New naphthalene derivative isolated from Diaporthe sp. host to Syzygium cordatum Hochst.ex Krauss plant

Abstract

Fungal endophytes are regarded as inexhaustible sources of pharmaceuticals and agrochemicals with profound antibacterial, anticancer or antifungal activities. Diaporthe sp., an endophytic fungus residing in medicinal plant S. cordatum, showed a good antagonism against bacterial pathogens of beans; Pseudomonas syringae pv phaseolicola (Psp) and Xanthomonas axonopodis pv phaseoli (Xap), with zones of inhibitions of 14.00 ± 1.15 and 17.00 ± 0.58 mm against the test organisms respectively. Large scale fermentation of Diaporthe sp. was performed on rice media after which ultrasonic extraction on methanol was done to yield methanol crude extract. Methanol crude extract was then partitioned between hexane and ethyl acetate to yield their respective crude extracts. Ethyl acetate fraction of Diaporthe sp. yielded one new naphthalene derivative compound which was accorded IUPAC name as 3-methoxy-5-methylnaphthalene-1, 7-diol after series of purifications on column chromatography as well as preparative high-performance liquid chromatography (pHPLC). Structure determination of isolated compounds was performed on 1D and 2D Nuclear Magnetic Resonance (NMR) spectroscopy experiments as well as a mass spectrometer to affirm its molecular mass. The F3 that yielded compound 1 had palpable antibacterial activities against Psp and Xap, with corresponding Minimum Inhibitory Concentration (MIC) values of 2.50 mg/ml (7.00 ± 0.00 mm) and 1.25 mg/ml (7.67 ± 0.33 mm) against the tests organisms respectively. These slight MIC values are chiefly attributed to the presence of active secondary metabolites in the fungal extracts that act against the test pathogens. This has therefore confirmed that fungal endophytes and their extractives have desirable antibacterial activities hence can be used in the formulation of agrochemicals or used as bio-control agents in crop protection especially in common beans (Phaseolus vulgaris L).