Linkage conformations, calculated

Figure 15-1S. A QM energy surface covering space for the cellobiose analog, THP-O-THP (see text). Also shown are all of the observed linkage conformations in Figures 15-8, 15-9, 15-11, and 15-12, as well as the conformation of a heavily modified cellobiose (Ernst and Vasella 1996) at the bottom of the map. This surface was calculated with B3LYP/6-311++G" theory based on B3LYP/ 6-3IG geometries (see French and Johnson 2004b)...

The calculated optical rotations of methyl p-D-arabinofuranoside, methyl P-D-fhictofuranoside and sucrose as a function of ring conformations and, in the case of sucrose, of linkage conformation, has been described. " Anomeric C-(substituted)phenyl D-glucopyranosides can be distinguished on the basis of their Cotton effects at 260-280 nm. ... 

One reason for studying the conformation of the disaccharide maltose is that it contains the same interresidue linkage as found in amylose and amylopectin, the polymers of starch. Therefore, conformations of the maltosyl linkages found in maltotriose or panose would certainly be of interest in the comparison with a calculated energy surface. It would be obvious to include a-maltose, -maltose, and methyl- -maltoside, molecules that differ only at the anomeric center, which is as distant as possible from the disaccharide linkage and therefore unlikely to affect the linkage conformation very much. 

Conformation and stability of thiopeptides (formed by replacing the amide oxygen atom with a sp2 sulfur atom) have been investigated by calculations. It has been confirmed that insertion of a thioamide linkage into a peptide structure is not conformationally neutral. It is predicted to be more rigid than peptide and produces substantial changes in peptide structure, primarily in the residues on the C-terminal side of the thioamide.78 80... 

The MD-tar distribution of conformers obtained for every particular gly-cosidic linkage is shown in Eig. 2a, superimposed on the MM3 steric maps previously calculated. It can be observed that for the I/II linkage, a major population is centered around 0/V = -55°/-45°. A very minor population around 4>/ P = -25°/30° was also detected. In contrast, the IV/III linkage is characterized by a high degree of flexibility, with two different conformations almost equally populated located at

/ P =-50°/45°. Nevertheless, both glycosidic linkages exhibit common features (p values are... 

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