The origin of natural aromatic materials


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The origin of natural aromatic materials from Personal Care magazine, Sept. 2011, pp. 73-80

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The origin of natural aromatic materials

  1. 1. Murray Hunter, University Malaysia Perlis, Malaysia FRAGRANCES The origin of natural aromatic materialsPlants contain a number of chemicalsbased on simple sugars and carbohydrates. Oxygen PhotosynthesisThese include fatty acids, lipids, amino Polysaccharides andacids, nucleotides, nucleic acids and disaccharidesproteins, etc. Some chemicals act asprimary metabolites which are vital to aplant’s life and survival or act as precursors Carbon Pentose phosphate pathway dioxide Glycosefor secondary metabolites and areconcerned with the plant’s interactions withthe surrounding eco-system, principallyacting as deterrents and attractants topathogens. Some of these chemicals Glycolysismake up essential oils which comprise Nitrates andof materials from a number of chemical mineral salts Erythrosegroups. Only as recently as fifty years 4-phosphateago the isolation of natural materialshad to be undertaken physically, by Phosphoenolchemical reactions to identify compounds. pyruate Shikimate Water pathwayThis limited the ability to identify more than Aromaticjust a few compounds in essential oils. amino acidsThe advent of spectroscopic methodscreated a revolution in natural product 6-deoxyxylulosechemistry which enabled the identification Pyruvate Hydroxy-of trace constituents and more detailed benzoic acidunderstanding of the chemistry of plants. The spectrum of odorous substances isvery narrow where only materials with a Amino acids and nucleotidesmolecular weight below 300-400 and anappreciable vapour pressure at room Isoprenoidstemperature have noticeable odours to (terpenoids)humans. Relatively few organic materials KREBS CYCLE Alkaloidshave pleasant odours, with the majorityof materials diffusing acetic, propionic, Mevalonic acidbutyric and lactic odours. Essential oils are not the only chemicalsubstances found in plants. Metabolites, Phenylpropanoidslike fats, fatty acids, waxes, oils,coumarins, anthraquinones and alkaloids Acetyl-CoAare also soluble in ethanol and other Complexsolvents and can be extracted by alkaloidsdistillation. Thus, materials extracted fromplants contain both volatile aromatic and Flavanoids Triglyceridesodourless substances. Generally, essential oils can bephysically distinguished from other Malonyl-CoAcompounds because a drop of a volatile oilon paper will completely evaporate, unlike Complex Complexfatty oils. Essential oils are generally a pale isoprenoids Polyketides flavonoidsto clear or slightly yellowish liquid, mostly (terpenoids)insoluble in water, with specific gravities Metabolites: I Primary I Secondarybetween 0.8 to 1.2. The odour of anessential oil will resemble the source flora, Figure 1: The plant as a chemical factory. September 2011 P E R S O N A L C A R E 73
  2. 2. FRAGRANCESmade up of a large number of constituents,sometimes into the hundreds. Someessential oil odours are dominated by a Shikimatesingle constituent, like citral in lemongrass p-aminobenzoate Aromaticoil, but most oils rely on a complex mixture amino acidsof constituents to provide the overall odourprofile. Chorismate Constituents in essential oils can beput into three classes: p-hydroxybenzoate Those greater than 1%, which are main constituents. Those present in parts per thousand, Flavonoids Prephenate which are minor constituents. And those less than one part per Anthranilate thousand, which are trace constituents. Phenyl-C3Given the vast number of different odours compoundsand chemical structures in essential oils, Tryptophanmost compounds are biosynthesised by Phenylalaninea small number of metabolic pathways.Although these pathways are common Cinnamicto all plants, small genetic differences acidsintroduce important differences in thesepathways, thereby producing variances in Tyrosinebiosynthesis.1 These numerous reactionsand transformations create exotic fragrance Phenyl-C1blends, which we call essential oils. compounds AlkaloidsThe plant metabolismA plant is metaphorically like a “chemicalfactory”, producing a wide range of Figure 2: The shikimic acid pathway.complex compounds to promote growthand health (primary metabolites), some importance as an intermediate for the synthesis and the production of hydroxy-for defence and co-existence with the Krebs cycle. This process can be carried benzoic acid through the shikimatesurrounding ecosystem (secondary out both aerobically and