合成路线1

D-Phenylalanine (I) was protected as the methyl carbamate (II) by acylation with methyl chloroformate under Schotten-Baumann conditions. The N-methoxy amide (III) was then prepared by coupling of (II) with O-methyl hydroxylamine in the presence of EDC. Cyclization of (III) to the N-methoxy quinolinone (IV) was accomplished by treatment with bis(trifluoroacetoxy)iodobenzene in the presence of trifluoroacetic acid. Simultaneous reduction of the N-methoxy lactam and carbamate functions of (IV) by means of borane-methyl sulfide complex provided diamine (V). The aliphatic amino group of (V) was then selectively protected as the benzyl carbamate (VI) by using N-(benzyloxycarbonyloxy)succinimide at -40 C. Reaction of (VI) with phosgene, followed by treatment of the intermediate carbamoyl chloride with O-methyl hydroxylamine gave rise to the N-methoxy urea derivative (VII). This was cyclized with bis(trifluoroacetoxy)iodobenzene to the imidazoquinolinone (VIII). The N-methoxy and N-benzyloxycarbonyl groups of (VIII) were then removed by hydrogenolysis in the presence of Pearlman's catalyst, and the title compound was finally converted to the corresponding maleate salt.