Development of a Kilogram-Scale Asymmetric Synthesis of a Potent DP Receptor Antagonist

Abstract

An efficient asymmetric synthesis of a unique sulfenylated prostaglandin DP receptor antagonist candidate is described. The synthesis is characterized by a novel intramolecular Friedel−Crafts cyclization of an imino-pyrrole to prepare the azaindole core. Other key steps include a highly selective Horner−Wadsworth−Emmons olefination of a tricyclic ketone intermediate and subsequent catalytic asymmetric hydrogenation of a trisubstituted α,β-unsaturated ester to install the chirogenic center. Finally, a new indole sulfenylation protocol was developed to install the aromatic thioether functionality in good yield.