Phytochemistry (PPC 303) Lecture 1

Phytochemistry (PPC 303) Lecture (1)

• Volatile oils, essential oils, and ethereal oils are discussed.
• Volatile oil is obtained by steam distillation of plants or other methods.
• Most volatile oils come from plants, but some come from animals (e.g., musk from male deer, ambergris from whales).
• Volatile oils occur in all plant tissues and are localized to specific plant parts, such as petals, barks, leaves, stems, and fruit rind.

Definition

• Volatile oils are obtained by steam distillation of plants or by alternative methods.

Occurrence of V.O. in plant tissues

• Volatile oils occur in all parts of the plant.
• They can be found in specific plant parts, including:
  • Petals of flowers (e.g., rose)
  • Barks and leaves (e.g., cinnamon)
  • Pericarp of fruits (e.g., Umbelliferous fruits)
  • Stems and leaves with glandular hair (e.g., mentha)
  • Petals and rind of fruits and leaves (e.g., orange)

Forms & Combination of Volatile Oils

• Volatile oils can exist in a free form.
• They can combine with a sugar to form glycosides.
• They can combine with gums, resins or both, to form oleo-gums, oleo-resins, or oleo-gum resins.

Medicinal, pharmaceutical and commercial uses of V.O.

• Used in aromatherapy (external and internal).
• Used in perfume industries, cosmetics, and soap manufacture.
• Found in spices and condiments with preservative action.
• Used as flavoring agents in pharmaceutical industries.

A- External application

• Volatile oils are easily absorbed through the skin and mucosa due to their lipoid solubility.
• They can cause a hyperemic effect, improving local blood circulation (and potentially influencing internal organs).
• Depending on the degree of skin irritation, they can act as rubefacients (increasing blood flow) or vesicants (causing blisters).

Benefits of Hyperaemic effect

• Cardiac ointments for angina pectoris pain relief.
• Skeletal muscle pain relief (e.g., using eucalyptus oil, gaultheria oil, or camphor oil in liniments, ointments, or gels).
• Hair growth & re-growth improvement by improving blood flow and strengthening blood vessels (using clove bud oil and rosemary oil).

Anti-inflammatory effect

• Essential oils exhibit anti-inflammatory effects, partly due to antimicrobial action.
• Examples include chamomile and arnica flower oils.

Antiseptic effect

• Volatile oils have lipoid solubility, dissolving fats in bacterial cell walls.
• Phenol coefficient expresses the bactericidal activity of a compound compared to phenol.

Insecticide and insect repellent effect

• Citronella oil (from lemon grass) is used as a mosquito repellent.

B-Internal applications

• Inhalation of essential oils can quickly deliver them into the bloodstream, effective for expectoration.

• Effects include secretolytic effect (breaking down secretions), secretomotor effect (moving secretions), and bronchospaasmolitic effect.

  • Examples include anise, thyme, and peppermint oils.

• Stimulating secretions of digestive glands (appetite stimulation) via saliva and gastric enzyme stimulation. Stimulation of bile production (choleretic effect).

Carminative effect

• Essential oils like anise, basil, fennel, chamomile, and coriander relieve intestinal and bladder spasms.

Circulation stimulating effects

• Some volatile oils, like camphor, rosemary, and lavender oils, stimulate respiration and circulation.

Undesirable side effects of V.O.

• Allergic effect: exposure to terpene hydrocarbons can lead to allergic reactions due to the formation of hydroperoxides during storage.
• Phototoxic and photosensitizing effect: Some volatile oils containing furanocoumarins can cause phototoxic reactions (erythema, increasing blood flow causing blisters) after initial exposure.
• Abortion-provoking effect: Misuse of essential oils with uterine-stimulating properties can lead to abortion.
• Carcinogenic effect: some volatile oils can harm human lymphocytes and have liver damaging carcinogenic activity (e.g., beta-asarone and safrole).

Estragole (methyl chavicol)

• Present in some fennel oils.
• Has carcinogenic and mutagenic properties.
• Use should be avoided, especially by children.

Methods of preparation of V.O.

• Hydrodistillation: Using heat to separate water and volatile oils. - Plant material is comminuted before distillation.

• Scarification and expression: Expressing oils out of materials with glands that produce volatile oils (e.g., citrus peels).

• Extraction with solvents: Using volatile solvents to extract volatile oils, useful for delicate constituents.

• Enzymatic hydrolysis: Using enzymes to release odoriferous substances from glycosides.

• Supercritical fluid extraction (SFE): Using high pressure and temperature to separate oils from botanical materials .

Disadvantages of distillation

• High temperature in the presence of water causes hydrolysis, removing water from tertiary alcohol.
• Volatile amines and volatile degradation products pass over during distillation, contaminating the volatile oil product.
• Loss of water-soluble components retained in the water-phase is lost during the separation process.

2. Scarification and expression method

• Useful for thermolabile volatile oils.
• Extracts oils from glands in the outer layers of fruit (rind).
• Example: orange and lemon oils.

3. Extraction with solvents method

• Useful for thermolabile volatile oils.
• Used to extract volatile oil, example, in small quantities in flowers (roses, jasmine, violet).
• Using light petroleum extracted by percolation (continuous method).

4. Enfleurage Method for extraction with cold fat

• Method to extract volatile oils (e.g., jasmine) using cold fat, which has high absorption capacity. - Fat acts as solvent to absorb fragrant compounds, and the plant material is regularly renewed.

5. Supercritical Fluid Extraction (SFE)

• Method using high pressure and temperature to extract volatile oils in a pressure vessel. - Uses gas (e.g., CO2) capable of high penetration and solubilization.

Physical methods of examination of V.O.

• Color: Most oils are colorless when fresh. Colors may develop with exposure to air. Rectification can make volatile oils colorless.
• Odor: Characteristics vary.
• Taste: Characteristics vary.
• Specific gravity: Relative Density: indicating chemical composition (comparing density to water).
• Optical activity: Rotatory power detects adulteration, using differences in rotation angles. Example, lemon oil differs with turpentine oil.
• Refractive Index: Measuring how light changes speed through the volatile oil. Detects extraneous substances (e.g., alcohol).
• Congealing point: The temperature when the oil solidifies, which indicates presence of certain constituents that crystallize easily.

Chemistry of Volatile Oils

• Volatile oils are broadly classified into:
  • Terpenes (related to isoprene units, acyclic or cyclic).
  • Aromatic compounds (e.g., phenyl propanoids).
  • Nitrogen, sulfur, and lactone-containing compounds.

How Terpenes are Synthesized

• Mevalonic acid pathway produces isoprene units, which leads to hydrocarbon terpenes.
• Oxygenation of terpenes can lead to alcohols and other natural compounds.

Structure of Terpenes

• Terpenes are based on the isoprene unit and are characterized by the number of isoprene components.
  • Monoterpenes (2 isoprene units)
  • Sesquiterpenes (3 isoprene units)
  • Diterpenes (4 isoprene units) etc.

How to Synthesize Phenyl Propanoids

• Shikimic pathway produces cinnamic and p-hydroxycinnamic acid, from aromatic amino acids phenylalanine and tyrosine.
• These compounds contain a phenyl ring and propane side chain, sometimes abridged.

This quiz covers the key concepts of volatile oils, essential oils, and ethereal oils in phytochemistry. Learn about their extraction methods, occurrence in various plant tissues, and specific examples of plants containing these oils. Test your understanding of how these compounds contribute to the chemistry of plants.