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Mevalonic Acid Pathway

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

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Mevalonic Acid Pathway

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  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)

  2. 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 from geranyl-PP )

  3. 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)

  4. 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: • Hemiterpenes C5* • Monoterpenes C10** • Sesquiterpenes C15** • Diterpenes C20 • Sesterpenes C25 • Triterpenes C30 • Teteraterpenes C40 • Polyterpenes >C40 *found together with mixed terpenoid substances; alkylating agents **mainly volatile substances

  5. Synthesis of active isoprene units through MVA

  6. Terpenes Classes Corresponding to Parent Molecules/ Polymerization

  7. 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.,….

  8. Common properties of volatile oils • 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 H2OEXCEPT clove, cinnamon & sassafras oils • Oxidized by O2 from air (resinification) • Light exposure oxidation (small, amber glass containers) • Do not stain filter paper (fixed oils do) • Evaporate at room temp. • Obtained by steam distillation (pharmaceutical use), water distillation, expression (citrus oils), organic solv. extraction

  9. 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.

  10. Uses of Volatile Oils Cosmetic & Toiletries Dental Preparations Insecticides Industry Paint Industry Volatile Oils Pharmaceutical Industry Textile Industry Tobacco Industry Adhesives (Glues & tapes) Paper & Printing Industry Food & Hygiene Industry

  11. Pharmaceutical uses of the volatile oils • Carminative • Antiseptic • Diuretic • Expectorant • Sedative • Antiphlogistic • Stomachic • Anthelmintic

  12. 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

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