Isolation and antibacterial activity of anomanol B and other secondary metabolites from the stem bark of Anonidium mannii (Annonaceae)

A new Lanosta-7,9(11),22-trien-3,15,20-triol named Anomanol B 1, together with five known compounds: manniindole 2, arborinine 3, polycarpol 4, 8,9-dimethoxyphenanthridin-6(5H)-one 5 and 3-O-& beta;-D-glucopyranosyl-& beta;-sitosterol 6 were isolated from the stem bark extract of Anonidium mannii by routine chromatography techniques. 8,9-dimethoxyphenanthridin-6(5H)-one 5, was reported from natural origin for the first time. The structures of the compounds were established by comprehensive elucidation of spectroscopic data and by comparison with literature data. Evaluation of the isolates on Gram-negative bacteria such as Escherichia coli, Enterobacter aerogenes, Klebsiella pneumoniae, Providencia stuartii, and Pseudomonas aeruginosa showed that, compound 1 had weak antibacterial activity with minimal inhibitory concentrations (MIC) varying from 128 to 256 & mu;g/mL. Compounds 3, 5, and 6 exhibited moderate to weak activity with MIC of 32 to 128 & mu;g/mL and 64 to 256 & mu;g/mL compared to the reference drug chloramphenicol which inhibited the growth of all studied bacteria with MIC values of 16 to 64 & mu;g/mL.