Application of Dmb-Dipeptides in the Fmoc SPPS of Difficult and Aspartimide-Prone Sequences

Mutter’s pseudoproline dipeptides and Sheppard’s Hmb derivatives are powerful tools for enhancing synthetic efficiency in Fmoc SPPS. They work by exploiting the natural propensity of N-alkyl amino acids to disrupt the formation of the secondary structures during peptide assembly. Their use results in better and more predictable acylation and deprotection kinetics, enhanced reaction rates, and improved yields of crude products. However, these approaches have certain limitations: pseudoproline dipeptides can only be used for sequences containing serine or threonine, and the coupling of the amino acid following the Hmb residue can be extremely difficult. To alleviate some of these shortcomings, we have prepared a range of Fmoc-Aaa-(Dmb)Gly-OH dipeptides and tested their efficacy in the synthesis of a number of challenging hydrophobic peptides. We also compared the efficiency of N-Dmb against N-Hmb backbone protection in preventing aspartimide formation in the Fmoc SPPS of peptides containing the Asp-Gly sequence.