Reaction SMILES: [NH2:1][CH2:2][CH2:3][CH2:4][CH2:5][C@H:6]([NH:14][C:15](=[O:34])[NH:16][C@@H:17]([CH2:25][CH2:26][C:27]([O:29][C:30]([CH3:33])([CH3:32])[CH3:31])=[O:28])[C:18]([O:20][C:21]([CH3:24])([CH3:23])[CH3:22])=[O:19])[C:7]([O:9][C:10]([CH3:13])([CH3:12])[CH3:11])=[O:8].[C:35]([O:39][C:40](=[O:100])[CH2:41][N:42]([CH2:92][C:93](=[O:99])[O:94][C:95]([CH3:98])([CH3:97])[CH3:96])[C:43](=[O:91])[CH2:44][N:45]1[CH:49]=[CH:48][N:47]=[C:46]1[CH2:50][N:51]([CH2:65][C:66]1[N:67]([CH2:71][C:72](=[O:90])[N:73]([CH2:82][C:83](=[O:89])[O:84][C:85]([CH3:88])([CH3:87])[CH3:86])[CH2:74][C:75](=[O:81])[O:76][C:77]([CH3:80])([CH3:79])[CH3:78])[CH:68]=[CH:69][N:70]=1)[CH2:52][CH2:53][CH2:54][CH2:55][CH2:56][CH2:57][CH2:58][CH2:59][CH2:60][CH2:61][C:62](O)=[O:63])([CH3:38])([CH3:37])[CH3:36].CCN=C=NCCCN(C)C.C1C=CC2N(O)N=NC=2C=1.CCN(C(C)C)C(C)C>C(Cl)Cl>[C:85]([O:84][C:83](=[O:89])[CH2:82][N:73]([CH2:74][C:75](=[O:81])[O:76][C:77]([CH3:80])([CH3:79])[CH3:78])[C:72](=[O:90])[CH2:71][N:67]1[CH:68]=[CH:69][N:70]=[C:66]1[CH2:65][N:51]([CH2:50][C:46]1[N:45]([CH2:44][C:43]([N:42]([CH2:92][C:93]([O:94][C:95]([CH3:97])([CH3:96])[CH3:98])=[O:99])[CH2:41][C:40](=[O:100])[O:39][C:35]([CH3:38])([CH3:36])[CH3:37])=[O:91])[CH:49]=[CH:48][N:47]=1)[CH2:52][CH2:53][CH2:54][CH2:55][CH2:56][CH2:57][CH2:58][CH2:59][CH2:60][CH2:61][C:62](=[O:63])[NH:1][CH2:2][CH2:3][CH2:4][CH2:5][C@@H:6]([C:7]([O:9][C:10]([CH3:13])([CH3:12])[CH3:11])=[O:8])[NH:14][C:15](=[O:34])[NH:16][C@H:17]([C:18]([O:20][C:21]([CH3:22])([CH3:23])[CH3:24])=[O:19])[CH2:25][CH2:26][C:27]([O:29][C:30]([CH3:33])([CH3:32])[CH3:31])=[O:28])([CH3:86])([CH3:87])[CH3:88]
Reactant: CC(C)(C)OC(=O)CC[C@H](NC(=O)N[C@@H](CCCCN)C(=O)OC(C)(C)C)C(=O)OC(C)(C)C
Reactant: CC(C)(C)OC(=O)CN(CC(=O)OC(C)(C)C)C(=O)Cn1ccnc1CN(CCCCCCCCCCC(=O)O)Cc1nccn1CC(=O)N(CC(=O)OC(C)(C)C)CC(=O)OC(C)(C)C
Agent: CCN=C=NCCCN(C)C
Agent: On1nnc2ccccc21
Solvent: CCN(C(C)C)C(C)C
Solvent: ClCCl
Product: CC(C)(C)OC(=O)CC[C@H](NC(=O)N[C@@H](CCCCNC(=O)CCCCCCCCCCN(Cc1nccn1CC(=O)N(CC(=O)OC(C)(C)C)CC(=O)OC(C)(C)C)Cc1nccn1CC(=O)N(CC(=O)OC(C)(C)C)CC(=O)OC(C)(C)C)C(=O)OC(C)(C)C)C(=O)OC(C)(C)C
Yield: 21.3 %

Procedure:
A solution of (S)-di-tert-butyl 2-(3-((S)-6-amino-1-tert-butoxy-1-oxohexan-2-yl)ureido)pentanedioate (85 mg, 0.174 mmol), 11-(bis((1-(2-(bis(2-tert-butoxy-2-oxoethyl)amino)-2-oxoethyl)-1H-imidazol-2-yl)methyl)amino)undecanoic acid (118 mg, 0.127 mmol), EDCI (38 mg, 0.20 mmol), HOBt (26 mg, 0.20) and DIPEA (0.30 mL) in DCM (5.0 mL) was stirred at rt for overnight. The reaction mixture was purified by biotage eluting with 1% to 10% MeOH in DCM to afford (19S,23S)-tri-tert -butyl 1-(1-(2-(bis(2-tert-butoxy-2-oxoethyl)amino)-2-oxoethyl)-1H-imidazol-2-yl)-2-((1-(2-(bis(2-tert-butoxy-2-oxoethyl)amino)-2-oxoethyl)-1H-imidazol-2-yl)methyl)-13,21-dioxo-2,14,20,22-tetraazapentacosane-19,23,25-tricarboxylate (38 mg, 21%) as a colorless oil. 1H NMR (400 MHz, CDCl3) 6.95 (d, J=1.2 Hz, 2 H), 6.83 (d, J=0.80 Hz, 2 H), 5.97 (s, 1 H), 5.28 (d, J=7.6 Hz, 1 H), 5.23 (d, J=8.4 Hz, 1 H), 4.94 (s, 4 H), 4.33-4.25 (m, 2H), 4.12 (s, 4 H), 4.03 (s, 4 H), 3.63 (s, 4 H), 3.25-3.16 (m, 2 H), 2.53 (t, J=7.4 Hz, 2 H), 2.33-2.24 (m, 2 H), 2.15 (t, J=7.6 Hz, 2 H), 2.08-2.03 (m, 2 H), 2.02-1.20 (m, 85 H); MS (ESI), 701.6 (M/2+H)+.