Figure 5

Synthesis of 6–7. Reagents and conditions: (a) N2,N6-Bis(benzyloxycarbonyl)-L-lysine, BOP, Et3N, THF, 3.5 h, rt, 64%; (b) 1 atm H2(g), Pd/C 10%, THF, 6 h, rt, quantitative; (c) Boc-Arg(Boc)2-OH, BOP, Et3N, THF, 2 h, rt, 95%; (d) TFA, CH2Cl2, 2 h, rt, 79%.