合成路线1

Swern oxidation of N-(benzyloxycarbonyl)-(R)-phenylalaninol (I) with DMSO and oxalyl chloride afforded the corresponding aldehyde (II). Subsequent pinacol dimerization by treatment with VCl3 and Zn gave diol (III) with a 98% diastereomeric purity. After protection of the hydroxyl groups of (III) as the [2-(trimethylsilyl) ethoxy]methyl (SEM) ethers upon treatment with SEMCl and diisopropyl ethylamine, (IV) was obtained, then the N-benzyloxycarbonyl groups were removed by hydrogenolysis in the presence of Pd/C. The resulting diamine (V) was cyclized with carbonyl diimidazole and pyridine to furnish the cyclic urea (VI). Alkylation with benzyl bromide (VII) and NaH provided the bisbenzylated compound, which was subsequently deprotected by treatment with HCl in MeOH-dioxan to give (VIII) (1). The stereoselective hydroxyl inversion of the diol was then achieved Swern by oxidation to the ketol (IX), followed by reduction with NaBH4 in EtOH, and purification of the major isomer by column chromatography.