Scheme 3. Synthesis of tetrarhamnoside-containing BA (6). Reagents and conditions: (a) inverse procedure, 12 (5.0 equiv.), TMSOTf (0.1 equiv.), 4 Å MS, DCM, −15 to 0 °C, 25 min; (b) 10% Pd/C, H₂, EtOAc, 80 °C, 3 h; (c) NaOMe, MeOH/DCM 2 : 1, rt, 16 h, 37% (three steps).