2,6-Dihydroxypyridine

2,6-Dihydroxypyridine is an alkaloid with the molecular formula C5H3N(OH)2. It is a colorless solid. 2,6-Dihyroxypyridine is an intermediate in the degradation of nicotine.

Preparation
2,6-Dihydroxypyridine is an intermediate in the degradation of nicotine by the aerobic bacterium Arthrobacter nicotinovorans. The following reaction shows the formation of the intermediate from L-nicotine of tobacco.


 * Degradation of L-nicotine by A. nicotinovorans.png

The figure represents the pathway for the degradation of L-nicotine by A. nicotinovorans to 2,6-dihydroxypyridine

Another reaction of 2,6-dihydroxypyridine highlights its function as a substrate for oxygenase. One example is the enzyme monooxygenase, which oxidizes the substrate by transferring one oxygen atom of O 2 to the substrate. The other oxygen atom is reduced to water. The product of the oxidase reaction was determined to be 2,3,6-tri-hydroxypyridine because of the results of the stoichiometry as well as the results of the ultraviolet spectrum. This reaction can be shown by the following equation:


 * Enzyme2,6-dihydroxypyridine.png

Arthrobacter oxydans, when grown on agar plates, were most active in the oxidation of 2,6-dihydroxypyridine.

Structure and properties
2,6-Dihydroxypyridine in principle can exist in five tautomers:


 * 2,6-dihyrdroxypyridine tautonomers.JPG

The distribution of these tautomers is solvent-dependent. Studies show that tautomer II is most common in ethanol, water, and DMSO.

Other Applications
2,6-Dihydroxypyridine has been investigated in an oxidation method of dyeing hair. The process utilizes 2,6-dihydroxypyridine as a coupling agent, and 2,4,5,6-tetraaminopyrimidine as a primary intermediate. This oxidation method intensifies the color of the dyed hair for several days.

Main Reactions
2,6-dihydroxypyridine is a key intermediate in the degradation of nicotine by certain bacteria. The enzyme 2,6-dihydroxypyridine-3-hydroxylase, which is produced in Escherichia coli, is responsible for catalyzing the sixth step of nicotine degradation in the bacterium Arthrobacter nicotinovoran. 2,6-dihydroxypyridine is hydroxylated by hydroperoxy-FAD. This reaction yields 2,3,6-tri-hydroxypyridine. This is shown in the following reaction::


 * Enzymology2,6dihydroxy.png

2,6-dihydroxypyridine hydroxylase is a dimeric flavoprotein, with one bound FAD molecule attached. The reaction is NADH-dependent and the enzyme only accepts 2,6-dihydroxypyridine as a substrate. Furthermore, the enzyme is inhibited by 2,6-dimethoxypyridine and 2,3-dihydroxypyridine.