N-Linked Glycosylatedβ-Peptides Are Resistant to Degradation by Glycoamidase A

Beta-peptides are resistant to degradation by a variety of proteolytic enzymes that rapidly degrade natural alpha-peptides. This is one of many characteristics that make beta-peptides an attractive class of compounds for drug discovery efforts. To further understand the molecular recognition properties of beta-peptides and the ability of enzymes to degrade them, we have synthesized a series of N-linked glycosylated beta- and alpha-peptides, and tested their stability towards a glycosidase. We found that glyco-beta-peptides that contain N-acetylglucosamine (1) or N,N-diacetylchitobiose (2) are completely stable to degradation by glycoamidase A. In comparison, the glyco-alpha-peptides 3 and 4 containing N-acetylglucosamine or N,N-diacetylchitobiose are degraded. Inhibition experiments using increasing concentrations of a glyco-beta-peptide fail to inhibit degradation of the corresponding glyco-alpha-peptide, even when the glyco-beta-peptide is at a 128-fold higher concentration than the glyco-alpha-peptide. Evidently, the glyco-beta-peptides have a much weaker affinity for the active site of the glycosidase than the corresponding glyco-alpha-peptide. These and the results with proteolytic enzymes suggest that the additional CH(2) group introduced into the alpha-amino acid residues causes beta-peptides not to be recognized by hydrolytic enzymes. The results described herein suggest the potential of beta-peptides that are functionalized with carbohydrates for biological and biomedical investigations, without having to be concerned about the carbohydrate being removed.