The rise in antibiotic resistance is a major threat for human health. Basidiomycete fungi represent an untapped source of underexploited antimicrobials, with pleuromutilin—a diterpene produced by Clitopilus passeckerianus—being the only antibiotic from these fungi leading to commercial derivatives. Here we report genetic characterisation of the steps involved in pleuromutilin biosynthesis, through rational heterologous expression in Aspergillus oryzae coupled with isolation and detailed structural elucidation of the pathway intermediates by spectroscopic methods and comparison with synthetic standards. A. oryzae was further established as a platform for bio-conversion of chemically modified analogues of pleuromutilin intermediates, and was employed to generate a semi-synthetic pleuromutilin derivative with enhanced antibiotic activity. These studies pave the way for future characterisation of biosynthetic pathways of other basidiomycete natural products in ascomycete heterologous hosts, and open up new possibilities of further chemical modification for the growing class of potent pleuromutilin antibiotics.

A new strategy is described for the direct conversion of unsaturated 3,5-dihydroxy-diarylheptanoids to dimeric products assembled on trans-2,8-dioxabicyclo[4.4.0]decane frameworks. The key atom-economical acid-mediated coupling creates 2 rings and 4 new stereocenters in a single-pot process. Oxygen-18 labelling studies are in accord with reactions proceeding via a cascade mechanism involving carbocationic intermediates. This approach enabled the concise total syntheses of analogues of the natural product blepharocalyxin D in 4 steps from simple starting materials.