Antipodes, optical

Jl exists in this form only in solution, though stable derivatives of the aldehyde structure are known. The optical antipode of D-glucose in which the positions of every H and OH are transposed is L-glucose. 

Care should be exercised when attempting to interpret in vivo pharmacological data in terms of specific chemical—biological interactions for a series of asymmetric compounds, particularly when this interaction is the only parameter considered in the analysis (10). It is important to recognize that the observed difference in activity between optical antipodes is not simply a result of the association of the compound with an enzyme or receptor target. Enantiomers differ in absorption rates across membranes, especially where active transport mechanisms are involved (11). They bind with different affinities to plasma proteins (12) and undergo alternative metaboHc and detoxification processes (13). This ultimately leads to one enantiomer being more available to produce a therapeutic effect. 

Levopropoxyphene [2338-37-6] (42), the optical antipode of the dextrorotatory analgetic propoxyphene, is an antitussive without analgetic activity. The 2-naphthalenesulfonate salt has a less unpleasant taste than the hydrochloride salt, and is widely used. Clinical effectiveness has been demonstrated against pathological and artificially induced cough, but the potency is somewhat less than codeine. The compound is reported not to cause addiction. Levopropoxyphene can be prepared (62) by first resolving [ -dimethylamino-CX-methylpropiophenone with dibenzoyl-(+)-tartaric acid. The resolved... 

Confirmation of this constitution was provided by Spath and Becke, > who identified 5-methoxy-3 4-methylenedioxy-o-phthalic acid as an oxidation product of anhalonine. The synthetic df-anhalonine was resolved by crystallisation of the f-tartrate from methyl alcohol, into f-anhalonine, m.p. 85-6°, — 56-3° (CHCI3) and its optical antipode,... 

Phaeanthine, C3JH42O0N2. (Item 8 list, p. 350.) This alkaloid was isolated by Santos.It has m.p. 210°, [a]u°° — 278° (CHCI3), yields a hydriodide, m.p. 268°, picrate, m.p. 263°, aurichloride, m.p. 170-1°, and a platinichloride, m.p. 280° (dec.), and contains four methoxyl and two methylimino groups. By the Hofmann degradation process it yields an optically inactive methine base A, m.p. 173°, which is oxidised by potassium permanganate in acetone to 2-methoxy-5 4 -dicarboxydiphenyl ether (p. 348). A comparison of the properties of phseanthine and tetrandrine by Kondo and Keimatsu indicates that these two alkaloids are optical antipodes, so that phseanthine will be represented by either (XXXIX) or (XL) as given on p. 348, 1 and of these two formula (R = Me) one must represent oxyacanthine methyl ether and the other berbamine methyl ether (centres of asymmetry d- and 1-) tetrandrine (centres of asymmetry both d-) and phseanthine (centres of asymmetry both 1-). 

Beckmann has examined the characters of the optically active men-thones. The oxidation of natural Z-menthol by chromic acid mixture yielded Z-menthone [a]n = - 28 5° which when treated with 90 per cent, sulphuric acid is converted into a d-menthone [ajn = 4- 28 1°, which, however, is not the optical antipode of the first it behaves as a mixture of d- and Z-menthone, but is more strongly dextro-rotatory than it would be if it were only a mixture of the two optical antipodes. 

The coefficient of xV in the three expressions indicates that there exist four different derivatives of cyclopropane of the form (disubstituted cyclopropane with two identical substituents). Two of the four derivatives are mirror images of each other, that is, they form a pair of optical antipodes. If the spatial arrangement is disregarded, only two distinct cyclopropanes with formula are... 

They rotate the plane of polarized light in opposite directions, though in equal amounts. The isomer that rotates the plane to the left (counterclockwise) is called the levo isomer and is designated ( —), while the one that rotates the plane to the right (clockwise) is called the dextro isomer and is designated (-t-). Because they differ in this property they are often called optical antipodes. 

Most of the phosphorus compounds described in the previous sections are chiral and racemic. Attempting their resolution - that is a physical separation of the enantiomers - was obviously attractive and this was realized as early as 1965 by Hellwinkel, who obtained both optical antipodes of 2 [18]. A patent on the synthesis and possible applications of enantiopure phosphate 2 was even filed at the time [103]. 

Enantiomeric. Optical antipode enantiomers are a pair of optical isomers. 

The tropane alkaloids contain as a common structural element the azabicyclo [3.2.1] octane system, and the systematic name of tropane is 8-methyl-8-azabicyclo [3.2.1] octane (Fig. 1). Contradictory results concerning the C-6 and/or C-7 substitution of several C-3,C-6- and C-3,C-7-disubstituted and C-3,C-6,C-7-trisubstituted tropane alkaloids have been presented in the literature. In many cases both optical antipodes of these tropane alkaloids are known, either separately or as a racemic mixture. 

NMR methods of diastereomeric excess determination were used in the separation of 2-methyl-l-boraadamantane into optical antipodes (see Section 12.13.2.5.1) <2003MC121>. Total assignment of H (Figure 4) and 13C NMR spectra (Table 3) of THF-2-methyl-l-boraadamantane 15 was based upon COSY and HSQC experiments <2003MC121>. 

