Stereochemical assignment of the protein-protein interaction inhibitor JBIR-22 by total synthesis

Abstract

Recent reports have highlighted the biological activity associated with a sub-family of the tetramic acid class of natural products. Despite the fact that members of this sub-family act as protein-protein interaction inhibitors of relevance to proteasome assembly, no synthetic work has been reported. This may be because this sub-family contains an unnatural 4,4-disubstitued glutamic acid, the synthesis of which provides a key challenge. Here we describe a highly stereoselective route to a masked form of this unnatural amino acid. This enabled the synthesis of two of the possible diastereomers of JBIR-22 and allowed its relative and absolute stereochemistry to be assigned.