Antimicrobial and cytotoxic activities of indole alkaloids and other constituents from the stem barks of Rauvolfia caffra Sond (Apocynaceae)

Twenty indole alkaloids, among which two undescribed ones named rauvolfianoids A (1) and B (2), were isolated from the stem barks of Rauvolfia caffra Sond along with eight other compounds from other biosynthetic pathways. The structures were elucidated by analysis of spectroscopic data, including 1 D and 2 D NMR; absolute configurations of 1 and 2 were determined by CD exciton chirality method. Compounds 1 and 2 were evaluated for antimicrobial and anticancer activities against three bacterial strains (Escherichia coli, Shigella sp and Salmonella sp) and CRC-related opportunistic pathogens. 1 showed moderate antibacterial activity against Salmonella sp with the MIC value of 25 mu g/ml, while 2 exhibited weak selective activity against all tested pathogens. In addition, these alkaloids were characterized as weak apoptosis inducers in HCT116 human colon carcinoma cell line.