VOLATILE OILS & RELATED TERPENES PHARMACOGNOSY-II PHR 205

Definition Volatile or essential oils, as their name implies, are volatile in steam. They differ entirely in both chemical and physical properties from fixed oils. They are secreted in oil cells, in secretion ducts or cavities or in glandular hairs. They are frequently associated with other substances such as gums and resins and themselves tend to resinify on exposure to air.

Volatile oil Fixed Oil Also called as an essential oil. Also called as natural non-volatile oil. Volatile oil can evaporate when placed under room temperature Fixed oils do not evaporate at room temperature They can be extracted easily by the distillation process They require some specific techniques for extraction. There is no spot (no permanent stain) left after evaporation Some type of spot (permanent stain) left after evaporation They are unable to undergo saponification Fixed oils can be easily sponified. Mixtures of cleoptenes & stearoptenes are termed as volatile oils Esters of higher fatty acids & glycerin are called as fixed oils. Posses high refractive index Posses low refractive index These are optically active. These are optically inactive. Their primary source is leaves,roots,in petals and bark. Their major source is seeds of the plant.

Preparation of volatile oils The principal methods used in the preparation of volatile oils from plants depend on: Distillation in water or steam. Scarification. Extraction with solvents. Enzymatic hydrolysis (for glycosidic volatile oils e.g. mustard oil). Enfleurage (extraction of oils used in perfumery).

Production and uses of volatile oils The total annual production of volatile oils is estimated to be in the region of 45,000 tones, worth approximately US$700 million. There are about 100 commercially valuable volatile oils directly derived from plants. Volatile oils are used for their therapeutic action , for flavoring (e.g. oil of lemon), in perfumery (e.g. oil of rose) or as starting materials for the synthesis of other compounds (e.g. oil of turpentine).

Therapeutic uses of volatile oils For therapeutic purposes they are administered as inhalations (e.g. eucalyptus oil), orally (e.g. peppermint oil), as gargles and mouthwashes (e.g. thymol) and transdermally (many essential oils including those of lavender, rosemary and bergamot are employed in the practice of aromatherapy). Those oils with a high phenol content, e.g. clove and thyme have antiseptic properties, whereas others are used as carminatives. Oils showing antispasmodic activity, and much used in popular medicine

Composition of volatile oils Volatile oils are generally mixtures of hydrocarbons and oxygenated compounds derived from these hydrocarbons. The odour and taste of volatile oils is mainly determined by these oxygenated constituents, which are to some extent soluble in water but more soluble in alcohol. Practically all volatile oils consist of chemical mixtures that are often quite complex; they vary widely in chemical composition. Almost any type of organic compound may be found in volatile oils (hydrocarbons, alcohols, ketones, aldehydes, ethers, oxides, esters, and others). “usually volatile oils are classified according to the type of organic compounds”. It is not uncommon for a volatile oil to contain over 200 components, and often the trace constituents are essential to the odor and flavor. The absence of even one component may change the aroma.

Biosynthesis and chemical composition Biosynthesis and chemical composition Chemical constituents of volatile oils may be divided into 2 broad classes, based on their biosynthetic origin: Terpene derivatives formed via the acetate-mevalonic acid pathway. Aromatic compounds formed via the shikimic acid-phenylpropanoid route. 1. Terpene derivatives: 2. Aromatic compounds:

Classification of Volatile Oils Example Source Hydro-carbon α-pinine Turpentine oil 2. Alcohol-volatile oil Linalool Peppermint oil 3. Aldehyde-volatile oil Cinnamaldehyde Cinnamon oil 4. Ketone-volatile oil Carvone Spearmint oil 5. Phenol-volatile oil Eugenol Clove oil

α-Pinine Cinnamaldehyde Linalool Carvone Eugenol

Classification of Volatile Oils Example Source 6. Phenolic-ether-volatile oil Safrole Nutmeg oil 7. Oxide-volatile oil Cineol Eucalyptus oil 8.Ester-volatile oil Menthyl acetate Oil of wintergreen 9.Peroxide-volatile oil Ascardiol Chenopodium oil 10. others Methyl salicylate

Safrole Cineol Menthyl acetate Methyl salicylate Ascardiol

Physical properties Although volatile oils differ greatly in their chemical constitution, they have a number of physical properties in common: They possess characteristic odors. They are characterized by high refractive indices (Refractive index measures the speed at which light passing through an essential oil is refracted). Most of them are optically active. Their density is generally lower than that of water (the essential oils of sassafras, clove, or cinnamon are the exceptions). As a rule, volatile oils are immiscible with water, but they are sufficiently soluble to impart their odor to water. The aromatic waters are dependent on this slight solubility.

Chemistry of volatile oil: Volatile oil consists of the following compounds: Terpene type compounds Aromatic type compounds Terpene type compounds: Terpenes are defined as natural products whose structure may be divided into isoprene units. These units arise from acetate-mevalonate pathway and are branched chain of 5-carbon units containing two unsaturation in head and tail fusion.

