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

2 Terpenes/Terpenoids Large structurally diverse family of natural products >35,000 Formed from C 5 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 (C 5 ) n n=number of isoprene units Classes of Terpenes: 1)Hemiterpenes C5* 2)Monoterpenes C10** 3)Sesquiterpenes C15** 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

5 Synthesis of active isoprene units through MVA

6 Terpenes Classes Corresponding to Parent Molecules/ Polymerization

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.Liquids at room temperature (exemptions!) 2.Colourless or slightly yellowish 3.Low solubility in H 2 O 4.Soluble in organic solvents 5.Optically active 6.High refractive index 7.Mostly lighter than H 2 O EXCEPT clove, cinnamon & sassafras oils 8.Oxidized by O 2 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 Volatile Oils Insecticides Industry Paint Industry Textile Industry Cosmetic & Toiletries Paper & Printing Industry Dental Preparations Pharmaceutical Industry Adhesives (Glues & tapes) Tobacco 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