PEPTIDE MODELS .18. HYDROXYMETHYL SIDE-CHAIN INDUCED BACKBONE CONFORMATIONAL SHIFTS OF L-SERINE AMIDE - ALL AB-INITIO CONFORMERS OF FOR-L-SER-NH2

Using ab initio conformational energy mapping (HF/3-21G) a maximum of nine characteristic backbone conformation clusters (alpha L, alpha D, beta L, gamma L, gamma D, delta L, delta D, epsilon L, and epsilon D) were previously established for differenr amino acid diamides (e.g., F or-L-Ala-NH2, For-L-Val-NH2, and For-L-Phe-NH2). Most of the above nin e backbone conformers have been located in the [phi,psi] space for var ious side-chain conformers. The present conformation analysis derives structural parameters of For-L-Ser-NH2 molecule based on a systematic investigation of the side-chain conformational energy maps {E = E(chi( 1),chi(2))} associated with characteristic backbone structures. The sy stematic mapping of the E E(phi,psi,chi(1),chi(2)) four-dimensional Ra machandran-type map has revealed 44 minima. This finding thus establis hed the complete conformational set for For-L-Ser-NH2. Specific intram olecular hydrogen bonds of the 44 geometry optimized structures were a nalyzed. These ab initio structures can now be used with greater confi dence during force field parameterizations, NMR, and X-ray structure e lucidations or even for the characterization of protein backbone struc tures.