合成路线1

The esterification of (2R,4R)-4-hydroxypyrrolidine-2-carboxylic acid (I) with ethanol and sulfuric acid gives the expected ethyl ester (II), which is N-protected with benzyl bromide and DIEA in dichloromethane to the N-benzyl derivative (III). The oxidation of (III) with oxalyl chloride in DMSO affords the pyrrolidinone (IV), which is cyclized with ammonium carbamate and KCN in hot ethanol/water to afford the spiro imidazolidinedione (V). Opening of the imidazolidinedione ring of (V) with refluxing 3N NaOH, followed by esterification with ethanol/SOCl2 provides (2R,4R)-4-amino-1-benzylpyrrolidine-2,4-dicarboxylic acid diethyl ester (VI), which is protected at the amino group with tert-butoxycarbonyl anhydride giving the carbamate (VII) (1). Hydrogenolysis of the N-benzyl group of (VII) in the presence of Pd/C yields (VIII) with a free imino group, which is alkylated with 1-(chloromethyl)naphthalene (IX) by means of DIEA and Bu4NI affording the naphthylmethyl derivative (X). Removal of the Boc protecting group of (X) with HCl in ethyl ether gives (2R,4R)-4-amino-1-(1-naphthylmethyl)pyrrolidine-2,4-dicarboxylic acid diethyl ester (XI), which is finally hydrolyzed with NaOH to the target diacid (2).