## Abstract Cyclodipeptides containing L‐Thr and L‐His residues have been studied by ^1^H NMR in D~2~O and DMSO‐__d__~6~. In the neutral form in D~2~O as in DMSO‐__d__~6~, the folded form of the L‐His residue is not unique. The diketopiperazine ring seems to be not strictly planar.
Solution conformation and hydrolytic activity of cyclo(D-leu-L-His)
✍ Scribed by Masao Tanihara; Yukio Imanishi; Toshinobu Higashimura
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1977
- Tongue
- English
- Weight
- 631 KB
- Volume
- 16
- Category
- Article
- ISSN
- 0006-3525
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
It has been reported previously that a cyclic dipeptide, cyclo(D‐Leu‐L‐His), showed a high hydrolytic activity toward a hydrophobic ester, p‐nitrophenyl laurate. In order to determine the reason for the high catalytic activity, the conformation of cyclo(D‐Leu‐L‐His) in aqueous solution was investigated by nuclear magnetic resonance and circular dichroism spectroscopy and compared with the conformation of cyclo(L‐Leu‐L‐His), which was nearly inactive in otherwise the same conditions for the hydrolysis. It was demonstrated that the spatial arrangement of the hydrophobic isobutyl group of the D‐leucyl residue and of the nucleophilic imidazolyl group of the L‐histidyl residue in cyclo(D‐Leu‐L‐His) matches very well with the long acyl chain and the active ester function of p‐nitrophenyl laurate. On the other hand, in cyclo(L‐Leu‐L‐His) the hydrophobic and the nucleophilic pendant groups are too close with each other to cooperate intramolecularly for the hydrolysis. It was concluded that the different steric structures of the diastereomers can explain the large difference of the catalytic activities.
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