Scheme 1. Synthesis of TrmD Inhibitors Based on the Thienopyrimidinone Scaffold; Synthesis of Compounds 9–26 and 31–34 Using Reductive Amination Method.

Conditions: (a) sulfur, triethylamine DMF, 50 °C; (b) formamidine acetate, ethanol, reflux; (c) ethylene glycol, pyridinium-p-toluenesulfonate, Dean–Stark; (d) LiAlH₄, THF, 0 °C to room temparature; (e) Et₃N, EtOH, reflux; TFA, DCM, 0 °C to ambient temperature; (f) amine, NaCNBH₃, cat. acetic acid, MeOH; (g) 4 N HCl in dioxane.