Development of a Practical Synthesis of a Purine Nucleoside Phosphorylase Inhibitor: BCX-4208

A practical synthesis of the purine nucleoside phosphorylase (PNP) inhibitor BCX-4208 (1) was accomplished in three telescoped steps. Mannich condensation of the 4-benzyloxy-9-deazahypoxanthine with (3R,4R)-3-hydroxy-4-(hydroxymethyl)pyrrolidine and formaldehyde followed by removal of the protecting group and crystallization furnished the desired product as a hydrochloride salt in 85% overall yield and 99.8% purity. A scalable synthesis of 9-deazahypoxanthine is also reported.