Solid-State and Solution-Phase Conformations of Pseudoproline-Containing Dipeptides

Jack K. Clegg; James R. Cochrane; Nima Sayyadi; Danielle Skropeta; Peter Turner; Katrina A. Jolliffe

doi:10.1071/CH09151

RESEARCH FRONT

Solid-State and Solution-Phase Conformations of Pseudoproline-Containing Dipeptides

Jack K. Clegg ^A , James R. Cochrane ^A , Nima Sayyadi ^A , Danielle Skropeta ^A , Peter Turner ^A and Katrina A. Jolliffe ^A ^B

+ Author Affiliations

- Author Affiliations

^A School of Chemistry, The University of Sydney, NSW 2006, Australia.

^B Corresponding author. Email: jolliffe@chem.usyd.edu.au

Australian Journal of Chemistry 62(7) 711-719 https://doi.org/10.1071/CH09151
Submitted: 14 March 2009 Accepted: 5 June 2009 Published: 13 July 2009

Abstract

The conformations of 14 threonine-derived pseudoproline-containing dipeptides (including four d-allo-Thr derivatives) have been investigated by NMR. In solution, the major conformer observed for all dipeptides is that in which the amide bond between the pseudoproline and the preceding amino acid is cis. For dipeptides in which the N-terminus is protected, the ratio of cis- to trans-conformers does not depend significantly on the side chain of the N-terminal amino acid, or the stereochemistry of the Thr residue. However, for dipeptides bearing a free N-terminus, there are significant differences in the ratios of cis- to trans-conformers depending on the side chain present. Three dipeptides were crystallized and their X-ray structures determined. In two cases, (benzyloxycarbonyl (Cbz)-Val-Thr(Ψ^Me,Mepro)-OMe and Cbz-Val-Thr(Ψ^Me,Mepro)-OH), the dipeptides adopt a trans-conformation in the solid state, in contrast to the structures observed in solution. In the third case, (9-fluorenylmethoxycarbonyl (Fmoc)-Val-d-allo-Thr(Ψ^Me,Mepro)-OH), a cis-amide geometry is observed. These structural differences are attributed to crystal-packing interactions.

Acknowledgements

We thank the Australian Research Council for financial support and for the award of a Queen Elizabeth II research fellowship to K.A.J.

References

Solid-State and Solution-Phase Conformations of Pseudoproline-Containing Dipeptides

Abstract

Acknowledgements

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