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Heterocyclic Compounds with Biological Meaning

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Heterocyclic compounds with biological meaning 1 Heterocyclic compounds Cyclic, organic compounds which besides carbon atoms have one or more heteroatom (other elements than C). Heterocyclic atoms: – nitrogen, N – sulphur, S – oxygen, O – phosphorus, P – barium, Ba – zinc, Zn – silicon, Si. 2 Heterocyclic compounds From the biological point of view, the most important are heterocyclic compounds with 5- and 6-membered rings, containing: S, N, O. Most of the heterocyclic compounds have their common names. Substituent’s position in the ring is described by : – number – position of heteroatom – no. 1 – Greek letter – describes carbon atom the closest to heteroatom as a, then β and γ, respectively. 3 Heterocyclic compounds Heterocyclic compounds are: • widespread in nature • biologically active • some of them are toxic (e.g. coniine, coumarin and derivatives). Occurrence in: • natural dyes - heme, chlorophyll • alkaloids – atropine and nicotine • amino acids such as tryptophan and histidine • enzymes, nucleoproteins, antibiotics • vitamins • many synthetic pharmaceuticals. 4 Heterocyclic compounds Aromatic character of heteroatom-containing ring comes from aromatic sextet which consists of: • „not bound” electron pairs of heteroatoms • four electrons π from carbon atoms Pyrrole Furane Thiophen 5 5- membered ring heterocyclic compounds with one heteroatom 5-membered rings: • contain mostly oxygen, sulphur and nitrogen • are flat • are aromatic 6 5- membered ring heterocyclic compounds with two heteroatoms oxazole imidazole thiazole pyrazole 7 5- membered ring heterocyclic compounds With one heteroatom With two heteroatoms Condensation products with benzene 8 Pyrrole and derivatives • Pyrrole derivatives: • pyrroline • pyrrolidone • proline, • Hydroksyproline. • Condensation’s products of pyrrole with benzene: – indole, – tryptophan, – serotonin. • Condensation’s products of pyrrole with formaldehyde: – heme – hemoglobin – billirubin – porphyrins – Biliverdin. 9 Pyrrole and derivatives. Porphyrin structure Heme: cyclic tetrapyrrole containing iron atom. Present as prostetic group of hemoglobin, mioglobin, and cytochromes. Terapyrrols belong to a family of “dyes” Chlorophylls are cyclic tetrapyrrole compounds containing magnesium atom: • photosynthesis center in plants • light-absorbing dyes 10 Pyrrol derivatives. Porphyrins structure and metabolism Tetrapyrrols have character of dyes. degradation (green dye) Porphyrin arrangement (yellow dye) Bilirubin + albumin is transported to liver where it combines with glucuronic acid which increases its solubility. 11 5-membered rings with one heteroatom 5-hydroxytryptophan serotonin (5-hydroxytryptamine) Serotonin (5-hydroksytryptamine): biologicaly activ amine hormon which is also neurotransmitter in central nervous system and in gastrointestinal tract necessary for sleep - the intermediate product is converted in enzymatic reaction to melatonin (animals with blocked serotonin production are sleepless) deficiency causes apathy or agression, depression, increased appetite for carbohydrates may also be a cause of Sudden Infant Death Syndrome 12 (SIDS) 5-membered ring with two heteroatoms oxazole thiazole imidazole decarboxylation - CO2 histidine histamine Histidine .Structural element of hydrolytic enzymes. Histamine (tissue hormone) : . present in plant and animal tissues . natural factor increasing permeability of veins leading to edema (swelling) . causes angiectasia (dilation of a lymphatic or blood vessel) . causes decreasing of blood pressure . when binding to H2 receptors, causes vasodilation, stimulation of gastric acid secretion 13 5-membered ring with two heteroatoms Thiamine – Vitamin B1 - two-rings system: Pyrimidine and thiazole rings connected by methylene group Thiamine pyrophosphate (cocarboxylase): •coenzyme of pyruvate dehydrogenases (citiric acid cycle) •recommended in Beri-beri disease (nerves inflammation caused by B1 deficiency.) 14 6-membered ring - heterocyclic compounds pyran pyridine pyrazine pyrimidine The most important derivatives of pyrane are monosaccharides: • glucopyranose • galactopyranose • mannopyranose Pyridine derivatives – biologically active compounds: • vitamin B6 • nicotine • vitamin PP 15 Vitamin PP – nicotinic acid derivative Nicotinic acid nicotine vitamin PP It participates in: • redox processes in human body (as coenzymes) • regulation of sugar level in blood • regulation of cholesterol level • regulation of blood flow in veins • maintaining appropriate skin condition (deficiency of vit. PP – pellagra, from latin: pella agra – rough skin) • hormones synthesis (estrogen, progesterone) 16 Vitamin B6 – pyridoxine, pyridoxal phosphate Pyridoxine piridoxal Pyridoxal phosphate • Vitamin B6 – water soluble – part of three natural pyridine compounds – coenzyme for 50 different enzymes • Takes part in : – protein transformation (coenzyme of transaminases) – transformation of tryptophan to serotonin – protein and nucleic acid synthesis Its necessary for hemoglobin synthesis. 