toxins Review Tremorgenic Mycotoxins: Structure Diversity and Biological Activity Priyanka Reddy 1,2, Kathryn Guthridge 1, Simone Vassiliadis 1 , Joanne Hemsworth 1, Inoka Hettiarachchige 1, German Spangenberg 1,2 and Simone Rochfort 1,2,* 1 Agriculture Victoria, AgriBio, Centre for AgriBioscience, Bundoora, Victoria 3083, Australia;
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[email protected] Received: 24 April 2019; Accepted: 22 May 2019; Published: 27 May 2019 Abstract: Indole-diterpenes are an important class of chemical compounds which can be unique to different fungal species. The highly complex lolitrem compounds are confined to Epichloë species, whilst penitrem production is confined to Penicillium spp. and Aspergillus spp. These fungal species are often present in association with pasture grasses, and the indole-diterpenes produced may cause toxicity in grazing animals. In this review, we highlight the unique structural variations of indole-diterpenes that are characterised into subgroups, including paspaline, paxilline, shearinines, paspalitrems, terpendoles, penitrems, lolitrems, janthitrems, and sulpinines. A detailed description of the unique biological activities has been documented where even structurally related compounds have displayed unique biological activities. Indole-diterpene production has been reported in two classes of ascomycete fungi, namely Eurotiomycetes (e.g., Aspergillus and Penicillium) and Sordariomycetes (e.g., Claviceps and Epichloë).