Esterification of 4-nitro-D-phenylalanine (I) with HCl/MeOH provides the amino ester (II). This is subsequently acylated with 3,5-dimethylbenzoyl chloride (III), yielding amide (IV). Alkylation of amide (IV) by means of iodomethane and NaH affords the N-methyl amide (V). The nitro group of (V) is then reduced to amine (VI) by catalytic hydrogenation over Pd/C. Clauson-Kaas condensation of amine (VI) with 2,5-dimethoxytetrahydrofuran (VII) leads to the pyrrole derivative (VIII). The methyl ester function of (VIII) is then hydrolyzed with LiOH to provide the carboxylic acid (IX).

1-Amino-1-cyclopropanecarboxylic acid (X) is protected as the N-Boc derivative (XI) employing Boc2O and NaOH in aqueous dioxane. Carbonyldiimidazole-mediated coupling of the Boc-aminoacid (XI) with butanesulfonamide (XII) produces the N-acyl sulfonamide (XIII). The N-Boc group of (XIII) is then cleaved under acidic conditions to give amine (XIV). This is finally coupled with acid (IX) in the presence of EDC and HOAt to furnish the corresponding amide.