The title compound was prepared by N-alkylation of the known dihydropyridine (I) with ethyl iodide in the presence of LDA.

The intermediate hydroxy lactone (IV) was prepared by two alternative procedures: Compound (II) was prepared by N-alkylation of the known dihydropyridine (I) with ethyl iodide in the presence of LDA (1). Bromination of the lithium derivative of (II) at -78 C followed by aqueous hydrolysis provided hydroxy lactone (IV). This intermediate was also prepared by basic treatment of formyl ester (III). Hydroxy lactone (IV) was oxidized to cyclic anhydride (V) by treatment with trifluoroacetic anhydride in DMSO. Then, basic hydrolysis of anhydride (V) provided the title disodium dicarboxylate salt.