Follwing types of isoprenes are usually found- Monoterpene(C10H16): composed of 2 isoprene units Sesquiterpene(C15H24): composed of 3 isoprene units Diterpene(C20H32): composed of 4 isoprene units Triterpene(C30H48): composed of 6 isoprene units Tetraterpene(C40H64): composed of 8 isoprene units  Most of the volatile oil are composed of monoterpenes are classified into two groups. Acyclic; e.g. Geraniol

Cyclic monoterpenes are classified into- i.Monocyclic; e.g. Limonene ii.Dicyclic; e.g. α-pinine

Aromatic type compounds: Volatile oils having benzene ring with a propane side chain belong to these group of compounds. These type of compounds are generally biosynthesized by a Shikimic acid pathway; e.g. Cinnamaldehyde, Anethole

Turpentine oil Common names: Turpentine , gum turpentine, gum thus, turpentine oil , turpentine balsam Biological name: Turpentine oil or spirits of turpentine is the volatile oil obtained by distillation of Oleoresin present in Pinus palustris and other species of Pinus Family: Pinaceae Habitat: Portugal, Greece, Poland, France Constituents: It contains-(65%)α-pinine, (30%) β -pinine and 5% other including α-terpenene, β-terpenene Uses: Carminative; Stimulant; Tonic; Expectorant; Diuretic; Antiseptic; Counter irritant; Flavouring agent, as wax solvent.

Functions of volatile oil Functions in plants: They sometimes protect plants from harmful effects of animals and insects. Sometimes helps in pollination through insects Therapeutic function: Carminative; e.g. clove oil Antispasmodic; Bitter almond oil Antibacterial; e.g. Pine tar oil Aromatic stimulant; e.g. peppermint oil Anthelmintic; e.g. thymol Expectorant e.g. turpentine oil Antiseptic; e.g. Eucalyptus oil Diuretic; e.g. Juniper oil Antipruritic (used to relieve itching.); e.g. Camphor Pharmaceutical use As a flavoring agent As a preservative  

Uses of drugs containing essential oils Uses of drugs containing essential oils Pharmacy Perfumery Food technology Miscellaneous industries (as starting materials for the synthesis of the active principles of medicines, vitamins, and fragrances).

Definition Terpenes - class of >20,000 compounds containing carbon atoms in multiples of five Terpenoids - oxygen-containing terpenes or oxygenated derivatives, e.g. alcohols, aldehydes, ketones, phenols, oxides & esters. Terpenoids contain only the most volatile terpenes (i.e. molecular weight is not too high)- mono and sesquiterpenes The name "terpene" is derived from the word "turpentine" Terpenes and terpenoids are the primary constituents of the essential oils of many types of plants and flowers.

Different types of Terpenes

“Head” - branched end of isoprene “Tail” - unbranched end of isoprene The basic molecular formulae of terpenes are multiples of that, (C5H8)n where n is the number of linked isoprene -Isoprene-2-methyl-1,3-butadiene- units. This is called the isoprene rule or the C5 rule. Compounds containing carbon atoms in multiples of 5 suggest a C5 building block - isoprene units linked in a “head-to-tail” fashion 2-methyl-1,3-butadiene “Head” - branched end of isoprene “Tail” - unbranched end of isoprene

Finding the isoprene building block - cyclic compounds Finding the isoprene building block - sesquiterpenes (C15)

Finding the isoprene building block - triterpenes (C30) Squalene has a natural and vital part in the synthesis of all plant and animal sterols, including cholesterol, steroid hormones, and vitamin D in the human body

Finding the isoprene building block - tetraterpenes (C40) Lycopene's eleven conjugated double bonds give it its deep red color and are responsible for its antioxidant activity. Lycopene is responsible for the red color in tomatoes and watermelon -carotene is the compound that causes carrots and apricots to be orange

Classification of Terpenes Hemiterpenes consist of a single isoprene unit. Isoprene itself is considered the only hemiterpene, but oxygen-containing derivatives  are hemiterpenoids such as prenol (found in citrus fruits, cranberry, grapes, raspberry, blackberry, tomato, white bread…)  and isovaleric acid (found in in essential oils). Monoterpenes consist of two isoprene units and have the molecular formula C10H16. Examples of monoterpenes are: geraniol, limonene and terpineol. Sesquiterpenes consist of three isoprene units and have the molecular formula C15H24. Examples of sesquiterpenes are: humulene, farnesenes, farnesol.

found in the essential oils of Humulus lupulus  humulene Prenol  found in the essential oils of Humulus lupulus  isovaleric acid limonene terpineol a strong smell of oranges found in pine oil

Diterpenes are composed of four isoprene units and have the molecular formula C20H32. Examples are cafestol, kahweol, cembrene and taxadiene (precursor of taxol). Diterpenes also form the basis for biologically important compounds such as retinol, retinal, and phytol. They are known to be antimicrobial and antiinflammatory. Sesterterpenes, terpenes having 25 carbons and five isoprene units, are rare relative to the other sizes. An example of a sesterterpene is geranylfarnesol. Triterpenes consist of six isoprene units and have the molecular formula C30H48. The linear triterpene squalene, the major constituent of shark liver oil. Tetraterpenes contain eight isoprene units and have the molecular formula C40H64. Biologically important tetraterpenes include the acyclic lycopene, the monocyclic gamma-carotene, and the bicyclic alpha- and beta-carotenes. Polyterpenes consist of long chains of many isoprene units. Natural rubber consists of polyisoprene in which the double bonds are cis.

Taxadiene from enzymes Retinol is one of the forms of vitamin A taxol used in cancer chemotherapy

EXAMPLES OF TERPENES LIMONENE MENTHOL BORNEOL SESQUITERPENES

i. LIMONENE Structural classification: Monocyclic terpene Functional Classification: Unsaturated HC Occurrence: Citrus fruit

ii. MENTHOL Structural classification: Monocyclic with hydroxyl group Functional classification: Alcohol Occurrence: Peppermint

iii. BORNEOL Functional Classification: //// Occurrence: Cinnamon

iv. SESQUITERPENES (Contain 3 isoprene units) Acyclic – E.g. Farnesol Monocyclic – E.g. Bisobolol Bicyclic e.g. Chamezulene (Chamomile)