Enantiomer levorotatory

Chemical Properties. Because of its chiral center, malic acid is optically active. In 1896, when tartaric acid was first reduced to malic acid, the levorotatory enantiomer, S(—), was confirmed as having the spatial configuration (1) (5,6). The other enantiomer (2) has the R configuration. A detailed discussion of configuration assignment by the sequence rule or the R and S system is available (7). 

More then a dozen representatives of the above ring systems were introduced into the human therapy. Actisomide (2) and trequinsin (3) are used as antiarrhytmic and antihypertensive agents, respectively. Sunepitron (4), a a 2-adrenoceptor antagonist, is under clinical trials for the treatment of anxiety and depression. Representatives of the third generation of antibacterial quinolone-3-carboxylic acids the blockbluster ofloxacin (5), its levorotatory enantiomer, levofloxacin (6), and rufloxacin (7) have gained wide acceptance for the treatment of bacterial infections of the respiratory and urinary tracts, skin, and soft tissues, as well as sexually transmitted diseases, and pazufloxacin (8) is under development. Praziquantel (9) is widely applied for the treatment of schistosomes- and cestode-caused infection in both veterinary and human therapies (Scheme 4). 

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. 

An equal molar mixture of the dextrorotatory and levorotatory enantiomers of a chiral compound is called a racemic mixture or a racemate. Racemates do not show overall optical rotation because the equal and opposite rotations of the two enantiomers cancel each other out. A racemic mixture is designated by adding the prefix (+) or rac- before the name of the molecule. 

Compared with the dextrorotatory form, the levorotatory enantiomer possesses a greater than 100-fold higher affinity for the p-receptor and is, therefore, practically alone in contributing to the p-blocking effect of the racemate. 

Another substrate for the synthesis of hexoses, frons-5,6-dihydro-6-(hydroxymethyl)-2-methoxy-2/7-pyran (211), was obtained in both optically active forms by resolution of its 6-camphanyl ester.1 2 From the levorotatory enantiomer, methyl 2,3,6-tri-0-acetyl-4-deoxy-a-D-.r //o-hexopyranoside (606) was synthesized, thus confirming its (2S) (6S) configuration, corresponding to the D configurational series. 

Since cetirizine dihydrochloride (4) is a mixture of two enantiomers, they have been separated and tested individually. The levorotatory enantiomer of cetirizine displays a better pharmacological profile than the racemic mixture, and is currently... 

The single most important physical property that differentiates enantiomers is their ability to rotate the plane of plane polarized light. This property is called optical activity and is displayed only by chiral molecules. Thus, stereoisomers which are also chiral are known as optical isomers. Chiral molecules that rotate polarized light in a clockwise fashion are termed dextrorotatory (d) while those that rotate the beam counterclockwise are levorotatory (/). Enantiomers have optical rotations of die same magnitude but of different signs (d or /). 

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 ... 

Dihydrobenzo[6]thiophene-2-carboxylic acid has been resolved212 the levorotatory enantiomer exhibits a plain negative rotatory dispersion curve which allows it to be assigned a D-configura-tion.218 The corresponding 3-carboxylic acid could not be resolved.212... 

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. 

In the presence of (+)-ephedrine, ( )-l-acetylcyclo-octene 59dE photoisomerizes to enantiomeric (Z)-isomer, which is trapped by cyclo-pentadiene to give the Diels-Alder adduct 62d in 22% ee (Sch. 21) [118]. Direct irradiation at >280 nm of doubly bridged (Z)-l(10)-bicyclo[8.8.0] octadecen-2-one 87Z in diethyl (+)-tartrate as a solvent affords the (E)-isomer 87E in favor of the levorotatory enantiomer where the EjZ ratio is 7 (Sch. 31) [162]. 

Chiral recognition of epinephrine by an enzyme. Only the levorotatory enantiomer fits into the active site of OH rV0H... 

L-isomer. Compare with D-Prefix used to designate a levorotatory enantiomer. 

