310_25 - Organic Organic Lecture Series CH 310 N LECTURE 25...

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Unformatted text preview: Organic Organic Lecture Series CH 310 N LECTURE 25 Textbook Assignment: Chapter 25-Carbohydrates Homework (for credit): Problem Set – 8 Posted Today’s Topics: Haworth projections; common reactions; mutarotation; polysaccarides Notice & Announcements: EXAM 3- Grading in Progress 1 Organic Lecture Series • Haworth projections the designation βmeans that the OH on the anomeric carbon is cis to the terminal -CH2OH; α- means that it is trans to the terminal -CH2OH α β 2 Organic Organic Lecture Series Groups on the right side go down on the Haworth. 3 Organic Lecture Series – six-membered hemiacetal rings are shown by the infix -pyran– five-membered hemiacetal rings are shown by the infix -furan- O Furan O Pyran 4 Organic Organic Lecture Series Conformational Formulas – five-membered rings are close to being planar that Haworth projections are adequate to represent furanoses 5 Organic Lecture Series Conformational Formulas – for pyranoses, the six-membered ring is more accurately represented as a chair conformation 6 Conformational Formulas Organic Organic Lecture Series – compare the orientations of groups on carbons 1-5 in the Haworth and chair projections of β-D-glucopyranose, in each case they are up-down-up-down-up respectively All Groups axial 7 Organic Lecture Series Mutarotation: the change in specific rotation that occurs when an α or β form of a carbohydrate is converted to an equilibrium mixture of the two Slight preference for equatorial 8 Glycosides Organic Organic Lecture Series • Glycoside: a carbohydrate in which the OH of the anomeric carbon is replaced by -OR – methyl β-D-glucopyranoside (methyl β-Dglucoside) 9 Organic Lecture Series Glycosides • Glycosidic bond: the bond from the anomeric carbon of the glycoside to an OR group • Glycosides are named by listing the name of the alkyl or aryl group bonded to oxygen followed by the name of the carbohydrate with the ending -e replaced by -ide – methyl β-D-glucopyranoside – methyl α-D-ribofuranoside 10 Organic Organic Lecture Series N-Glycosides • The anomeric carbon of a cyclic hemiacetal also undergoes reaction with the N-H group of an amine to form an N-glycoside – N-glycosides of the purine and pyrimidine bases are structural units of nucleic acids Pyrimidine Purine 11 Organic Lecture Series The Bases of Nucleic Acids Pyrimidine 12 Organic Organic Lecture Series The Bases of Nucleic Acids Purine 13 Organic Lecture Series N-Glycosides – the β-N-glycoside formed between Dribofuranose and cytosine 5’ 3’ 14 Organic Organic Lecture Series Reduction to Alditols • The carbonyl group of a monosaccharide can be reduced to an hydroxyl group by a variety of reducing agents, including NaBH4 and H2/M (metal catalyst) “Sugar alcohol” additive 15 Organic Lecture Series other alditols which are naturally occurring Used as “sugarless” sweetners 16 Organic Organic Lecture Series Oxidation to Aldonic Acids • The -CHO group can be oxidized to -COOH 17 Organic Lecture Series Oxidation to Aldonic Acids 2-Ketoses are oxidized to aldonic acids under the conditions of the oxidation, 2-ketoses equilibrate with isomeric aldoses CH 2 OH CHOH CHO C= O C- OH CHOH ( CHOH ) n ( CHOH ) n ( CHOH ) n CH 2 OH CH 2 OH CH 2 OH A 2-ketose An enediol An aldose At first glance-this appears to be a transposition of a carbonyl group 18 Organic Organic Lecture Series Oxidation to Uronic Acids Enzyme-catalyzed oxidation of the terminal OH group gives a -COOH group CHO COOH H OH enzyme-catalyzed H OH COOH oxidation O HO H HO H HO H OH H OH HO OH H OH H OH CH2 OH CH2O H D -G lucose D -G lucuronic acid (a uronic acid ) OH 19 Organic Lecture Series Oxidation to Uronic Acids – in humans, D-gluconic acid is an important component of the acidic polysaccharides of connective tissue – it is also used by the body to detoxify foreign hydroxyl-containing compounds, such as phenols and alcohols; one example is the intravenous