B Pharmacy Sem 3: Pharmacognosy & Phytochemistry I

Subject 2. Pharmacognosy & Phytochemistry I

  1. Introduction to Pharmacognosy & Sources of Crude Drugs
2. Cultivation, Collection & Drying of Plant Drugs
3. Study of Carbohydrate & Glycoside-Producing Families (e.g. Fabaceae)
4. Study of Alkaloid-Producing Families (e.g. Solanaceae)
5. Volatile Oils & Resins: Occurrence & Extraction
6. Phytochemical Screening Methods & Preliminary Tests

Unit 1: Introduction to Pharmacognosy & Sources of Crude Drugs

This unit lays the groundwork for understanding pharmacognosy—the study of medicines derived from natural sources—and surveys the major categories and characteristics of crude drugs used in pharmacy.

1.1 Definition, Scope & Historical Perspectives

1.1.1 Definition of Pharmacognosy

• The branch of pharmacy that deals with the identification, extraction, characterization, and standardization of drugs obtained from natural sources (plants, animals, minerals).

• Integrates botany, chemistry, biochemistry, and pharmacology.

1.1.2 Historical Evolution

• Ancient Traditions: Use of herbal remedies recorded in Ayurvedic (c. 1500 BCE), Traditional Chinese Medicine, and Egyptian papyri.

• Renaissance to 19th Century: Systematic botanical classification (Linnaeus), isolation of first plant alkaloid (morphine, 1805).

• Modern Era: Phytochemical standardization, discovery of microbial natural products (penicillin), biotechnology and genomics.

1.2 Classification of Crude Drugs

1.2.1 Based on Source

• Plant Drugs: Leaves (Digitalis), roots (Glycyrrhiza), bark (Cinchona), seeds (Castor), flowers (Chamomile).

• Animal Drugs: Tissues or metabolic products (Cod liver oil, insulin from porcine pancreas, honey).

• Mineral Drugs: Inorganic compounds (Kaolin, Epsom salt, Glauber’s salt).

1.2.2 Based on Chemical Constituents

• Alkaloidal Drugs: Contain basic nitrogenous compounds (Atropa belladonna → atropine).

• Glycosidal Drugs: Yield sugars plus aglycone (Digitalis → cardiac glycosides).

• Resins & Volatile Oils: Terpenoid mixtures responsible for aroma (Peppermint oil, turpentine).

• Tannins & Phenolics: Astringent, antioxidant (Oak bark, green tea).

• Fixed Oils & Fats: Glycerides (Castor oil, olive oil).

1.3 Sources of Plant Drugs

1.3.1 Botanical Identification

• Taxonomy: Genus, species, family; binomial nomenclature ensures unambiguous naming.

• Macroscopy: Organoleptic evaluation—color, odor, taste, texture.

• Microscopy: Powder microscopy—cell types, starch granules, stone cells, trichomes.

1.3.2 Collection & Storage

• Optimal Harvesting Time: Depends on organ and active constituent (e.g., morning dew for volatile oils; post‑flowering for alkaloids).

• Post‑Harvest Handling: Removal of extraneous matter, drying (shade vs. sun), storage in airtight containers to prevent degradation.

1.4 Sources of Animal & Mineral Drugs

1.4.1 Animal-Derived Drugs

• Examples:

  • Insulin: Extracted from bovine or porcine pancreas.

  • Cochineal: Insect-derived red dye (carminic acid).

  • Sera & Vaccines: Antitoxins from horse serum.

• Quality Considerations: Purity, immunogenicity, ethical sourcing.

1.4.2 Mineral Drugs

• Examples:

  • Kaolin (hydrated aluminum silicate): antidiarrheal.

  • Magnesium sulfate (Epsom salt): laxative, emetic.

  • Calamine (zinc carbonate + ferric oxide): topical protectant.

• Purity Tests: Heavy metal limits, insoluble matter, pH.

1.5 Importance in Modern Pharmacy

• Lead Compounds: Natural products as templates (e.g., paclitaxel from Taxus brevifolia).

• Standardization: Ensuring batch‑to‑batch consistency via marker compounds (HPLC profiling, TLC).

• Regulatory Framework: WHO guidelines on quality, Good Agricultural and Collection Practices (GACP).

1.6 Key Points for Exams

• Define pharmacognosy and outline its multidisciplinary nature.

