Dextrorotatory enantiomer

Tartaric acid and tartrates are poorly absorbed from the intestine. Their metaboHsm is different from that of citric acid in that tartaric acid is only slightly oxidized. The acid that is absorbed is excreted unchanged in the urine. So far as is known, all nutritional and physiological investigations have been made with the dextrorotatory enantiomer. 

One further point needs to be mentioned—the matter of absolute configuration. How do we know that our assignments of R,S configuration are correct in an absolute, rather than a relative, sense Since we can t see the molecules themselves, how do we know that the R configuration belongs to the dextrorotatory enantiomer of lactic acid This difficult question was finally solved in 1951, when J. M. Bijvoet of the University of Utrecht reported an X-ray spectroscopic method for determining the absolute spatial arrangement of atoms in a molecule. Based on his results, we can say with certainty that the R,S conventions are correct. 

Sulfoxides without amino or carboxyl groups have also been resolved. Compound 3 was separated into enantiomers via salt formation between the phosphonic acid group and quinine . Separation of these diastereomeric salts was achieved by fractional crystallization from acetone. Upon passage through an acidic ion exchange column, each salt was converted to the free acid 3. Finally, the tetra-ammonium salt of each enantiomer of 3 was methylated with methyl iodide to give sulfoxide 4. The levorotatory enantiomer was shown to be completely optically pure by the use of chiral shift reagents and by comparison with a sample prepared by stereospecific synthesis (see Section II.B.l). The dextrorotatory enantiomer was found to be 70% optically pure. 

Where M+ is the mole fraction of the dextrorotatory enantiomer, and M the mole fraction of the levorotatory one. 

A prior art Sanofi patent disclosed the racemate that the dextrorotatory enantiomer found in Plavix was separated from. 

Thus, Sanofi had two superior and unexpected results that (1) the dextrorotatory enantiomer separated from racemate PCR 4099 contained substantially all of the antiplatelet activity and (2) was essentially devoid of the neurotoxicity associated with PCR 4099. 

Finally, concerning the possible FDA mandate, the court concluded that "Sanofi undertook this separation [of enantiomers] in order to study adverse neurological effects of [the racemate that the dextrorotatory enantiomer found in Plavix was separated from], and not because of a possible future regulatory requirement [24]."... 

The (5 -configuration at the sulfur atom was assigned (49) to the naturally occurring L-methionine sulfoxide 28 based on the results of its thermal decarboxylation, leading to the formation of the dextrorotatory enantiomer of 3-methylsulfinylpropylamine 187 of known absolute (iS)-configuration at chiral sulfur. 

Luciduline, as an example of an alkaloid whose synthesis -either in its racemic form or as the natural optically pure dextrorotatory enantiomer-, has been accomplished by different research groups following essentially two different strategies. One of the strategies involves the disconnection of the 1,3-C bifunctional... 

When a poly-(L)-amino acid is used in the epoxidation of chalcone, the predominant optical isomer is laevorotatory [10]. The laevorotatory enantiomer of epoxychalcone has been shown [7] to have absolute configuration 2R, 3S). As anticipated, the use of a poly-(D)-amino acid as the epoxidation catalyst gives rise to the dextrorotatory enantiomer [10]. 

Enantiomers have eqnal and opposite rotations. The (+)- or dextrorotatory enantiomer is the one that rotates the plane of polarization clockwise (as determined when facing the beam), and the (—)- or laevorotatory enantiomer is the one that rotates the plane anticlockwise. In older pnblications, d and / were nsed as abbreviations for dextrorotatory and laevorotatory respectively, bnt these are not now employed, thns avoiding any possible confnsion with D and L (see Section 3.4.10). 

The sample thus contains 43.8% of laevorotatory enantiomer and 100 — 43.8% = 56.2% of racemate, the latter contributing no overall optical activity. The racemate contains equal amounts of laevorotatory and dextrorotatory enantiomers, i.e. it contributes 28.1% of each isomer to the overall mixture. Therefore, we have 43.8 + 28.1 = 71.9% of laevorotatory enantiomer, and 28.1% of dextrorotatory enantiomer in the partially racemized mixture. 

He also performed the KR of aldol intermediate 19 in the Sinha-Lemer synthesis of epothilone A on a 1.2-g scale, thus affording the natural dextrorotatory enantiomer in 47% yield and 98% ee s = 107) (Scheme 8) [82]. 

