Diasteltoxins A–C, Asteltoxin-Based Dimers from a Mutant of the Sponge-Associated Emericella variecolor Fungus

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Three novel asteltoxin-bearing dimers namely diasteltoxins A-C (1-3) along with asteltoxin were isolated from a mutated strain of a sponge-derived fungus Emericella variecolor XSA-07-2. Their structures were determined by extensive spectroscopic analyses including the computed electronic circular dichroism (ECD) data for the configurational assignment. The biogenetic formation of the dimers through [2 + 2] cycloaddition of asteltoxin was postulated. Diasteltoxins 1-3 exerted inhibitory effects against the tumor cell lines H1299 and MCF7 and exhibited significant inhibition against thioredoxin reductase (TrxR).