Phytochemistry 1 - Monosaccharides Lecture 2 PDF

Dr. Khaled A. Nematallah Physical Properties of Carbohydrates  1) Condition - Monosaccharides as glucose and fructose & most disaccharides as sucrose are white crystalline solids & melt sharply. - Higher polysaccharides: e.g. starch & cellulose a...

Dr. Khaled A. Nematallah Physical Properties of Carbohydrates  1) Condition - Monosaccharides as glucose and fructose & most disaccharides as sucrose are white crystalline solids & melt sharply. - Higher polysaccharides: e.g. starch & cellulose are amorphous solids & do not melt sharply.  2) Taste - Low molecular weight sugars are sweet. - There are different degrees of sweetness. - The reference degree of sweetness is that of sucrose (sweetness = 1)  3) Solubility - Soluble in cold water & in hot alcohol: Monosaccharides. - Soluble in water & insoluble in alcohol: Gums. - Soluble with difficulty in cold water, easily soluble in hot water, insoluble in alcohol: Mucilage, pectins, starch and glycogen. - Insoluble in cold & hot water, soluble in dil. alkalis: Hemicellulose. - Insoluble in above solvents: Cellulose.  4) Optical activity of sugars A compound is optically active, when in solution it is capable of rotating the plane of polarized light either to: The right The left - dextrorotatory - levorotatory - (+) symbol - (-) symbol - d. - l. Monosaccharides and water soluble oligosaccharides are optically active  4) Optical activity of sugars It is measured by a device called polarimeter  Monosaccharides - Simplest carbohydrates (of only one unit). - Can not be further hydrolyzed. - Condition: White crystalline solids - Functional group: a single aldehyde or ketone - Optical activity: All monosaccharides are optically active - Most monosaccharides found in nature are in the D- configuration. - Naturally occurring monosaccharides contain 3 – 7 carbon atoms  Reaction of Monosaccarides Similar to carbonyl Specific for compounds Similar to alcohols carbohydrates - Glycoside formation - Ether formation - Osazone formation - Oxidation - Ester formation - Action of mineral acids - Reduction - Effect of alkalis - Reaction with oxidizing cations  I- Reactions similar to carbonyl compounds 1) Glycoside formation (acetal formation): - Carbohydrates acetals are called glycosides - E.g. acetals of glucose are called glucosides OH OH H H H + H Glycosidic O CH3OH/H O HO H H linkage HO + HO H2O/H HO H H OH OH H OH H O CH3 α-glucopyranose methyl-α- (Hemiacetal) glucopyranoside (acetal)  I- Reactions similar to carbonyl compounds 2) Oxidation HO O C Aldonic acid H O HO O C on C ti x ida CH2OH l dO Mi Strong Oxidation Aldaric acid Co ntr oll H O ed Ox C ida tio C CH2OH n HO O Aldose Alduronic acid C HO O  I- Reactions similar to carbonyl compounds 2) Oxidation COOH Oxidation of Aldoses H OH HO H H OH D-Gluconic acid H 2O H OH O Br 2, C-1 H n at CH2OH o ati C id H OH Ox CHO HO H H OH H OH Controlled oxidation HO H D-Glucuronic acid H OH H OH CH2OH Oxidation at C-6 H OH D-glucose COOH Ox HN ida O COOH tio 3 na H OH tC HO H -1 D-Glucaric acid & H OH C- 6 H OH (Saccharic acid) COOH  I- Reactions similar to carbonyl compounds 2) Oxidation Glucuronic acid importance: - The body uses glucuronic acid to detoxify foreign alcohols and phenols. - These compounds are converted in the liver to glycosides of glucuronic acid and then excreted in the urine. - E.g. The intravenous anesthetic propofol is converted to the water- soluble glucuronide and excreted. Glucuronidation in liver Propofol Propofol glucuronide  I- Reactions similar to carbonyl compounds 2) Reduction - Aldoses are reduced to alditols. - Ketoses are also reduced. H O C CH2OH OH H H OH H OH H NaBH4 O HO H HO H HO H HO H OH H OH H OH H OH H OH H OH α-D-glucopyranose CH2OH CH2OH α-D-Glucose D-Glucitol (D-Sorbitol)  I- Reactions similar to carbonyl compounds 2) Reduction H O C CH2OH HO H HO H HO H NaBH4 HO H Mannose Mannitol H OH H OH H OH H OH CH2OH CH2OH H O C CH2OH