Preparation and properties of p-nitrophenyl esters of several 9-fluorenylmethyloxycarbonyl (Fmoc) amino acids are described. The Fmoc derivatives of the hindered amino acids valine and isoleucine were converted to the more reactive o-nitrophenyl esters while N-Fmoc-0- benzyl-L-tyrosine was esterified with pentachlorophenol. In the selection of experimental conditions for coupling reactions an effort was made to keep premature cleavage of the ...