Abstract:
Fungal natural products have been used for spiritual and medicinal purposes through history and have given the world answers to some of the most pressing medical issues of our time. With more than 5 million species of fungi spanning the globe and inhabiting most niches, fungi have become an invaluable source of bioactive natural products. From Phoma herbarum westend 1852, a rust fungus that infects grasses and pasture legumes; six natural products were isolated. Fractionation of crude extract using a standard extraction procedure led to the isolation of two α-pyrones; taiwapyrone and xylariolide D, two furanones; (2Z)-cillifuranone and (2E)-cillifuranone, one acetamide; N-(5-hydroxypentyl) acetamide, and one anthraquinone; pachybasin. None of the natural products isolated showed significant activity against a variety of human pathogens. The total synthesis of xylariolide D was attempted, however progress came to a halt when dehydrogenation of the α-pyrone ring failed. (2Z)-Cillifuranone was postulated to exist as it is a critical moiety in another class of larger natural products; the sorbifuranones. Previous studies have isolated both (2E)-cillifuranone and sorbifuranone A -C in the same extract, therefore it was postulated that (2Z)-cillifuranone must exist under fungal conditions. A time-controlled experiment was conducted, and it was shown that in ambient temperature and light (2Z)-cillifuranone spontaneously isomerises to (2E)-cillifuranone. Interestingly the proposed biosynthesis of (2Z)-cillifuranone can double as a proposed biosynthesis for taiwapyrone if an alternative ring closure process occurs. A 1-13C acetate labelled experiment to determine the biosynthesises of these natural products was performed. It was shown that pachybasin is biosynthesised via cyclisation of an octaketide, biosynthesised from the acetate polyketide pathway. Literature values for pachybasin were found to be incorrect and were corrected using extensive 1D/ 2D NMR and a1-13C acetate labelled experiment.