anaerobically. pathway, discussed later in this section.metabolites) and some chemicals for Pyruvate is carried through to the Krebs Finally a pathway, polyamine biosynthesisreasons that are still unknown to science. cycle which is a series of enzyme catalysed through 6-deoxyxylulose is known toPlants are complex, open systems chemical reactions, not exclusive to plants, produce a number of precursors for thewith both positive and negative entropy. but all living cells. Pryuvate is combined synthesis of terpenoids.2Plants, through processes not fully with coenzyme A, to form acetyl CoA, The factors that influence theseunderstood, are dynamic systems under carbon dioxide and nucleic acids, through complex reactions very briefly summarisedcontinual change, utilising sunlight, carbon the route of nicotinamide adenine above are still the subject of researchdioxide, oxygen, moisture and soil nutrients dinucleotide (NAD), a coenzyme and and thorough understanding.4 Primaryin the synthesis of various chemical FADH2, an energy-carrying molecule to metabolites provide the precursors forcompounds (see Fig. 1).2 form macromolecules comprising aromatic chemical production in plants. A plant metabolism is the set of deoxyribonucleic acid (DNA) and ribonucleic They are also the precursors of a numbermetabolites which can be categorised acids (RNA), known as ATPs. ATPS play of other compounds that are present inas primary and secondary. The primary a role in signalling and carrier molecules plants. These types of compoundsmetabolites are concerned with the basic for amino acids in protein synthesis. include:life functions of the plant and provide Mevalonic acid is also formed from acetyl Carbohydrates.precursors for the production of secondary CoA through the route of 3-hydroxy-3- Lipids.metabolites. Secondary metabolites are methylglutaryl CoA (HMG-CoA), which goes Amino acids.concerned with the plant’s interactions to form terpenoid and steroid compounds. Nucleotides.with the surrounding eco-system and Coenzyme A breaks down to form malonyl Lectins.principally act as deterrents and attractants CoA which plays a role in fatty acid and insects. polyketide synthesis. And various enzymes. The two most important primary Another pathway, the pentosemetabolite processes are the glycolysis phosphate pathway also processes The metabolic pathwaysprocess and the Krebs or TCA (tricarboxylic sugars through oxidation and synthesis. One of the functions of primaryacid) cycles. Through the breakup of This is an alternative pathway to glycolysis, metabolites is to provide feed-stocksglucose into other compounds, energy although it also involves the oxidation of for secondary metabolite also produced. The glycolysis process glucose. Through different processes of This is undertaken through three primaryoxidises glucose produced in the plant dehydrogenation, hydrolysis, oxidative pathways. The mevalonic acid pathway,by photosynthesis, releasing both energy decarboxylation and isomerisation assisted sometimes called the terpenoid pathway,and a series of chemicals, of which by enzymes, a number of precursors are is responsible for the synthesis of a widepyruvate (pyruvic acid) is of prime produced for fatty acid and amino acid range of metabolites and terpenoids.74 P E R S O N A L C A R E September 2011
  3. 3. The metabolites produced through this Chemically, terpenes, which are verypathway include the phytol chain found in important in flavour and fragrances, arechlorophyll and plant growth regulators or very similar to terpenoids, where methylpseudo hormones, gibberellins and abscisic groups are adjusted or removed or oxygenacid, discussed above. The mevalonic acid atoms added.pathway is an enzymically controlled route The shikimic acid pathway producesto the formation of mevanolic acid, which precursors for a number of metabolites,through a number of steps synthesises amino acids, plant regulators, alkaloidesinto isopentenyl pyrophosphate (IPP) and and phenolic compounds. This pathwaydimethylallyl pyrophosphate (DMAPP) is unique to plants and continues on fromwhere they are oxidised, reduced or the pentose phosphate pathway, wherehydrated into a wide range of terpenoids carbohydrate precursors derived fromand steroids. Recently, a mevalonic acid glycolysis as erythrose-4-phosphate reactindependent pathway to IPP and DMAPP with phosphoenol pyruvate to form shikimichas been found utilising deoxyxylulose acid.6 The shikimic acid pathway breaksphosphate and methylerythritol phosphate into a number of branches as shown inas precursors.5 The following groups of Figure 2.2terpenoids are produced by these