Improved and High Yield Synthesis of the Potent Arginase Inhibitor: 2(S)-Amino-6-boronohexanoic Acid

A simple three-step synthesis of the potent arginase inhibitor 2(S)-amino-6-boronohexanoic acid (ABH) has been developed. The key step was alkylation of the NiII complex of the Schiff base derived from glycine and (S)-2-[N‘-(N-benzylprolyl)amino]benzophenone (BPB) with pinacol 4-bromobutylboronate. Acidic hydrolysis afforded ABH in 50% overall yield, high enantiomeric excess, and quantitative recovery of the chiral auxiliary.