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. Author manuscript; available in PMC: 2021 Mar 26.
Published in final edited form as: J Med Chem. 2020 Mar 10;63(6):2854–2876. doi: 10.1021/acs.jmedchem.9b01189

Scheme 4.

Scheme 4.

Synthesis of isostere containing derivatives 19a-fa

aReagents and conditions: (a) 3b, toluene, 130 °C, 2–3 h; ii) NaBH(OAc)3, acetic acid, THF, 25 °C, 12 h, 8–80%; (b) LiOH·H2O, THF/CH3OH/H2O, 12 h, 13%.