3-Substituted 2-phenyl-indoles: privileged structures for medicinal chemistry

Privileged structures have been used in drug discovery targeting G protein-coupled receptors ( GPCR) and other protein classes for more than 20 years. Their rich activity profiles and drug-like characteristics lend themselves to increased productivity in hit identification and lead optimisation. Recently we discovered two allosteric modulators 1 and 2 for the G protein-coupled receptor GPRC6A incorporating the privileged 2-phenyl-indole scaffold, functionalised at the 3-position. In order to develop new potential GPRC6A ligands we engaged in the development of synthetic routes to provide 2-phenyl-indoles with a variety of substituents at the indole 3-position. Herein we describe the development of optimised and efficient synthetic routes to a series of new 2-phenyl-indole building blocks 3 to 9 and show that these can be used to generate a broad variety of 3-substituted 2-phenyl-indoles of interest to medicinal chemists.