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Chemistry of Essential Oils

Dwi SetyaningsihThe Islands of Spice

4PROPERTIES OF VOLATILE OILSAlmost entirely volatile without decompositionDensity: Most are less than 1g/mlheavier Cinnamon and Clove oilSoluble in ether, chloroform & alcoholSlightly soluble in water: give it a characteristic odour & taste. All are characteristic odoursMost are colourless, Most are optically activeOxidize on exposure to air and resinify colour becomes darker (odour changes slightly)

VOLATILE OIL COMPOSITION

VOLATILE OIL COMPOSITIONMixtures of hydrocarbon and oxygenated compounds derived from these HCs.Oil of turpentine mainly HCsOil of clove mainly oxygenated compoundsException: Oils derived from glycosides ( bitter almond & mustard oil)Oxygenated compounds responsible for the odour/smell of the oil. Slightly water soluble Rose water & Orange water; more alcohol solubleMost volatile oils are terpenoid. Some are aromatic (benzene) derivatives fixed with terpenesSome compounds are aromatic, but terpenoid in origin (Thymol Thyme)CHEMICAL COMPOSITIONCHEMICAL COMPOSITIONVolatile oils are divided into 2 main classes based on their biosynthetic originTerpene derivatives (acetate mevalonic acid pathway)Aromatic compounds (shikimic acid-phenylpropanoid route)Miscellaneous Origin

CO2PhotosynthesisCarbohydratesPentose phosphate pathwayErythrase 4-phosphateGlycolysisPhosphoenol pyruvic acidAcetyl CoAMelonic acid pathwayTricarboxylic acidAlphatic amino acidsAromatic amino acidsIPP + DMAPPShikimic acid pathwayNitrogen containing secondary metabolitesPhenolic compoundsMevalonic acid pathwayTerpenesTERPENESTerpenes/terpenoids, the largest group of secondary metabolitesConstitute one of the most diverse families of natural products, with over 40 000 different structures of terpenoidsAll formed from acetyl CoA or glycolytic intermediatesTerpenoids contain only the most volatile terpenes (MW is not too high) mono and sesquiterpenesAll terpenes are formed from 5-C elementsIsoprene is the basic structural elementMay occur as oxygenated derivatives : alcohols, aldehydes, ketones, phenols, oxides & estersCan oxidate or polymerise easily changing odour and lessening volatility

CLASSIFICATIONUnsaturated hydrocarbons Monoterpenes and sesquiterpenes used in flavours and fragrancesWeak odours not fully represented they come fromSometimes poorly soluble in weak ethanolic solutionsTerpenoids

headtailIsoprene unitC5The biologically active isoprene units were identified as the pyrophosphate esters IPP (Isopentenyl pyrophosphate)and DMAPP (Dimethylallyl pyrophosphate) Form a large and structurally diverse family of natural products derived from C5 isoprene units joined in a head to tail fashion Isoprene(2-methyl-1,3-butadiene)

Mevalonic acidDMAPP (C5)IPP (C5)GPP (C10)Monoterpens & Iridoids (C10)IPP

FPP (C15) Sesquiterpenes (C15)IPP

GGPP (C20)Diterpenes (C20)2 x FPP Triterpenes (C30)2 x GGPPTetraterpens (C40)Steroids (C18-C30)ORIGIN OF TERPENESsqualeneSesterpene (C25)Hemiterpenes (C5)

Terpenoids are enzymatically synthesized from acetyl CoA and pyruvate provided by the carbohydrate pools in plastids and the cytoplasm. TERPENES BIOSYNTHESIS IN PLANT CELL9

Classification of Terpenes C10-Monoterpenes :Regular monoterpenes (EO, oleoresins, iridoids)Irregular monoterpenes (pyrethrins)C15-Sesquiterpenes : essential oils, sesquiterpenoid, lactonsC20-Diterpens : retinolC30-Triterpens & steroids : saponins, cardiac glycosidesC40-tetraterpenes : b-carotenes

10TerpenesMyrcene (isolated from oil of bayberry) is a typical terpeneCH2CH3CH3CCHCH2CH2CCHCH2

orThe Isoprene UnitAn isoprene unit is the carbon skeleton of isoprene (ignoring the double bonds)

Myrcene contains two isoprene units

The Isoprene UnitThe isoprene units of myrcene are joined "head-to-tail."

headtailtailhead

REPRESENTATIVE MONOTERPENESa-Phellandrene(eucalyptus)Menthol(peppermint)

(lemon grass)

OH

OH

OH

OH

Citral - oxygenated monoterpene - seldom comprises > 2% of the essential oil of lemon - largely carries the lemon flavora-Selinene(celery)

HREPRESENTATIVE SESQUITERPENES

H

Vitamin A

OHREPRESENTATIVE DITERPENES

OH

Squalene(shark liver oil)

tail-to-tail linkage of isoprene unitsREPRESENTATIVE TRITERPENESFrom 15 Carbons to 20Farnesyl pyrophosphate is extended by another isoprene unit by reaction with isopentenyl pyrophosphate.

OPP

OPPCyclizationRings form by intramolecular carbon-carbon bond formation.

