AMINO-ACIDS AND PEPTIDES .41. EXAMINATION OF SOME NEW AMINO-PROTECTING GROUPS

In an investigation of the effect of the introduction of basic sites on the stability of alkoxycarbonyl groups to acid the following new amino-protecting groups have been examined: di-2-pyridylmethoxycarbonyl [e.g. (1)], 4-pyridylisopropoxycarbonyl [e.g. (4)], 3-diethylamino-1,1- diphenylpropoxycarbonyl [e.g. (10)], and 1,4-dimethylpiperidin-4-yloxycarbonyl [e.g. (13)]. In each case the stability to acid is considerably enhanced. The last-named group provides protection which is more stable to trifluoroacetic acid than is the t-butoxycarbonyl group, is stable to hydrogenolysis, and is cleaved by hydrogen bromide in acetic acid. In an investigation of amino-protecting groups designed to increase the solubility of derivatives by the incorporation of dimethylcarbamoyl substituents, the preparation of 2-dimethylcarbamoylethyl-isopropoxycarbonyl [e.g. (18)] and 2- dimethylcarbamoylbenzyloxycarbonyl [e.g. (24)] amino-acids is reported.