Application of in Situ Silylation for Improved, Convenient Preparation of Fluorenylmethoxycarbonyl (Fmoc)-Protected Phosphinate Amino Acids

Abstract

A convenient and efficient method has been developed for the preparation of 9-fluorenylmethoxycarbonyl (Fmoc)-protected 1-aminoalkylphosphinic acids. Reproducible procedures for the synthesis and purification of free alpha-amino H-phosphinates are provided. Protection of free amino phosphinates as the N-Fmoc derivative was achieved by in situ trimethylsilylation of aminoalkylphosphinic acids, which then reacted with Fmoc-Cl to provide corresponding products in excellent yields and in high purity after simple extractive isolation. Mechanistic aspects of the silylation are discussed, and the application of the procedure to another class of amino phosphorus acids is presented.