Amino-acids and peptides. Part XXVII. Further studies on esters of 1-hydroxypiperidine

Abstract

Acylamino-acid 1-piperidyl esters have been obtained in a high state of purity by the use of ‘Reagent K’[3-(2-ethyl-5-isoxazolio)benzenesulphonate], and new esters prepared by this and by previously known methods are reported. Standard recemisation tests showed that the new procedure gave an optically pure ester from benzyloxycarbonylglycyl-L-phenylalanine, but some racemate was formed from benzoyl-L-leucine. Other reactions of 1-piperidyl esters are reported. The optimum molar proportion of acetic acid to amine in the condensation of benzyloxycarbonyl-L-leucine 1-piperidyl ester with glycine ethyl ester in chloroform has been found to be between 1 and 2; 1,2,4-triazole catalyses this reaction (with dimethylformamide as solvent) and also that of the ester with benzylamine, but acetic acid is more effective. The preparation of t-butyl 1-piperidyl carbonate, and its use in forming t-butoxycarbonylglycine, are described. With L-lysine, benzyl 1-piperidyl carbonate gives ε-benzyloxycarbonyl-L-lysine in 58% yield. The cleavage of the phthalimido-group of phthalimido-esters by glycine ethyl ester in the presence of acetic acid is reported.