An improved synthesis of sunitinib malate via a solvent-free decarboxylation process

To search for an economical and convenient synthesis of sunitinib and its malate salt, optimization of a scalable synthetic route was explored by designing a standard experimental protocol on laboratory scale using commercially available materials including acetyl ethyl acetate, 4-fluoroaniline, and N (1),N (1)-diethylethane-1,2-diamine. The optimal conditions were established based on investigating the main reaction steps, including cyclization, hydrolysis, decarboxylation, formylation, and condensation, giving optimized yields for each step of 94.4, 97.6, 98.5, 97.1, 91.0, 86.3, 85.5, 88.2, 99.1, 97.3, and 58.7 %, respectively. The synthesis process of 5-formyl-2,4-dimethyl-1H-pyrrole-3-carboxylic acid as the important intermediate was significantly improved by using solvent-free decarboxylation instead of the traditional process in a high-boiling-point solvent. The subsequent formylation was conducted directly using the dichloromethane solution of the crude product from decarboxylation, leading to an almost quantitative combined yield of these two steps. The overall yields of sunitinib and its salt using the optimal synthesis process were 67.3 and 40.0 % based on acetyl ethyl acetate. The obtained data could be used as reference for future industrialization, especially for avoiding expensive solvents and reducing reaction time.