Synthesis of Metforminium Succinate by Melting. Crystal Structure, Thermal, Spectroscopic and Dissolution Properties

Abstract

The reaction by melt mixing at 220 °C of the antihyperglycemic drug metformin hydrochloride 1 with dehydrated sodium succinate yields efficiently the organic salt [MET]₂[SUC] 2 (H-MET⁺= metforminium and SUC^2- = succinate). Solid state CPMAS NMR ¹³C spectroscopy experiments, powder X-ray diffraction and FT-IR results support the formation of the pharmaceutical salt 2 in good yields. Besides, the charged-assisted hydrogen bonding interactions of type N-H^…-O(carboxylate) were thoroughly analyzed by single crystal X-Ray diffraction techniques. Thus, the pharmaceutical salt 2 possesses considerable thermal differences when compared to the pure starting reagents. In addition, intrinsic dissolution rate experiments in buffered aqueous solutions at pH= 6.8 showed a sustained-release behavior of the drug in 2 with a constant value of K_int = 0.885 mg/min * cm²