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. Author manuscript; available in PMC: 2021 Feb 15.
Published in final edited form as: Bioorg Med Chem. 2019 Nov 30;28(4):115237. doi: 10.1016/j.bmc.2019.115237

Scheme 1:

Scheme 1:

Synthesis of compound 25 and 37

Reagents and conditions: a) Diethyl oxalate, EtONa, EtOH, reflux, 6 h, 97%; b) Isobutylhydrazine trifluoroacetate/cyclopentylhydrazine trifluoroacetate, EtOH, reflux, 16 h; 40/73% c) LiOH, MeOH/THF/H2O, rt, 18 h, 96/98%; d) (S)-tert-butyl 3-amino-5-cyclohexylpentanoate, BOP, Et3N, THF, rt, 1.5 h, 91/87%; e) TFA, DCM, rt, 1.5 h, 54/94%; f) cyclobutylamine, BOP, Et3N, THF, rt, 3 h, 61/75%.