2- or 3-Hydroxypyridine → 2,5-Dihydroxypyridine<br>2- or 3-Carboxypyridine → 2,5-Dihydroxypyridine<br><br>Comments:<br>This rule handles the upper substituted pyridine pathway for 2- or 3-hydroxypyridine, 2-carboxypyridine (2-picolinate), 3-carboxypyridine (nicotinate) and intermediates of nicotine degradation (<a href="http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=5835946">Gherna et al., 1965</a>). These compounds, and possibly others, have been found to degrade to the common metabolite, 2,5-dihydroxypyridine (<a href="http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=8840783">Kaiser et al., 1996</a>). 2- or 3-Hydroxypyridine and 3-carboxypyridine undergo an initial para hydroxylation to form 2,5-dihydroxypyridine and 2-hydroxy-5-carboxypyridine respectively. The latter product is subject to oxidative decarboxylation to form the 2,5-dihydroxy product. This rule also handles intermediates in this pathway.
