Isolation of isoeleutherol from microwave assisted methanol extract of Eleutherine bulbosa bulbs, its crystal structure elucidation and cytotoxicity evaluation

Abstract

Different extraction methods (Soxhlet, Serial soxhlet, Cold, and microwave-assisted extraction) were executed for the extraction of phytochemicals from the bulbs of Eleutherine bulbosa Miller (Urban), an important medicinal plant in the family Iridaceae. Among the different methods, most efficient (especially in terms of extraction time) was the microwave-assisted extraction (MAE) using methanol as the extraction solvent. The microwave assisted methanolic extract was subjected to column chromatography and a naphthalene compound, isoeleutherol was isolated. Starting from, about two grams of the crude methanol extract, 21 mg of pure compound (isoeleutherol) was obtained as yellow needle like crystals with an Rf value of 0.53 in TLC. The structural characterization was done by Single crystal X-ray diffraction analysis. The study also tested the cytotoxic activity of the compound against two cancer cell lines (HeLa and MCF-7) and one normal cell (Chang liver cells) line by MTT assay. Results of the cytotoxicity evaluation showed that isoeleutherol has potent activity on both the cancer cell lines with LC 50 values of 35.4 and 23.8 μg/ml against HeLa and MCF-7 cells, respectively. Isoeleutherol exhibitted less cytotoxicity towards normal cells (Chang liver cells). At the highest concentration used (100 μg/ml), 60.99 ± 1.92% normal cells were viable. This is the first report of isolation of a compound from E. bulbosa through microwave-assisted extraction, a faster and environment friendly technique for the phytochemical extraction. The present study also reports detailed structural elucidation of isoeleutherol by X-ray crystallography for the first time.