Hmb and Dmb dipeptides disrupt hydrogen bonding in the peptide backbone and reduces aggregation. Incorporated into long or difficult peptides, N-Dmb dipeptides can improve peptide yield and purity. When the Dmb protecting group is attached to the amino acid preceding Asp in a peptide, Dmb blocks aspartimide formation and the side products resulting from aspartimide formation (Quibell, M.; et al. J. Chem. Soc., Chem. Commun. 1994, 2343-4). In SPPS the N-Dmb group is removed with TFA during peptide cleavage from the resin.
Guidelines for Using Hmb- or Dmb-Protected Amino Acids
1. If possible, the Hmb- or Dmb-protected amino acid should be inserted before hydrophobic regions.
2. There should be at least 2 amino acids between the Hmb- or Dmb-protected amino and other backbone H-bonding disrupters such as prolines, pseudoprolines or isoacyl dipeptides.
3. The optimum spacing between H-bond dirupting elements is 5-6 amino acids.