THE ROLE OF THE LOCAL CONFORMATION OF A CYCLICALLY CONSTRAINED β-AMINO ACID IN THE SECONDARY STRUCTURES OF A MIXED α/β DIASTEREOMER PAIR

Blodgett, Karl N.

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https://hdl.handle.net/2142/96988 Copy

Description

Title

THE ROLE OF THE LOCAL CONFORMATION OF A CYCLICALLY CONSTRAINED β-AMINO ACID IN THE SECONDARY STRUCTURES OF A MIXED α/β DIASTEREOMER PAIR

Author(s)

Blodgett, Karl N.

Contributor(s)

Zwier, Timothy S.

Issue Date

6/21/2017

Keyword(s)

Conformers, isomers, chirality, stereochemistry

Abstract

Synthetic foldamers are non-natural polymers designed to fold into unique secondary structures that either mimic nature’s preferred secondary structures, or expand their possibilities. Among the most studied synthetic foldamers are $beta$-peptides, which lengthen the distance between amide groups from the single substituted carbon spacer in $alpha$-peptides by one ($beta$) additional carbon. Cyclically constrained $beta$-amino acids can impart rigidity to the secondary structure of oligomers by locking in a particular conformation. The $beta$-residue emph{cis}-2-aminocyclohexanecarboxylic acid (emph{cis}-ACHC) is one such amino acid which has been shown to drive vastly different secondary structures as a function of the local conformation of the cyclohexane ring. We present data on two diastereomers of the mixed $alpha$/$beta$ tri-peptide Ac-Ala-$beta$$_{ACHC}$-Ala-NHBn which differ from one another by the chirality along the ACHC residue (SRSS vs. SSRS). The first oligomer is known to crystallize to a 9/11 mixed helix while the second forms no intramolecular hydrogen bonds in the crystal state. This talk will describe the conformation-specific IR and UV spectroscopy of the above two diastereomers under jet cooled conditions in the gas phase. Assignments based on comparison with calculations show the presence of incipient 9/11 mixed helices and competing structures containing more tightly folded hydrogen-bonded networks. The calculated global minimum structures are observed in each case, and in each case these folded structures are reminiscent of a $beta$-turn.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

English

Permalink

http://hdl.handle.net/2142/96988

DOI

10.15278/isms.2017.WC07

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