Phenylglycine racemization in Fmoc-based solid-phase peptide synthesis: Stereochemical stability is achieved by choice of reaction conditions
2017
Liang, Zhen | Behnam, Mira A.M. | Sundermann, Tom R. | Klein, Christian D.
Phenylglycine-containing peptides have broad applications in medicinal chemistry, but their synthetic accessibility is complicated by the risk of epimerization during solid-phase peptide synthesis (SPPS). Phenylglycine is therefore often considered a troublesome residue. This work studies the extent of Phg racemization under different Fmoc-SPPS reaction conditions. It is shown that the base-catalyzed coupling of Fmoc-Phg is the critical step for racemization. However, racemization can be reduced to a negligible level if DEPBT or COMU combined with TMP or DMP are employed during this step. Resin-bound peptides are remarkably resistant against epimerization during extended incubation under basic conditions and the free peptides were stable in buffer solutions used for biological assays.
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