17 Pyrimidine bases and their derivatives Pyrimidine: 1,3- diazine – aromatic heterocyclic compound containing two atoms of nitrogen at position 1 and 3 Derivatives: cytosine uracyl thymine 18 Pyrimidine bases and derivatives Keto-enol tautomerism: result of hydrogen atom migration, due to it, pirimidine bases are present in the following forms: • Lactam, keto structure (=O) • Lactim, enol structure (-OH) cytozine uracyl thymine In physiological conditions quantitatively dominant tautomeric form: • in thymine and uracyl is lactam • in cytozine is lactim 19 Condensed rings with heteroatoms Vitamin H • Participate in: – proteins and fats metabolism – fatty acids synthesis – vitamin C absorption – amino acid and sugars metabolism • resistant to heating, acids and bases. 20 Purine base and their derivatives Purine have pyrimidine ring combined with imidazol ring. 21 Purine bases and derivatives Purines contain pyrimidine ring combined with imidazol ring In nature purine does not exist in free form but as amino and keto derivatives Amine groups attached to aromatic ring of purine act similarly to amine group from amino acids, i.e. can transform into cationic form after H+ addition. 22 Purine bases and derivatives Adenine Guanine Hypoxanthine In physiological conditions main tautomeric forms are: • for guanine and hypoxanthine - lactam • for adenine – lactim –amino form 23 Purine bases and derivatives Uric acid xanthin uric acid . easily undergos keto-enol transformations . mammals have uric acid in small quantities in blood, liver, spleen and urine . in humans uric acid is a final product of purine bases metabolism of food as well as of degradation of endogenous nucleic acids . about 75% is excreted with urine and 25% goes to gastrointestinal tract where it is decomposed by gut microflora . slightly soluble in water and therefore has a tendency to accumulate in kidneys (uric stones) and in joints 24 . in basic environment creates easily soluble urates. Purine bases and derivatives Teophilin Caffeine Theobromine (1,3-dimethylxanthine) (1,3,7-trimethylxanthine) (3,7-dimethylxanthine) • Methylated purines are present in plants as plant’s bases (alcaloids) • caffeine is present in coffee beans • teophilin is present in tea leaves • theobromine is present in cacao beans (harmful for dogs and horses) 25 All of them have pharmacological application Condensed rings with heteroatoms Riboflavin - vitamin B2 • mononucleotide consisting of : – nitrogenous base called isoalloxazine rybitol (polycyclic heterocyclic compound ) – ribitol esterified by isoalloxazine (flavin) B2 participate in: - oxydo/reduction processes, - normal functioning of nervous system, Isoalloxazine (flavin) eyes, mucous membranes, respiratory system, - amino acids and lipids transformation 26 Active forms of riboflavin adenine AMP D-ribose orthophosphate pyrophosphate D-ribitol flavin riboflavin mononucleotide (FMN) flavin adenine dinucleotide (FAD) - created as a result of ATP-dependent - adenine nucleotide is attached to FMN phosphorylation of riboflavin (requires ATP): FMN + ATP → FAD + PPi (pirophosphate) - represent flavoprotein prosthetic groups connected with an apoenzyme – enzymes from oxyreductases family (ex. participating in Krebs’ cycle) + - participate in electron transfer and H ions (reduced forms: FADH2 and FMNH2) 27 Structure of nucleosides Nucleosides consist of nitrogenous base (A,G,C,T,U) and ribose or deoxyribose. Name depends on the type of purine or pyrimidine bases. A nitrogenous base (A,G,T,C,U) H (ribose or deoxyribose) 28 Structure of nucleotides Nucleotides have three characteristic components: a nitrogenous base, a five-carbon sugar (ribose or deoxyribose) and at least one phosphate group. A phosphate group A nitrogenous base (pyrimidines or purine base) A, G,T,C,U (ribose or deoxyribose) 29 Nucleotides and nucleic acids Nucleotides are the building blocks of nucleic acids Nucleotide RNA DNA 30 Roles of nucleotides • building blocks of nucleic acids (RNA, DNA) (like amino acids in proteins); • ATP: adenosine triphosphate - "molecular unit of currency" of intracellular energy transfer; energy source; • structural components of many enzyme cofactors (NAD+/NADH: nicotinamide adenine dinucleotide) 31 Nucleic acids are biopolymers with molecular weight about 106 daltons RNA - contains ribose (D-ribose) DNA – contains deoxyribose ( D-2-deoxyribose) DNA: contains adenine, guanine, cytosine , thymine RNA: contains adenine, guanine, cytosine, and uracil 32 Nucleotide nomenclature 33 DNA structure
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