High-performance liquid chromatography of 2,4-disubstituted-5(4H)-oxazolones, anhydrides and other activated forms of N-acyl- and N-alkoxycarbonylamino acids.

Normal phase high-performance liquid chromatography has been achieved of the common activated forms of valine on a LiChrosorb-CN or a muPorasil (underivatized silica) column using hexane containing 1.5 or 5% tert.-butanol as solvent. Compounds examined include the 2-alkoxy-5(4H)-oxazolones and symmetrical and mixed anhydrides of N-tert.-butoxycarbonyl-, N-benzyloxycarbonyl-, and N-9-fluorenylmethoxycarbonylvaline, the chloride of the latter, a p-nitrophenyl ester, 2-methyl-4-isopropyl-5(4H)-oxazolone, valine-N-carboxyanhydride, and the N- and O-ethoxycarbonyl adducts of l-hydroxybenzotriazole. The 5(4H)-oxazolones from N-tert.-butoxycarbonylvaline and N-benzyloxycarbonylglycylvaline decomposed during chromatography on the muPorasil but not the LiChrosorb-CN column. The method allows direct monitoring of reactions involving generation or consumption of activated forms of amino acids.