Phytochemistry Lecture 3 PDF

Phytochemistry Lecture 3 Composition of Volatile oil Volatile oils are a complex of organic compounds Hydrocarbons (mono & sesquiterpenes), Oxygenated compounds (alcohols, esters, aldehydes, ketones) Aromatic benzenoids Compounds containing sulfur or nitrogen Oxygen...

Phytochemistry Lecture 3 Composition of Volatile oil Volatile oils are a complex of organic compounds Hydrocarbons (mono & sesquiterpenes), Oxygenated compounds (alcohols, esters, aldehydes, ketones) Aromatic benzenoids Compounds containing sulfur or nitrogen Oxygenated compounds are responsible for the volatile oils’ odor  Removal of Terpenoid Hydrocarbons (Preparation of Terpeneless Oil) Oils with high percentage in terpenoids are: Liable to rapid deterioration on storage through oxidation and polymerization to yield bad smelling (turpentine odor) Having less aroma Less soluble in low-strength alcohols Resenify rapidly Terpene-less oils are expensive because they are: More stable More soluble in low strength alcohol Smaller amount used to give the same strength of aroma Richer in oxygenated compounds Thus, a considerable amount of the terpenoid hydrocarbons could be removed by: 1-Fractional distillation under reduced pressure; hydrocarbons have lower boiling points and therefore, distill first and are discarded. 2-Column chromatography on silica gel, by eluting hydrocarbons with n-hexane then oxygenated compounds with absolute alcohol. 3-Selective extraction of the oxygenated components by dilute alcohol followed by distillation.  Terpenoids Terpenoids were proved to be synthesized from Isoprene. Isoprene is also known as isopentene or 2 methyl-buta- 1: 3-diene The isoprene units are branched five-carbon units containing two unsaturated bonds. Each group of terpenes arises from the head-to-tail condensation of a variable number of isoprene units Abbreviated structure 1 h h=head, t=tail 4 t 2 3 Isoprene, 2-methyl 1:3 butadiene, isopentene  CH2 h ║ CH2 C C CH3 isoprene t H= head T= tail ║  Metamenthane Isoprene Acyclic Paramenthane monoterpenoid C10 Monocyclic Monoterpenoid C10 Bornane Fenchane iso- Thujane Carane Pinane (Camphane) Camphane Bicyclic monoterpenes (C10) Isoprene Isoprene Isoprene Acyclic sesquiterpene Monocyclic sesquiterpene Sesquiterpenes (C15)  Terpenoids in essential oils Monoterpenoids (C10H16) Volatile Sesquiterpenoids (C15H24) low mol weight They may be: -Acyclic (aliphatic) -Alicyclic (cyclic) -Hydrocarbons (90% of Citrus oil) -Oxygenated (alcohols, aldehydes, ketones, esters, ethers, oxides or peroxides) -They are optically active Compounds arising from terpenes degradation: Ionones (from oxidation of carotenes) Irones (from oxidation of bicyclic triterpenes)  Phenyl propanoids in essential oils They are natural products found in various volatile oils, with 6-carbon aromatic phenyl group & 3-carbon propene tail They exhibit pharmacological activities and have applications in pharmaceutical industry Volatile oil isolates: 1-Hydrocarbons. 2-Alcohols. 3-Phenols and phenolic ethers. 4-Aldehydes and ketones. 5-Oxides and Peroxides. 6-Esters. 7-Organo-nitrogen and organo-sulphur compounds  1-Hydrocarbons in volatile oils Hydrocarbons or unoxygenated constituents detected in volatile oils belong mainly to the following groups: 1.Acyclic mono-and sesqui-terpenoids. 2.Alicyclic mono-and sesquiterpenoids ✓ Monocyclic monoterpenoids ✓ Bicyclic monoterpenoids ✓ Monocyclic sesquiterpenoids ✓ Bicyclic sesquiterpenoids ✓ Tricyclic sesquiterpenoids 3. Aromatic hydrocarbons  1. Acyclic terpeniods A-Acyclic monoterpenoid hydrocarbons h t Myrecene Ocimene oil of hops (Humulus lupulus, Cannabinaceae). And oil of oils of Ocimum basilicum bay (Myrcia acris, Myrtaceae) or Pimenta racemosa Isolation Since the oils are rich in phenolic cmpds. + NaOH H2O soluble phenates Then, separate non-phenolic fraction (oily layer) Fractional distillation individual hydrocarbons  B-Acyclic Sesquiterpenoids hydrocarbons Sesquicitronellene Farnesene oil of oil of hops (Humulus citronella (Cymbopogon lupulus, Cannabinaceae). nardus, Gramineae). ** Farnesene is Considered as the Sesquiterpene analogue of myrecene Myrecene KMnO4 & farnesene Oxidation  2- Alicyclic terpenoid hydrocarbons Monoterpenes Monocyclic Bicyclic monoterpenoid Monoterpenoid hydrocarbons Hydrocarbons Sesquiterpenes Monocyclic Bicyclic Tricyclic i-Monocyclic monoterpenoid hydrocarbons d-Limonene Occurs in (citrus oils e.g. oils of orange (90%), lime, grapefruit, bitter orange (oil of neroli), mandarin, bergamot) l-limonene In turpentine oil Limonene and Dipentene Dipentene (dl- form) “racemic” Occurs in oil of turpentine, lemon grass, pepper, nutmeg, neroli, fennel and turpentine Limonene could be