Method for the preparation of gyk-dtpa

Abstract

Disclosed herein is a novel method for preparing a DPTA tripeptide-chelator. In particular, a method for preparing GYK-DTPA is described. The method disclosed herein is an improvement over the known methods of preparation based on the cost and labor savings of the present invention. The present invention utilizes t-butyloxycarbonyl (Boc) protecting groups to facilitate the polypeptide-chelator production.

What is claimed is: 
     
       1. A method for preparing a tripeptide-chelator comprising: (a) reacting a N-ε-carbobenzyloxy lysine with benzyl alcohol in a solution of p-toluenesulfonic acid in toluene to form a carboxy protected N-ε-carbobenzyloxy lysine;   (b) reacting a tyrosine residue having a Boc-protecting group with said carboxy protect N-ε-carbobenzyloxy lysine in the presence of a suitable coupling agent selected from the group consisting of 1-ethyl-3(3-dimethylamino propyl)-carbodiimide, benzotriazol-1-yloxytris (dimethylamino)phosphonium hexafluorophosphate and dicyclohexylcarbodiimide to form a Boc-tyrosine (N-ε-CBZ) lysine ester dipeptide having a Boc protected amine terminus and a carboxy terminus protected as an ester;   (c) removing said Boc protecting group from said Boc protected amine terminus by treatment with an acid effective to form an acid salt of said dipeptide, said acid being in a suitable solvent selected from the group of toluene, ethylacetate, methanol, ethanol, isopropyl alcohol, dioxane, dimethoxyethane, dimethylformanide, methylene chloride and tetrahydrofuran;   (d) reacting a glycine residue having a Boc-protecting group with said acid salt of the dipeptide in the presence of a suitable coupling agent selected from the group consisting of 1-ethyl-3(3-dimethylamino propyl)carbodiimide, benzotriazol-1-yloxytris (dimethylamino) phosphonium hexafluorophosphate and dicyclohexylcarbodiimide to form a tripeptide having a Boc-protected amine terminus and a protected carboxy terminus;   (e) reacting said tripeptide with a hydrogen gas in the presence of a suitable catalyst selected from the group consisting of pallidum on carbon, platinum on carbon and platinum oxide in a solvent selected from the group consisting of methanol and ethanol to remove protecting groups from both the lysine side chain and the carboxy terminus to form a partially deprotected tripeptide;   (f) reacting said partially deprotected tripeptide with DTPA-disuccinimdyl ester to form a Boc-protected GYK-DTPA; and   (g) reacting asid Boc-protected GYK-DTPA with an acid to remove said Box protecting group from said Boc protected amine terminus to form GYK-DTPA in the acid salt form.   
     
     
       2. A method of preparing a tripeptide-chelator comprising: (a) reacting a tyrosine residue having a Boc-protecting group with a carboxy protected N-ε-carbobenzyloxy lysine in the presence of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide to form a dipeptide Boc-tyrosine (N-ε-CBZ) lysine ester having a Boc protected amine terminus and an ester protected carboxy terminus;   (b) removing said Boc protecting group from said Boc-protected amien terminus by treatment with hydrogen chloride in ethyl acetate to form a hydrochloride salt of said dipeptide;   (c) reacting a glycine residue having a Boc-protecting group with said hydrochloride salt of the dipeptide in the presence of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide to form a tripeptide having a Boc-protected amine terminus;   (d) reacting asid tripeptide with hydrogen gas in the presence of palladium on carbon in an ethanol solvent to from a tripeptide containing a Boc protecting group at the amine terminus;   (e) reacting said tripeptide with diethylenetriaminepentaacetic disuccinimdyl ester to form a Boc protected GYK-DTPA; and   (f) reacting said Boc protected GYK-DTPA with aqueous HCl to remove said Boc-protecting group to form a GYK-DTPA or GYK-DTPA HCl.