3-Hydroxy-2-naphthoic acid (I) is iodinated by means of NaI and NaOCl to afford 3-hydroxy-4-iodo-2-naphthoic acid (II). Subsequent alkylation with dimethyl sulfate provides the methoxynaphthoate ester (III). Direct conversion of ester (III) to the corresponding nitrile (IV) is accomplished by treatment with dimethylaluminum amide in boiling xylene. Carbonylation of iodonaphthalene (IV) using carbon monoxide in the presence of Pd(OAc)2 and methanol yields the methyl naphthoate (V). Saponification of ester (V) using LiOH gives acid (VI), which is further activated as the acid chloride (VII) by treatment with oxalyl chloride and DMF
Reductive amination of the N-Boc amino aldehyde (VIII) with (S)-4-(2-methylsulfinylphenyl)piperidine (IX) in the presence of NaBH3CN affords the Boc-protected diamine (X). Deprotection of (X) by means of trifluoroacetic acid yields amine (XI) (1). Acylation of (XI) with acid chloride (VII), followed by treatment with citric acid, gives rise to the title compound