The resolution of DL-4-oxalysine†

Both enantiomorphs have been isolated from racemic Nα, Nδ-diphthaloyl-4-oxalysine in optically pure form via brucine salts and converted into (+)-and (-)-4-oxalysine by acid hydrolysis. (-)-4-Oxalysine has a negative Cotton-effect from which we conclude that this stereoisomer possesses the D-configuration. This conclusion is corroborated by the formation of a quasi-racemic compound between (+)-Nα, Nδ-diphthaloyl-4-oxalysine, stereochemically corresponding to (-)-oxalysine, and Nα, Nδ-diphthaloyl-L-4-thialysine.