Geometry and Conformation of the α-Aminoisobutyric Acid Residue in Simple Derivatives and Dipeptides. Four New X-ray Structural Analyses and a Statistical Analysis from Known Crystal Data
✍ Scribed by Valle, Giovanni ;Crisma, Marco ;Formaggio, Fernando ;Toniolo, Claudio ;Jung, Günther
- Publisher
- John Wiley and Sons
- Year
- 1987
- Tongue
- English
- Weight
- 673 KB
- Volume
- 1987
- Category
- Article
- ISSN
- 0947-3440
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✦ Synopsis
The results of X-ray diffraction analyses on two m-aminoisobutyric acid (Aibl derivativcs, methyl u-(acetylamino)isobuknoate (Ac-Aib-OMc. I ) and bcnzyl a-[(beazyloxycarbonyl)arnino]isobutanoate (2-Aib-OBA, 2), and two terminally blocked, Aib-conlining dipcptides, methyl cr-[(acctyl-~-alanyl)nmino]isabutanoaie (Ac-~-Aln-Aib-OMe. 3) and tm-butyl u-{[(benzyloxycarbony l)amino]isobutanoy I)-L-alaninate (Z-Aib-~-Ala-OrBu, 4) are dcscribed. In thc asymmetric unit of all four compounds two indcpcndcnt moIcculcs were found. In all c a m but one (molecule A of 3) thc Aih rcsiduc is roldcd. the scts of @, $ (or @. torsion angles falling in thc region o l [he conformational energy map whcrc both a-and 31u-helims are found. A correlaling natistiutl analysis or bond lengths, bond angles, and torsion angles from availablc crystal structures or 20 Aib derivatives and 11 Aibcontaining linear dipeptidcs was also performcd to obtaiu precise information on the geometry and conformation of the Aib rcsidue withoui thc influence of [he constraints irnposcd by thc intramolecular hydrogen bonds characterizing highcr-order folded and helical pcptidcs.