1 Department of Physical Sciences, School of Science and Technology, University of Kabianga, 20200, Kericho, Kenya
2 Department of Chemistry, Faculty of Science, Egerton University, PO Box 536-20115, Njoro, Kenya
Fungal endophytes are regarded as a prolific source of secondary metabolites with desirable antibacterial, anticancer, antifungal and antidiarrheal properties. In this study, the fungal endophyte Diaporthe sp. host to the plant Syzygium cordatum yielded three novel antibacterial compounds after extraction with ethyl acetate and purification using column chromatography and preparative high-performance liquid chromatography. The eluted fraction that yielded the three compounds showed significant antibacterial activity against selected bean bacterial pathogens; Pseudonomas syringae and Xanthonomas axonopodis with their corresponding zones of inhibition of 10.7 mm and 14 mm, respectively. The structural determination of the three compounds was achieved using spectral information from 1D and 2D NMR as well as mass spectrometry. Two enol geometric isomers that were accorded trivial names as Z-cordatenol, E-cordatenol, and a phenolic derivative was accorded a trivial name as alpha-cordenol. Bioactivity of Z-cordatenol and E-cordatenol was attributed to hydroxylation on the aliphatic alkene chains, whereas, in alpha-cordenol, hydroxylation of the benzene ring and side chain aziridine ring enhanced its activity. These results are evident that endophytic fungi are rich sources of secondary metabolites that can be utilized to control phytopathogens.