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. Author manuscript; available in PMC: 2020 Oct 15.
Published in final edited form as: Bioorg Med Chem. 2013 Feb 27;21(9):2623–2634. doi: 10.1016/j.bmc.2013.02.020

Scheme 2.

Scheme 2.

Reagents and conditions: (a) isobutylamine (2.2 equiv), THF, 0 °C, 2.5 h, 97%; (b) (1) 4 N NaOH, MeOH/1,4-dioxane (v/v, 1/4), rt, 0.5 h; (2) Fmoc-OSu, pH 8.5–9.0, 1,4-dioxane, rt, 1 h, 60% for two steps.