Scheme 2

Synthesis of Compounds 15a − n. Reagents and conditions: (g): Pyridine, (C₂H₅)₃N, (NH₄)₂S₅ (h): 1,3-Dichloroacetone, EtOH, reflux (i): K₂CO₃, DMF (j): Pimelic acid anhydride, 1,4-dioxane, reflux (k): MeOH, Cat. SOCl₂, reflux (l): NH₂OH·HCl, KOH, MeOH.