methods: Approximately 20% of all carbon fixed Hemiterpenoids: consist of a single in a plant’s leaves is processed through isoprene unit. Example: phenol. this pathway, which makes up around Monoterpenoids: consist of two isoprene 30% of a plant’s dry weight.7 Shikimic acid units. Examples: geraniol, limonene undergoes hydrolysis to break off pyruvic and terpineol. Sesquiterpenoids: consist of three acid and through a number of other steps converts to chorismic acid, a precursor Combat isoprene units. Example farnesol. for a number of compounds. Chorismic Diterpenoids: composed of four isoprene units. Example: cafestol. acid is a precursor of salicyclic acid, a plant hormone. Chorismic acid also dandruff the Sesterterpenoids: comprise of five isoprene units. Example: cericerane. undergoes a Claisen type rearrangement to form prephenic acid, which converts into gentle way. Triterpenoids: comprise of six isoprene tyrosine and phenylalanine. Tyrosine, an units. Example: squalene. amino acid, is believed to be involved in Tetraterpenoids: comprise of eight the photosynthesis process, acting as isoprene units. Example: gamma- an electron donor in the chloroplasts to carotone, alpha- and beta-carotenes. reduce oxidised chlorophyll, the signal Polyterpenoids: long chains of many transduction process in proteins, and isoprene untis. Example: polyisoprene to assist in producing insect deterring NEW! in rubber. glucosinolates. Tyrosine is also a precursor dermosoft® decalact Environment changes Plant The new dermosoft® decalact Heat Drought is 100 % natural while providing the Signals UV stress same performance as conventional Insect elicitors Flood and waterlogging antidandruff actives. And what´s Lack of nutrients more, it´ll leave behind nothing but Physical protection Plant damage Direct and a pleasant feeling - it is kind to your Increase/decrease indirect Plant architecture scalp and to your pocket. Dual action Leaf shapes Herbivory (predators) Increase/ decrease Colours production Insects Special features Vary (ie spikes etc) Avoid “dangerous” production metabolites and Secondary Produce counter dissipation metabolites metabolites (ie digestion Responses Repellents enzymes) Signal Attractants Time/spatial Ingestion inhibitors avoidance Taste Camouflage odours Direct and indirect responses Plant repair intelligence behind beautyFigure 3: A plant’s defence system.
  4. 4. FRAGRANCESto the pigment melanin. Phenylalanine, Acetyl CoAalso an amino acid derives a number offlavonoids, lignin and coumarins, and also Mevalonate pathwayassists in producing insect-deterring 3-methylglutaryl CoAglucosinolates, similar to tyrosine. (HMG-CoA) Deoxyxylulose Through another path, anthranilate and phosphate pathwayits derivatives are produced. Little is knownabout the purpose of anthranilates in Mevalonateplants, although they occur as both methyl Glyceraldehydeand acid forms in many plants. phosphateAnthranilates are precursors for alkaloids Isoprenyldiphosphate (IPP) andand tryptophan. Tryptophan is another C5 (1 isoprene unit) dimethyllallyldiphosphate (DMAPP)amino acid and is a building block for Pyruvateproteins and a precursor for niacin, anumber of alkaloids and indole. Finally Monoterpenes Geranyl pyrophosphatethrough the shikimic acid pathway, a (GPP)number of phenyl propanoid compounds C10 (2 isoprene units)are formed through cinnamic acid by Sesquiterpenes Farnesylpyrophosphateelimination of ammonia phenylalanine. (FPP)Common phenyl propanoids include methyl C15 (3 isoprene units)chavicol, methyl eugenol, eugenol, methyl Diterpenes andcinnamate and vanillin. Phenyl propanoid carotenoids Geranyl geranylaccumulation in the plant metabolism is pyrophosphate C20 (4 isoprene units)still an area where little is known. (GGPP) Flavonoids and anthocyanins arepigments and phenolic compoundsresponsible for the colours of flowers in Other terpeneshigher plants. Flavones provide the yellow (Triterenes and tetraterpenes) Iononesand orange colours and the anthocyanins C30+ (6 isoprene units +) (from degraded carotenoids)are the source of red, violet and blues.Flavonoids play some role in attracting Figure 4: Mevalonate and deoxyxylulose phosphate pathways to terpene formation.insects to feed and pollinate, while othershave bitter tastes and repel insects like compounds and also from storage of constituents of essential oils originate andcaterpillars. Flavonoids are also considered foliage after harvesting lead to the also a number of other economic products.antioxidants. Another important small group formation of a number of compounds. The secondary metabolites are unique toof polyphenols are the