H OH H OH HO H NaBH4 HO H Dulcitol Galactose HO H HO H H OH H OH CH2OH CH2OH  I- Reactions similar to carbonyl compounds 2) Reduction Reduction of Fructose CH2OH CH2OH CH2OH O H OH HO H HO H NaBH4 HO H HO H H OH H OH H OH H OH H OH H OH Fructofuranose CH2OH CH2OH CH2OH Fructose Glucitol Mannitol  II- Reactions similar to alcohols 1) Ether Formation OH OCH3 H H H H O Dimethyl Sulphate O H H3CO H HO H3CO HO NaOH H H OH OCH3 H OCH3 H OCH3 Methyl glucoside Pentamethyl glucoside Ethers are used for determination of ring size  II- Reactions similar to alcohols 1) Ether Formation Determination of ring size  II- Reactions similar to alcohols 2) Ester Formation OH OAc H H H H O CH3COOH O H AcO H HO AcO HO Pyridine H H OAc OH H OAc H OH Glucose Pentaacetyl glucoside  III- Reactions specific to carbohydrates 1) Osazone formation (reaction with phenyl hydrazine) Glucose Phenyl hydrazine Glucosazone  III- Reactions specific to carbohydrates 1) Osazone formation (reaction with phenyl hydrazine) Mechanism  III- Reactions specific to carbohydrates 1) Osazone formation (reaction with phenyl hydrazine) - All monosaccharides and reducing disaccharides form osazones. - Osazones form beautiful crystals. - Osazones are different in physical properties (shape, and m.p.).  III- Reactions specific to carbohydrates 1) Osazone formation (reaction with phenyl hydrazine) Give reason: Why Glucose, Fructose and Mannose give the same osazones?? O H O H CH2OH C C C O HO C H H C OH HO C H HO C H HO C H H C OH H C OH H C OH H C OH H C OH H C OH CH2OH CH2OH CH2OH Glucose Fructose Mannose  III- Reactions specific to carbohydrates 2) Action of mineral acids Hot conc. mineral acids (e.g. HCl or H2SO4) cause the elimination of water (dehydration) from the monosaccharides a) Pentoses O H C HO C H Conc. HCl or H2SO4 H H C OH C -3 H2O O H C OH O CH2OH Furfural D-Arabinose  III- Reactions specific to carbohydrates 2) Action of mineral acids O H b) Methyl Pentoses C HO C H Conc. HCl or H2SO4 H HO C H H3 C C -3 H2O O H C OH O Methyl Furfural H C OH CH3 Rhamnose c) Hexoses O H C H C OH Conc. HCl or H2SO4 HO H HO C H C C -3 H2O H2 O H C OH O Glucose Hydroxymethyl furfural H C OH CH2OH  III- Reactions specific to carbohydrates 2) Action of mineral acids - Furfural and its derivatives form colored complexes with: - Phenolic compounds (e.g. alpha-naphthol) (Molish’s test). - Amines (e.g. aniline) (Aniline acetate paper test) - Colored complexes are used for qualitative and quantitative determination of monosaccharides  III- Reactions specific to carbohydrates 3) Effect of Alkalis - Strong alkalis: Polyermization - Weak alkalis: Isomerization H C=O CHOH CH2OH CH OH C OH C=O HO CH HO CH HO CH CH OH CH OH CH OH CH OH CH OH CH OH CH2OH CH2OH CH2OH D-Glucose D-Fructose CHO HO CH HO CH CH OH CH OH CH2OH D- Mannose  III- Reactions specific to carbohydrates 4) Reaction with oxidizing cations - All monosaccharides and reducing disaccharides are oxidized by metal ions in alkaline medium. - E.g. Fehling’s test - Fehling A: CuSO4, Fehling B: Potassium sodium tartrate & NaOH Cu2+ reduction Cu+ (CuO) (Blue) (Cu2O) (Red) CHO COOH CH OH CH OH Fehling's HO CH HO CH CH OH CH OH CH OH CH OH CH2OH CH2OH D-Glucose Gluconic acid Barfoed’s test: Cu Acetate/Acetic acid, gives positive with monosaccharides only, as acidic medium decrease the oxidation power of Cu2+ - Pentoses - Ribose, Xylose, Arabinose and Apiose. - Hexoses - Glucose, Mannose, Galactose and Fructose - Deoxysugars - Deoxyribose, Rhamnose, Digitoxose and Cymarose - Sugar derivatives - Gluconic acid, Glucuronic acid, Sorbitol, Mannitol and Ascorbic acid.  