations (Column chromatography and preparative thin layer chromatography) and crystallization which led to isolation of seven compounds. By the use of spectroscopic methods including IR, UV, MS and NMR CH, l3C, DEPT, COSY, HMQC and HMBC) and direct TLC comparison with authentic samples in some cases, these compounds were identified as the monomeric anthraquinones chrysophanol (1), aloesaponarin II (2), aloesaponarin I (3), laccaic acid D-methyl ester (4), emodin (5); thepre-anthraquinone aloesaponol I (6); and the naphthoquinone derivative 8-hydroxy-2,7- dimethoxy-3-methylnaphthalene-l,4-dione (7). Of these, the naphthaquinone derivative (7) is a new compound. More over this is the first report on the occurrence of a naphthaquinone in the genus Aloe. The isolated compounds from Aloe secundiflora were tested for antiplasmodial activity and aloesaponarin I (3), aloesaponarin II (2), aloesaponol I (6) and the naphthoquinone derivative (7) showed significant activities. Amongst these, aloesaponarin I (3) was the most active with an ICso value of O.92±O.071lg/ml against the chloroquine-resistant (W2) strain. This investigation has shown the potential of the aloesaponarin I (3) as a lead structure for the development of antimalarial drugs.

Antibacterial and antifungal tests were also carried out for some of the isolated compounds against three bacterial strains viz. Staphylococcus aureus, Escherichia coli, Pseudomonas eruginosa and four fungal strains viz. Candida albicans, Cryptococcus neoformans, Trichophyton mentagrophytes and Microsporum gypsum. Amongst those tested, aloesaponarin II (2) was the most active showing activity against Staphylococcus aureus and Cryptococcus neoformans with an MIe value of 18.8 ug/disc for both organisms. No significant activity was observed for any of the isolated compounds against Gram-negative bacteria, Escherichia coli and Pseudomonas eruginosa..........