• Classify crude drugs by source and by major chemical group, with two examples each.

• Describe botanical identification techniques (macroscopy vs. microscopy).

• List three animal‑derived and three mineral‑derived drugs, including one quality test for each.

• Explain the role of standardization and marker compounds in ensuring drug quality.

Unit 2: Cultivation, Collection & Drying of Plant Drugs

This unit details the agricultural and post‑harvest practices critical for ensuring high quality and consistency of plant‑derived crude drugs.

2.1 Cultivation of Medicinal Plants

2.1.1 Site Selection & Soil Requirements

• Climate: Temperature, rainfall, and photoperiod must match the species’ native habitat.

• Soil Type: pH, texture, drainage, and organic‑matter content influence root development and phytochemical yield.

• Crop Rotation & Intercropping: Reduces disease pressure and maintains soil fertility (e.g., intercropping with legumes for nitrogen fixation).

2.1.2 Propagation Methods

• Sexual Propagation (Seeds): Genetic variability—used when diversity is desired or seeds are abundant (e.g., Digitalis).

• Asexual Propagation (Vegetative): Clonal uniformity—cuttings, layering, tissue culture for true‑to‑type plants and rapid multiplication (e.g., Aloe, Catharanthus).

2.1.3 Nutrient Management & Fertilizers

• Macronutrients: N–P–K ratios tailored to growth stage (e.g., higher nitrogen for leafy drugs).

• Micronutrients: Fe, Mn, Zn, Cu, Mo in trace‑element fertilizers to optimize enzyme‑mediated biosynthesis of active principles.

2.1.4 Pest & Disease Control

• Integrated Pest Management (IPM): Combines biological (predatory insects), cultural (crop sanitation), mechanical (traps), and chemical (botanical pesticides) strategies.

• Weed Management: Mulching and manual weeding to prevent competition.

2.2 Optimal Harvesting Practices

2.2.1 Determination of Harvest Time

• Physiological Maturity: Stage when active constituents peak (e.g., pre‑flowering for alkaloids, fruiting for gums).

• Diurnal Variation: Time of day affects volatile oil content (e.g., morning harvest for essential‑oil leaves).

• Seasonal Considerations: Harvest season tailored to species (e.g., winter rhizomes for ginsenosides).

2.2.2 Harvesting Techniques

• Manual Harvesting: Selective picking of leaves, flowers to avoid contamination.

• Mechanical Harvesting: For roots or bulk material; must minimize physical damage.

2.3 Post‑Harvest Handling & Drying

2.3.1 Cleaning & Pre‑Drying

• Removal of Foreign Matter: Soil, stones, insects, other plant parts.

• Washing: When necessary, followed by surface moisture removal to prevent microbial growth.

2.3.2 Drying Methods

2.3.3 Quality Control of Dried Drugs

• Moisture Content: ≤12% to prevent mold and enzymatic degradation.

• Physical Appearance: Color, texture, and fragmentation should match pharmacopeial standards.

• Organoleptic Tests: Odor and taste compared against authentic samples.

2.4 Storage & Stability

2.4.1 Packaging Materials

• Moisture‑Proof Containers: Glass jars, laminated pouches with desiccants.

• Light‑Resistant Packaging: Amber glass or opaque bags for photosensitive drugs.

2.4.2 Storage Conditions

• Temperature & Humidity Control: 15–25 °C, RH < 60%.

• Pest Control: Regular inspections; use of inert atmospheres or fumigation where necessary.

2.4.3 Shelf‑Life Determination

• Accelerated Stability Testing: 40 °C/75% RH for 6 months to predict long‑term stability.

• Marker Compound Assay: Periodic HPLC or TLC to monitor active‑constituent content.

2.5 Key Points for Exams

• Explain factors in site selection and soil preparation for a given medicinal plant.

• Compare seed vs. vegetative propagation in terms of genetic variability and uniformity.

• Describe how harvest time (diurnal/seasonal) affects phytochemical yield.

• List four drying methods, their operating conditions, and pros/cons.

• Detail storage requirements and methods used to determine shelf‑life of crude plant drugs.

Unit 3: Study of Carbohydrate & Glycoside‑Producing Families (e.g., Fabaceae)

This unit examines major plant families rich in carbohydrates and glycosides, focusing on their taxonomy, phytochemistry, characteristic constituents, and pharmaceutical applications.

