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. 2021 Feb 13;14(2):155. doi: 10.3390/ph14020155

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© 2021 by the authors.

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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Scheme 5 — (A) Synthetic procedure for the preparation of 5a. Reagents and conditions: (a) dry MeOH, conc. H₂SO₄, reflux, 3 h, N₂ atm; (b) NH₂NH₂∙H₂O, MeOH, r.t., overnight; (c) TEA, DCM, r.t., 2 h; (d) TEA, DCM, TsCl, r.t., 2 h; (e) 1. NaOH, THF-H₂O 1:1, r.t., 1 h; 2. Amberlite IR120, 0 °C. (B) Synthetic procedure for the preparation of 5b. Reagents and conditions: (a) EtOH, conc. H₂SO₄, reflux, overnight; (b) NH₂NH₂∙H₂O_, EtOH, reflux, overnight; (c) 86% PPA, 120-130 °C, 1.5 h; (d) 1. LiOH, THF-H₂O 1:1, r.t., 1 h; 2. Amberlite IR120, 0 °C.