5-Chloro-2-thiophenecarboxylic acid → 3-{2-[(5-Chloro-thiophene-2-carbonyl)-amino]-ethanesulfonylamino}-azetidine-1-carboxylic acid tert-butyl ester

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3-{2-[(5-Chloro-thiophene-2-carbonyl)-amino]-ethanesulfonylamino}-azetidine-1-carboxylic acid tert-butyl ester was prepared by an analogous procedure as described in example 5 iii) starting from 240 mg (1.3 equiv.) 5-chloro-thiophene-2-carboxylic acid and 308 mg (1.1 mmol) 3-(2-amino-ethanesulfonylamino)-azetidine-1-carboxylic acid tert-butyl ester. Final purification by preparative RP-HPLC (CH3CN/H2O gradient+0.1% TFA) gave pure 3-{2-[(5-chloro-thiophene-2-carbonyl)-amino]-ethanesulfonylamino}-azetidine-1-carboxylic acid tert-butyl ester. The title compound was obtained in form of a colorless amorphous material.

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