tannins that bind These trace compounds, some desirable each plant species, unlike the primaryand precipitate proteins and may assist in while others undesirable will contribute to metabolites which are common acrossthe repair of damaged plant tissue, in the odour profiles of a number of essential the flora genus.conjunction with phytoalexins, which are oils. Unsaturated C6 aldehydes can arisereported to have antimicrobial properties.8 in green tissue wherever they are cut, Secondary metabolites andTannins are very important flavonoids in damaged or attacked by insects, through plant defence systemsteas, wines and some fruits. Tannins are enzymic degradation of linolenic acid.11 The secondary metabolites, primaryused in the preparation of leather, the The degradation of lipids in plants leads to terpenoids, alkaloids, phenolics andmanufacture of colours and as dietary the formation of short chain alcohols and nitrogen compounds evolve within thesupplements. aldehydes, such as the n-hexanol and metabolism and are utilised to improve Saponins are glycosides of steroids, cis-3-hexanol, compounds that provide a plant’s chances of survival againststeroid alkaloids or triterpenes found green notes to an essential oil. Only with herbivory, primarily insect predators.primarily in the outer tissue of plants as a much more sensitive analytical equipment Plants utilise a number of attributeswaxy protective layer, although they are over the last few last years have volatile against predators which include physicalalso found in other parts including the constituents contributing to the flavour of characteristics, such as surfaceroots.9 Many saponins are toxic and fruits and vegetables been discovered. protections,12 the production of complexthought to be part of the metabolism to However, their enzymic pathways are often polymers that inhibit digestion of thedeter insect predators. Saponins are not still unknown. In some plants, essential plant,13 the production of insolublefound in all plants. Within the last few oil constituents are free within or bound terpenoids to inhibit digestion, theyears a number of medical and industrial with glycosides within the plant. production of toxins through the alkaloids,uses have been found for saponins. Some The pathways create the through-fare and the production of volatiles to attractof the existing uses include foaming agents from which the primary metabolites predators of the insect herbivores.14in soft drinks and beer, fire extinguishers, produce a set of secondary metabolites Conversely, insect herbivores utilise aphotographic emulsions, and food primarily concerned with the plant’s number of counter measures to overcomesweeteners. In the medical field, saponins interaction with the immediate plant defences such as detoxificationare used for cough medicines and environment. The secondary metabolite of toxic compounds,15 avoidancecholesterol. Research is ongoing utilising compounds concern themselves with mechanisms,16 sequestration of poisons18saponins to fight cancer.10 defences against predators, parasites, and adulteration of the gene pattern.19 Remnants and artefacts from the diseases, interspecies competition and Multiple defence systems are requiredpathways and degradation of fatty acids, facilitate the reproductive processes. It is because of different parts of a plant20 andamino acids, nitrogen and sulphur from the secondary metabolites that the different types of herbivory.21,22 These76 P E R S O N A L C A R E September 2011
  5. 5. FRAGRANCESdefences also assist the plant during timesof stress due to droughts, water logging, Estersintensive UV radiation and plant damage.In the reproductive cycle, plants emitaromatic odours to attract insects to assist Transacylasein pollination. An overview of the plant (coenzyme)defence system is depicted in Figure 3.2 Within the eco-system, plants andinsects interact, co-exist and competecontinuously in very complex ways. This is Acids (carboxlic) Alcoholsan evolutionary process as both plants and and acyl CoAinsects modify their defences and attackstrategies continually. Therefore from the Dihtdrofolate reductase Dihtdrofolate reductaseplant perspective, different chemical (coenzyme) (coenzyme)defences will be utilised at different timesto meet these evolving threats andstresses.23 Thus as plants grow, they Aldehydes andchange in leaf, branch and other physical ketonescharacteristics, including the growth offlowers and fruits which involves certain Figure 5: The acetyl coa pathway for the biosynthesis of aldehydes, alcohols and esters.chemical changes within the plantmetabolism, where certain