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Volume 212, 2018
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Stereochemistry-dependent hydrogen bonds stabilise stacked conformations in jet-cooled cyclic dipeptides: (LD) vs. (LL) cyclo tyrosine–tyrosine

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Abstract

Tyrosine-containing cyclic dipeptides based on a diketopiperazine (DKP) ring are studied under jet-cooled conditions using resonance-enhanced multi-photon ionisation (REMPI), conformer-selective IR-UV double resonance vibrational spectroscopy and quantum chemical calculations. The conformational landscape of the dipeptide containing natural L tyrosine (Tyr), namely c-LTyr–LTyr strongly differs from that of its diastereomer c-LTyr–DTyr. A similar family of conformers exists in both systems, with one aromatic ring folded on the dipeptide DKP ring and the other one extended. Weak NH⋯π and CH⋯π interactions are observed, which are slightly different in c-LTyr–LTyr and c-LTyr–DTyr. These structures are identical to those of LL and LD cyclo diphenylalanine, which only differ from c-Tyr–Tyr by the absence of hydroxyl on the benzene rings. While this is the only conformation observed for c-LTyr–DTyr, c-LTyr–LTyr exhibits an additional form stabilised by the interaction of the two hydroxyls, in which the two aromatic rings are in a stacked geometry. Stereochemical effects are still visible in the radical cation, for which one structure is observed for c-LTyr–DTyr, while the spectrum of the c-LTyr–LTyr radical cation is explained in terms of two co-existing structures.

Graphical abstract: Stereochemistry-dependent hydrogen bonds stabilise stacked conformations in jet-cooled cyclic dipeptides: (LD) vs. (LL) cyclo tyrosine–tyrosine

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Submitted
22 Apr 2018
Accepted
06 Jun 2018
First published
09 Jul 2018

Faraday Discuss., 2018,212, 399-419
Article type
Paper

Stereochemistry-dependent hydrogen bonds stabilise stacked conformations in jet-cooled cyclic dipeptides: (LD) vs. (LL) cyclo tyrosine–tyrosine

F. BenNasr, A. Pérez-Mellor, I. Alata, V. Lepere, N. Jaïdane and A. Zehnacker, Faraday Discuss., 2018, 212, 399
DOI: 10.1039/C8FD00079D

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