Scheme 5. Synthesis of the Monovalent Ligands VZMC014, VZMC018, and VZMC020a.
a Reagents and conditions: (a) 31 (1.2 equiv), EDCI (1.5 equiv), HOBt (1.2 equiv), Et3N (2 equiv), 4 Å MS, anhydrous DMF, 0 °C to r.t., 27%–47%; (b) 10% Pd/C, MeOH, 60 psi H2, r.t., 69%–100%; (c) diglycolic anhydride (1 equiv), DMF, r.t., 92%–100%; (d) 24 (1.2 equiv), EDCI (4 equiv), HOBt (4 equiv), Et3N (4 equiv), 4 Å MS, anhydrous DMF, 0 °C to r.t., 21%–46%.