isolated from orange oil by: Fractional distillation of the oil, and collection of the fraction at 176ºC. Uses: Limonene & dipentene are widely used as: 1-Flavoring agents for cosmetics, soaps & pharmaceuticals 2-Substitutes for preparation of orange oil 3- Together with other V.O. constituent in aqua cool syrup used as antiflatulence and antispasmodic. * Toxicity: Skin irritant and sensitizer  Hot mineral Heat with S acids isomrization p-Cymene dehydrogenation Limonene & Dipentene ┼ Air & moisture p-Cymene (in orange oil) α-Terpinene Cold mineral acids ┼ Carvone Carveol Terpine hydrate Terpineol *in badly stored orange oil by auto oxidation Caraway-like odor ii-Bicyclic monoterpene hydrocarbons Parent classes Fenchane Carane Pinane Bornane Thujane (Camphane) Have tendency to undergo: a)- molecular rearrangement (pinane camphane) b)- shifting of double bond c)- oxidation, hydrogenation, dehydrogenation d)- opening of the rings on treatment with acids monocyclic monoterpenes ii-Bicyclic monoterpene hydrocarbons A-Thujane derivatives Sabinene: It is obtained from oils of savin (Juniperus sabina, Pinaceae, 30%) by fractional distillation On exposure to air and light, it yields α-thujene due to shift of the double bond. On treatment with acids, rapid opening of the second ring cycle occurs Cold dilute acids produce terpineol and/or terpin hydrate. Boiling with dilute H2SO4 results in formation of α - terpinene  (+) Sabinene bioling with dil. H2SO4 cold dil. acids α-Terpinene Terpineol Terpin hydrate α -Thujene  B-Pinane derivatives α-and β-Pinenes (+)–ß-pinene (+)-α-pinene α-Pinene (main constituent in oil of turpentine) -l-form(French oil of turpentine) -d-form(American oil of turpentine) -Obtained from oil by Fractional distillation Uses: starting material for semi-synthesis of camphor, borneol and terpineol  HCl gas Isomerization Molecular -10oC Rearangement Bornyl chloride Pinene Pinene hydrochloride KOH HNO3 Oxidation Borneol Camphor Auto-oxidation Sobrerol (Pinol hydrate) (+)–ß-pinene (+)-α-pinene (Mucolytic) Derivatives of pharmaceutical importance Sobrerol or pinol hydrate, used as mucolytic in cough mixtures is formed by auto-oxidation of α-pinene in the presence of water and especially in sunlight. α-pinene is also incorporated in Bilichol cap For bile therapy and acts as cholagogue iii-Monocyclic sesquiterpenoid hydrocarbons Zingiberene is the main constituent of ginger oil (Zingiber officinalis, Zingiberaceae) Zingeberene It is obtained from ginger oil by fractional distillation under vacuum (due to its high boiling point). S / Heat Zingiberene Cadalene iv-Bicyclic sesquiterpenoid hydrocarbons Naphthalene derivatives It is obtained from oils of cade, savin, cubebs, lemon grass etc…by fractional distillation under vacuum ß-Cadinene S/heat S/heat Zingiberene Cadalene (aromatic HC) ß-Cadinene Uses It is occasionally used in perfuming soaps to give a gin-like flavor. Oil of cade itself has been used as anti-eczematic. v-Tricyclic sesquiterpenoid hydrocarbons Santalene It is obtained by repeated fractional distillation of Sandal wood oil.  3. Aromatic Hydrocarbons A-P-Cymene Source This compound is widely spread in essential oils such as those of lemon, sage, thyme, Origanum, lavender, nutmeg, cinnamon etc… p-Cymene It is probably an artifact formed during Para-cymene hydro distillation by cyclization, (or Cymol) dehydrogenation or reduction of monoterpenoids. Prepared by fractional steam distillation. Used for perfuming soaps  Semi-synthesis 1. Reduction Se/heat Or S / heat Thymol p-Cymene Limonene 2. Cyclic monoterpenoid hydrocarbons e.g. limonene, pinene and terpinene yield p-cymene on dehydrogenation by heating in presence of S or Se. 3. Oxygenated monoterpenoids e.g carvone and citral yield p-cymene on dehydrogenation and cyclization. B-Azulene derivatives (C15H18) They are highly conjugated (colored) found in pigments of Mushrooms, guaiac wood oil, some marines Mostly occur as colorless precursors called pro-azulenes Isolation: through adduct formation with mineral acids(≠H2O) The parent hydrocarbon is azulene, C10H8. The naturally occurring azulenes are substituted with alkyl groups and are C15 compounds(closely related to sesquiterpenes) Exhibit anti-inflammatory & anti-ulcerative effects  Azulene Chamazulene Guaiazulene gives the blue color From dehydrogenated From decomposition of of oil of chamomile Guaiacum wood oil matricin Uses of Chamazulene: Chamazulene is widely used in cosmetic preparations, as anti-inflammatory and mild antiulcerative. The volatile oil of chamomile is used in GIT disturbances and has spasmolytic properties. The ulcer protective properties are mainly attributed to its bisabolol and bisabolol oxide content.