Introduction to Phytochemistry PDF

9/29/2024 1 Introduction to Phytochemistry 2 1  9/29/2024 Phytochemistry Studying chemical structure, biosynthesis, occurrence, and biological activity of plant...

9/29/2024 1 Introduction to Phytochemistry 2 1  9/29/2024 Phytochemistry Studying chemical structure, biosynthesis, occurrence, and biological activity of plant secondary metabolites Biochemistry Organic Pharmacology Chemistry Phytochemistry 3 Plant Constituents (organic substances formed and accumulated by plants) Primary metabolites: essential for life (carbohydrates, fats, proteins,..) Secondary metabolites: pharmacologically active produced by a specific organism or group of organisms. Function as biodefense, attractant, dye,.. Etc. Some natural products can be assigned in both categories as they can be sugars or lipids but of limited occurrence and with specific biological activities. 4 2  9/29/2024 Classification according to chemistry & common physical properties 1. Volatile oils 2. Resins & Resin combinations 3. Alkaloids 4. Carbohydrates 5. Glycosides 6. Bitter Principles = Bitters 7. Tannins 5 5 Nomenclature ▪ Trivial names of plant secondary metabolites are derived from; ▪ Name of the discoverer: pelletierine ▪ Name of the plant, genus, species: Salicin ▪ Pharmacological action: emetine ▪ Prefixes: ▪ Suffixes usually indicates chemical class - Hydroxy-, methoxy-, methyl-, dihydro-, - oside (glycoside) , for added substitutions - ine (alkaloid) - Deoxy-, demethoxy-, demethyl-, - one (ketone) dehydro-, nor-, for removed substitutions 6 3  9/29/2024 Plants Vs Phytochemicals A plant's active constituents vary in different areas, climates, and seasons. Active constituents usually exist with other compounds that can have toxic or unpredictable activity. Phytochemicals can be assayed and used in accurately measured doses. 7 Roadmap to phytochemical Fractionation steps 8 4  9/29/2024 Extraction of plant metabolites First step in obtaining an active compound is extraction. Separating the medically active compounds of plant or animal tissue by using selective solvents. Extraction solvents are chosen so that they selectively dissolve plant active constituents. Solubility of a molecule in a certain solvent is affected by their polarity “like dissolves like” 9 Traditional extraction Maceration / Digestion Percolation Steam distillation (Percolator) Decoction 10 5  9/29/2024 Maceration / Digestion Most simple Used for small or large amounts No special equipment The powdered plant is soaked in the solvent with frequent stirring If gentle heat is applied it is called digestion Ends with filtration and evaporation of solvent Time - consuming 11 Infusion Water is the solvent Used in traditional medicine Plant is soaked in hot water for short period (infusion) Decoction The plant is boiled with water for 15-30 mint (decoction) For polar water-soluble compounds Not suitable for thermolabile constituents 12 6  9/29/2024 Percolation It is maceration followed by a continuous slow flow of fresh solvent through Plant material (using percolator) Plant material is soaked in solvent and more solvent is added on top and allowed to percolate dropwise. Time consuming Not suitable for plants containing mucilage 13 Continuous hot extraction Uses a special equipment (Soxhlet extractor) It is a continuous process; the solvent in the flask is evaporated, recondensed and used for extraction again. Less time consuming Uses lower volume of solvent Extract is continuously heated Not suitable for large amount 14 7  9/29/2024 Steam Distillation Used for plant volatile oil. The plant is heated with water or steam, the vapors evaporated contain both steam and volatile constituents of the plant. Vapor is condensed and separates into 2 immiscible liquids Only for volatile constituents Not suitable for thermolabile compounds 15 Supercritical fluid extraction Uses liquefied gas (CO2 or N2O) under certain pressure and temperature (above the critical point). It is used to extract target compounds from solid samples. CO2 is chemically inert, non-inflammable, easy to eliminate, has a low critical temp, non-toxic, and its polarity can be easily adjusted using modifier solvents. Extracted PC are of close composition to natural PC. Absence of hydrolysis, decomposition, and rearrangement of plant PC. 16 8  9/29/2024 Ultrasonic assisted extraction Extraction is facilitated by the use of ultrasound pulses (20 KHz) The flask is placed on an ultrasound bath or is stirred using an ultrasound probe (homogenizer). Ultrasound pulses help breakdown the cell wall and help extraction by creating cavitation Not suitable for large amount 17 Microwave-assisted Extraction Heating of the solvent in contact with the sample by means of microwave energy. Heat generated by MW enhances solvent penetration into PM, allowing better dissolution of the target compounds. Reduces cost, extraction time, energy , and solvent consumption. 18 9  9/29/2024 Solid Phase Extraction (SPE) SPE is a physical extraction/fractionation process involving the use of solid phases, in pre-packed columns containing stationary phases. 001988 19 Solid Phase MicroExtraction (SPME) Analysis of some V.O. containing drugs. Adsorptive phase: silicone derivative fibers Reduces solvent consumption, and plant material. Less opportunity for oxidation of vol. comps. Rapid and reproducible 20 10  9/29/2024 Fractionation of extract Solvent/solvent Precipitation By mixing the extract with less polar miscible solvent. For example, saponins can be precipitated from methanol extract by addition of acetone. Liquid/liquid extraction Uses two immiscible solvents that after being mixed can be separated into 2 layers. Depends on partition coefficient of the solutes Can be done in a single contact or multiple contacts (successive addition of solvents) 21 Concentration The enriched plant extract is concentrated using: 1-Rotatory evaporator (known as rotavap) in order to remove excess solvents from samples by applying heat to a rotating flask at reduced pressure. Rotatory evaporator 2-Lyophilizer 22 11  9/29/2024 Isolation of pure compounds Sublimation (caffeine) Fractional distillation (volatile oil) Fractional crystallization Chromatography 23 Natural Products in Modern Medicine 1. Provide useful drugs: that cannot be commercially produced by synthesis e.g. Morphine, Penicillin, Ergotamine, Ergometrine, Vincristine 2. Precursor for semisynthetic comps: to produce more effective or less toxic drugs by modifications e.g. Salicin→ Aspirin 3. Used as a template: to produce synthetic analogs through drug design e.g. Procaine and related local anesthetics. 24 12