OPP

OPP

+E double bondZ double bond

+

OHH+H2OLimonenea-TerpineolBicyclic Terpenes

+

+

+

b-Pinene+

a-Pinene

LIMONENEStructural classification: a monoterpene hydrocarbon Monocyclic terpeneFunctional classification: Unsaturated HCOccurrence: Citrus fruitThe major terpene in many or most citrus products. Orange > 95% Lemon ~ 65%

EXAMPLES OF TERPENESMENTHOLStructural classification: Monocyclic with hydroxyl groupFunctional classification: AlcoholOccurrence: Peppermint

BORNEOL

OH

Occurrence: Cinnamon NEROLCis-3,7-Dimethylocta-2,6-1-olColourless to pale liquidStableApplication: Magnolia, Neroli, Jasmin, Lilac and other floral perfumesOrigin: Rose, Neroli, Petitgrain, Lavender, Lemongrass, Palmarosa and citrus oils

Trans-3,7-Dimethylocta-2,6-dien-olColourless liquidStableApplications: Floral and most other perfumesOrigin: Rose, Citronella, Geranium and Palmarosa

3,7-Dimethylocta-1,6-dien-3-olColourless LiquidStableApplications: Almost universal application in fragrances, especially floralOrigin: Rose, rosewood, Lavender, minor constituent of othersLINALOOLGERANIOL

EXAMPLES OF TERPENESSESQUITERPENESContain 3 isoprene unitsAcyclic Farnesol

Monocyclic Zingiberine

Bicyclic Chamezulene (Chamomile)

Regular IrregularIridaneIridoidThe iridan skeleton found in iridoids is monoterpenoid in origin and contains a cyclopentane ring which is usually fused to a six-membered oxygen heterocyclePyrethrinsMONOTERPENE SKELETONS

EXAMPLES OF TERPENESApocarotenoid formation

Carotenoid substrates are oxidatively cleaved to yield the apocarotenoid derivatives (right).Many terpenoids are non-volatile and are involved in important plant processes such as membrane structure (sterols), photosynthesis (chlorophyll side chains, carotenoids), redox chemistry (quinones) and growth regulation (gibberellins, abscisic acid, brassinosteroids)29Carotenoids are tetraterpenoid pigments that accumulate in the plastids of leaves, flowers and fruits, where they contribute to the red, orange and yellow coloration. In addition to their roles in plants as photosynthetic accessory pigments and colorants, carotenoids are also precursors of apocarotenoids (also called norisoprenes) such as the phytohormone abscisic acid, the visual and signaling molecules retinal and retinoic acid, and aromatic volatiles such as b-ionone. Evidence, based on comparative genetics, has indicated that carotenoid pigmentation patterns have profound effects on the apocarotenoid and monoterpene aroma volatile compositions of tomato and watermelon fruits. This work indicated that the various flavors and aromas of otherwise similar fruit of different colors have a real chemical basis and are not solely due to psychological preconception. Indeed, enzymes capable of cleaving carotenoids at specific sites were found to be involved in the synthesis of a number of apocarotenoids. Carotenoid cleavage dioxygenases (CCDs) catalyze the oxidative cleavage of carotenoids, resulting in production of apocarotenoids. CCDs often exhibit substrate promiscuity, which probably contributes to the diversity of apocarotenoids found in nature. Apocarotenoids are commonly found in the flowers, fruits, and leaves of many plants, and possess flavor aroma properties together with low aroma thresholds. They are found among the potent flavor compounds in wines and contribute to floral and fruity attributes. Therefore, they have been subject to extensive research in recent years with regard to their structure and flavor potential.

AROMATIC COMPOUNDSMany phenols are phenol esters

- Vanillin

PhenolsCompounds with 1 or 2 hydroxy groups, similar to benzyl alcoholsTend to be toxic and causticProne to oxidizationBasically clean type odoursEugenol

4-allyl-2-methoxyphenolStableColourless liquidApplications: Carnation, spicy fragrances, rose and oriental perfumesOrigin: Clove, cinnamom leaf oil, patchouli, Ylang YlangMajor classes of phenolic compound Number of C atomsBasic skeletonClassExample7C6-C1Benzoicp-Hydroxybenzoic acidVanillic acidProtocatechuic acid9C6-C3Hydroxycinnamic acidsCaffeic acid15C6-C3-C6Flavoids AnthocyaninsCyanidin-Flavonoids glycosidesRutinIridoidsOleuropin LigstrosidenLigninsTanninsAlcoholsHydroxy compunds consisting of hydrocarbon chainsPrimary, secondary and tertiary alcohols (i.e., no. carbon atoms), also aliphatic alcoholsTerpenoid alcohols very important chemicals found in many plantsPolyhydric alcohols (2 or more hydroxy groups) odourless, but solventsAcyclic alcohols faint odours (close to phenols)Phenylethyl Alcohol

2-PhenylethanolColourless liquidStableSweet rosy like odourApplications: widely used in synthetic formFrom floral to aldehydic, chypre and fougereFragrancesOrigins: Rose, Neroli, Geranium and Ylang YlangEugenolOHOct-1-en-3-olColourless liquid, StableStrong, fatty, orange like, balsamicApplications: In the reconstruction of lavender and lavindin oilsOrigin: in some mushrooms and savory oilCitronellol

