Scheme 3. Synthesis of the tetrameric PRP fragment 1 containing the aminopentyl linker. Reagents and conditions: (a) PivCl, pyridine, 0 °C, then I2, pyridine/H2O, RT, 85%; (b) (i) TCA, DCM, RT; (ii) 9, PivCl, pyridine, 0 °C, then I2, pyridine/H2O, RT, 80% (over two steps); (c) hydrazine acetate, DCM, RT, 90% or 70% (one pot; three steps); (d) Pd/C, H2, EtOAc/MeOH/50% AcOH(aq.), 89%. PivCl = pivaloyl chloride, TCA = trichloroacetic acid.
