Scheme 2. Synthesis of dimeric PRP fragments 10, 11, and 12. Reagents and conditions: (a) 14, PivCl, pyridine, 0 °C, then I₂, pyridine/H₂O, RT, 85%; (b) TCA, DCM, RT, 90%; (c) (i) hydrazine acetate, DCM, RT, 90%; (ii) PCl₃, Et₃N, imidazole, DCM, 0 °C. PivCl = pivaloyl chloride, TCA = trichloroacetic acid.