Amino Group Blocking. Improved Method for N-Phthaloylation Using N-(Ethoxycarbonyl)phthalimide

Abstract

N-Phthaloylation, as a means of protecting primary amino groups, especially in the synthesis of peptides, has been known for some time.¹ That N-phthaloylamines generally are easily crystallized, and that the phthaloyl group can readily be removed by hydrazinolysis or phenylhydrazinolysis have been recognized advantages in using this approach for the protection of amino groups during syntheses.^1,2,3 The reaction of phthalic anhydride with amino acids, as a method of N-phthaloylation, requires heating, and can cause recemization.^1,4 This problem was overcome through the introduction by Nefkens et al.⁵ of N-(ethoxycar-bonyl)phthalirnide (1) which reacts with arnines under mild conditions to produce the N-phthaloyl derivatives (2) and ethyl carbarnate (3).