Development of a Kilogram-Scale Manufacturing Route for Bis-Tac-dG: Essential Building-Block for Guadecitabine

Guadecitabine (SGI-110) is a dinucleotide that is a prodrug of decitabine. The dinucleotide contains decitabine (top fragment) and 2′-deoxyguanosine ( 9; dG; bottom fragment) connected via a 3′ → 5′ phosphodiester bond. The manufacturing process of guadecitabine requires a large quantity of N 2, 3′- O -(4- tert -butylphenoxyacetyl)-protected dG ( 2; Bis-Tac-dG) to incorporate the bottom fragment. The protected 2 being a critical starting material of the dinucleotide imposes stringent quality requirements for its synthesis and isolation. Presented herein is the development work leading to a practical and scalable route for compound 2 starting from commercial dG. Salient features of the approach included one-pot protection of 5′-OH group of N 2 -Tac-dG ( 3 ) with 4,4′-dimethoxytrityl (DMT) group followed by 3′- O -Tac protection furnishing fully protected dG 8, thus reducing the cycle time with fewer isolation steps and lowering the solvent usage. Subsequently, cleavage of DMT group from 8 utilizing NaIO 4 enabled a mild, highly selective, and robust route to produce high purity (>99%) Bis-Tac-dG on kilogram-scale. The structure and origin of major impurities were determined by comparison with reference standards and carefully controlled to an acceptable level in compound 2 . The improved synthesis was scaled to prepare multiple ∼60 kg batches of 2 to supply all clinical studies up to phase III.