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Keywords:
alternariol; Diaporthe; endophytic fungi; hemiketal polyketide
Abstract
From a fresh root of Trema guineensis (Ulmaceae). endophytic fungi were isolated, among which a taxon belonging to the new species Diaporthe cameroonensis. This strain was fermented in shake flask batch cultures and the broth was extracted with ethyl acetate. From the crude extract, a hemiketal polyketide 1. and an acetylated alternariol 2 were isolated, along with fifteen known secondary metabolites. Their structures were established by extensive NMR spectroscopy and mass spectrometry analyses, as well as by comparison with literature data of their analogs.
Introduction
Endophytic fungi are organisms that reside almost ubiquitously inside the fresh healthy tissue of plants, and they may increase the resistance of the host tropical trees to survive in extreme conditions [1]. As the global diversity of endophytic fungi is far from being accessed [2.3], they have been considered as an untapped microbial reservoir capable of producing a wide range of structurally unique natural products with potent pharmacological effects [4]. However, the production of biologically active compounds by filamentous fungi, especially those exclusive to their host plants, is not only important from a biomolecular standpoint but also from an ecological perspective. In continuation of our interest to explore secondary metabolites of rare and hitherto unexplored fungi hosted in Cameroonian medicinal plants [5.6], we investigated the chemical constituents of another new species of Diaporthe. This genus contains many plant pathogenic, endophytic, and saprobic species [7]. So far. the investigations of chemical constituents of Diaporthe species, have led to the isolation and characterization of a myriad of potent natural products with great structural variability such as polyketides. terpenoids, polyketide synthase-nonribosomal peptide synthetase (PKS-NRPS) alkaloids. and cytochalasins, which have been considered as taxonomic markers of the genus [7-10]. However, it is worthwhile to mention that the name Phomopsis should no longer be used since the introduction of the 1F1N concept in 2013. as explained by Chepkirui and Stadler [7]. Unfortunately, some authors who have been working on these fungi ever since the 1F1N concept was established in 2013 are apparently not aware of the fact Diaporthe is the older name and therefore takes preference over Phomopsis. Regarding the potent talents of Diaporthe. we are on the quest to the exploration of...