aReagents and conditions: (a) DIAD, PPh3, THF, 85%; (b)MeOH, NaN3, 40 °C, 96%; (c) Boc-NH-O-Boc, DEAD, PPh3, THF, 45%; (d) 50% TFA, CH2Cl2, 98%; (e) Fmoc-L-Arg(NO2)-Cl, Collidine, THF, 74%; (f) (i) 20% piperidine, DMF; (ii) Boc2O, NaHCO3, dioxane, 83% for two steps; (g) 5% LiOH, THF, 94%; (h) iButylchloroformate, NMM, NH4OH, THF, 65%; (i) 50% TFA, CH2Cl2, ~quant.