The circular dichroism of N-thiobenzoyl-L-α-amino-acids. Part VI. Assessment of the resolution of amino-acids as their N-thiobenzoyl derivatives

Abstract

C.d. spectra of crops and mother liquors obtained during fractional crystallisation of diastereoisomeric alkaloidal salts of N-thiobenzoyl-DL-α-amino-acids indicate directly the degree of resolution and, in principle, the absolute configuration of the predominant N-substituted amino-acid component in each fraction. Improvements resulting from c.d. monitoring of the resolution of a DL-amino-acid as its N-thiobenzoyl derivative include the ability to operate on a scale smaller than that possible by polarimetric methods, as illustrated for the resolution of 2-amino-3,3-dimethylbutyric acid (for which a new synthesis from ethyl acetoacetate is described).