Core Modifications of GSK3335103 toward Orally Bioavailable αvβ6 Inhibitors with Improved Synthetic Tractability

The αvβ6 integrin has been identified as a target for the treatment of fibrotic diseases, based on the role it has in activating TGF-β1, a protein implicated in the pathogenesis of fibrosis. However, the development of orally bioavailable αvβ6 inhibitors has proven challenging due to the zwitterionic pharmacophore required to bind to the RGD binding site. This work describes the design and development of a novel, orally bioavailable series of αvβ6 inhibitors, developing on two previously published αvβ6 inhibitors, GSK3008348 and GSK3335103. Strategies to reduce the basicity of the central ring nitrogen present in GSK3008348 were employed, while avoiding the synthetic complexity of the chiral, fluorine-containing quaternary carbon center contained in GSK3335103. Following initial PK studies, this series was optimized, aided by analysis of the physicochemical and in vitro PK properties, to deliver lead molecules (S)-20 and 28 as potent and orally bioavailable αvβ6 inhibitors with improved synthetic tractability.