Isolation and structure elucidation of bioctive compounds from Rauvolfia Caffra Sond

Abstract

Rauvolfia caffra Sond, a species of evergreen trees and shrubs in the dogbane family, (Apocynaceae), is used as a medicinal plant among traditional communities in many countries for the treatment of malaria, diabetes, coughs, gastrointestinal disturbances, skin infections, impotence, insomnia, diarrhoea, dysentery, scabies, worm infections, and both parasitic and microbial infections. Phytochemical studies have revealed that indole alkaloids are the major constituents of the stem bark. However, there are limited studies linking the compounds with the ethnomedicinal uses. The aim of this study is to isolate and characterize bioactive compounds from Rauvolfia caffra Sond. The highest phenolic content found in a fraction was 16.06±0.125 mg GAE/g, while the highest flavonoid content measured was 9.453±0.081 mg QE/g. In the DPPH free radical scavenging activity and reducing power tests, a lowest IC50 value of 0.022±0.003 μg/mL and IC0.5 value 0.518±0.044 μg/mL, respectively, was found. Six compounds were isolated from the stem bark, including lupeol, a pentacyclic tri-terpenoid isolated for the first time from the genus Rauvolfia; raucaffricine, a rare glycoalkaloid of the monoterpenoid indole class; N-methylsarpagine, an indole alkaloid isolated for the time from R. caffra and spegatrine, an indole alkaloid isolated for the first time from R. caffra, respectively. Concerning antimicrobial activity, the highest activity of a fraction was against B. cereus with MIC values as low as 12.5 mg/mL. One fraction at the tested concentration (250 μg/mL) decreased the viability of Plasmodium falciparum (4.149±6.979 %) with an IC50 value of 6.533 μg/mL. The crude extract and some fractions affected the viability of the Trypanosomes at the tested concentration (250 μg/mL), giving -0.133 ± 0.206 %, 11.334 ± 2.692 %, 1.026 ± 0.143 % and 20.769 ± 9.054 % with IC50 values of 18.50 μg/mL, 14.15 μg/mL, 15.58 μg/mL and 34.71 μg/mL, respectively. Furthermore, the fractions did not show significant cytotoxic effects at a concentration of 50 μg/mL.