Phytochemistry Lecture 2 PDF

Phytochemistry lecture 2/ Dr. Haala / Dr. Abdelrahman Samy/FOPPU21 Quantitative determination of volatile oils percentage in plant materials For estimation of volatile oil content in raw plant materials, Clevenger's cohobation apparatus was used depending on whether...

Phytochemistry lecture 2/ Dr. Haala / Dr. Abdelrahman Samy/FOPPU21 Quantitative determination of volatile oils percentage in plant materials For estimation of volatile oil content in raw plant materials, Clevenger's cohobation apparatus was used depending on whether oil is lighter or heavier than water. Detection of Adulteration of Volatile oils Physical and chemical characteristics of the oil are very important parameters for the detection of adulteration. Volatile oils could be adulterated by 1. Addition of cheap organic solvents and mineral oil. 2. Addition of byproducts of oils isolated from same oil or similar ones >>> difficult to be detected. Since physicochemical properties of oil and adulterant are very close The quality of the oils can be judged based on A) Estimation of specific active constituents: Specific oils characterized by presence of specific constituents as a major component. Estimation of these specific components will give an idea about oil adulteration Determination of esters, of alcohols, of aldehydes and ketones, of phenols and of oxides and peroxides. b) Detection of Adulteration Pure oil requires tests for moisture content (Karl Fischer’s method) organic solvents as alcohol, chloroform, and benzene, fixed oils and fats; turpentine oil; mineral oil, resin and balsams, carboxylic acids esters, and heavy metals c) Determination of specific physical properties 1-Color 2-Odor 3-Nature To control color changes, oils Essential oils are mostly liquid at room temperature. should be stored in air-tight, Cooling certain oils may deposit solid crystals, as menthol from peppermint oil. dark containers at low The crystals are called Stearopetene” while supernatant called “Oleopetene”. temperatures. Other oils as oil of anise completely solidify at low temp. and melt at high temp 4- Optical rotation 5-Volatility 6-Specific gravity Most volatile oils when Specific gravity is ratio of weight of known volume of oil, at specified temperature, to placed in beam of polarized weight of same volume of water at same temperature. light possess property of Volatile oils have Sp. gr. values of 0.696-1.188 at 15°C. rotating plane of polarization ❖ Oils with lower values contain high percentage of terpenes as turpentine oil. to right (+, dextrorotatory) or ❖ Oils with moderate value contain more alcohols, esters, and ketones as Mentha oil. to left (-, levorotatory). ❖ Oils with higher values contain more aromatic compounds as cinnamon and clove oils. 7- Refractive index 8- Solubility 9- Congealing point 10- Melting point Volatile oils having refractive index solubility of oil in alcohol highest temperature at which oil Determination of m. p. range from 1.43-1.61. of different strengths congeals or solidifies. for crystalline isolates will Changes in refractive index values offers valuable means to changes in congealing point refer to give an idea about their always refer to changes in detect adulteration of changes in chemical constitution of purity chemical constitution of oil volatile oils oil.  