Epoxyketone 4 is an isolated intermediate in the manufacturing route to the commercial proteasome inhibitor carfilzomib (Kyprolis). Commercial process development and optimization efforts toward the preparation of epoxyketone 4 highlighted several opportunities for process improvement. In this article, three case studies are presented that demonstrate how a detailed understanding of the reaction mechanism led to improvements that increased the overall robustness of the process. In the first case study, the mechanism of racemization of an α-chiral enone was investigated, resulting in the development of an improved aqueous workup procedure. Next, the stability of a bleach/pyridine mixture used for the step 3 epoxidation reaction was studied, leading to the identification of pyridine as a key raw material and improved reaction conditions and control strategy to meet the conversion target. Finally, oxidized butylated hydroxytoluene (oBHT) was identified as an impurity arising from the use of BHTstabilized tetrahydrofuran in steps preceding the oxidation. The process understanding obtained from these investigations led to the implementation of process improvements that improved the robustness of the process. The development of a second-generation route to 4 is the subject of part 2 in this series (