The Development and Scale-up of a Route to ATR Inhibitor AZD6738

AZD6738 is currently being tested in multiple phase I/II trials for the treatment of cancer. Its structure, comprising a pyrimidine core decorated with a chiral morpholine, a cyclopropyl sulfoximine, and an azaindole, make it a challenging molecule to synthesize on a large scale. We describe the evolution of the chemical processes, following the manufacture of AZD6738 from the initial scale-up through to multikilos on plant scale. During this evolution, we developed a biocatalytic process to install the sulfoxide with high enantioselectivity, followed by introduction of the cyclopropyl group first in batch, then in a continuous flow plate reactor, and finally through a series of continuous stirred tank reactors. The final plant scale process to form AZD6738 was operated on 46 kg scale with an overall yield of 18%. We discuss the impurities formed throughout the process and highlight the limitations of this route for further scale-up.