Bicyclic heterocyclic compounds – purine, pteridine and derivatives.
Purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. Therefore, purine is a tetraaza heterocycle.
Purine derivatives
Hypoxanthine is a naturally occurring purine derivative (purin-6-one, known also as 6-hydroxypurine). It isoccasionally found as a constituent of nucleic acids where it is present in the anticodon of tRNA in the form of inosine. Hypoxanthine is a necessary additive in certain cell, bacteria, and parasite cultures as a substrate and nitrogen Source.
Xanthine (2,6-dihydroxypurine) is a product of purine catabolism (degradation). Its diketo form is the stable one.
- It is created from guanine (2-NH2) by guanine deaminase.
- It is created from hypoxanthine by xanthine oxidoreductase.
Xanthine is subsequently converted to uric acid. Several mild stimulants are derived from xanthine, including caffeine and theobromine.
N-Methyl xanthine derivatives. Alkaloids in coffee (caffeine), tea (caffeine and theophylline), and cacao beans (theobromine) are N-methyl xanthine derivatives. These alkaloids are psychoactive substances.
These alkaloids have common physiological action:
- central nervous system stimulatory effect;
- relaxing smooth muscle;
- increasing heart muscle contractility and efficiency;
- increasing heart rate;
- increasing blood pressure;
- increasing renal blood flow (they nave diuretic effect)
- some anti-inflammatory effects.
Uric acid
Uric acid is the final oxidation (breakdown) product of purine metabolism. Uric acid is excreted in urine.
Purine bases
Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are long polymers of nucleotides. The DNA, RNA skeleton, is made of sugars and phosphate groups.
The purine bases are adenine and guanine. A nucleotide is nucleoside connected to phosphate group.
Adenine and guanine bonded at N (9) to ribose or 2-deoxyribose give the four possible nucleosides from purine bases: adenosine, deoxyadenosine, guanosine, and deoxyguanosine.
ADENINE- Adenine (6-aminopurine) is a purine derivative with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate (ATP, a nucleotide) and the cofactors nicotinamide adenine dinucleotide (NAD, as a nucleotide) and flavin adenine dinucleotide (FAD). Adenine plays an important role in protein synthesis and as a chemical component of DNA and RNA. In them, the amino group and the adjacent nitrogen are engaged in hydrogen bonding (dashed lines).
Guanine.
Guanine (2-amino-6-hydroxypurine) has two tautomeric forms. Major is the keto form; the 6-OH (lactam, or enol) form has no biochemical relevance in regard to DNA, RNA. The amino and the keto groups, along with the nitrogen between them are