Chiral macromolecules

Chiral macromolecules have been used as the chiral auxiliary in a number of enantioselec-tive epoxidations with moderate success. Cyclodextrin and hydrogen peroxide were employed11 to produce epoxides with low (<10%) enantiomeric excess. 

Similar to many other cases of biologically active compounds, stereochemistry influences the pharmacological effect of a chiral drug. This can be explained by the fact that there is only one energeticaUy favorable (specific) interaction of an active molecule with its receptor, both being chiral structures. Qualitative and quantitative differences are caused by different receptor affinities as demonstrated in Fig, 1 (1). The metabolism (biotransformation) of drugs is mainly caused by enzymes, which are chiral macromolecules and discriminate between substrate molecules of different stereochemistry, This may result in metabolites of different activity and in different pharmacokinetics, resorption, and excretion. Therefore, racemic drugs should be looked on as a 1 1 mixture of two different compounds. 

The extent and degree of interactions between chiral macromolecules of the body and stereoisomers is a source of observable differences in isomeric drug distribution. Stereoselectivity in drug distribution may occur when tissue or protein binding or uptake is associated with structurally specific receptor, protein, or enzyme binding. Since only unbound or free drug is susceptible to elimination and distribution to receptors and other tissues and fluids, differences in the protein and tissue binding of stereoisomers are reflected in their overall pharmacokinetic profiles. 

We have developed a simple physical model suggesting that for most, if not all, chiral macromolecules, their terahertz absorption will be accompanied by terahertz circular dichroism. Ab initio methods have been used to successfully calculate the vibrational circular dichroism spectra of small molecules, however, these models have largely focused on spectra in the near-infrared, spectra dominated by bond stretching and bending, and the wagging of small... 

Chapter 11 draws our attention towards the possibility of synthesizing chiral polymers via biocatalytic pathways. It becomes obvious in that chapter that chiral macromolecules can be achieved by enzymatic polymerizations that would not be synthesizable via traditional methods. 

A co-oligomer of a multifunctional binaphthyl molecule and p-biphenylene was reported Bedworth, P. V., and Tour, J. M., Synthesis of a chiral nonracemic. segmented screwlike oligomer. An unusual form of molecular chirality. Macromolecules, 27, 622... 

Enantiomerically pure SSCs (79), readily available through resolution of the racemic C2-symmetric Brintzinger-type a sa-metallocenes (59,473-475), have attracted considerable interest in catalytic and enantioselective C—C bond formation reactions (476). Despite the aforementioned symmetry concerns, these catalysts have opened new possibilities in synthesis and design of chiral macromolecules. 

Muellers, B. T. Park, J.-W. Brookhart, M. Green, M. M. Glassy state and secondary structures of chiral macromolecules Polyisocyanates and polyketones. Macromolecules 2001, 34, 572-581. 

As in low molecular weight compounds, optical activity can be observed only in chiral macromolecules, that is, macromolecules for which all allowed conformations lack reflection symmetry elements. 

Comparison of the recorded and simulated NMR spectra and the assumption that polyester chain growth is accompanied by exchange of chiral macromolecules on alien active centers indicated that the resulting macromolecules were composed of stereoblocks with 11 repeating units derived from LA monomer of a given kind (toluene, 70 °C). Enantiomerically pure (R)- or (S)-SB02A1-0R initiators have been shown to polymerize preferentially one of the enantiomers of rac-LA, that is, (R,R)- or (S,S)-LA, respec-tively. This enantiospecific preference was indicated by the stereoselectivity ratio fep(R/RR)/fep(R/SS) (or fep(S/SS)/fep (S/RR)) equal to 28, what corresponds to Pm = 0.96 (i.e., probability of isotactic enchainment formation, equal to m diad content in the resulting polymer). 

Investigations on synthetic or natural chiral macromolecules making use of rotatory power, ORD or CD techniques, to study conformational or interactional problems. The narrow field of Synthetic Optically Active Polymers has progressively expanded during the past decade. Evaluations and confrontations of results and interpretations are now needed with polymers of the purely synthetic world and with those which nearly imitate nature and are effective model molecules. 

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