Peptide conformations. Part 30. Assignment of the 1H-, 13C-, and 15N-NMR spectra of cyclosporin A in CDCl3 and C6D6 by a combination of homo- and heteronuclear two-dimensional techniques

Authors

  • Horst Kessler,

    Corresponding author
    1. Institut für Organische Chemie der J.-W.-Goethe-Universität Frankfurt, Niederurseler Hang, D–6000 Frankfurt 50
    • Institut für Organische Chemie der J.-W.-Goethe-Universität Frankfurt, Niederurseler Hang, D–6000 Frankfurt 50
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  • Hans-Rudolf Loosli,

    Corresponding author
    1. Sandoz Ltd., Pharmaceutical Division, Preclinical Research, CH–4002 Basle
    • Sandoz Ltd., Pharmaceutical Division, Preclinical Research, CH–4002 Basle
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  • Hartmut Oschkinat

    1. Institut für Organische Chemie der J.-W.-Goethe-Universität Frankfurt, Niederurseler Hang, D–6000 Frankfurt 50
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  • Part 29: [1]

Abstract

The 1H-, 13C-, and 15N-NMR spectra of the immunosuppressive cyclic undecapeptide cyclosporin A (1) have been analyzed at 300 MHz in CDCl3, C6D6, and mixtures of these solvents. A combination of different homo- and heteronuclear two-dimensional NMR techniques enable complete assignment of all H-, C- and 4 N-signals. Recognition of the proton spin systems has been achieved via1H,1H–COSY and double-quantum-1H-NMR spectroscopy. NOESY spectra yield some sequence assignments, but two techniques using coupling across amide bonds have been applied to get independent assignments of all amino acids in the sequence: (i) An 1H,1H-COSY spectrum optimized for small coupling constants enables the detection of long-range couplings from N-methyl groups to both α-protons attached to that amide bond. (ii) An 1H, 13C-COSY spectrum optimized for C,H-long-range couplings (J = 5 to 10 Hz) to the eleven CO groups again yields coupling to both α-protons attached to that amide bond. Additionally these two experiments yield the assignment of N-methyl protons and carbonyl C-atoms. Normal and relayed 1H,13C-COSY in both solvents have been applied to assign all C-atoms via their directly attached and remote protons. An 1H,13C-COLOC spectrum at 500 MHz in CDCl3, which uses H,C-long-range couplings confirms the assignment of all proton spin systems as well as the C-signals of each individual amino acid. Ambiguities in the assignment of the C(δ)'s of MeLeu have thus been removed. An 1H,15N-COSY spectrum enables the assignment of the 4 NH N-atoms.

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