Optical compensation for polymers with chiral monomeric units may also occur when the racemic polymer consists of crystallites, each composed only of the rectus chains or only of the sinister polymer chains, and a same amount of optical antipode crystallites is present. This intercrystallite optical compensation211 has been found, for instance, in isotactic poly(propylene sulfide),212 poly ((3 -methy lpropiol ac (one),213 and poly(isopropylethylene oxide),214 where isochiral 2/1 helical chains are included in orthorhombic unit cells according to the space group P2 2 2. ... 

Let us now differentiate between structures which are asymmetric and dissymmetric. The word asymmetric conveys the idea that the molecule is completely devoid of the elements of symmetry. Dissymmetric on the other hand means not completely devoid of elements of symmetry but possessing so few elements of symmetry that on the whole it will posses two structures which will be the mirror images of each other. Therefore to avoid confusion the term asymmetric is used to cover examples which rotate the plane polarized light. The two forms of an optically active compound are called enantiometers or enantiomorphs or optical antipodes. They are also said to have enantiomeric relationship to each other. 

Usually polarimetric measurements are carried out to find out a given optical antipode and the result is reliable, but the sign of rotation, is not always a direct expression of configuration because rotation, as already stated, depends on nature of solvent, concentration of solution and temperature etc. as the following example shows -... 

Again concentrating our attention on one asymmetric carbon compound, lactic acid and viewing the projection based on C asym-H bond, the optical antipodes can be written as follows, like Neuman s projection formulae ... 

A quasi-racemate or pseudo-racemate is a true racemate like molecular compound formed between optical antipode of different (but related) compounds. The quasi-racemate also has a melting point ciin c resembling the curve of a true racemate but with quasi-racemic compounds the curves are unsymmetrical, because the melting points of the components are different as shown in Fig. (9.3). The curve A represents the melting point of a true-racemate formed by mixing (+) mandelic acid XXII and (-) hexahydromandelic acid XXIII while B represents that of a mixture of (+) XXII and (+) hexa hydro-mandelic acid XXIII. 

In racemisation we have the formation of an equimolecular mixture of optical antipodes, represented as ... 

The dotted line divides the projection into an upper and a lower half. The isomers in which the substituents are on the same side of the dotted line are cis while those in which they are on the opposite side are trans. Both the isomers a and b, sine they have no plane of symmetry, they can be resolved into their optical antipodes. 

The binding sites of most enzymes and receptors are highly stereoselective in recognition and reaction with optical isomers (J, 2 ), which applies to natural substrates and synthetic drugs as well. The principle of enantiomer selectivity of enzymes and binding sites in general exists by virtue of the difference of free enthalpy in the interaction of two optical antipodes with the active site of an enzyme. As a consequence the active site by itself must be chiral because only formation of a diasteromeric association complex between substrate and active site can result in such an enthalpy difference. The building blocks of enzymes and receptors, the L-amino acid residues, therefore ultimately represent the basis of nature s enantiomer selectivity. 

The new polysiloxanes are excellently suited as stationary phases for the gas chromatographic separation of the optical antipodes of different compounds classes over a temperature range from 70° to 240° C. 

D,L-10-Camphorsulfonyl chloride may be oxidized to ketopinic acid (p. 55). The optically active forms of the sulfonyl chloride are useful for resolving alcohols and amines into optical antipodes. 

D,L-10-Camphorsulfonic acid is used for the preparation of the corresponding chloride (p. 14). The optically active acid has been used widely for the resolution of basic compounds into optical antipodes. 

Like other methods of asymmetric synthesis, the solid-state ionic chiral auxiliary procedure has an advantage over Pasteur resolution in terms of chemical yield. The maximum amount of either enantiomer that can be obtained by resolution of a racemic mixture is 50%, and in practice the yield is often considerably less [47]. In contrast, the ionic chiral auxiliary approach affords a single enantiomer of the product, often in chemical and optical yields of well over 90%. Furthermore, either enantiomer can be obtained as desired by simply using one optical antipode or the other of the ionic chiral auxiliary. 

Several syntheses resulting in mixtures of stereoisomers (C-4 and C-2") have been developed (6,301,397) (Sect. 8.5). Pseudomonas fluorescens CHAO produces enantio-pyochoYm (394). The two optical antipodes are not accepted reciprocally by the two Pseudomonas species. 

Mtinzinger M, Taraz K, Budzikiewicz H, Drechsel H, Heymann P, Winkelmann G, Meyer JM (1999). S,S-Rhizoferrin (enantio-rhizoferrin) a Siderophore of Ralstonia (Pseudomonas) pickettii DSM 6297 - the Optical Antipode of R,R-Rhizoferrin Isolated from Fungi. BioMetals 12 189... 

Youard ZA, Mislin GLA, Majcherczyk PA, Schalk U, Reimmarm C (2007) Pseudomonas fluorescens CHAO Produces enantio-Pyochelin, the Optical Antipode of the Pseudomonas aeruginosa Siderophore Pyochelin. J Biol Chem 282 35546... 

Further evidence upon the role of the 3-methyl substituent in reversed ester of pethidine is available from a recent investigation of enantiomorphs of a- and /3-prodine [280] (Table 5.11). It is to be noted that activity is governed by C-4 rather than C-3 geometry since the two more active optical antipodes (dextro a- and /3-prodine) have identical C-4 but different C-3 configurations. This result supports the view that the importance of the 3-methyl substituent lies in its influence upon the conformation of the molecule. Its effect upon activity in (-i-)-a-prodine where it is equational and favours a chair conformation is minor as seen by the similar potencies of (+)-a-prodine and 3-desmethylprodine. Both... 

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