Evaluation of Potential Second-Generation Manufacturing Routes to Palbociclib

Abstract A potential next-generation manufacturing route to Palbociclib was developed to reduce step count and cycle time relative to the first-generation commercial process while improving overall process sustainability. The final tert-butoxycarbonyl (Boc) deprotection step from the original route was retained to preserve established late-stage impurity clearance and API attributes. The revised synthesis is based on the preparation of a common chloropyridone intermediate (8a) from a readily crystallized hydroxy-pyridone precursor (9), followed by a convergent late-stage C–N bond formation between two advanced heterocyclic fragments. Several coupling approaches, including nucleophilic aromatic substitution and palladium-catalyzed Buchwald–Hartwig amination, were evaluated. High-Throughput Experimentation combined with Design-of-Experiments studies identified a homogeneous palladium-catalyzed amination as the preferred manufacturing solution. Isolation of the coupling product (20) was achieved by reactive crystallization, enabling direct preparation of the advanced intermediate in high purity. Final Boc cleavage with formic acid, followed by basification, afforded palbociclib in high yield and purity. Overall, the route provides a shorter and operationally streamlined manufacturing process, enabling a two-step synthesis of palbociclib (1) from key starting materials 10e and 3b.