Crystal structure of l-leucyl-l-isoleucine 2,2,2-tri-fluoro-ethanol monosolvate.

Carl Henrik Görbitz

doi:10.1107/s2056989016005302

Carl Henrik Görbitz

Open Access

https://doi.org/10.1107/s2056989016005302

Copy DOI

Abstract

Hydro-phobic dipeptides with either l-Leu or l-Phe constitute a rather heterogeneous group of crystal structures. Some form materials with large water-filled channels, but there is also a pronounced tendency to incorporate organic solvent mol-ecules, which then act as acceptors for one of the three H atoms of the charged N-terminal amino group. l-Leu-l-Ile has uniquely been obtained as two distinct hydrates, but has so far failed to co-crystallize with a simple alcohol. The present structure of C12H24N2O3·CF3CH2OH, which crystallizes with two dipeptide and two solvent mol-ecules in the asymmetric unit, demonstrates that when 2,2,2-tri-fluoro-ethanol is used as a solvent, its high capacity as a hydrogen-bond donor leads to formation of an alcohol solvate.

Highlights

Hydrophobic dipeptides with either l-Leu or l-Phe constitute a rather heterogeneous group of crystal structures
The present structure of C12H24N2O3CF3CH2OH, which crystallizes with two dipeptide and two solvent molecules in the asymmetric unit, demonstrates that when 2,2,2-trifluoroethanol is used as a solvent, its high capacity as a hydrogen-bond donor leads to formation of an alcohol solvate
Dipeptides with at least one hydrophobic residue such as Val, Leu, Ile and Phe have a high propensity to form crystal structures that are divided into hydrophobic and hydrophilic layers (Görbitz, 2010)

Summary

Chemical context

Dipeptides with at least one hydrophobic residue (i.e. lacking a functional group) such as Val, Leu, Ile and Phe have a high propensity to form crystal structures that are divided into hydrophobic and hydrophilic layers (Görbitz, 2010). The latter include two C(8) head-to-tail chains with two of the three Nterminal amino H atoms acting as donors and the C-terminal carboxylate group as acceptor, and a C(4) or C(5) chain using the peptide >N—H group as donor and, respectively, the peptide carbonyl group or the carboxylate group as acceptor. B is needed to relieve a short contact between H91B and F2C, Fig. 2

Supramolecular features

Synthesis and crystallization

Refinement details