Cardenolides and dihydro-ß-agarofuran sesquiterpenes from the seeds of Salacia staudtiana.

Phytochemical studies of the seeds of the Cameroonian medicinal plant, Salacia staudtiana, resulted in the isolation and identification of five new cardenolides (1-5) as well as a new dihydro-ß-agarofuran (9), along with eight known compounds. The structures of all compounds were elucidated by 1D/2D NMR, ESI-HRMS data and comparison with literature data. The relative configurations of the new compounds were defined by X-ray crystallography analysis, NOESY correlations and coupling constants. We evaluated their antibacterial efficacy against two commonly dispersed environmental strains of Escherichia coli and Bacillus subtilis, and two pathogenic strains of Staphylococcus aureus and Pseudomonas aeruginosa, compared to the standard antibiotics, streptomycin and gentamicin. Moreover, we assessed the antibacterial activity of the crude extract of the seeds in parallel to evaluate the plausible synergistic effects of the compounds in chemical defense of the seeds during germination and plant reproduction. The isolated compounds showed moderate antibacterial activities against the tested organisms. Compounds 1 and 3 and the crude extract exhibited distinct antibacterial activities against B. subtilis and S. aureus. The isolated compounds showed weak DPPH radical scavenging properties compared to the reference standard (Trolox). Our study lends evidence to the antibacterial chemical defense of S. staudtiana seeds by seed-borne compounds.

Cardenolides from the stem bark of Salacia staudtiana.

Seven new cardenolides, staudtianoside A-F (1-6) and staudtianogenin A (8), were isolated along with six known compounds from the stem bark of the Cameroonian medicinal plant Salacia staudtiana Loes. ex Fritsch. The structures were elucidated by means of ESI-HRMS and NMR spectroscopic methods and by comparison with literature data. The relative configurations of the new compounds were determined by X-ray diffraction analysis, NOESY correlation and coupling constants. We evaluated the antibacterial efficacy of the isolated compounds against two commonly dispersed environmental strains of Escherichia coli and Bacillus subtilis, as well as against two human pathogenic clinical strains of Staphylococcus aureus and Pseudomonas aeruginosa. Compounds 1, 2 and 8 exhibited marked antibacterial potencies against the clinically relevant P. aeruginosa that were comparable to the standard antibiotics. Compound 2 was also active against S. aureus and E. coli. Further, compounds 5 and 8 demonstrated efficacy against E. coli as well as B. subtilis. The structure-activity relationship of the tested compounds is discussed.