Acylation of 1-acetyl-1,2,3,4-tetrahydroquinoline (I) with 2-chloropropionyl chloride (II) by means of AlCl3 provides the quinoline derivative (III), which is deacetylated by treatment with HCl to give 1,2,3,4-tetrahydro-6-(2-chloropropionyl)quinoline (IV). Condensation of compound (IV) with O-ethyl hydrazinethioformate (V) in refluxing acetonitrile yields the thiadiazinone (VI), which is then N-acylated at the quinoline ring with 3,4-dimethoxybenzoyl chloride (VII) by means of Et3N in methylene chloride to give the racemate EMD-53998 [rac-(VIII)]. Optical resolution of EMD-53998 can be performed by two different ways: a) enantioseparation via chromatography with Chiralpak AD in 100% EtOH as eluent and b) acylation of EMD-53998 with (S)-camphanoyl chloride (IX) by means of Et3N in methylene chloride followed by treatment with morpholine in the same solvent to afford a mixture of (?-EMD-53998 (EMD-57439) and the camphanoyl amide (X), which are separated by chromatography. Finally, the (+)-enantiomer, EMD-57033, is isolated by further treatment of amide (X) with morpholine in methylene chloride.