3.1 Overview of Glycosides

• Definition: Compounds in which a sugar moiety (glycone) is bonded via a glycosidic linkage to a non‑sugar aglycone (genin).

• Classification by Aglycone Type:

  • Cardiac Glycosides (steroids): Digitalis glycosides

  • Anthraquinone Glycosides: Senna, Aloe

  • Cyanogenic Glycosides: Amygdalin (in almonds, seeds)

  • Flavonoid Glycosides: Rutin, quercetin derivatives

• Role of Sugar Moiety: Affects solubility, bioavailability, and enzyme‑mediated activation.

3.2 The Fabaceae Family (Leguminosae)

3.2.1 Taxonomy & Distribution

• One of the largest angiosperm families: ~750 genera, 19,000 species.

• Widely distributed; many species cultivated for food and medicine (beans, peas, licorice).

3.2.2 Characteristic Phytochemicals

• Polysaccharides: Galactomannans (e.g., guar gum from Cyamopsis tetragonoloba), used as viscosity modifiers.

• Saponin Glycosides: Soyasaponins (in Glycine max), exhibiting surfactant and immunostimulant properties.

• Flavonoid Glycosides: Isoflavone glycosides (genistin, daidzin) in soy, with phytoestrogenic activity.

3.2.3 Representative Drugs & Uses

3.3 Other Key Glycoside‑Rich Families

3.3.1 Rubiaceae

• Example: Cinchona spp. → Cinchona bark glycosides (quinine, quinidine) used as antimalarials and antiarrhythmics.

3.3.2 Lamiaceae

• Example: Salvia miltiorrhiza (Danshen) → Tanshinone glycosides; cardiovascular protectants.

3.3.3 Apocynaceae

• Example: Digitalis purpurea → Cardiac glycosides (digitoxin, digoxin) for heart failure.

3.4 Extraction & Isolation of Glycosides

1. Defatting: Non‑polar solvents (hexane) remove lipids.

2. Extraction: Polar solvents (methanol, ethanol, water) recover glycosides.

3. Hydrolysis: Acid or enzymatic cleavage to separate sugar and aglycone for identification.

4. Purification: Column chromatography (silica, reverse‑phase); crystallization of aglycone or glycoside salt.

3.5 Pharmacological Importance

• Prodrugs: Many glycosides require enzymatic hydrolysis in vivo to release active aglycone (e.g., cardiac glycosides).

• Excipient Use: Polysaccharide gums from Fabaceae as suspending and emulsifying agents in formulations.

• Dietary Supplements: Soy isoflavone glycosides in menopausal symptom management.

3.6 Key Points for Exams

• Define glycosides and distinguish glycone vs. aglycone.

• Describe characteristic constituents of the Fabaceae family and their pharmaceutical uses.

• Compare extraction strategies for glycosides vs. aglycones.

• Name two other glycoside‑producing families and their representative drugs.

• Explain the role of enzyme‑mediated hydrolysis in glycoside bioactivation.

Unit 4: Study of Alkaloid‑Producing Families (e.g., Solanaceae)

This unit examines plant families rich in alkaloids—nitrogenous secondary metabolites with potent pharmacological activities. We’ll focus particularly on the Solanaceae, then survey other key alkaloid‑bearing families.

4.1 Alkaloid Basics

4.1.1 Definition & General Properties

• Alkaloids are naturally occurring, basic, nitrogen‑containing compounds, often with significant physiological activity.

• Classification by Biosynthetic Origin:

  • True Alkaloids: Nitrogen derived from amino acids (e.g., tropane, isoquinoline).

  • Protoalkaloids: Nitrogen not part of a heterocycle (e.g., mescaline).

  • Pseudoalkaloids: Heterocyclic N derived from non‑amino acid precursors (e.g., caffeine).

4.1.2 Chemical Characteristics

• Usually alkaline (pKa of conjugate acid ~7–9), bone‑dry basis solids or oils.

• Often optically active and complex ring systems.

• Found as free bases or salts (e.g., hydrochlorides) in plant tissues.

4.2 The Solanaceae Family

4.2.1 Taxonomy & Distribution

• Commonly called the nightshade family; ~100 genera, 2,700 species.

• Includes important medicinal plants (Atropa, Datura, Hyoscyamus) and food species (tomato, potato, pepper).

