Question

Explain why β-peptides, d-peptides and peptoids are more resistant to proteolytic cleavage than l-peptides. Of the four types of polymers here, which one(s) are potentially prone to racemisation in the coupling step

Answer 1

Proteolysis is the breakdown of proteins in to smaller peptides or aminoacids. This is an important process in any organism.. and is catalysed by enzymes and proteases in the body.

Peptoids: Peptoids are poly N-substituted peptides generally glycines. i.e. the sidechain of one aminoacid is coupled to the nitrogen rather than the alpha-carbon atom. Since there are no amide bons (CONH) in peptoids, they are very resistant to chemical and thermal denaturation.

Beta-peptides are formed when the amino group is bonded to the beta carbon atom and not the alpha carbon (carbon next to the carboxyl group). The beta-beta peptide bond are much stronger.

Generally modification in peptides from enzymatic degradation are brought by alteration to their amide bond either by cyclization, conjugation to a molecule or by incorporation of beta aminoacids or D-aminoacids. These all form different secondary structure and the bond strength being much stronger does not undergo proteolysis.

The optically active amino acids undergo racemisation. Generally L-aminoacids are prone to racemisation.