Scheme 1. Route of synthesis of novel diaminodiacid building block; reagents and conditions: (a) TfN₃, CuSO₄·5H₂O, K₂CO₃, water/MeOH/DCM, rt, 12 h, 78%; (b) (i) 4 M HCl/1,4-dioxane, rt, 2 h; (ii) pDob-N₃, Et₃N, DMF, rt, 12 h; (iii) pDobb-OH, DCC, DMAP, DCM, rt, 12 h, 65% in three steps; (c) (i) FmocOSu, Na₂CO₃, water/1,4-dioxane; (ii) tBuOH, DCC, DMAP, DCM, rt, 12 h, 71% in two steps; (d) CuI, DIPEA, THF, rt, 12 h, 86%; (e) TFA/DCM (1 : 1, v/v), rt, 2 h, 96%.