Turrealabdane, turreanone and an antisalmonellal agent from Turraeanthus africanus

Phytochemical investigation of the seeds of Turraeanthus africanus (Meliaceae), a Cameroonian plant species traditionally used in the treatment of typhoid fever, afforded eight compounds, including two labdanes, a C-arabinoside derivative, a sesquiterpene, and several triterpenes, two of which are new: 15',16'-dihydroxy-15(12'),15'(16')-diolidebislabd-8(17),8'(17'),12-trien-16-al ( 1), trivially named turrealabdane and a C-arabinoside derivative ( 2), trivially named turreanone. The other compounds are 12,15-epoxylabda-8(17),12,14-trien-16-acetate ( 3), (+)-eudesmanol- O-L-arabinoside, cyclolaudenol, stigmasterol, sitosterol glucoside and lupeol. Acetylation and oxidation of turrealabdane yielded 15',16'-diacetoxyturrealabdane and 15,12'-dioxoturrealabdane-15',16'-dial, respectively. Their structures were determined by means of spectroscopic data including 1D and 2D NMR in combination with MS. The compounds were evaluated for antibacterial activities, chloramphenicol and amoxicillin being used as standard. Compound 3 was the only active principle, possessing the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of respectively 25 microg/mL and 100 microg/mL against Salmonella typhi, S. paratyphi a and S. paratyphi B.This compound did not show any activity against Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus.