Glucose enantiomers

L-glucose enantiomer (Figure 5.38). Correspondingly, the green cholesteric liquid crystalline phase becomes red upon addition of D-glucose and blue upon addition of L-glucose. Diasteromeric hexoses gave similar effects. ... 

The reaction is used for the chain extension of aldoses in the synthesis of new or unusual sugars In this case the starting material l arabinose is an abundant natural product and possesses the correct configurations at its three chirality centers for elaboration to the relatively rare l enantiomers of glucose and mannose After cyanohydrin formation the cyano groups are converted to aldehyde functions by hydrogenation m aqueous solution Under these conditions —C=N is reduced to —CH=NH and hydrolyzes rapidly to —CH=0 Use of a poisoned palladium on barium sulfate catalyst prevents further reduction to the alditols... 

There are interesting examples of enantiomers that not only are found separately but also have different chemical properties when reacting with some reagent which is itself an enantiomer. For example (+ )-glucose is metabolized by animals and can be fermented by yeasts, but (—)-glucose has neither of these properties. The enantiomer ( + )-carvone smells of caraway whereas (—)-carvone smells of spearmint. 

Recently, two examples of the separation of enantiomers using CCC have been published (Fig. 1-2). The complete enantiomeric separation of commercial d,l-kynurenine (2) with bovine serum albumin (BSA) as a chiral selector in an aqueous-aqueous polymer phase system was achieved within 3.5 h [128]. Moreover, the chiral resolution of 100 mg of an estrogen receptor partial agonist (7-DMO, 3) was performed using a sulfated (3-cyclodextrin [129, 130], while previous attempts with unsubstituted cyclodextrin were not successful [124]. The same authors described the partial resolution of a glucose-6-phosphatase inhibitor (4) with a Whelk-0 derivative as chiral selector (5) [129]. 

As you can see from their structures, a- and /3-glucose have several chiral carbon atoms. Both isomers are optically active they are not enantiomers (mirror images of one another) because they differ in configuration only at carbon atom 1. As it happens, both a- and /3-glucose rotate the plane of polarized light to the right (clockwise). 

The conformational symbols for enantiomers are different. It is therefore important to state in the context whether the d or the L form is under consideration. Enantiomers have the same reference plane (see 2-Caib-7.3), and it should be noted that the mirror image of a-D-glucose-4Ci is a-L-glucose-C4. 

Nishi et al. [110] used dextran and dextrin as chiral selectors in capillary-zone electrophoresis. Polysaccharides such as dextrins, which are mixtures of linear a-(l,4)-linked D-glucose polymers, and dextrans, which are polymers of D-glucose units linked predominantly by a-(l,6) bonds, have been employed as chiral selectors in the capillary electrophoretic separation of enantiomers. Because these polymers are electrically neutral, the method is applicable to ionic compounds. The enantiomers of basic or cationic drugs such as primaquine were successfully separated under acidic conditions. The effects of molecular mass and polysaccharide concentration on enantioselectivity were investigated. 

All carbohydrates can exist in either of these two forms and the prefix of D or L only refers to the configuration around the highest numbered asymmetric carbon atom. Enantiomers have the same name (e.g. D-glucose and L-glucose) and are chemically similar compounds but have different optical properties. The majority of naturally occurring monosaccharides, whether they be aldoses or ketoses, are of the D configuration. 

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