Synthesis and application of N,N-bis-(1-adamantyloxycarbonyl) amino acids

The preparation of novel bis-(1-adamantyloxycarbonyl) amino acid derivatives has been undertaken and their properties studied. Among them, the p-nitrophenyl esters were subsequently applied to the stepwise synthesis of Leu-enkephalin. In the last coupling step, some hydantoin formation was encountered but it could be nearly completely overcome by working with more concentrated solution. The preparation of a tyrosine derivative presented special problems owing to the existence of the phenolic group in the precursor. The relative stability of 1-adamantyloxycarbonyl as N- and O-protecting groups was also studied.