Nine novel process impurities of N-[N-benzoyl-O-(2-dimethylaminoethyl)-L-tyrosyl]-L-phenylalaninol (Y101) observed during the laboratory optimization and later during its bulk synthesis are described in this article. The impurities were monitored by HPLC, and their structures were tentatively assigned on the basis of fragmentation patterns in LC-MS/MS and NMR spectroscopies. All of the impurities were synthesized, and their assigned constitutions were confirmed by co-injection in HPLC. In addition to the formation, synthesis, and characterization, the strategy for minimizing these impurities to a level accepted by the International Conference on Harmonisation (ICH) was also described.Electronic supplementary material The online version of this article (