However, a new crystallization method was identified. The acetonitrile/water crystallization system allowed us to reach a higher corrected isolated yield of 78% of MRTX0902 free base dihydrate. Last, some improvements were made to the fumarate salt formation 12. The addition of fumaric acid as a solid, as discussed above, was deemed not ideal. Therefore, the fumaric acid was used as a 95/5 EtOH/water solution requiring generous amount of solvent due to its low solubility. In addition, seed material of MRTX0902 fumarate salt 12 was also used to initiate the crystallization upon controlled addition of the fumaric acid solution. Ultimately, MRTX0902 fumarate salt 12 was isolated in 97% corrected yield with minimal loss in the mother liquors.