An alternative practical synthesis of triquinacene-2-carboxylic acid (as the dextrorotatory enantiomer) has l n described by Deslongchamps and Soucy Their protocol begins with hydroxy ketone 467 and passes via the 2-methyl derivative (Scheme XXXVIII). Selenium dioxide oxidation of the hydrocarbon provided the aldehyde which was further oxidized and then hydrolyzed to arrive at the add. 

Both the bisoxido- and bisimino-(cis)bridged dibromo[14]anulenes 115 and 116 with C2-symmetry could be quantitatively separated into their enantiomers by chromatography on triacetylcellulose in ethanol at 1.7 bar 124). The dextrorotatory enantiomers with [a]546 values of 1700° 115) and 1500° 116) in ethanol were eluted first. They exhibit very similar CD-curves with strong Cotton effects around 260... 

In another approach 145, dibromocarbene was added to ( + )-cyclononadiene 127 to give (after reduction of the outside adduct) ( + )-trans-bicyclo[7.1.0]decane 132). From the dextrorotatory enantiomer of the above-mentioned dibromo-derivative 128, ( + )-trans-bicyclo[6,1.0]nonane 129) was accessible. Comparison of the chiroptical properties of (+)-129 and (+)-132 led to the conclusion that 127 had the (+)(/ )(axial) chirality145) in agreement with the results reported above 144). 

The absolute configurations of helicenes have been firmly established by calculations 95 98), by X-ray analysis 99) and by synthesis l00).6 The dextrorotatory enantiomers of hexahelicene and a thiahexahelicene have been shown to possess the right-handed (P) helicity. From the correspondence of the ORD- and CD-curves of these hexahelicenes and higher helicenes positive rotations correspond in all cases with P-helicenes. 

Main constituents of the oils are cM-7-irone (usually 30-40%) and cw-a-irone (usually 20-30%) which are also responsible for the typical odor. I. pallida oil contains the dextrorotatory enantiomers while I. germanica oil contains the laevorotatory enantiomers [675, 676]. 

The circular dtchroism spectra] data for the dextrorotatory enantiomer of irist/ ./ -rriius-l -chaininocyclohexane)cobal((IIh cation, (+ H v-ICotf ./ -chxn ,p. if listed in Table 12—5. would appear as follows ... 

The X-ray crystal structure of Ihe dextrorotatory enantiomer of Irist/ .R-trans-1 -2-di-ammocyclohexane)cobali(lll) cation, (+) y- Co / . -chxnlt). may be solved io give Fig. 12.53 as one of the /ho possible enantiomeric solutions. 

Fig. 12.53 One of IWu possible enantiomeric solutions to the X-ray crystal structure of the dextrorotatory enantiomer of ins(/ ./ -tr .v-l,2-di-aminocyclohexane) cobalt(lll) cation. <+WlCo(/ ./ -...

Other methods, called kinetic resolutions, are excellent when applicable. The procedure takes advantage of differences in reaction rates of enantiomers with chiral reagents. One enantiomer may react more rapidly, thereby leaving an excess of the other enantiomer behind. For example, racemic tartaric acid can be resolved with the aid of certain penicillin molds that consume the dextrorotatory enantiomer faster than the levorotatory enantiomer. Asa result, almost pure (—)-tartaric acid can be recovered from the mixture ... 

A racemic mixture contains equal amounts of the (+) enantiomer and the (-) enantiomer and has the designation (+/-). Racemic mixtures are not optically active, because the rotation of the dextrorotatory enantiomer cancels out the rotation of the levorotatory enantiomer. Synthesis or isolation of a single enantiomer in the laboratory is a challenging task, and most syntheses of chiral molecules result in a racemic mixture containing both enantiomers. The Food and Drug Administration (FDA) policy statement drafted in 1992 and updated in 20053 requires pharmaceutical companies to characterize the properties of single enantiomers, and this adds difficulty, time, and expense to development of new medicines. 

The title compound 52, a-(4-fhiorophenyl)-4-(5-fluoro-2-pyrimidinyl)-l-piperazinebu-tanol, is an antipsychotic agent without side effects74,75. Its dextrorotatory enantiomer, (+)BMY 14802, is about ten times more potent than its levorotatory isomer76. (+)BMY 14802, [I8F]-52, has been synthesized77 (5-7% yield, 130-140 min) as outlined in equations 33a and 33b. The compound [I8F]-52 binds to cr-receptors with stereoselectivity (rat brain regions with high concentrations of cr-receptors). 

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