Scheme 2: Synthesis of chalcone derivatives [17]. Reagents and conditions: (a) PPA, heating at 100°C; (b) 4-hydroxybenzaldehyde, piperidine, dry benzene, reflux; (c) ethyl bromoacetate, anhy. K2CO3, dry acetone, reflux; (d) NaOH, methanol, reflux; (e) alkylamines, DCC, HOBt, DMAP, CH2Cl2, reflux.