insects can themselves to form various aromatic Terpene hydrocarbonstake advantage.24 This is an important compounds. Methane, a colourless and Terpenes are a very large group of plantconsideration in essential oil production as odourless gas, is the simplest hydrocarbon. hydrocarbons formed by polymerisation ofthe desired oil constituent profile may only Some hydrocarbons are non-terpenoid and five carbon atom units (isoprenes) thatdevelop during a particular part of the plant exist as short chain alcohols and aldehydes form in both chains and rings. They maylifecycle.25 formed through degradation of be reduced and oxidised into a vast array phospholipids and fatty acids. Saturated of other compounds including alcohols,Aromatic compounds homologous straight chain structures are lactones, acids and aldehydes, thus thefound in plants alkanes and their unsaturated forms starting point of synthesis of the majority ofWith the exception of compounds that are alkenes. Alkenes can form as isomers, a aromatic compounds. Terpenes are presentproducts of catabolic breakdowns of lipids, molecule with the same chemical formula in the resinous foliage of leaves. Terpeneamino acids, fatty acids and terpenoids, with the same bonds between atoms, but compounds are heavier than diterpene andthe plant metabolism is directly responsible arranged differently. These are mostly as do not contribute to the odour of essentialfor producing aromatic compounds within a stereo isomers in the cis- and trans- form, oils, although they may be present.plant through a limited number of pathways where the two molecules appear as adiscussed above. Specific and unique “mirror” image of each other. Molecules Monoterpenesextensions of these pathways exist in with three carbon atoms form straight Monoterpene compounds are foundparticular plants, yielding specific aroma chains, where those with four carbons or in nearly all essential oils and have acompounds found in certain plants. In more can form either straight or branched structure of ten carbon atoms (twoaddition there are also a number of chains. Terpenoids usually have a carbon isoprene units) with at least a doublearomatic compounds found in fruits and base of 10, 15, 20 or 30 atoms, where bond. They quickly react to air and heatvegetables. five carbon atoms are called an isoprene and consequently lack stability and long Through the plant metabolism, essential unit. Various types of terpene compounds shelf life as they are quickly oxidised.oils comprise a large number of volatile can be classified according to the number Monoterpenes are present in citrus,terpenoid and non-terpenoid compounds of isoprene units they contain as Table 1. conifers, herbaceous plants as well aswhich are based on hydrocarbons and lists. vegetables and fruits. Monoterpenes areoxygenated derivatives, although some A single isoprene unit is a hemiterpene, formed through the mevanolate pathway bycontain nitrogen or sulphur derivatives. when two isoprene units link together the conversion of methylallyl pyrophosphateThe hydrocarbons are connected by single, they form a monoterpene, three form a with isopentenylpyrophosphate (IPP) todouble or triple bonds to form higher sesquiterpene, four form a diterpene, form geranyl pyrophosphate, the precursormolecular weight hydrocarbons, through and so on. of monoterpenes (Fig. 4).2 Compoundsrings or chains. Oxygen, hydrogen, nitrogen, The types of aromatic compounds found like alpha-pinene and beta-pinene aresulphur, and other carbon atoms attach in plants are: formed through cyclisation from geranyl pyrophosphate through linaloyl Table 1. Classification of terpenoids according to isoprene units. pyrophosphate. A large number of monocyclic compounds, like myrcene Terpene Classification Carbon Atoms Isoprene Units are also derived through this route. Hemiterpenes 5 1 Sesquiterpenes Monoterpenes 10 2 Sesquiterpenes consist of 15 carbon Sesquiterpenes 15 3 atoms or three isoprene units linked to Diterpenes 20 4 each other, head to tail. This formation Triterpenes 30 6 can produce more than 300 different Tetraterpenes 40 8 hydrocarbon sesquiterpenes. Sesquiterpenes have great diversity in September 2011 P E R S O N A L C A R E 77
