First Steps for the Direct Purification of l-Leu-l-Leu Dipeptide through Co-Crystallization

Trifluoroacetate salt contamination of peptides represents a challenging issue related to solid phase peptide synthesis and purification because it affects the chemical and biological properties of peptides. Purification of such materials is typically performed through a two-step post-synthetic procedure based on chromatography followed by ion exchange. For the first time, co-crystallization is presented in this study as a possible alternative and advantageous single-step method for the obtaining of TFA-free crystals of a dipeptide. A trifluoroacetate-contaminated L-Leu-L-Leu dipeptide has been used for co-crystallization experiments along with different solid coformers. New multicomponent crystals containing only the title compound and the second co-crystal formers are described in this work. Such results represent a novelty in the field of peptide chemistry and a valid proof for the use of crystal engineering-based method for a combined purification and crystallization strategy