A new β-amino acid, trans-3-aminopyran-2-carboxylic acid (APyC), was designed and synthesized from (R)-glyceraldehyde derivative and used in the synthesis of α/β-peptides in a 1 : 1 alternating pattern with d-Ala. The presence of oxygen atom at the Cβ(2)-position in APyC was envisaged to provide opportunity for additional interaction. These hybrid peptides have shown the presence of 9/11-helix through extensive NMR and MD studies. The amide protons of d-Ala, in addition to participating in 9-mr H-bonding with CO of succeeding β-residue, were also involved in additional electrostatic interaction with pyran ring oxygen of preceding β-residue, which facilitated further stabilization to the 9/11-mixed helix. The study thus results in a new 'motif' for a 9/11-helix, and the first example from a cyclic β-amino acid.

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http://dx.doi.org/10.1039/c1ob06279dDOI Listing

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Rationale: Differentiation and structural characterization of positional isomers of non-natural amino acid hybrid peptides by using electrospray ionization tandem mass spectrometry (ESI-MS(n) ) is desirable because of their fundamental importance from the view point of peptide mass spectrometry and also of their increasing importance in the area of research towards biomedical and material applications; hence, the present study is undertaken.

Methods: Electrospray ionization ion-trap tandem mass spectrometry (ESI-MS(n)) was used to characterize and differentiate three pairs of positional isomers of Boc-N-protected hybrid peptides containing repeats of D-Ala-APyC and APyC-D-Ala (D-Ala = D-alanine and APyC = trans-3-aminopyran-2-carboxylic acid).

Results: ESI-MS(n) spectra of protonated and alkali-cationized positional isomeric peptides display characteristic fragmentation involving the peptide backbone, the Boc group, and the side chain.

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A new β-amino acid, trans-3-aminopyran-2-carboxylic acid (APyC), was designed and synthesized from (R)-glyceraldehyde derivative and used in the synthesis of α/β-peptides in a 1 : 1 alternating pattern with d-Ala. The presence of oxygen atom at the Cβ(2)-position in APyC was envisaged to provide opportunity for additional interaction. These hybrid peptides have shown the presence of 9/11-helix through extensive NMR and MD studies.

View Article and Find Full Text PDF

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