Synthesis and Biological Activity of 4-Amino-5-chloro-2-ethoxy-3-hydroxybenzamides, Metabolites of a New Gastroprokinetic Agent, Mosapride

To confirm the proposed structures of the minor metabolites of a potential gastroprokinetic agent, mosapride, 4-amino-5-chloro-2-ethoxy-3-hydroxy-N-(2-morpholinylmethyl)benzamide (3) and the N-(5-oxo-2-morpholinyl)-methyl analogue 4 were prepared. As the common intermediate, 2-ethoxy-3-hydroxy-4-nitrobenzoic acid (15) was propared via the regioselective ethylation of 2, 3-dihydroxybenzaldehyde (10) and subsequent nitration of the resultant 2-ethoxy-3-hydroxybenzaldehyde (11). The key intermediate 15 was converted into the benzamides 3 and 4. After enzymatic treatment of the isolated metabolites, their structures were identified by comparison with the synthetic compounds. Serotonin-4 receptor binding affinity of these metabolites was found to be lower than that of mosapride.