4.2.2 Key Tropane Alkaloids

• Biosynthesis: From ornithine/arginine → tropinone → tropine → esterification with tropic acid.

4.3 Other Major Alkaloid‑Producing Families

4.3.1 Papaveraceae (Poppy Family)

• Example: Papaver somniferum → Morphine, Codeine, Thebaine.

• Uses: Analgesics, cough suppressants, opiate derivatives (e.g., semi‑synthetic opioids).

4.3.2 Rubiaceae

• Example: Cinchona spp. → Quinine, Quinidine.

• Uses: Antimalarial, anti‑arrhythmic.

4.3.3 Fabaceae

• Example: Physostigma venenosum → Physostigmine.

• Uses: Reversible acetylcholinesterase inhibitor (glaucoma, myasthenia gravis).

4.3.4 Amaryllidaceae

• Example: Nerium oleander → Cardiac glycosides (not true alkaloids) and Amaryllidaceae alkaloids (e.g., galanthamine).

• Uses: Alzheimer’s therapy (galanthamine).

4.4 Extraction & Isolation of Alkaloids

1. Defatting: Non‑polar solvent (hexane) to remove fats and pigments.

2. Acidic Extraction: Grind drug in dilute acid (pH 2–3) to convert alkaloids to water‑soluble salts.

3. Basification: Raise pH (pH 9–10) to liberate free base.

4. Organic Solvent Partition: Extract free base into chloroform or ether.

5. Purification: Re‑acidify and recrystallize as salt (e.g., atropine sulfate).

4.5 Pharmacological Significance

• Tropane Alkaloids (e.g., atropine): Block muscarinic receptors → dilate pupils, reduce secretions, treat bradycardia.

• Isoquinoline Alkaloids (e.g., morphine): Bind opioid receptors → potent analgesia, sedation; high abuse potential.

• Quinolone Alkaloids (e.g., quinine): Interfere with Plasmodium metabolism → antimalarial therapy.

• Cholinesterase Inhibitors (e.g., physostigmine): Enhance acetylcholine levels → treat glaucoma, myasthenia gravis.

4.6 Key Points for Exams

• Define alkaloids and distinguish true, proto‑, and pseudoalkaloids.

• Describe the tropane alkaloid pathway and name two Solanaceae species with their alkaloids and uses.

• Outline a general extraction scheme for plant alkaloids.

• List one representative alkaloid, its family, and its primary pharmaceutical application for each of Papaveraceae, Rubiaceae, Fabaceae.

• Explain why alkaloids are often isolated as salts rather than free bases.

Unit 5: Volatile Oils & Resins – Occurrence & Extraction

This unit covers the classification, biosynthesis, plant localization, methods of extraction, chemical composition, and pharmaceutical applications of volatile oils (essential oils) and resins.

5.1 Volatile Oils (Essential Oils)

5.1.1 Definition & Characteristics

• Volatile oils are complex mixtures of low‑molecular‑weight, lipophilic, aromatic compounds (terpenes, phenylpropanoids) that readily evaporate at room temperature.

• Responsible for plant aroma and defense.

5.1.2 Biosynthesis & Localization

• Biosynthetic pathways:

  • Mevalonate pathway (sesquiterpenes, triterpenes)

  • Deoxyxylulose phosphate (DXP) pathway (monoterpenes)

• Sites in plant: Oil glands (citrus peels), secretory hairs (mint), resin ducts (pine bark), oil cells (eucalyptus leaves).

5.1.3 Major Constituents

• Monoterpenes (C₁₀): Limonene, pinene, geraniol

• Sesquiterpenes (C₁₅): Caryophyllene, humulene

• Phenylpropanoids: Eugenol, cinnamaldehyde

5.2 Resins

5.2.1 Definition & Characteristics

• Resins are viscous, non‑volatile mixtures of terpenoid compounds (resin acids, neutral terpenes) that harden on exposure to air.

• Often secreted in response to injury.

5.2.2 Types of Resins

• Soft resins: Contain volatile oil + resin (e.g., balsams, oleoresins).

• Hard resins: Predominantly non‑volatile, solid (e.g., rosin from Pinus).

• Gum resins: Contain gums, resins, and volatile oils (e.g., myrrh, asafoetida).

