Total synthesis of violaceimides A-E and consideration of the reported stereochemistry

Here we report the first total synthesis of violaceimides A-E, a family of sulfur-containing metabolites from Aspergillus violaceus, a sponge-associated fungus. A concise, convergent and enantioselective synthesis was developed for all five family members, from a common advanced intermediate. However, while the NMR spectral data matched that of the reported natural products, the optical rotations were of opposite sign. This result prompted the enantioselective synthesis of all four diastereomeric pairs of violaceimide E, and suggests that the stereochemistry might have been misassigned. (C) 2019 Elsevier Ltd. All rights reserved.