Development of a Scalable Process for the PPAR‑α Agonist GW641597X Incorporating Baeyer–Villiger Chemistry and Retrospective ICH M7 Assessment

The development of the synthetic process to the PPAR-α receptor antagonist 5-((4-(tert-butoxy)-3-methylphenoxy)­methyl)-3-(4-(tert-butyl)­phenyl)-1,2,4-oxadiazole (GW641597X) 1 is described. The discussion ranges from the initial supply route, used to deliver early batches for preliminary safety studies to enable dosing in man, to an efficient manufacturing route, which delivered 35 kg of drug substance following on from a pilot plant campaign. The process includes a key oxidative Baeyer–Villiger reaction, where process development identified sodium perborate in acetic acid as a safer alternative to m-chloroperoxybenzoic acid that was used in the initial supply route. Described within is a discussion of impurities, how they are formed, and the process modifications incorporated to either reduce or remove them. There is also a discussion of potential mutagenic impurities within the synthetic process and a retrospective evaluation using ICH M7 control options. Finally, an alternative route to GW641597X is described, which offers the advantage that all intermediates are crystalline facilitating material handling, offering purification opportunities through recrystallization if required, and potentially providing greater controls for the process. This new route was also retrospectively assessed using ICH M7 option controls and highlighted that ICH M7 option 4 controls can be implemented even with excess mutagenic reagents being introduced near to the drug substance as long as the science for its purging is well understood.