Isolation and in-vitro assessment of two indole alkaloids from Pericopsis laxiflora leaf extract for their antibacterial potentials

Abstract

Traditionally, Pericopsis laxiflora leaf is useful in the treatment of fevers and bacterial infections in different cultures. Qualitative and quantitative screening of the 70% ethanol leaf extract of the plant (P) revealed a strong presence of alkaloids, which were extracted and separated out as crude alkaloids (Pa). Fractionation of portion Pa using various chromatographic techniques led to the isolation and purification of two indole alkaloids whose structures were elucidated based on physical, chemical and spectral data in comparison with literature data. They were identified as H-indol-5-ol, 3-[2’-(dimethylamino) ethyl (Pa1a) and 7-methoxy-1,9-dimethyl -9 H-pyrido [3,4-b] indole (Pa2a1). In-vitro antibacterial and anti-typhoid assessment of P, Pa, Pa1a and Pa2a1 using the agar dilution method revealed that extract, P and alkaloidal portion, Pa at 1000 and 500 μg/cm3 respectively displayed broad-spectrum potentials against the bacterial, typhoid and paratyphoid strains, though at higher concentrations when compared with Ciprofloxacin. For the isolated compounds, the β-carboline derivative (compound Pa2a1) exhibited better activity than the hydroxyl tryptamine derivative (compound Pa1a) both at 100 μg/cm3. Generally, all test compounds (P, Pa, Pa1a and Pa2a1) displayed significant broad-spectrum antibacterial and anti-typhoid potentials, justifying the use of the plant traditionally in the treatment of bacterial and typhoid infections.