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. 2023 Jun 16;66(13):8600–8613. doi: 10.1021/acs.jmedchem.3c00258

Scheme 2. Synthetic Procedure for the Precursors for LMW Substrates and Bifunctional Chelating Agents with FGK Linkage.

Scheme 2

Reagents and conditions: (a) (1) H-Phe-OtBu, COMU, DIEA, DMF, rt for 2 h; (2) 10% anisole/TFA, rt for 3 h, DO3AiBu-Bn-F in 5.3% and DOTA-Bn-F in 14.8%; (b) (1) Fmoc-amino acids, DIC, HOBt, DMF, rt for 2 h, (2) 20% piperidine/DMF, rt for 20 min; (c) (1) DIC, HOAt, DMF, rt for 15 h, (2) TFA: triisopropylsilane: water (95/2.5/2.5), rt for 4 h, DO3AiBu-Bn-FGK in 99.3% and DOTA-Bn-FGK in 52.6%; (d) (Boc)2O, sat. NaHCO3, dioxane, rt for 2 h, DO3AiBu-Bn-FGK(Boc) in 53.8% and DOTA-Bn-FGK(Boc) in 71.8%; (e) N-methoxycarbonylmaleimide, sat. NaHCO3, 0 °C for 2 h, DO3AiBu-Bn-FGK(Mal) in 40.7% and DOTA-Bn-FGK(Mal) in 26.7%.