Phytochemistry lecture 2/ Dr. Haala / Dr. Abdelrahman Samy/FOPPU21 Chemistry of Essential oils Volatile oil are complex mixture of different groups of chemical compounds generally of hydrocarbon and oxygenated hydrocarbons known as Terpenes”, derived from German “Terpentine formula “C10H16” is called “true terpenes” and present in low boiling point fraction of oil. In practice, “terpenes” applied to all C10isoprenoid compounds including those containing oxygen may contain one major component as clove oil [contain not less than 85% eugenol] or entirely composed of one constituent as bitter almond oil [benzaldehyde], oil of winter green [methyl salicylate], mustard oil [allylisothiocyanate]. Terpenoids Natural products whose structures can be divided to isoprene units (C5H8) linked in head to tail fashion during formation of terpene Isoperene: a branched-chain, 5C unit, 2 Unsaturated bonds that arise from acetate via Mevalonic Acid pathway Isoprene-Phosphorylation >>> isopentenyl pyrophosphate (IPP >>> Dimethylallyl pyrophosphate (DMAPP) IPP + DMAPP >>> Geranyl pyrophosphate (GPP) (precursor of C10 monoterpenes). GPP +IPP + Farnesyl pyrophosphate (FPP) (precursor of C15 sesquiterpenes). FPP + IPP + Geranylgeranyl pyrophosphate (GGPP) (precursor of C20 diterpenes)  Phytochemistry lecture 2/ Dr. Haala / Dr. Abdelrahman Samy/FOPPU21 ❖ Classification of essential oils acc. To biogentic origin A) Terpenes&Terpenoids B) Phenylpropanoid (C6-C3) derived aromatics C- Isothiocyanates Monoterpenes Sesquiterpenes (C6-C3) compounds or (C6-C2) Acyclic Allicyclic Aromatic Acyclic Allicyclic Aromatic or (C6-C1) based on no. of Monocyclic Bicyclic Monocyclic Bicyclic carbon side chain ❖ Classification of essential oils acc. To functional groups Hydrocarbons Oxygenated derivatives (O) Sulfur compounds nitrogenous compounds 1- Alcohols 2- Phenols 3- Aldehydes. 4- Ketones. 5- Esters. 6- Acids. 7- Oxides. 8- Peroxides. (S) (N) 1-Acyclic Monoterpenes and isomers change in stereochemistry New double bond in trans (E) from geranyl PP by ionization to allylic cation allowing change at double bond to Z in attachment of diphosphate group to tertiary carbon  Phytochemistry lecture 2/ Dr. Haala / Dr. Abdelrahman Samy/FOPPU21 Biosynthesis of of Mono-cyclic monoterpenes of aromatic monoterpene ❖ Cyclization not expected to occur with precursor geranyl ❖ Mevalonate Pathway resulting in aliphatic PP because E stereochemistry of double bond HC or oxygenated terpenes. unfavourable for ring formation. ❖ However, aromatic monoterpenes are ❖ Neryl PP or linalyl PP, however, have favourable formed through dehydrogenation of stereochemistry. Either or both would seem more monocyclic terpenes. through Skimate immediate precursors of monocyclic menthane system (Shikimic) Pathway → (Phenyl Propane) Mechanism of Cyclization Monoterpene cyclase enzymes are able to accept all three diphosphate with Linalyl PP being best substrate. These enzymes first isomerize substrate as well as to cyclize them. So, species involved in cyclization as delocalized allylic cation tightly bound to diphosphate anion. Isolation of hydrocarbon 1- Fractional Distillation 2- By formation of crystalline adducts, especially for those containing double bonds, with Cl2, Br2, HX, N2O3, N2O4, NOCl and NOBr. Each adduct hasits own specific physical characters as m.p ( reagent add to double bond) 3- By counter-current extraction. 4- By chromatography as GLC, HPLC, and TLC.  Phytochemistry lecture 2/ Dr. Haala / Dr. Abdelrahman Samy/FOPPU21 Monoterpenoids Name Myrecene and Ocimene Para-cymene (or Cymol) Limonene and dipentene class Unsaturated Acyclic Monoterpenoid hydrocarbons Aromatic Monoterpenoid hydrocarbons Monocyclic monoterpenoid hydrocarbons Structure p-Menthadiene derivatives (∆ 1:8 p-menthadiene) Source Myrecene: component of essential oil of several plants widely spread in essential oils as those of lemon, Limonene: d(+) form in citrus oils e.g. including bay, cannabis, wild thyme, parsley, and hops, e.g cumin, thyme, origanum, lavender, nutmeg, oils of orange, grapefruit, bitter orange, Humulus lpulus, Family cannabinaceae cinnamon mandarin. Ocimene: In oils of Ocimum basilicum (basil) ‫الريحان‬, Family The dl form (racemic =Dipentene) in oils Labiatae of lemon grass, nutmeg and fennel Properties ❖ Both liquids (b.p.