Chiral conformers, induced

For example, Wakayama and coworkers discovered the formation of two oppositely orientated domains of 5,10,15,20- lclrakis(3,5-di-ferf-bulylphcnyl)-porphine deposited onto a Cu surface using low-temperature scanning tunneling microscopy [124]. It was demonstrated that the twin domains were produced by a pair of chiral conformations induced by a combination of symmetrical tilting and twisting rotation of the phenyl rings with respect to... 

G. LE BAS, C. DE RANGO, N. RYSANEK, and G. TSOUCARIS / Chiral Conformations Induced by Cyclodextrin... 

The chemical stracture of the polymers shown in Fig. 33 was confirmed by MALDI mass analysis of THF-soluble polymers (Fig. 38). Therefore, the polymers obtained in this study have no chiral ligand fragment attached to the chain and have no stereocenters in the main or side chain. Hence, the CD absorptions are unambiguously ascribed to a chiral conformation induced during the polymerization process. 

The importance of the o-hydroxyl moiety of the 4-benzyl-shielding group of R,R-BOX/o-HOBn-Cu(OTf)2 complex was indicated when enantioselectivities were compared between the following two reactions. Thus, the enantioselectivity observed in the reaction of O-benzylhydroxylamine with l-crotonoyl-3-phenyl-2-imi-dazolidinone catalyzed by this catalyst was 85% ee, while that observed in a similar reaction catalyzed by J ,J -BOX/Bn.Cu(OTf)2 having no hydroxyl moiety was much lower (71% ee). In these reactions, the same mode of chirality was induced (Scheme 7.46). We believe the free hydroxyl groups can weakly coordinate to the copper(II) ion to hinder the free rotation of the benzyl-shielding substituent across the C(4)-CH2 bond. This conformational lock would either make the coordination of acceptor molecules to the metallic center of catalyst easy or increase the efficiency of chiral shielding of the coordinated acceptor molecules. 

Figure 7.15 Chirality transfer from dopant to solvent. Chiral inducer with an (M)-helidty aligned with its biaryl axis parallel to biphenyl axis of solvent can have close contact only with molecules of solvent having same helicity Chirality is therefore transferred from dopant to near solvent molecule and from this to next near one and so on, via chiral conformations.

Can the chirality of the core unit be transferred to a distant part of the molecule and induce a chiral conformational order ... 

Several doublets for methylene protons with AS = 0.73-0.89 ppm confirm the all-jyn-like orientation of adjacent aromatic groups in compounds 53 and 54. On the basis of Cotton effects that are clearly observed in the CD spectra of 53 and 55 (and with much lower intensity in the case of 54), a chiral arrangement of the aromatic groups is proposed, which is induced by the presence of the chiral groups in these molecules.107 The stabilization of these chiral conformations by hydrogen bonds was proved by a much lower intensity of the Cotton effects in hydrogen-bond breaking solvents such as methanol. 

Use of achiral additives without chiral conformations 3.7.3 Metal Geometry-Induced Ligand Asymmetry... 

There are few processes that can be predictably scaled up from laboratory to production scale without difficulties. Preparative high-performance liquid chromatography (HPLC), for example, is not a linear scale-up it is expensive and uses large volumes of solvents. The product can become hydrolyzed by or react with the column, which can induce chemi-cal/steric/chiral conformation changes and often requires significant prepurification with further risk of degradation. 

The generality of this new type of shape-activity correlation is demonstrated for five receptor/substrate systems trypsin/arylammonium inhibitors the D2-dop-amine receptor/dopamine derivative agonists trypsin/organophosphate inhibitors acetylcholinesterase/organophosphates and butyrylcholinesterase/organo-phosphates. The correlations were obtained both for active-site induced chiral conformers and for inherently chiral inhibitors. Interestingly, for some of these cases the correlation of activity with structure is hidden when classical parameters, such as chain length, are taken, but is revealed with this shape descriptor. 

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