Enantiomers, also

Section 7 8 Both enantiomers of the same substance are identical m most of then-physical properties The most prominent differences are biological ones such as taste and odor m which the substance interacts with a chiral receptor site m a living system Enantiomers also have important conse quences m medicine m which the two enantiomeric forms of a drug can have much different effects on a patient... 

Today, we would describe Pasteur s work by saying that he had discovered enantiomers. Enantiomers, also called optical isomers, have identical physical properties, such as melting point and boiling point, but differ in the direction in which their solutions rotate plane-polarized light. 

ANSWER Elaine Sanders-Bush has done those, and the enantiomers do differ, but the enantiomers also differ in half-life, and it is probable that the difference in long-term toxicity is simple because of that differenee in half-life. 

The (n)-enantiomer of penicillamine is used clinically in man either as the hydrochloride or as the free amino acid [1], although the (L)-enantiomer also forms chelation complexes. Penicillamine is an effective chelator of copper, mercury, zinc, and lead, and other heavy metals to form stable, soluble complexes that are readily excreted in the urine [2,3]. 

Racemic Compounds existing as a racemate, or a 50-50 mixture of two enantiomers also denoted as dl or ( + ). Racemates are also called racemic mixtures. 

For example, our ability to taste and smell is regulated by chiral molecules in our mouths and noses that act as receptors to sense foreign substances. We can anticipate, then, that enantiomers may interact differently with the receptor molecules and induce different sensations. This appears to be the case. The two enantiomers of the amino acid, leucine, for example, have different tastes—one is bitter, whereas the other is sweet. Enantiomers also can smell different, as is known from the odors of the two carvones. One has the odor of caraway and the other of spearmint. 

No reports are yet available on the separation of enantiomerically enriched fractions arising from incomplete asymmetric reactions. It should be noted that enantiomerically enriched mixtures may be fractionated in racemate and excess enantiomer also on achiral stationary phases (Gil-Av and Schurig, 1994 Nicoud et al., 1996) by adopting the principle of re-crystallization of mixtures enriched in one enantiomer leading to the pure enantiomer. 

Racemic mixture (Section 7.4) An equal mixture of enantiomers. Also called a racemate. Racemization (Section 8.4) The stereochemical result of a reaction in which complete randomization of stereochemistry has occurred in the product (50% inversion and 50% retention). 

The Soai system is sensitive to any chiral additive. NaClC>3 single crystals [135], inorganic complexes [136], penta- and hexahelicenes [137], or d- and /-quartz [138] are examples ee values of up to > 95% of the secondary alcohol can be obtained. The system responds to the sense of chirality of the dopant enantiomers also with opposite signs of ee and is ready for stimulation by cpl via the induced ees of reactants or products [139] the cpl-induced hexahelicene formation with 2% ee amplifies to an ee of > 90% in a Soai system [140]. A review is found in Ref. 141. Unfortunately, the system does not amplify the ee of the dopant. 

The ability of CPT to separate two enantiomers also depends on the individual detuning parameters Ay and on the related dynamical phase 2 2 r. At resonance Ay = 0 and

population transfer from state 1) to a combination of states 2) and 3). In that case, the p2/p3 branching ratio of the final populations is given, as in the double STIRAP case [98,99], by the IfWfinl2 ratio, and no enantiomeric selectivity is then possible. 

The non-superimposability of mirror images that brings about the existence of enantiomers also, as we shall see, gives them iheir optical activity, and hence enantiomers arc often referred to as (one kind of) optical isomers. We shall make no use of the leim optical isomer, since it is hard to define- indeed, is often used undefined and of doubtful usefulness. 

Vedaprofen is a propionic acid derivative that, like carprofen and ketoprofen, exists as two enantiomers with different pharmacokinetic profiles in the horse. For example, the plasma disposition of S(-t-)-vedaprofen is characterized by a very rapid decline with a plasma half-life of less than 1 h while R(-)-vedaprofen has a more prolonged elimination phase with a plasma half-life of over 2h (Lees et al 1999). Both enantiomers also accumulate in and exhibit a delayed elimination from inflammatory exudates. In horses, vedaprofen appears to be slightly selective for the COXl enzyme. For example, the median effective concentration for inhibition of serum TXB2 production, which is assumed to be a reflection of COXl activity, was much lower than that for inhibition of inflammatory infiltrate PGE2 production, which is assumed to be a reflection of COX2 activity. Although the results of these studies are promising, there are no published data on the clinical effectiveness and safety of vedaprofen in horses. 

Chemical correlations toward a known enantiomer also sometimes take place with unwanted epimerizations so that scrutinity must be exerted in all the identification steps. Indeed, some data from the literature have given rise to controversial results. 

The three geometric isomers (diastereomers) for M(AAAA)B2 complexes, one of which is of trans geometry with respect to the two simple ligand B (centre), and two of which are of cis geometry (cis-ft at left, cis-a at right) and in those cases have enantiomers, also drawn. 

Molecular ellipticity is analogous to specific rotation in that two enantiomers have exactly opposite values at every wavelength. Two enantiomers also show CD spectra having opposite signs. A compound with several absorption bands may show both positive and negative bands. Figure 2.3 illustrates the CD curves for both enantiomers of 2-amino-1 -phenyl-1 -propanone." ... 

Enantiomers also are referred to as chiral compounds, antipodes, or enantiomorphs. When introduced into an asymmetric, or chiral, environment, such as the human body, enantiomers will display different physicochemical properties, producing significant differences in their pharmacokinetic and pharmacodynamic behavior. Such differences can result in adverse side effects or toxicity, because one or more of the isomers may exhibit significant differences in absorption (especially active transport), serum protein binding, and metabolism. With the latter, one isomer may be converted into a toxic substance or may influence the metabolism of another drug. To discuss further the influence of stereochemistry on drug action, some of the basic concepts of stereochemistry need to be reviewed. 

---