Reaction chromatography alkyl groups

These derivatives for the analysis of amino acids have been widely investigated and various combinations of acyl and alkyl groups have been tested in order to find the properties most suitable from the viewpoint of chromatography, the reaction yields and the reaction time for the whole group of amino acids. Their preparation is based on the first, i.e., esterification step, when common esterification reactions are applied with minor modifications, and the second step, when amino and other functional groups are acylated with anhydrides, chlorides or other acylating agents. 

Besides simple alkyl-substituted sulfoxides, (a-chloroalkyl)sulfoxides have been used as reagents for diastereoselective addition reactions. Thus, a synthesis of enantiomerically pure 2-hydroxy carboxylates is based on the addition of (-)-l-[(l-chlorobutyl)sulfinyl]-4-methyl-benzene (10) to aldehydes433. The sulfoxide, optically pure with respect to the sulfoxide chirality but a mixture of diastereomers with respect to the a-sulfinyl carbon, can be readily deprotonated at — 55 °C. Subsequent addition to aldehydes afforded a mixture of the diastereomers 11A and 11B. Although the diastereoselectivity of the addition reaction is very low, the diastereomers are easily separated by flash chromatography. Thermal elimination of the sulfinyl group in refluxing xylene cleanly afforded the vinyl chlorides 12 A/12B in high chemical yield as a mixture of E- and Z-isomers. After ozonolysis in ethanol, followed by reductive workup, enantiomerically pure ethyl a-hydroxycarboxylates were obtained. 

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