Xanthine (), (3,7-dihydro-purine-2,6-dione), is a purine base found in most body tissues and fluids and in other organisms.

Reactions

Xanthine is a product on the pathway of purine degradation.

• It is created from guanine by guanine deaminase.
• It is created from hypoxanthine by xanthine oxidoreductase.

Xanthine is subsequently converted to uric acid by the action of the xanthine oxidase enzyme.

Pathology

People with the rare genetic disorder xanthinuria lack sufficient xanthine oxidase and cannot convert xanthine to uric acid.

Clinical significance of xanthine derivatives

Derivatives of xanthine, known collectively as xanthines, are a group of alkaloids commonly used for their effects as mild stimulants and as bronchodilators, notably in treating the symptoms of asthma. In contrast to other, more potent stimulants, they only inhibit the actions of sleepiness-inducing adenosine, making them somewhat less effective as stimulants than sympathomimetic amines. Due to widespread effects, the therapeutic range of xanthines is narrow, making them merely a second-line asthma treatment. The therapeutic level is 10-20 micrograms/mL blood; signs of toxicity include tremor, nausea, nervousness, and tachycardia/arrhythmia.

Methylated xanthine derivatives include caffeine, paraxanthine, theophylline, and theobromine. These drugs inhibit phosphodiesterase and antagonise adenosine. Xanthines are also found very rarely as constituents of nucleic acids.

Caffeine: R₁ = R₂ = R₃ = CH₃
Theobromine: R₁ = H, R₂ = R₃ = CH₃
Theophylline: R₁ = R₂ = CH₃, R₃ = H

References

See also

• Murchison meteorite

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