A convenient synthesis of amino acid p-nitroanilides; synthons in the synthesis of protease substrates

Article abstract of DOI:10.1016/0040-4020(95)00671-T

A method is described for the synthesis of N(α)-protected bi- and trifunctional amino acid p-nitroanilides. The reaction uses phosphorus oxychloride as the condensing agent. The synthesis is simple, rapid, free of racemization and affords yields between 70-90%. The synthesis can be performed not only with amino acid derivatives of the urethane type including acid-labile (Z, Boc) and base-labile (Fmoc, Msc) N(α)-protective functions or allyl-derived protections, but also with N(α)-trityl amino acids, albeit in lower yield. The reaction runs in pyridine and its mechanism implies carboxyl activation by formation of a mixed anhydride with phosphorodichloridic acid (HOPOCl₂).