6‐Strand to Stable 10/12 Helix Conformational Switch by Incorporating Flexible β‐hGly in the Homooligomers of Camphor Derived β‐Amino Acid: NMR and X‐Ray Crystallographic Evidence

Author:

Sukumar Genji12,Rahul 34,Nayani Kiranmai14ORCID,Mainkar Prathama S.14ORCID,Prashanth Jupally54,Sridhar Balasubramanian54ORCID,Sarma Akella V. S.34ORCID,Bharatam Jagadeesh34ORCID,Chandrasekhar Srivari14ORCID

Affiliation:

1. Department of Organic Synthesis and Process Chemistry CSIR-Indian Institute of Chemical Technology Hyderabad 500007 India

2. Department of Chemistry Adikavi Nannaya University, Rajamahendravaram Andhra Pradesh 533296 India

3. Centre for NMR, Department of Analytical & Structural Chemistry CSIR-Indian Institute of Chemical Technology Hyderabad 500007 India

4. Academy of Scientific and Innovative Research (AcSIR) Ghaziabad 201002 India

5. Centre for X-ray Crystallography, Department of Analytical & Structural Chemistry CSIR-Indian Institute of Chemical Technology Hyderabad 500007 India

Abstract

AbstractRational design of unnatural amino acid building blocks capable of stabilizing predictable secondary structures similar to protein fragments is pivotal for foldamer chemistry/catalysis. Here, we introduce novel β‐amino acid building blocks: [1S,2R,4R]exoCDA and [1S,2S,4R]endoCDA, derived from the abundantly available R(+)‐camphor, which is traditionally known for its medicinal value. Further, we demonstrate that the homooligomers of exoCDA adopt 6‐strand conformation, which switches to a robust 10/12‐helix simply by inserting flexible β‐hGly spacer at alternate positions (1 : 1 β‐hGly/exoCDA heterooligomers), as evident by DFT‐calculations, solution‐state NMR spectroscopy and X‐ray crystallography. To the best of our knowledge, this is the first example of crystalline‐state structure of left‐handed 10/12‐mixed helix, that is free from the conventional approach of employing β‐amino acids of either alternate chirality or alternate β2/β3 substitutions, to access the 10/12‐helix. The results also show that the homooligomers of heterochiral exoCDA don′t adopt helical fold, instead exhibit banana‐shaped strands, whereas the homodimers of the other diastereomer endoCDA, nucleate 8‐membered turns. Furthermore, the homo‐exoCDA and hetero‐[β‐hGly‐exoCDA] oligomers are found to exhibit self‐association properties with distinct morphological features. Overall, the results offer new possibilties of constructing discrete stable secondary and tertiary structures based on CDAs, which can accommodate flexible residues with desired side‐chain substitutions.

Publisher

Wiley

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