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This manuscript details the process research and development of a convergent and safe approach to 1 on a multikilo scale. Specific highlights of the process development efforts will be described, including the development of a dehydrogenation method for dihydropyrimidines and a thermochemically safe synthesis of a 1,2,4-aminotriazole fragment. A key feature of the synthesis is the use and optimization of a modified Julia-Kocienski olefination reaction. Specifically, we report an unprecedented dependence of the product olefin geometry on reaction temperature, where an E:Z ratio as high as 200:1 can be obtained. Initial insights into the mechanistic rationale for this observation are also provided. Finally, a purity upgrade sequence via an intermediate crystalline form is highlighted as a method of controlling the final API quality.

This report describes the large-scale synthesis of 1 that features a Fischer indole strategy to form an advanced intermediate followed by reduction to the indoline to construct the tetracyclic core of the molecule. Resolution using dibenzoyl-D-tartaric acid affords access to a single enantiomer, from which a Suzuki coupling builds in the biaryl functionality. Deprotection followed by salt formation furnishes the desired target molecule.

This work presents a process modeling-based methodology towards quality by design that was applied throughout the development lifecycle of the ibipinabant API step. By combining mechanistic kinetic modeling with fundamental thermodynamics, the degradation of the API enantiomeric purity was described across a large multivariate process knowledge space. This knowledge space was then narrowed down to the process design space through risk assessment, target quality specifications, practical operating conditions for scale-up, and plant control capabilities. Subsequent analysis of process throughput and yield defined the target operating conditions and normal operating ranges for a specific pilot-plant implementation. Model predictions were verified via results obtained in the laboratory and at pilot-plant scale. Future efforts were focused on increasing fundamental process knowledge, improving model confidence, and using a risk-based approach to reevaluate the design space and selected operating conditions for the next scale-up campaign.

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