The condensation of 2-bromo-1-indanone (I) with 1-methylimidazole-2-carboxamide (II) in hot DMF produced the tetracyclic ammonium salt (III), which was further demethylated to (IV) by means of imidazole at 160 C. Regioselective nitration of (IV) employing KNO3 in H2SO4 produced nitro derivative (V), which was reduced to amine (VI) by catalytic hydrogenation over Pd/C. Amine (VI) was converted to urea (VII) by treatment with methyl isocyanate. Subsequent base-catalyzed condensation of (VII) with glyoxylic acid monohydrate (VIII) produced hydroxyacid (IX). This was dehydrated with ZnCl2 and acetic anhydride to give unsaturated acid (X), which was finally hydrogenated over Pd/C to furnish the title compound.

The tetracyclic imidazoindenopyrazinone (IV) was obtained by condensation of 2-bromoindanone (I) with 1-methylimidazole-2-carboxamide (II), followed by demethylation of the resulting imidazolium salt (III) in molten imidazole at 160 C (1). Reaction of (IV) with isoamyl nitrite in the presence of NaH produced oxime (V), which was reduced with zinc powder in acetic acid to yield acetamide (VI). Regioselective methylation of (VI) using methyl iodide and NaH gave (VII). Subsequent nitration of (VII) by means of KNO3 and H2SO4 afforded the 8-nitro derivative (VIII), which was reduced to amine (IX) by hydrogenation over Pd/C. Condensation of amine (IX) with methyl isocyanate in DMF produced urea (X). Finally, the acetamido group of (X) was hydrolyzed in refluxing 6 M HCl.

In a related procedure, tetracyclic compound (IV) was first condensed with glyoxylic acid (VIII) giving hydroxyacid (XI), which was dehydrated to (XII) with ZnCl2 and Ac2O. Subsequent nitration of (XII) with KNO3 and H2SO4 afforded nitro derivative (XIII). Reduction of (XIII) with simultaneous esterification using iron and HCl in MeOH gave rise to amino ester (XIV). Urea (XV) was then obtained by condensation of (XIV) with methyl isocyanate. Finally, saponification of the ester group provided the title carboxylic acid.