Improvements to Enable the Large Scale Synthesis of 1-{[(2S,3S,4S)-3-Ethyl-4-fluoro-5-oxopyrrolidin-2-yl]methoxy}-7-methoxyisoquinoline-6-carboxamide (PF-06650833)

An improved process for the large scale synthesis of 1-{[(2S,3S,4S)-3-ethyl-4-fluoro-5-oxopyrrolidin-2-yl]­methoxy}-7-methoxyisoquinoline-6-carboxamide (1), a candidate currently in clinical development, was developed. Key objectives were to eliminate chromatographic purifications, to maximize the reproducibility of each step, and to improve the yield and efficiency of each step relative to the previous discovery syntheses of 1. This work was focused on improvements to the synthesis of the stereochemically complex lactam 2. Steps of particular concern were the preparation of the unsaturated lactam 6, the cuprate conjugate addition reaction to produce 7, and the conversion of 7 to 8 with a high degree of diastereoselection. The solutions to these challenges have permitted the synthesis of 2 in excess of 100 kg, which in turn has permitted 1 to be prepared in sufficient amounts to support further development.