Ligands design, conformational analysis

Principles of conformational analysis may be invoked to rationalize the face-selectivity of these compounds. Note, however, that there are two broad types of auxiliary those that contain a second carbonyl and those that do not. The former may function by chelating the metal of the Lewis acid catalyst, while the latter can only act as monodentate ligands to the metal of the Lewis acid. Figure 6.13a illustrates the probable transition state conformations of ester dienophiles when bound as monodentate ligands to the Lewis acid catalyst, M (auxiliaries 6.12a-f). The C(=0)-0 bond prefers the Z (or cis) conformation for a variety of reasons [163], but the preference is large probably >4 kcal/mole. Because of this constraint, the C-0 bond may be considered to be similar to a double bond (hence the E/Z or cis/trans designation). A subtle consequence of this constraint is the effect it has on... 

In all our studies so far, the choice of an appropriate molecule was based on model building, considering the coordination geometry of the metal ion and the nature of the coordinating ligands. However, it was considered that it would be of further aid to the molecular design if the conformation of the designed molecule can be predicted before its synthesis. Recent advances in theoretical conformational analysis [11] have laid down the necessary framework for such a prediction. 

Structural and conformational analysis which complements aspects in Section 4 of carbohydrate-protein interaction at the macromolecular level. This is due to an increased number of studies on the preparation of ligands for combinatorial chemistry and the design of carbohydrate microarrays (a recently popular activity coming of age along with genomic and proteomic methods). 

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