Liquid Chromatography–Mass Spectrometry and Proton Nuclear Magnetic Resonance Characterization of Trace Level Condensation Products Formed Between Lactose and the Amine‐Containing Diuretic Hydrochlorothiazide

Trace levels of condensation products between lactose and the amine‐containing diuretic hydrochlorothiazide are formed when a mixture of the two solids containing 30% weight water is heated at 60 °C for 2 weeks. The two most abundant condensation products were characterized by liquid chromatography‐mass spectrometry (LC‐MS) and proton nuclear magnetic resonance (1H NMR) spectroscopy. Under these relatively mild conditions of formation, the amine–lactose reaction products are limited to those involving the elimination of only a single molecule of water, rather than the multiple‐water eliminations associated with later stages of the Maillard reaction. The spectroscopic data clearly show that the primary condensation products are cyclic N‐substituted glycosylamines rather than Schiff base, 1,2‐enolic forms, or Amadori rearrangement products of identical mass. In solution, the two most abundant N‐substituted glycosylamines are shown to be in a kinetically slow equilibrium with each other, most likely through a mutarotation involving the intermediate formation of the acyclic Schiff base. © 2000 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 89: 920–929, 2000