(4-Isocyanato-phenoxy)-acetic acid methyl ester → {4-[2-(4-Methoxycarbonylmethoxy-phenylcarbamoyloxy)-ethoxycarbonylamino]-phenoxy}-acetic acid methyl ester

To [4-(2-Hydroxyethoxycarbonylamino)-phenoxy]-acetic acid methyl ester 5 (1 g, 3.72 mmol) in toluene (10 ml) was added (4-Isocyanatophenoxy)-acetic acid methyl ester 4 (0.8 gram, 3.8 mmol) at room temperature and heated to 50° C. for 20 hours. Toluene was distilled off and water (10 ml) was added. Crude 6 was extracted into chloroform, dried over sodium sulphate, distilled and purified by column chromatography on silica gel using chloroform as eluant to g pure 6 (1 gram, 56.5%) as a white fluffy powder.