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Fmoc-protected β³hserine (β³hSer) was prepared and O-linked to suitably protected N-acetylgalactosamine (GalNAc) and N-acetylglucosamine (GlcNAc) derivatives. Glycosylation of β³hSer was made by two independent routes: either by direct glycosyl linkage to the β³hSer, or linkage to natural L-Ser and then utilizing the carbohydrate moiety as a protecting group in an Arndt–Eistert homologation. Both procedures gave the novel glycosylated β³-amino acids Fmoc-β³hSer(α-D-GalNAc(Ac)₃)-OH (1a), its β-anomer (1b), and Fmoc-β³hSer(β-D-GlcNAc(Ac)₃)-OH (2), which were utilized in the solid-phase peptide synthesis of four glycosylated dipeptides (3a–d) and two heptapeptides (4a–b). The preparation of β-amino acids bearing common post-translational modifiers represents an important step towards functionalized foldamers with broad applications in biomedical research.

The molecular recognition of a novel kind of hybrid conjugates, composed of artificial biomimetic β-peptide oligomers with an O-linked natural N-acetyl-galactosamine (the Tn-antigen) residue, by four different GalNAc specific lectins was investigated using surface plasmon biosensor technology. The influence of the peptide and the glycosyl moiety on the recognition was studied using two glycosylated β³-heptapeptides, a glycosylated α-heptapeptide, two β-amino acid containing dipeptides, and monomeric αGalNAc-O-Thr. Although all four lectins displayed a decreased affinity for the carbohydrate residue when attached to a peptide, as compared to the monomeric Tn-antigen, the peptide part was found to have distinct effects on the binding kinetics - indicating that varying degrees of protein-peptide interactions occurred in the recognition process. Likewise, the lectins did not discriminate between β³-peptides and the α-peptide, but the β- linkage of the galactose had a detrimental effect for at least two of the lectins.

Herein, we report studies on the influence of chiral, beta(2)-amino acids in the design of conformationally homogeneous cyclic tetrapeptide scaffolds. The cyclic alpha-tetrapeptide cyclo(-Phe-D-Pro-Lys-Phe-) (1) and its four mixed analogues, having one of the alpha-Phe replaced by either an (S)-or an (R)-beta(2)hPhe residue (i.e., cyclo(-(R)-beta(2)hPhe-D-Pro-Lys-Phe) (2a), cyclo(-(S)-beta(2)hPhe-D-Pro-Lys-Phe-) (2b), cyclo(-Phe-D-Pro-Lys-(R)-beta(2)hPhe-) (3a), and cyclo(- Phe- D- Pro- Lys-( R)-, 2hPhe-) ( 3b)), were all synthesized through solidphase procedures followed by solution- phase cyclization. Initially, all five cyclo- peptides were analyzed by H-1 NMR spectroscopic studies in different solvents and at variable temperatures. Subsequently, a detailed 2D NMR spectroscopic analysis of three of the mixed peptides in water was performed, and the information thus extracted was used as restraints in a computational study on the peptides' conformational preference. An X- ray crystallographic study on the side chain- protected (Boc) 2a revealed the solid- state structure of this peptide. The results presented herein, together with previous literature data on beta(3)-amino acid residues, conclusively demonstrate the potential of beta-amino acids in the design of conformationally homogeneous cyclic peptides that are homologous to peptides with known applications in biomedicinal chemistry and as molecular receptors.

Biomimetic oligomers are of large interest both as targets for combinatorial and parallel synthetic efforts and as foldamers. For example, shorter peptoid derivatives of beta-peptides, i.e., oligo-N-substituted beta-Ala, have been described as potential lead structures. Herein, we describe a solid-phase synthetic route to beta-peptoids with alpha-chiral aromatic N-substituents up to 11 residues long. Furthermore, the folding propensities of these oligomers were investigated by circular dichroism (CD) spectroscopy.