Synthesis of bestatin-based ABPs. Reagents and conditions: (a) i-20% Piperidine/DMF; ii-Fmoc-Lys(Biotin)OH, HBTU, HOBt, DIEA; (b) i-20% Piperidine/DMF; ii-Fmoc-BpaOH, HBTU, HOBt, DIEA; iii-20% Piperidine/DMF; iv—Fmoc-NHPEGOH (20 atoms), HBTU, HOBt, DIEA; v-20% Piperidine/DMF; vi-Fmoc-LeuOH, HBTU, HOBt, DIEA; vii-20% Piperidine/DMF; viii-N-Boc-(2S,3R)-3-amino-2-hydroxy-4-phenyl butyric acid, HATU, DIEA; (c) 95% TFA:2.5% TIS:2.5% H2O.