Development of a Concise Process for the Synthesis of the Azaindazole Core of the CD73 Inhibitor AB680

AB680 is a highly potent small-molecule CD73 inhibitor discovered and developed by Arcus Biosciences, currently in clinical trials for the treatment of pancreatic cancer. Herein, we report a concise synthesis of 4,6-dichloro-1H-pyrazolo[3,4-b]pyridine 3, which is the central azaindazole core of AB680. The process consists of four synthetic operations and three isolations, including a PMB-protected pyrazole formation, a telescoped two-step cyclization and aromatization sequence, and finally a one-pot PMB deprotection and chlorination to furnish 3. This chemistry was successfully scaled up to provide >200 g of 3 in 44% overall yield and 97.6% HPLC purity. Overall, the route developed toward 3 represents an efficient construction of an azaindazole core, which is a synthetically challenging yet prevalent structural motif.