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

Abstract

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-β-D-glucopyranosyl-β-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 µg/mL. Compounds 3, 5, and 6 exhibited moderate to weak activity with MIC of 32 to 128 µg/mL and 64 to 256 µg/mL compared to the reference drug chloramphenicol which inhibited the growth of all studied bacteria with MIC values of 16 to 64 µg/mL.

Graphical Abstract

Keywords:

• Anonidium mannii
• lanostane-type triterpene
• a phenanthridine-6(5H)-one alkaloid
• antibacterial activity

Acknowledgements

This work was financially supported by the NABSA and DAAD (German Academic Exchange Services).

Authors’ contributions

OMN, MGFG and JRNK carried out the study; VK and BN designed the experiments; ARN, PA elucidated spectra; OMN and GFC, wrote the manuscript; BN, VK and BTN supervised the work, all authors read and approved the final manuscript.

Disclosure statement

The authors declare they have no conflict of interest regarding this work.

Additional information

Funding

Network for Analytical and Bioassay Services in Africa (NABSA) hosted at the Department of Chemistry University of Botswana, and DAAD (German Academic Exchange Services) through theYaoundé-Bielefeld Graduate School of Natural Products with Anti-parasites and Antibacterial activities [YaBiNaPA project n˚57316173] for providing research facilities for isolation and identification of compounds.