N-Methylpyridoxamine: Novel canine vitamin B6 urine metabolite

Cation-exchange HPLC analysis of urine from dogs given large daily doses of pyridoxamine revealed an unidentified metabolite hypothesized to be N-methylpyridoxamine. Identity was established by N-methylpyridoxamine synthesis and HPLC comparison to the canine metabolite. Compound synthesis was confirmed by IR, NMR, UV–vis and emission spectroscopy. It seems to have less fluorescent character than other routinely-measured vitamin B6 metabolites. Upon administration of substantial pyridoxamine doses, N-methylpyridoxamine appears to be a quantifiable canine urine metabolite, although, at either pharmacological or dietary pyridoxamine intakes, its relevance to vitamin B6 metabolism in other species, including humans, is not yet determined.