Transcript Slide 1
Mevalonic Acid Pathway • Many constituents are unsaturated hydrocarbons • Ketons, alcohols, simple hydrocarbons are formed • Through acetate-mevalonate pathway synthesis • Acyclic, monocyclic, bicyclic,….. • Occur in a free form, as glycosides, esters of org. acids and with proteins • Meroterpenoids (=mixed terpenoids) 1 Terpenes/Terpenoids • Large structurally diverse family of natural products >35,000 • Formed from C5 Isoprene units joined together The fundamental building block for terpenes • Joining of C5 units through Head to tail or Tail to tail fashion • Classification is based on the number of isoprene units forming the carbon skeletons • Stereoisomers, optical isomers • Each member of a terpenoid subgroup is derived from a single parent compound(i.e. Monoterpenes 2 from geranyl-PP ) Mevalonic Acid and Methylerythritol Phosphate Pathways • Mevalonic acid (MVA) is an intermediate for isoprene units • MVA is a product of acetate metabolism (all living tissues cytosol [cytoplasmic matrix]) • Methylerythritol phosphate (MEP) is another intermediate for isoprene units (plants chloroplasts) • MEP arises from glyceraldehyde-3-phosphate and pyruvic acid (Lacked in animals and fungi) 1 HO2C 6 OH 3 2 4 5 OH Mevalonic acid (MVA) OH HO 1 2 3 4 OP OH 2-Methyl-D-erythritol 4-phosphate (MEP) 3 Classification of Terpenes • Based on the number of Isoprene units in the compound Carbon skeletons represented by (C5)n n=number of isoprene units Classes of Terpenes: 5 1) Hemiterpenes C5* 4 2) Monoterpenes C10** 2 1 3) Sesquiterpenes C15** 3 C5 isoprene Unit Isoprene 4) Diterpenes C20 5) Sesterpenes C25 6) Triterpenes C30 7) Teteraterpenes C40 8) Polyterpenes >C40 *found together with mixed terpenoid substances; alkylating agents **mainly volatile substances 4 Synthesis of active isoprene units through MVA O 3 SCoA acetyl-CoA Claisen Reaction E Aldol Condensation HO2C O OH SCoA 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) E = HMG-CoA Synthase IPP = Isopentyl Pyrophosphate DMAPP= Dimethylallyl Pyrophosphate 6 1 HO2C OH 5 OH 3 2 4 Mevalonic acid (MVA) Phosphorylation Decarboxylation 5 1 2 3 4 DMAPP OPP Steriospecific allylic isomerization 1 2 3 IPP 4 OPP 5 Terpenes Classes Corresponding to Parent Molecules/ Polymerization Mevalonic acid Methylerythritol phosphate OPP DMAPP IPP OPP Hemiterpenes (C5) Geraniol Geranyl diphosphate IP P Monoterpenes (C10) C10 OH Farnesol Farnesyl diphosphate Sesquiterpenes (C15) C15 IP P OH Geranylgeraniol C20 Geranylgeranyl diphosphate Diterpenes (C20) OH IP P Sesterpenes (C25) C25 Squalene C30 Triterpenes (C30) Steroids (C18-C30) Phytoene C40 Tetraterpenes (C40) 6 Volatile Oils Large group of natural products of a complex mixture of aromatic-smelling volatile components containing either phenylpropanes (shikimic acid-derived) or terpenes (acetate-derived) Can be classified according to the biogenetic origin or based on the functional groups: hydrocarbon v.o., alcohol v.o., aldehyde v.o., keton v.o.,…. Common properties of volatile oils 1. 2. 3. 4. 5. 6. 7. Liquids at room temperature (exemptions!) Colourless or slightly yellowish Low solubility in H2O Soluble in organic solvents Optically active High refractive index Mostly lighter than H2O EXCEPT clove, cinnamon & sassafras oils 8. Oxidized by O2 from air (resinification) 9. Light exposure oxidation (small, amber glass containers) 10. Do not stain filter paper (fixed oils do) 11. Evaporate at room temp. 12. Obtained by steam distillation (pharmaceutical use), water distillation, expression (citrus oils), organic solv. extraction 8 Further properties of volatile oils • Very complex, aromatic-smelling mixture of compounds (phenylpropenes/ terpenoids) evaporating when exposed to air at room temperature • Synthesized in plants in specific organs (glandular hairs, secretory ducts, oil cells) • 30% plant families are rich in VO • Apiaceae, Lamiaceae, Lauraceae, Myrtaceae & Rutaceae are richest V.O. families • Steam distillation is official method for V.O.-pharmaceutical grade • Economically valuable in pharmaceutical, food, cosmetic, paint and textile industries • GC-MS is the most suitable method for the identification of v.o. 9 Uses of Volatile Oils Insecticides Industry Cosmetic & Toiletries Dental Preparations Paint Industry Volatile Oils Textile Industry Adhesives (Glues & tapes) Pharmaceutical Industry Tobacco Industry Paper & Printing Industry Food & Hygiene Industry Pharmaceutical uses of the volatile oils • • • • • • • • Carminative Antiseptic Diuretic Expectorant Sedative Antiphlogistic Stomachic Anthelmintic Volatile oils • Monoterpene-rich volatile oils Some examples: • Peppermint oil • Lavender oil • Lemon oil • Camphor • Thyme oil • Turpentine oil • Phenylpropane-rich Volatile Oils Some examples: • Cinnamon oil • Anise oil • Fennel oil • Clove oil • Nutmeg oil • Peru balsam • Tolu balsam