Isolation and Identification of Alkaloids of Stem bark and Leaves of Erythrina abyssinica Lam.

Abstract

The present study aimed to isolate and identify the alkaloid constituents of stem bark, and leaves, of Erythrina abyssinica Lam.; leguminosae family (Fabaceae) growing in Sudan. A comparative phytochemical screening was carried out for the naturally active substances occurring in stem bark and leaves of this tree. The phytochemical screening results revealed that; the methanol extract is the richest fraction in its contents: alkaloids, anthraquinones, carbohydrates, cardiac glycosides, cyanogenic glycosides, flavonoids, saponins, and tannins. While the petroleum ether extract contained only coumarins, volatile constituents and unsaturated sterols & tri-terpenes. Chloroform extract not only contained trace of alkaloids, but also coumarins and unsaturated sterols & tri-terpenes. The Ethylacetate extract contained anthraquinones, coumarins and flavonoids. Quantitative estimation of the alkaloids content in the stem bark and leaves gave 0.002% for stem bark and 0.07% for leaves. The alkaloid constituents were isolated through fractionation using thin layer chromatography and column chromatography techniques. The identification of the isolated compounds was aided by the use of IR, UV, MS and NMR techniques with reference to the published data. The crude alkaloid content was isolated according to the `acid-base shakeout` method, after then, its cytotoxicity was evaluated in vitro, against: Hela (Cervix carcinoma human cell line) HepG2 )Liver carcinoma human cell line) HEP2 )Larynx carcinoma human cell line) HCT-116 (Human colon tumor cells) MCf 7 (Breast carcinoma human cell line) and HFB4 (Normal melanocytes), which resulted in IC50 = 13.8, 10.1, 8.16, 13.9, 11.4 and 12.2 μg/mL. Furthermore, chromatographic fractionation of the crude extract led to the isolation of two new Erythrina alkaloids for the first time in this species: 8-Oxoerythraline (IV) and 11-Methoxyerysodine (V); together with three other known alkaloids: Erythraline (I), Erysodine (II) and Erysotrine (III). All the isolated alkaloids were of the dienoid type of Erythrina alkaloids with a characteristic 1(6)-diene functionalties. The isolated alkaloids showed in vitro cytotoxic activity against HepG2 (Liver carcinoma human cell line) with IC50 = 17.6, 11.8, 15.8, 3.89 and 11.4 μg/mL, even greater than the standard drug Doxorubicin. While against HEP2 (Larynx carcinoma human cell line) they gave IC50 = 15.90, 19.90, 21.60, 18.50 and 11.50 μg/mL.