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. Author manuscript; available in PMC: 2016 Nov 1.
Published in final edited form as: Bioorg Med Chem Lett. 2015 Jun 23;25(21):4834–4837. doi: 10.1016/j.bmcl.2015.06.066

Scheme 1.

Scheme 1

General synthetic approach used to prepare compounds 4-23. Conditions: (a) isobutyl chloroformate, N-methylmorpholine, THF, −40 °C; (b) diazomethane, THF, 0 °C; (c) HBr, THF, 0 °C; (d) 2,3,5,6-tetrafluorophenol, KF, DMF, 0 °C; (e) 4Å molecular sieves, toluene, rt; (f) NaBH4, MeOH, 0 °C; (g) when Y = OH; HATU/DIEA/DMF; (h) sodium ascorbate, CuSO4, 1:1 H2O:t-BuOH