Enantiomers preparative

Racemic mixtures of sulfoxides have often been separated completely or partially into the enantiomers. Various resolution techniques have been used, but the most important method has been via diastereomeric salt formation. Recently, resolution via complex formation between sulfoxides and homochiral compounds has been demonstrated and will likely prove of increasing importance as a method of separating enantiomers. Preparative liquid chromatography on chiral columns may also prove increasingly important it already is very useful on an analytical scale for the determination of enantiomeric purity. 

For a nonracemic mixture of enantiomers prepared by resolution or asymmetric synthesis, the composition of the mixture was given earlier as percent optical purity (equation 1), an operational term, which is determined by dividing the observed specific rotation (Mobs) of a particular sample of enantiomer with that of the pure enantiomer ( max), both of which were measured under identical conditions. Since at the present, the amount of enantiomers in a mixture is often measured by nonpolarimetric methods, use of the term percent optical purity is obsolete, and in general has been replaced by the term percent enantiomeric excess (ee) (equation 2) introduced in 197163, usually equal to the percent optical purity, [/ ] and [5] representing the relative amounts of the respective enantiomers in the sample. 

Symmetrical incorporation of two units of 113 or 114 into one ring should yield either the monocyclic diallenes of D2 symmetry or of C-2h symmetry, depending upon the ways of combining the two enantiomers. Preparation of monocyclic diallenes in these two modifications was accomplished in Sondheimer s laboratory72a,b). 

The absolute configuration of the terpenoid core of taxine I was deduced by the X-ray analysis of the bromoderivative of a transformation product of its corresponding cinnamate (taxinine) [60], The L (1() absolute configuration of the dextrorotatory Winterstein acid obtained from the degradation of crude taxine was established by comparison with the rotatory power of the semisynthetic enantiomers prepared from D- and L P-phenyl-p-alanine [61]. 

Enantiomer Preparations of Inhaled Drugs. There has been much interest in the differences in effects of enantiomers of many medications, and beta agonist adrenergic bronchodilators have received much attention. Evidence suggests that the (R)-enantiomer of albuterol is mainly responsible for bronchodilation while the (S)-enantiomer may stimulate airway reactivity. Data suggest, however, that after aerosol delivery, the systemic absorption for (R)-albuterol is faster than for (S)-albuterol and that, conversely, the lung retention of (S)-albuterol is longer, which may be detrimental [29]. The extent to which enantiomers will displace racemic preparations is not yet determined. 

The preceding schemes for preparing estrone have the disadvantage that they yield the steroid as a mixture of the two enantiomers. Preparing material identical with that which occurs in Nature requires resolution of those diastereomers. This also implies loss of half of the mass of final product. A synthesis that produces estrone and its derivatives directly without the need for that extra step depends on the use of chiral auxiliaries in the formation of ring C. The crucial step in this synthesis involves Diels-Alder condensation of the diene 16-1 with the fumaric ester aldehyde 16-2 in the presence of the oxazaborolidinium salt shown in Figure 3.1 this reaction affords the tricyclic intermediate 16-3 as a single enantiomer (Scheme 3.16). 

Sopromidine has 7.4 times the potency of histamine on the atrium, but the (5)-enantiomer (prepared from D-histidine) is a competitive Hj antagonist with about a quarter the potency of metiamide. It is remarkable that this high stereoselectivity is shown by a receptor for the non-chiral histamine [317,318]. 

Louren90 CL, Batista JM, Furlan M, He Y, Nafie LA, Santana CS, Cass QB. Albendazole sulfoxide enantiomers preparative chiral separation and absolute stereochemistry. J. Ckroma-togr., A 2012 1230 61 5. 

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