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. 2019 Mar 19;141(14):5581–5592. doi: 10.1021/jacs.9b00638

Figure 7.

Figure 7

Synthesis of a 50-mer polymannoside to test the limits of AGA. A new capping procedure enables rapid access to longer oligosaccharide sequences. Reaction conditions 1. AGA: Method A for each coupling cycle i. acid wash: TMSOTf, DCM, −20 °C; ii. glycosylation: 6.4 equiv of 6 and NIS/TfOH in DCM/dioxane for −40 °C (1 min) → −20 °C (20 min) (repeated twice for cycles 46 to 50); iii. capping: py, Ac2O at 25 °C (30 min), repeated three times. iv. Fmoc deprotection: TEA (20% in DMF) at 25 °C (5 min), twice. Method B: for each coupling cycle i. acid wash: TMSOTf, DCM, −20 °C; ii. glycosylation: 6.5 equiv of 6 and NIS/TfOH in DCM/dioxane for −20 °C (5 min) → 0 °C (20 min); iii. capping: MsOH (2%) and Ac2O (10%) in anhydrous DCM at 25 °C (20 min). iv. Fmoc deprotection: piperidine (20% in DMF) at 25 °C (5 min). 2. Photocleavage: hν (305 nm).