5.3 Extraction Techniques

5.3.1 Hydro‑ or Steam‑Distillation (Volatile Oils)

1. Plant material is suspended in water or exposed to steam.

2. Volatile components vaporize, then condense in a cooled condenser.

3. Oil separates from water by decantation (due to immiscibility).

5.3.2 Solvent Extraction

• Cold maceration: Plant material soaked in solvent (hexane, petroleum ether) to yield “concrete,” then alcohol extraction to give “absolute.”

• Supercritical CO₂: Non‑toxic, tunable solvent for heat‑sensitive constituents.

5.3.3 Resin Collection & Processing

• Tapping: Incising bark or stem to collect exuded resin (e.g., benzoin).

• Solvent Dissolution: Crude resin dissolved in organic solvent, filtered, and solvent evaporated to purify.

• Drying & Pulverization: Hard resins broken into granules for dosage forms.

5.4 Chemical Composition & Analysis

• GC–MS: Profiles and quantifies individual volatile constituents.

• Thin‑Layer Chromatography (TLC): Rapid fingerprinting with reference standards.

• Infrared Spectroscopy: Identifies functional groups (e.g., resin acids).

5.5 Pharmaceutical Applications

• Aromatherapy: Volatile oils used for inhalation or topical applications.

• Formulation excipients: Resins in sustained‑release matrices and film coatings.

• Flavoring & Fragrance: Both volatile oils and resin tinctures in syrups, lozenges.

5.6 Key Points for Exams

• Differentiate volatile oils and resins by volatility, composition, and plant origin.

• Outline steam‑distillation vs. solvent extraction, including advantages and limitations.

• Name two monoterpenes and two resin acids, and state their pharmacological use.

• Describe one analytical technique for essential oils and one for resins.

• List three pharmaceutical applications of volatile oils and resins.

Unit 6: Phytochemical Screening Methods & Preliminary Tests

This unit presents the systematic approaches and classical tests used to detect and characterize major classes of phytochemicals in crude plant extracts, providing a foundation for further isolation and standardization.

6.1 Overview of Phytochemical Screening

• Definition: A sequence of qualitative assays designed to reveal the presence or absence of specific secondary metabolites (alkaloids, glycosides, flavonoids, tannins, saponins, terpenoids, phenolics).

• Purpose:

  1. Rapid Profiling of crude extracts.

  2. Guiding Extraction and purification strategies.

  3. Pre‑standardization: Ensuring batch‑to‑batch consistency.

6.2 Sample Preparation

1. Drying & Powdering of plant material to increase surface area.

2. Defatting with non‑polar solvent (hexane) to remove lipids.

3. Extraction (maceration or Soxhlet) with solvents of increasing polarity (e.g., petroleum ether → chloroform → ethanol → water).

4. Concentration under reduced pressure to yield crude fractions.

6.3 Tests for Major Phytochemical Classes

6.4 Thin‑Layer Chromatography (TLC) as a Screening Tool

• Stationary Phase: Silica gel plate.

• Mobile Phase: Solvent system chosen for class (e.g., chloroform:methanol 9:1 for alkaloids).

• Visualization:

  • UV Light (254 nm, 366 nm) for fluorescent compounds.

  • Spray Reagents: Dragendorff’s (alkaloids), vanillin–H₂SO₄ (terpenoids), anisaldehyde (phenolics).

• Rf Value: Ratio of distance travelled by compound to solvent front → helps identify known standards.

6.5 Preliminary Physicochemical Tests

• Loss on Drying: Moisture content determination by oven drying.

• Ash Values:

  • Total Ash: Inorganic residue after ignition.

  • Acid‑insoluble Ash: Siliceous matter.

• Extractive Values: Percent yield in different solvents → indicates relative content of polar vs. non‑polar constituents.

6.6 Reporting & Interpretation

1. Tabulate Results for each solvent fraction and test.

2. Compare with Standards: Use known reference compounds to confirm spot colors and Rf values.

3. Pre‐standardization Profile: Establish fingerprint for quality control.

6.7 Key Points for Exams

• Describe the principle and procedure of any two classical colorimetric tests (e.g., Mayer’s, Shinoda).

• Outline the steps of TLC screening, including choice of mobile phase and visualization methods for two phytochemical classes.

• Define total ash and extractive values and explain their significance in crude‑drug evaluation.

• Explain why defatting is crucial before phytochemical screening.

• Prepare a sample report table summarizing qualitative test outcomes for an ethanol extract.