While the monomeric vanadium complex 8m furnishes the expected levorotatory enantiomer of 6 in high yield [11 (ee = 59%), an excess... 

Modafinil is a benzhydrylsulfinylacetamide wake-promoting agent for oral administration (1). It selectively targets neuronal pathways in the sleep/wake centers of the brain. It is well absorbed and its half-life is about 12-15 hours, which largely reflects the half-life of its levorotatory enantiomer. It... 

Although the different enantiomers of a chiral molecule have the same phju ical properties, they usually have different biological properties. For exam pie, the dextrorotatory enantiomer oflimonene has the odor of oranges, ba the levorotatory enantiomer has the odor of lemons. 

Verapamil is a synthetic compound possessing slight structural similarity to papaverine. It can be separated into its optically active isomers, of which the levorotatory enantiomer is the most potent. It is absorbed rapidly after oral administration. The drug is metaboli zed quickly and. as a result, has low bioavailability. The liver is the main site of first-pass metaboli.sm. forming several products. The preferential metabolic step involves N-dealkylation. followed by O-demethylation. and subsequent conjugation of the product before elimination. The metabolites have no significant biological activity. Verapamil has an elimination half-life of approximately 5 hours. 

Racemate Levorotatory enantiomer Dextrorotatory enantiomer References... 

The substituted imidazo-thiazole, dexamisole, has antidepressant properties and its isomer, levamisole, possesses anthelmintic and immunostimulant properties. Enantiomers of HA-966 (3-amino-l-hydroxypyrrolid-2-one) exhibit distinct central nervous system effects (+)-HA-966 is a selective glycine/A-methyl-o-aspartate receptor antagonist, but (-)-HA-966 is a potent i-butyrolactone-Uke sedative." A comparison of (+) and (-)-3-methoxycypro-heptadine shows that aU of the anticholinergic activity of the ( )-3-methoxycyproheptadine resides solely in the dextrorotatory enantiomer, while the antiserotonin activity resides in the levorotatory enantiomer." ... 

The D/L labeling is unrelated to (+)/(-) it does not indicate which enantiomer is dextrorotatory and which is levorotatory. Rather, it says that tlie compound s stereochemistry is related to that of the dextrorotatory or levorotatory enantiomer of glyceraldehyde. Nine of the nineteen L-amino acids commonly found in proteins are dextrorotatory (at a wavelength of 589 nm), and D-fructose is also referred to as levulose because it is levorotatory-. 

The indoienine 386 was neatly used in the synthesis of ( )-strempeliopine (387), the levorotatory enantiomer of which occurs in Strempeliopsis strem-pelioides K. Schum. (256). Reductive rearrangement of 3M by means of zinc and copper sulfate in acetic acid gave the indoline 388, together with... 

Where A+ = % mole fraction of the dextrorotatory enantiomer A = % mole fraction of the levorotatory enantiomer ee = enantiomeric excess... 

These medicinal plants are now understood to owe their pharmacological and toxicological properties to several extremely potent alkaloids (Fig. 8-13). The first to be isolated in 1831 was atropine. Other solanaceous alkaloids are atroscine (which like atropine is racemic), hyoscyamine and scopolamine, and the levorotatory enantiomers of racemic atropine and atroscine, respectively. 

Balfourodine was reported to rearrange with acetic anhydride and pyridine into (+)-isobalfourodine acetate (122), which was hydrolyzed to (-t-)-isobalfourodine (overall 48% racemization), but it is now known that these products are derived from (+)-balfourodine rather than from the levorotatory enantiomer. Because (+)-balfourodine occurs in Balfourodendron riedelianum, and there is no indication that (—)-balfourodine was available from another source, it appears probable that (—)-balfourodine is a misprint for (+)-balfourodine in the earlier paper. Alternative mechanisms involving inversion at the chiral center were proposed for the rearrangement of balfourodine effected by acetic anhydride... 

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