Alkylation of 3-phenylpropylamine (I) with methyl bromoacetate (II) provided secondary amine (III), which was coupled with N-Boc-(2-chlorophenyl)alanine (IV) using diisopropyl carbodiimide (DIC) and 7-hydroxy azabenzotriazole (HOAt). After deprotection of the Boc group from the resulting amide (V) with trifluoroacetic acid, cyclization in the presence of Et3N in refluxing MeOH funished piperazinedione (VI). The amide N of (VI) was alkylated with tert-butyl bromoacetate, and the tert-butyl group was then removed using trifluoroacetic acid to provide piperazineacetic acid (VII). This was then coupled to protected amino acid (VIII) by means of O-(7-azabenzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HATU) and HOAt to give (IX). Finally, the 2,2,5,7,8-pentamethylchroman-6-sulfonyl protecting group of (IX) was removed with trifluoroacetic acid to furnish the target compound.