20 mg (0.048 mM) of 2-[3-[5-(o-fluorophenyl)-2,3-dihydro-1-methyl-2-oxo-1H-1,4-benzodiazepin-7-yl]ureido]ethyl acetate are dissolved in 2 ml of absolute methanol and stirred at 30°-40° C. for 1 hour with 13 mg of sodium methylate. The mixture is then buffered with a few drops of glacial acetic acid, diluted with methylene chloride, treated with 10% sodium bicarbonate solution and extracted several times with methylene chloride. The organic phases are combined, dried over sodium sulphate, filtered and concentrated. The residue is crystallised from acetone/ether. There is obtained 1-[5-(o-fluorophenyl)-2,3-dihydro-1-methyl-2-oxo-1H-1,4-benzodiazepin-7-yl]-3-(2-hydroxyethyl)urea which, according to the IR spectrum, is identical with a sample of this substance prepared in another manner (see Example 7).
