The Resolution of Inactive Cystine.

Abstract

Ever since the earlier investigators found that in the preparation of cystine continued hydrolysis with acid decreased the rotation of the cystine and resulted in the disappearance of the typical hexagonal crystals of cystine and the appearance of needle-like crystals, the question as to the identity of this product has been the subject of repeated investigation. Morner 1 heated horn with hydrochloric acid for 2 weeks and obtained cystine partly in needle form which was inactive. Rothera 2 made similar observations on the length of hydrolysis. Neuberg and Mayer, 3 studying the inactive material suggested the possibility that it was either meso cystine or a racemic mixture. They grew Aspergillus niger on some of the inactive material and obtained a dextro-rotatory product having a rotation of +93.78° while a 1% solution of l-cystine in 1 N HCl acid gives a rotation of about —210 at 26°. Van Slyke 4 and Plimmer 5 both found that on boiling l-cystine with 20% HCl acid it was converted into a more soluble form yielding a more soluble phosphotungstate. Recently Gortner and Hoffman 6 , 7 investigated the inactive cystine and synthesized for comparison many derivatives of the l-cystine and the inactive cystine. In all cases the derivatives had the same empirical formulas but in no instance did they find them to have the same melting point and in but few instances to be identical in crystal form. They attempted to obtain dextro cystine from the inactive material by growing Aspergillus niger on the inactive material but no optically active material was obtained. They tried to resolve the inactive benzoyl-cystine into its optical isomers but upon hydrolysis of the various fractions the cystine obtained was completely inactive. They suggested that the inactive cystine might be the internally compensated meso form.