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. 2019 Jan 10;10(4):504–510. doi: 10.1021/acsmedchemlett.8b00534

Scheme 2. Synthesis of Analogues 4–32.

Scheme 2

Reagents and conditions: (a) N-Boc-Inp-OH, DIPEA, HBTU in DMF, 80 °C, 80% yield; (b) TFA/CH2Cl2 1:1, 2 h, quantitative yield; (c) N-Boc-l-Pip-OH, DIPEA, HBTU in DMF dry, 80 °C, 78% yield; (d) N-Boc-l-Pro-OH, DIPEA, HBTU in DMF dry, 80 °C, 83% yield; (e) methyl 3-bromopropanoate, methyl 4-bromobutanoate, or methyl 5-bromopentanoate, DIPEA, in CH3CN dry, 60 °C, overnight, 65–92% yield; (f) LiOH in THF/H2O (2:1), 0 °C then room temperature, 24 h, 40–60% yield; (g) DIBAL-H (1 M in toluene) in THF dry, 0 °C, 48 h, 57–82% yield.