Esters of amino acids and peptides, and derivatives thereof

The invention comprises tertiary butyl esters of amino acids or peptides or of N-blocked derivatives of such amino acids or peptides in which the free amino groups are protected by groups such as carbobenzoxy, tosyl or phthaloyl. The butyl esters of the N-blocked derivatives are prepared by reacting the latter in a solvent medium with an esterifying agent having the hydrocarbon skeleton of tertiary butyl alcohol or hydrolyzable thereto, e.g. isobutylene in the presence of an acid catalyst. The butyl esters may also be prepared by reacting silver salts of the N-blocked derivatives with tertiary butyl iodide. N-Carbobenzoxy blocking groups may be subsequently removed by catalytic hydrogenation, while both the former groups and N-tosyl groups may be removed with sodium in a liquid ammonia medium. The butyl esters may be purified by conversion to the phosphorous acid or butanetetracarboxylic acid salts. The examples describe the preparation of tertiary butyl carbobenzoxyglycinate, tertiary butyl carbobenzoxy-L-tyrosinate, tertiary butyl carbobenzoxy-D-,L- and DL-phenylalaninates, tertiary butyl carbobenzoxy-DL-valinate, tertiary butyl glycinate, di-(tertiary butyl glycinate) butanetetracarboxylate, tertiary butyl L-tyrosinate, tertiary butyl DL-phenylalaninate, tertiary butyl D-phenylalaninate phosphite, tertiary butyl carbobenzoxy-L-leucinate, tertiary butyl L-leucinate phosphite, tertiary butyl glycyl-L-phenylalaninate, tertiary butyl carbobenzoxy glycyl-L-phenylalaninate and tertiary butyl phthaloylglycylglycinate; the preparation of phthaloylglycylglycine by treating tertiary butyl phthaloylglycylglycinate with hydrogen bromide in glacial acetic acid; the preparation of carbobenzoxyglycine by treating tertiary butyl carbobenzoxyglycinate with hydrogen chloride in diethyl phosphite; and the preparation of tertiary butyl carbobenzoxy-L-prolyl-L-leucinate by treating carbobenzoxy-L-proline with tertiary butyl L-leucinate phosphite.