Esterification of L-Dopa (I) with thionyl chloride in methanol leads to the methyl ester (II). The phenolic hydroxyls of (II) are further acylated by acetyl chloride in trifluoroacetic acid to produce diacetate (III). Treatment of the protected derivative of L-Dopa (III) with diphosgene gives rise to isocyanate (IV). This is then coupled to entacapone (V) in refluxing acetonitrile to furnish carbamate (VI). The acetate ester groups of (VI) are finally removed by treatment with 3N HCl in acetone.