(The following reaction is done in an anhydrous N2 atmosphere.) Dissolve {2′-[3-(3,4,5-Trimethoxy-phenyl)-propionylamino]-biphenyl-3-yl}-acetic acid methyl ester (72) (46 mg, 0.10 mmol) in anhydrous DCM (1.0 mL), cool the solution to −78° C. and add dropwise BBr3 (85 μL, 0.90 mmol). Stir the reaction mixture for 30 min at −78° C. and after slowly warming up for additional 2 h at rt. Add dropwise ice water, separate layers and extract aqu. layer with DCM (3 times). Wash combined organic layer with brine and dry with Na2SO4. Purify the crude product by preparative RP HPLC (gradient, water/CH3CN 95:5 to 5:95) to obtain {2′-[3-(3,4,5-Trihydroxy-phenyl)-propionylamino]-biphenyl-3-yl}-acetic acid methyl ester (73) (2 mg, 5%). 1H NMR (400 MHz, CD3CN): 2.43 (t, 2H, J=7.6 Hz); 2.69 (t, 2H, J=7.6 Hz); 3.66 (s, 3H); 3.70 (s, 2H); 6.25 (s, 2H); 7.18-7.34 (m, 5 H); 7.35-7.44 (m, 2H); 7.65 (br.s, 1H); 7.89 (br.d, 1H, J=8.3 Hz).
