Chiral compounds, Amino acids Camphor

Other methods to form carboxylic acids Cyanotrimethylsilane, 87 a-Substituted carboxylic acids (see also Amino acids, Halo carbonyl compounds, Hydroxy acids) Camphor-10-sulfonic acid, 62 Chiral compounds Alcohols... 

For the synthesis of carotenoids in optically active form, compounds ex chiral pool have been used extensively as starting materials, the synthesis of capsorubin (413) from (+)-camphor being one of the most prominent examples (see Chapter 3 Part ni.E). In the following examples, the preparation of chiral building blocks for the synthesis of chiral carotenoids starting from an amino acid and a terpene is described. 

Diastereomeric amides from camphor and camphor-related compounds have been used for the chiral resolution of amino acids by both gas and liquid chromatographic techniques. Nambara et al. [146] recommended the use of L-teresantalinyl chloride (56) to form the amides from alkylated amino acids for GC analyses. Although camphorsulphonamide p-nitrobenzyl esters have been used for LC separations [147,148], Aberhart el al. [149] found that these derivatives were difficult to prepare on a small scale, e.g. for enzyme assays. 

Recently, compounds of this type were also prepared by the stereoselective alkylation of a lithiated (LDA) chiral camphor-based phosphonoglycine imine with high selectivity (82— >99% ee). When using ( + )-ketopinic acid, S -configurated a-amino-a-alkyl diethylphospho-nates w crc obtained95. 

Many organosulfur compounds can be resolved into optically active forms (enantiomers) owing to the presence of a chiral (asymmetric) sulfur atom 5 important examples include sulfoxides and sulfonium salts. Chiral sulfoxides containing amino or carboxylic acid groups have been resolved by formation of the diastereoisomeric salts with d-camphor-10-sulfonic acid or d-brucine. The salts can then be separated by fractional crystallisation and the free optically isomeric sulfoxides liberated by acid hydrolysis. However, a more convenient synthetic procedure for the preparation of chiral sulfoxides of high optical purity is Andersen s method (see p. 30). 

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