3,7-Dimethyloct-6-en-1-olColourless liquid, StableApplications: used in floralsOrigin: Rose, citronella oils

Benzyl Alcohol

Carboxylic AcidsOrganic acids with a carbonyl and hydroxy groupUsually derived from aliphatic alcohols or aliphatic aldehydes through oxidizationOdours usually resemble precursorsColourless crystaline solidSlightly pungent odour

Benzoic AcidEstersDerived from alcohols in reversible reactionsFruity notesNot very pH stable Colourless liquid, StableApplications: Versitile in many fragrances, especially jasmin and gardeniaOrigin: Jasmin, Tuberose, neroli, Ylang YlangBenzyl Acetate

AldehydesFatty aldehydes have pungent odoursAliphatices used in perfumery and flavours mainly from synthetic sourcesUsually used in very diluted formsAldehydes are very reactive (oxidisation, polymerisation and acetal formations)BenzaldehydeColourless liquidCan oxidize to benzoic acidApplications: In traceable amounts in sweet floralsOrigin: Bitter almond oil, cassia

Aldehydes

AminesCompound with one or more hydrogen atoms of ammonia, replaced with hydrogen radical3 types, primary, secondary and tertiary Most foul smelling animalic

Methyl Anthranilate(Methyl 2-aminobenzoate)Colourless liquidDiscolourationFrom many flowers such as orange and ylang ylangLactonesNaturally ocuring in many fruitsMost often hydroxy group of alcohols which react with carboxylic acidsContain ester functional group in the cyclic part of the moleculeImportant fruit flavours & fragrances

g-butyrolactone anda-caprolactoneOCCURRENCEFlavonoids are widely distributed in the florathey can be found in petals, crops, seeds, leaves, stems, roots and barksit is the reddish brownish - yellowish colour of heartwoodflavonoids of ferns are C-methyl derivatives glycoflavonoids can be isolated from seaweedsmicroorganisms and algae species do not synthesize FLAVONOIDS42

Polyphenols, namely favonoids are low molecular weightThe skeleton can be represented as the C6 - C3 - C6 system Three main groups can be distinguished on the places of phenyl ring.STRUCTURE OF FLAVONOIDSThe chemical structure of flavonoids are based on a C15 skeleton with a chromane ring bearing a second aromatic ring B in position 2, 3 or 4. The oxidation state of propane chain means the difference. Oxidation degree rises from 0 to 643 OH groups number and position of O-methyl, O-alkil, O-glycosyl-groups variance of glycosyl groups, acylation with or without conjugated double bonds

The most often occuring substituents can bond to C3 -, C5 , C7 -, C3 -, C4 atoms.Sugars can bond: through oxygen atom (O-glycosides) directly to C-atom (C-glycosides)Antocyanides are always in their glycoside forms in vacuoles (in cell fluids)Catechines and procyanidines can be stored in their aglycone forms (tannic acid holders, dissolved in essential volatile oils)REASON FOR THEIR VARIETY

44Flavonoids are the secondary metabolites of plants, and they are providing the colour and flavour materials protect against UV-radiation, fungus, insect and snail pests they are signal for N-bound bacteria they modify enzyme reactions

75% of Angiospermae contain kaempferol and quercetin and 10% of them myricetinTHE ROLE OF FLAVONOIDS IN PLANTS

kaempferolquercetinmyricetin45Phenylpropanoid pathway : amino acid phenylalanine -- 4-coumarate-CoA combined with malonyl-CoA to yield the true backbone of flavonoids, called chalcones which contain two phenyl rings.

Conjugate ring-closure of chalcones results in the familiar form of flavonoids, the three-ringed structure of a flavone. SYNTHESIS OF FLAVONOIDS

46series of enzymatic modifications flavanonesdihydroflavonolsanthocyanins Along this pathway, many products can be formed : flavonols, flavan-3-ols, proanthocyanidins (tannins), polyphenolics.

BIOFLAVONOIDS

flavone, flavonol, flavanone, flavanonol 2-phenyl-benzo--pyronisoflavone3-phenyl-benzo--pyron

catechin

anthocyanidin High concentration of quercetin in in vitro causes DNA mutations in spite of this flavonoid prevents atherosclerosis, infarct 48

49ALKALOIDBoundary : contains atom which has base properties and become part of heterocyclic ringClassification : Base on the heterocyclic N ringBase on the plant source Base on biogenetic origin

PirolidinePiperidineQuinolineIsoquinolineIndol50Caharacteristics of Alkaloid Structure

Policyclic skeleton and substituen group are not varried

2. Nitrogen atom found as amine group (-NR2) or amide not as NO2 (nitro) or N=N- (diazo)

3. Oksigen substituen found as phenol (-OH), metoxy (-OCH3) or methylen dioxy (-OCH2-O) at para or para and meta position in aromatic ring

4. Substituen is frequently found

51THANK YOU FOR YOUR ATTENTION

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