The Isolation, Purification, and Characterisation of the Principal Urinary Metabolites of Melatonin

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Abstract
Melatonin is metabolised by hydroxylation to form 6-hydroxy-melatonin by demethylation to form N-acetyl-serotonin, which are excreted as sulphate glucuronide conjugates. We required these metabolites as pure powders therefore undertook their isolation characterisation. Three volunteers ingested 1 g each of melatonin, their urine was collected pooled. For the sulphate conjugates, a Lichoprep column was used to concentrate the metabolites to remove most of the urea. The sulphate conjugates were separated from the glucuronides on a Florisil column further purified on a fractogel column. They were separated by high-performance liquid chromatography (HPLC) resulting in white powders of 6-hydroxy-melatonin sulphate (SaMT) N-acetyl-serotonin sulphate (SNAS). For the glucuronide conjugates, an aliquot of the pooled urine was taken to dryness, the residue was dissolved in methanol, the solution was filtered. The methanol filtrate was taken to dryness, the residue was applied to a Florisil column. The isolated glucuronide conjugates were recrystallized prior to separation by HPLC, which gave pure white powders of N-acetyl-serotonin glucuronide (GNAS) 6-hydroxy-melatonin glucuronide (GaMT). Characterisation was achieved by using infrared ultraviolet spectroscopy, thin-layer chromatography (TLC), gas chromatography-mass spectrometry (GCMS). These techniques unambiguously confirmed the assigned structures for SaMT SNAS fully supported the assigned structures for GNAS GaMT. Three TLC solvent systems were used, in each case the individual conjugated metabolite appeared as a discreet spot. Purity, as assessed by GCMS, was shown to be greater than 95% for SNAS, SaMT, GaMT to be 88% for GNAS.