Typically, impurities are undesirables, and a purified product is the ultimate goal. According to Le Chatelier’s Principle, excess reagents are often used to drive the reaction to completion. In solid phase peptide synthesis (SPPS), a large excess is often used in each coupling to move the reaction equilibrium to desired products. Common impurities in SPPS can include truncation or deletion sequences, pyroglutamate formation, mis-folded or unfolded peptides, degradation products (oxidations, reductions, deamidations), partially removed protecting groups, amino acid racemization, and other undesirable synthetic byproducts. However, as a part of the New Drug Application (NDA) and Abbreviated New Drug Application (ANDA) processes of a new peptide Active Pharmaceutical Ingredient (API), there is a need to identify the impurities of these peptides, for characterization and safety profiling.1 In fact, it may be advantageous to characterize impurities in the pre-clinical and early clinical phase of drug development, to head off any erroneous conclusions brought about by impurity interactions.2,3 While peptide APIs need to be manufactured under current Good Manufacturing Processes (cGMP), their impurities often do not. New England Peptide | Peptides International has experience synthesizing both peptide therapeutics for pre-clinical research and their corresponding impurities. Should you need help synthesizing peptide impurities for your peptide therapeutic in any stage of your project, we are happy to offer a quote for these custom synthesis services.