  6. 6. FRAGRANCESconstruction, containing up to fourcarbocyclic rings. Sesquiterpenes are Primary sulphur reduction pathway Sulfatesynthesised from farnesylpyrophosphatewhich is condensed from Minor sulphurgeranylpyrophosphate, derived from ATP reduction pathwayisoprenyldiphosphate (IPP) and sulphurlyasedimethyllallyldiphosphate (DMAPP), along Adenylation APS kinasethe mevalonate pathway. Through furtheroxidative transformations, a number ofother terpene compounds are formed Adenosin 3’-phosphate(Fig. 4).2 5’-phosphosulphate 5’-phosphosulphate (APS) (PAPS)Ionones APS reductaseIonones and damascenones are potentaroma compounds derived from degrading Phosphorisedof high molecular weight terpenes orcarotenoids through oxidation. Carotenoids PAPS reductaseare found in a variety of plants and fruits, Ferrodoxin- Sulfiteespecially berries. dependent sulphite reductaseOxygenated compoundsOxygenated compounds contain oxygenmolecules within their structures.These include alcohols, aldehydes,amides, carboxylic acids, esters, ketones, O-acetylserine Sulfidenitro compounds and oxides. (thiol)lyasePhenols O-acetylserinePhenols are one of the three majorchemical groups in plants along with Cysteineterpenoids and alkaloids. Phenols originatefrom phenylalanine or tyrosine throughthe shikimic acid pathway. Phenylalanine Figure 6: The primary and minor sulphur reduction pathway.ammonia-lyase removes ammonia fromphenylalanine to produce trans-cinnamic way to alcohols.26 Fatty alcohols C8 (octyl, much more pungent than the otheracid. Cinnamic acid itself is not an caprylic) occur in citrus fruits with their aldehydes of the homologous group, whichimportant odourant but acts as a precursor corresponding esters and aldehydes. are extensively used in perfumery, i.e.,for numerous aromatic metabolites Alcohol C9 (nonyl, pelargonic) is found in benzaldehyde.including aldehydes, alcohols, lactones, orange and oakmoss. Alcohol C10 (decyl, Aldehydes are relatively unstableand esters, outside the phenolic group. capric) is found in orange and ambrette materials which are prone to oxidisation, Phenols are defined as any compound seed. Alcohol C11 (undecylenic) is found in polymerisation and acetal formation withinhaving molecules with one or more hydroxy the leaves of Litsea odorifera, and alcohol essential oils. Aldehydes, esters, alcoholsgroup bonded to a benzene ring. As such, C12 (lauric, dodecyl) is found in lime. and acids can be converted and can revertmany compounds including flavonols, Alcohols do not have the same pungency within plants through transformation andcatechins, anthrocyanins, isoflavones, as their corresponding aldehydes, although oxidation. These reactions are thought todihydroflavonols, chalcones, quercetin, as alcohols get higher in molecular weight be controlled through coenzymes. There isellagic and tannic acids, vanillin, caffeic their odour intensity increases, until a close interrelationship between acids,acid, curcumin, courmarins and lignans are nonanol C9, when they start to weaken aldehydes, alcohols and esters within thealso defined as phenols. Phenols oxidise again. Hydroxy hydrogen atoms of Krebs cycle originating from branchedeasily and are partly the reason why plant alcohols tend to carry some of the odour amino acids aldehydes are derived frommaterial darkens after cutting due to this characteristics of aldehydes, while corresponding acids through δ-oxidationreaction. Phenols in essential oils also maintaining the smoother alcohol notes.27 where it is decarboxylated. Through furtherdarken on exposure to air and tend to Due to the polarity of alcohols they tend to reduction the aldehyde will convert to itsoxidate. Phenols are acidic due to the be more soluble in water than most other corresponding alcohol and later undergo–OH group in the molecule. In plants, aromatic compounds. Alcohols transform esterification. This can reverse where thephenolic compounds usually couple into other compounds including their aldehyde can oxidise to a correspondingthemselves with glucosyl compounds. corresponding aldehydes, acids and acid, later leading to the conversion to esters through methanol dehydrogenase odd-chain esters.29 This process is capableAlcohols catalylisation.28 of producing a wide range of aromaticAlcohols are very similar to phenols and compounds (Fig. 5).2aldehydes in structure. Alcohols are derived Aldehydesfrom aldehydes through dehydrogenase Aldehydes are found in fruits and many Estersactivation. They are also produced plants with their corresponding alcohols Esters are formed from acids and alcohols,through amino acids through oxidative and esters. Aldehydes have more pungent usually benzenoid, carboxylic anddecarboxylation in ripening fruits. Coenzyme odours than their corresponding alcohols. monoterpenic acids to form esters inA esters may also be transformed in some Long chain or aliphatic aldehydes are essential oils. Esters are also found in fruit78 P E R S O N A L C A R E September 2011
