Secondary Metabolites PDF

# Secondary Metabolites ## Plant cell products are two types of metabolites: 1. **Primary metabolites** - Primary metabolites are produced as a result of photosynthesis and these products are further involved in the cell component synthesis - They are necessary for plant growth. - The...

# Secondary Metabolites ## Plant cell products are two types of metabolites: 1. **Primary metabolites** - Primary metabolites are produced as a result of photosynthesis and these products are further involved in the cell component synthesis - They are necessary for plant growth. - They are primarily used as industrial raw materials, food or food additives, e.g. Vegetable oils, fatty acids, and carbohydrate. 2. **Secondary metabolites** - considered as end products of primary metabolism and are in general not involved in metabolic activity, viz. alkaloids, phenolics, essential oils, steroids etc. ## Metabolites produced by plants are either: - **Primary metabolites:** necessary for their growth. - **Secondary metabolites:** they are not nutrient, have medicinal uses. - They protect plants against being eaten by herbivores and against being infected by microbial pathogens. - They may be the waste products of metabolism (detoxification). - They serve as attractants (odor, color, taste) for pollinators and seed-dispersing animals. ## Secondary plant metabolites (Active constituents) - They are divided into several classes: 1. Glycosides 2. Alkaloids 3. Carbohydrates and related compounds 4. Tannins 5. Oils ## Glycosides ### Glucose: - **Chemical Formula:** $C_6H_{12}O_6$ - **Diagram:** Images of different glucose configurations are shown - Fischer, Haworth, and Chair conformation. ### Definition: - GLYCOSIDE is an organic compound, usually of plant origin, that is composed of a sugar portion linked to a non-sugar moiety. - The sugar portion is called **glycone**, while the **non-sugar** portion is called **aglycone** or genin. ### Formation: - Glycosides are formed by the condensation of OH from the sugar and that of the aglycone, the loss of water and formation of oxide ring-O-C (ethers of sugars) or C-C glycosidic linkages ### Properties: - Non-reducing organic compounds hydrolyzed by acids, alkalies or enzymes - Soluble in water and hydroalcoholic solvents and the aglycones are soluble in organic solvents. ### Additional properties: - The glycosides are soluble in water and hydroalcoholic solvents. - The aglycones are soluble in organic solvents. - Most of them have bitter taste (Except: populin, glycyrrhizin, stevioside). ## Glycoside classification according to the non-sugar part structure: - **Phenolic glycosides:** - Simple phenolic - anthocyanins - flavonoids - anthraquinone glycosides - **Steroidal glycosides (cardiac glycosides)** - **Cyanophore glycosides (thioglycosides)** - **Saponins** ## A- Phenolic glycosides ### 1. Simple phenolic glycosides: - **Example:** Arbutin in ***Uva ursi***. - **Chemical test:** Arbutin + conc. HCl, hydrolysis > free hydroquinone (precipitate on cold slide to give white needle crystals) + sugar - Diagram of the reaction showing arbutin converting into hydroquinone and D-Glucose is shown. - **Sublime on cold surface to give needle crystals** ### 2. Flavonoid glycosides: - Flavonoids are polyhenolic compounds of 15 carbon atoms. - They may occur in free form (aglycone) or as glycosides. - They regard as C6-C3-C6 in which C6 is a benzene ring. - Diagram: A basic flavonoid structure of C6-C3-C6 is shown - with rings labelled as A, B, and C. ### 2. Flavonoid glycosides: - **Flavonols:** - Quercetin - Kaemferol - Rutin - Myricetin - **Flavanones:** - Naringenin - Naringin - Hesperidin - **Isoflavones:** - Genistein - Daizein - Diagram : A simplified diagram of the aforementioned flavonoids is shown. - They are yellow in color. - e.g. rutin in ***Ruta*** (used in vascular disorders) - and diosmin in ***Buchu leaves*** (used in capillary fragility). - **Chemical test:** Dissolve in aqueous alkalies (KOH) giving