Water-Based Solid-Phase Peptide Synthesis without Hydroxy Side Chain Protection

The development of protecting group-free synthesis has come to the forefront this century, as there is an increasing need to switch to greener synthetic methods. In peptide synthesis, a strategy of maximum protection offers the most efficient synthetic pathway, but minimal side chain protection is more favorable in terms of green chemistry. Here, we describe solid-phase peptide synthesis (SPPS) without hydroxy side chain protection based on an aqueous microwave (MW)-assisted method. First, we investigated the extent of O-acylation of the hydroxy side chain of Ser, Thr, and Tyr occurring in our method, which uses 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholi-nium chloride. Under aqueous MW-assisted conditions, the coupling reaction proceeded efficiently without substantial O-acylation. Next, we applied the aqueous synthetic protocol without hydroxy side chain protection to synthesis of a laminin-related peptide, H-Tyr-Ile-Gly-Ser-Arg-NH2. HPLC analysis of the crude peptide revealed a single peak, suggesting the absence of side reactions including O-acylation and racemization. We also succeeded in synthesizing a difficult peptide sequence, acyl carrier protein (65-74) peptide, by aqueous SPPS without hydroxy or carboxamide side chain protection. Based on the eighth criterion of the 12 principles of green chemistry, namely, reduce derivatives , our approach without hydroxy side chain protection will provide a greener peptide synthesis.

Automated summary

The development of protecting group-free synthesis in peptide synthesis has shown potential in reducing side reactions and offering a greener approach to peptide synthesis.