Pentoses - Simple sugars contain only 5 carbon atoms - They are unfermentable by yeast - Effect of mineral acids → Furfural - Rarely found in their free state, they are mainly found as pentosans or as glycosides. - Common pentoses in plants: Ribose, Xylose and Arabinose  Pentoses Item α-D-Ribose α-D-Xylose α-L-Arabinose O H O H O H C C C H C OH H C OH H C OH Structure H C OH HO C H HO C H H C OH H C OH HO C H CH2OH CH2OH CH2OH Part of nucleic acids Any woody material as Occurrence Gums or pectic substances (RNA) straw, bran and corncobs Common ----- Wood sugar Pectin sugar name 1- Boiling of woody material with acids. Hydrolysis of yeast Preparation 2- Fermenting glucose with Hydrolysis of gyms nucleic acid yeast and crystallizing the D-xylose  Pentoses Item α-D-Ribose α-D-Xylose α-L-Arabinose - Ribose is used to improve - Widely used as a diabetic - Originally commercialized as athletic performance and sweetener in food and a sweetener the ability to exercise by beverage. boosting muscle energy. - As a diagnostic agent to - Inhibitor of sucrase, the Pharmaceutical observe malabsorption. enzyme that breaks down Importance - Chronic fatigue syndrome - Reduction of xylose by sucrose into glucose and and Fibromyalgia catalytic hydrogenation fructose in the small produces the common food intestine. additive sweetener substitute xylitol  Pentoses Apiose - A rare pentose. - Has an unusual branched structure. - In leaves and seeds of parsley, as the sugar part of apiin glycoside  Pentoses Chemical test specific for pentoses: 1) Aniline acetate paper test → Red stain 2) Bial’s test (Orcinol/HCl with little FeCl3) → Bluish color  Hexoses - Simple sugars contain only 6 carbon atoms - They are fermentable by yeast - Effect of mineral acids → Hydroxymethylfurfural - Found in nature as: Free state Combined as glycosides Combined as oligosaccharides and polysaccharides.  Hexoses 1) Glucose (Dextrose ,grape sugar, blood sugar) - The most important & most abundant monosaccharide in plant and animal kingdoms. - A white crystalline solid, sweet taste. - Readily soluble in water. - Reduces Fehling’s and Barfoed’s reagents. - Osazone → Glucosazone (Yellow needled on hot). - Commercially prepared from starch by acid hydrolysis.  Hexoses 1) Glucose (Dextrose ,grape sugar, blood sugar)  Hexoses 1) Glucose (Dextrose ,grape sugar, blood sugar) Preparation of D-glucose Autoclaving Neutralize Aqueous starch with Na2CO3 Impurities with dil HCl Complete suspension skimmed & hydrolysis pH 4-5 (15-20%) At 150 oC solution filtered For 30 min Decolorize Solution is concentrated with charcoal under reduced pressure Filtrate & crystallized  Hexoses 1) Glucose (Dextrose ,grape sugar, blood sugar) Pharmaceutical Importance - Source of energy either by mouth or IV injection. - IV solutions to restore blood volume. - In case of hypoglycemic shocks after insulin administration - As sweetening agent.  Hexoses 1) Glucose (Dextrose ,grape sugar, blood sugar) Glucose assay - The most often analytical procedure performed in the clinical chemistry laboratory is the determination of glucose in blood, urine, or other biological fluids. - The glucose oxidase method is completely specific for D-glucose  Hexoses 1) Glucose (Dextrose ,grape sugar, blood sugar) Glucose assay - The dipstick contains the enzyme glucose oxidase, peroxidase and o- toluidine. Glucose Gluconic acid Glucose oxidase 2 H 2O + (Blood or Urine) Peroxidase H2O2 + O2 O-Toluidine Colored Product  Hexoses 1) Glucose (Dextrose ,grape sugar, blood sugar) Glucose assay - How glucometer works?  Hexoses 1) Glucose (Dextrose ,grape sugar, blood sugar) Liquid glucose - It is prepared by partial hydrolysis of starch (dil HCl & heating for 20 minutes under pressure). - Consists of dextrose with dextrin, maltose and water. - Thick syrupy colorless or yellowish sweety liquid. - Uses: Sweetening agent Substitute for sucrose As excipient in manufacture of pills.  Hexoses 1) Glucose (Dextrose ,grape sugar, blood sugar) Liquid glucose - In pills containing ferrous carbonate, as it preserves ferrous salt from oxidation and reduces any ferric salt present. - Not used in pills containing cupric salt (Why?) Because it will reduce it from cupric to cuprous - Not used intravenously (Why?) Because it's viscous and will block the veins Thank you