GB872332A - Derivatives of amino acids and peptides, and synthesis of peptides - Google Patents

Abstract

The invention comprises (1) N-t-butyloxy-carbonyl derivatives of a -amino-acids and of peptides; (2) the preparation of these derivatives by reacting the amino-acid or peptide with p-nitrophenyl t-butylcarbonate in the presence of water and a water-miscible organic solvent and at a pH of 8 to 12; and (3) a process for synthesizing peptides by reacting an N-t-butyloxycarbonyl derivative of an a -amino-acid or of a peptide with an a -amino-acid ester or a peptide ester in the presence of an alkyl pyrophosphite type peptide reaction promoting agent and one or more alkyl phosphite type acid-acceptors, removing the blocking group, i.e. cleaving, by the action of a hydrogen halide, and hydrolysing the ester group from the free peptide ester. The above amino-acids are those which comprise the building blocks for large peptides such as insulin, adrenocorticotropic hormones, oxytocin, various antibacterial agents and proteinaceous material in general, which group includes alanine, phenylalanine, arginine, aspartic acid, asparagine, cysteine, cystine, glutamic acid, glutamine, methionine, glycine, histidine, leucine, iso-leucine, norleucine, lysine, ornithine, proline, hydroxyproline, serine, tyrosine, valine, tryptophane and threonine. The preferred solvent for the preparation of the derivatives of the invention is t-butanol. Suitable reaction promoting agents for the peptide process include diethyl ethylene pyrophosphite or bis(ethylene pyrophosphite), and suitable acid-acceptors include dialkyl phosphites, tri-alkyl oralkenyl phosphites and alkyl alkylene phosphites, or mixtures of these. The cleavage is advantageously effected with hydrogen chloride or hydrogen bromide in a dialkyl phosphite, and the two-stage cycle of peptide-linkage formation and cleavage may be repeated as desired by adding to the solution of the cleaved peptide ester obtained at the end of the second stage a further t-butyloxycarbonyl derivative of an amino acid or peptide until a peptide of desired chain length and constitution is prepared, when, following the final cleavage reaction, the ester group is hydrolysed by conventional means. Examples describe (a) the preparation of t-butyloxycarbonyl derivatives of a number of the aminoacids specified above, mostly as their L-isomers and of e -carbobenzoxy-L-lysine and glycyl-DL-phenylalanine by process (2); (b) the preparation of ethyl t-butyloxycarbonylglycyl-DL-phenylalaninate, the hydrolysis thereof to the last-named product of (a), the cleavage thereof to ethyl glycyl-DL-phenylalaninate hydrobromide and the reaction of this hydrobromide with t-butyloxycarbonylglycine to give ethyl t-butyloxycarbonyl-glycyl-glycyl-DL-phenylalaninate; (c) the condensation of t-butyloxycarbonyl-L-leucine with ethyl glycinate, cleavage of the product and condensation of the cleaved product with carbobenzoxy-L-proline to give ethyl benzyloxycarbonyl-L-prolyl-L-leucyl-glycinate; (d) the preparation of ethyl t-butyloxycarbonyl-glycyl-DL-phenyalanyl-glycinate; and (e) the preparation of ethyl t-butyloxycarbonyl-L-phenylalanyl-glycinate, the cleavage thereof to ethyl L-phenylalanyl-glycinate hydrochloride and hydrobromide and the condensation of the latter with t-butyloxycarbonyl-L-valine to give ethyl t-butyloxycarbonyl-L-valyl-L-phenylalanyl-glycinate. The preparation of oxytoxin by the process of the invention is also referred to. Para-nitrophenyl t-butyl carbonate is prepared from t-butanol and p-nitrophenyl chloroformate in presence of a tertiary amine base.