Conformations, synthesized

Polymers with at least partial helical conformation, synthesized by isotactically polymerizing an achiral monomer using a chiral catalyst96-99, have also been used as CSPs. This is an interesting concept (see Figure 11) with considerable future potential. 

Large annulenes tend to undergo conformational distortion, cis-trans isomerizations, and sig-matropic rearrangements (p. 40 and p. 100). Methylene-bridged conjugated (4n + 2)-ic cyclopolyenes were synthesized with the expectation that these almost planar annulenes should represent stable HOckel arenes (E, Vogel, 1970, 1975). 

Hundreds of analogues of both oxytocin and vasopressin have been synthesized, and the conformations of many of these have been studied (22,23). 

Several hundred analogues to TRF have been synthesized. Some of them, like l-CH2-S-Dio-His-Pro-NH2 are more potent than TRF (116) others are conformationally restricted and equally as potent as TRF (117). 

Hydantocidin. Hydantocidin (182), C2H2QN2O3, is elaborated by S. hygroscopicus (278). It is unique in that the anomeric carbon of the ribosyl moiety forms the spHo bond of hydantoin (279). The ribofuranose moiety which has been reported to be in a Q -endo conformation (279) has been synthesized (280,281). Hydantocidin is a herbicidal nucleoside with activity against monocotyledenous and dicotyledenous plants. 

In order to examine whether this sequence gave a fold similar to the template, the corresponding peptide was synthesized and its structure experimentally determined by NMR methods. The result is shown in Figure 17.15 and compared to the design target whose main chain conformation is identical to that of the Zif 268 template. The folds are remarkably similar even though there are some differences in the loop region between the two p strands. The core of the molecule, which comprises seven hydrophobic side chains, is well-ordered whereas the termini are disordered. The root mean square deviation of the main chain atoms are 2.0 A for residues 3 to 26 and 1.0 A for residues 8 to 26. 

FIGURE 21.25 A model of the Fj and Fg components of the ATP synthase, a rotating molecnlar motor. The a, b, a, /3, and 8 snbnnits constitute the stator of the motor, and the c, y, and e subunits form the rotor. Flow of protons through the structure turns the rotor and drives the cycle of conformational changes in a and fi that synthesize ATP. 

Syntheses, conformations, electronic structures, and radical polymerization of IV-vinyllactams 98MI29. 

The stereochemical outcome of the reaction is determined by the geometry of the transition state for the Claisen rearrangement a chairlike conformation is preferred,and it proceeds strictly by an intramolecular pathway. It is therefore possible to predict the stereochemical course of the reaction, and thus the configuration of the stereogenic centers to be generated. This potential can be used for the planning of stereoselective syntheses e.g the synthesis of natural products. 

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