canary-yellow color. - Diagram: Pictures of pills containing "Diosed C 500 mg" and "Ruta C 60 tablets" as well as the chemical structures for Rutin and an unnamed structure are shown. ## 3. Anthocyanin glycosides: - They are related to flavonoids and colored depending the PH of the medium (red in acidic PH, violet in neutral, blue in alkaline medium). - They are the color pigments of flowers e.g. Karkadeh and used as natural coloring matter. - Diagram: An unidentified chemical structure and two test tubes with red, purple and blue liquids are shown ## 4. Anthraquinone glycosides: - It is the active constituents of many laxative and purgative plants e.g. Senna, Cascara, Aloe, Frangula and Rhubarb. - The aglycones are di, tri or tetrahydroxy methyl anthraquinone. - Give positive **Borntrager's** & modified Borntrager's tests. - Diagram: Images of an aloe vera plant and a fern are shown. - Diagram shows a basic anthraquinone structure with two 6-carbon rings connected by a three carbon bridge. ## Borntrager's test: 1. In a test tube put 1 gm powdered plant + 4ml alcholic KOH, boil for 2-3 min. 2. Dilute with 4ml water, filter. 3. Acidify with 5ml HCl, cool 4. Shake with benzene. 5. Separate the benzene layer. 6. Shake with 2 ml conc. NH3 gives rose red color in NH3 Layer (lower layer). - Diagram: A test tube with 2 layers of liquid is shown - the upper layer is yellow-orange while the lower layer is rose pink. ## Modified Borntrager's test: 1. In a test tube put 1 gm powdered plant + 4ml alcholic KOH, boil for 2-3 min. 2. Dilute with 4ml water. 3. Add 2 Drops H2O2, filter. 4. Acidify with 5ml HCl, cool 5. Shake with benzene. 6. Separate the benzene layer. 7. Shake with 2 ml conc. NH3 gives rose red color in NH3 Layer (lower layer). - Diagram: A test tube with 2 layers of liquid is shown - the upper layer is yellow-orange while the lower layer is rose pink. - Modified Borntrager's test is for combined anthraquinones - Diagram: A reaction scheme with sennoside A reacting with *H2O2* in presence of *alkaline KOH* and then with *HCl* to yield Aloe-emodin. ## B. Cyanophoric (cyanogenic ) glycosides: - They yield HCN on hydrolysis. - They don't have many applications as due to the poisonous properties of HCN, e.g., linamarin in Linseed. - The detection of them is done by sodium picrate paper (Guignard's paper test). - Diagram: The structure of Linamarin is shown. - They yield HCN on hydrolysis. - They don't have many applications as due to the poisonous properties of HCN, e.g., linamarin in Linseed. - The detection of them is done by sodium picrate paper (Guignard's paper test). - Diagram: A reaction scheme with linamarin getting hydrolyzed by *Linamarase* enzyme to yield glucose and acetone cyanohydrin, eventually decomposing into acetone and hydrogen cyanide. - Note: "Evaporates during processing" is mentioned alongside the arrow indicating the conversion of acetone cyanohydrin into hydrogen cyanide. ## Guignard's paper test: 1. Crushed seeds in test tube + HCl. 2. The tube covered with a piece of cork having a sodium picrate paper (yellow color). 3. Put on water bath for 30 minutes. 4. HCN will be evolved converting the yellow color to brick red stain. as it reduces Na picrate to Na picramate. - Diagram: Two test tubes are shown side by side. The test tube on the left has a yellow paper inside, while the test tube on the right has an orange colored paper. ## C. Thioglycosides (Thiocyanate or sulphated glycosides) - The aglycone part contains sulphur, which on hydrolysis produce SCN (thiocyanate). - e.g. Sinigrin from black mustard used as antirheumatic - Diagram: A spoon containing black mustard seeds is shown. - The structure of Sinigrin is shown. - The aglycone part contains sulphur, which on hydrolysis produce SCN (thiocyanate). - e.g. Sinigrin from black mustard used as antirheumatic - Diagram: A reaction scheme with Sinigrin getting hydrolyzed by Myrosinase enzyme and H2O to yield glucose and sulfate as well as *N=C=S*. - The structure of Sinigrin is shown.