Identification, synthesis, and characterization of β-isomer as process related impurity in production of methocarbamol from guaifenesin

Methocarbamol is a central nervous system depressant with skeletal muscle relaxant properties indicated to treatspasms. During the synthesis of methocarbamol from guaifenesin, both potential known and an unknown impurity(0.05%–0.1%), high performance liquid chromatography) were observed. The later was separated using preparativeliquid chromatography. Upon the findings of the 1H nuclear magnetic resonance, Mass, and IR spectral analysis, theunknown impurity was designated as a β-isomer of methocarbamol [1-hydroxy-3-(2-methoxy phenoxy) propan-2-ylcarbamate]. The impurity isolation, its structure elucidation, and the potential formation mechanism are discussed.