  7. 7. FRAGRANCESand vegetables. Examples of esters in that are found in plants. They are some role against pathogens and nitrogenessential oils are linalyl acetate, benzyl heterocyclic compounds and act as detoxication of plants.38 Little is also knownbenzoate and benzyl isobutyrate. Esters hormones in plants.36 about the sulphur pathways in plants, evenare formed through exiting the β-oxidation though sulphur is a necessary compoundacting on acetyl CoA during the Krebs Sulphur compounds for amino acid, proteins, polysaccharides,cycle.30 A few plants are known to contain volatile lipids and other sulphur containing sulphur compounds such as dimethyl secondary metabolites.39 SulphurKetones sulphide, dimethyl disulphide and compounds are believed to be derivedKetones are often present in small dimethylthiophene in garlic, onion, leek through a sulphur reduction pathwayquantities in plants and provide fruity and shallots. Blackcurrant (Ribes nigrum) (Fig. 6).2,40flavours in fruits. They are highly reactive and buchu (Agathosma betulina) also Volatile aromatic compounds are foundto air and heat and will easily convert to possess sulphur compounds, as well as within the Apiaceae (Umbelliferae),their corresponding acetals and alcohols. some citrus fruits, coriander, ylang ylang, Asteraceae (Compositae), Cupressaceae,Ketones are formed through the Krebs rose, peppermint, pepper, geranium, Hypericaceae, Lamiaceae, Lauraceae,cycle through β-oxidation of alcohols or chamomile, hops and davana.37 Little is Myrtaceae, Pinaceae, Piperaceae,with acyl CoA activation from carboxyl acids known about the purpose of sulphur Rutaceae, Santalaceae, Zingiberaceaeby hydrolysis causing decarboxylation. compounds in plants except they play and the Zygophyllaceae families. The wideLactonesLactones exist in essential oils asγ-lactones, a five membered cyclicring and δ-lactones, six memberedcyclic rings. Lactones are found in a sense of discoveryherbs, coffee, fruits, dairy products,with fruity, nutty and hay like odourprofiles. Macrocyclic lactones alsoexist in a number of essential oilsand are known as musk lactones.Coumarins, a lactone in tonkabean and hay is formed throughhydroxylation of trans-cinnamicacid to coumaric acid and thenglycosylation, which is stored incavities of plant tissue where itundergoes light-dependentisomerisation on rupture of the planttissue, crystals form.31 Furthersynthesis of coumaric acid will giverise to dihydrocoumarin. Coumarinsare widely used in fragrances forgrassy, hay-like green spicy notes.Another forms of lactones arebenzofluran derivatives foundas butylphthalides in celery andangelica.32Nitrogen compoundsMethyl anthranilate is a veryfreshly scented citrus-floral odour Discover what Honeywell’s Asensa® line scover what Honeywell’s Asensa® line of ofcompound. As secondary Personal Care products can do for you. ersonal Care products can do for you.metabolites, amines maybe generallyinvolved in growth regulation ofplants33 and, along with otheraromatic chemicals,34 methylanthranilate has been found to beboth a bird attractant and repellent.35Amines are very reactive to air anddarken on exposure, as well as beingphotosensitive. They can also react A sense of protection. A sense of feel. A sense of trust.with aldehydes to form aldimines.Amines are produced through adegradation pathway controlledby amine oxidase enzymes, withinthe amino acid pathway. Indole Discover how Honeywell Asensa can add value to your personal care products.and skatole are two other nitro Visit or call 1-866-245-3870compounds, aromatic compounds ©2011, Honeywell International Inc. All Rights Reserved. September 2011 P E R S O N A L C A R E 79
  8. 8. FRAGRANCESvariety of different plant metabolisms 23 Futujma P Slatkin M. Introduction, in Futujma P , ,producing a diverse range of aromatic Slatkin M, (Eds.) Coevolution 1983; Sunderland,compounds makes it difficult to Sinaver Associates Inc. MA. pp1-13.meaningfully classify volatile oil plants 24 Hochuli MD. Insect herbivory and ontogeny: howaccording to these families. Due to the do growth and development influence behaviour,current accepted methods of plant morphology and host use? Austral Ecology 2001;taxonomy chemical constituents play very 26 (5): 563-570.little role in plant family designation. PC 25 Porter NG, Smale PE, Nelson MA, Hay AJ, van Klink JW, Dean CM. Variability in essential Note: A version of this article was first published oil chemistry and plant morphology within a by the ASCC. Leptospermum scoparium population. New Zealand Journal of Botany 1998; 36: 125-33.References 26 Eskin NAM. Plant Pigments, Flavours and1 Pichersky E, and Gang DR. 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