anesthetic propofol 20 Organic Organic Lecture Series Glucose Assay • The analytical procedure most often performed in the clinical chemistry laboratory is the determination of glucose in blood, urine, or other biological fluid – this need stems from the high incidence of diabetes in the population 21 Organic Lecture Series Glucose Assay • The glucose oxidase method is completely specific for D-glucose 22 Glucose Assay Organic Organic Lecture Series – the enzyme glucose oxidase is specific for β-D-glucose – molecular oxygen, O2, used in this reaction is reduced to hydrogen peroxide H2O2 – the concentration of H2O2 is determined experimentally, and is proportional to the concentration of glucose in the sample 23 Glucose Assay Organic Lecture Series – in one procedure, hydrogen peroxide is used to oxidize o-toluidine to a colored product, whose concentration is determined spectrophotometrically 24 Organic Organic Lecture Series Sucrose • Table sugar, obtained from the juice of sugar cane and sugar beet Glucose and Fructose 25 Organic Lecture Series Lactose • The principle sugar present in milk – about 5 - 8% in human milk, 4 - 5% in cow’s milk Glucose and Galactose 26 Organic Organic Lecture Series Maltose • From malt, the juice of sprouted barley and other cereal grains Glucose and Glucose (Glucose Dimer) 27 Organic Lecture Series Artificial Sweeteners 28 Organic Organic Lecture Series •Saccharin is about 300 times as sweet as sucrose, but has an unpleasant bitter or metallic aftertaste, especially at high concentrations. •Unlike the newer artificial sweetener aspartame, saccharin is stable when heated, even in the presence of acids, does not react chemically with other food ingredients, and stores well. 29 Organic Lecture Series CH3 Equal Nutrasweet •Aspartame is the methyl ester of the dipeptide of the natural amino acids L-aspartic acid and L-phenylalanine. •Under strongly acidic or alkaline conditions, aspartame first generates methanol by hydrolysis. Under more severe conditions, the peptide bonds are also hydrolyzed, resulting in the free amino acids. 30 30 Organic Organic Lecture Series Sucralose-A Trichloro-Sucrose 31 Organic Lecture Series Comparison of Sucralose and Sucrose 32 Organic Organic Lecture Series •Sucralose is approximately 600 times sweeter than sucrose (table sugar), twice as sweet as saccharin, and four times as sweet as aspartame. •Unlike aspartame, it is stable under heat and over a broad range of pH conditions and can be used in baking or in products that require a longer shelf life. •Since its introduction in 1999, sucralose has overtaken Equal in the $1.5 billion artificial sweetener market, holding a 62% market share 33 Organic Organic Lecture Series Important Carbohydrate Polymers 1.Starch 2.Cellulose 3.Glycogen 34 Organic Organic Lecture Series Starch • Starch is used for energy storage in plants – it can be separated into two fractions; amylose and amylopectin; each on complete hydrolysis gives only D-glucose – amylose is composed of continuous, unbranched chains of up to 4000 D-glucose units joined by α-1,4-glycosidic bonds – amylopectin is a highly branched polymer of D-glucose; chains consist of 24-30 units of Dglucose joined by α-1,4-glycosidic bonds and branches created by α-1,6-glycosidic bonds 35 Organic Lecture Series α 36 Organic Organic Lecture Series α 37 Organic Lecture Series Cellulose • Cellulose is a linear polymer of Dglucose units joined by β-1,4glycosidic bonds – it has an average molecular weight of 400,000 g/mol, corresponding to approximately 2800 D-glucose units per molecule – both rayon and acetate rayon are made from chemically modified cellulose 38 Organic Organic Lecture Series Cellulose 39 Organic Lecture Series Glycogen Glycogen is the reserve carbohydrate for animals – glycogen is a nonlinear polymer of Dglucose units joined by α-1,4- and α-1,6glycosidic bonds bonds – the total amount of glycogen in the body of a well-nourished adult is about 350 g (about 3/4 of a pound) divided almost equally between liver and muscle 40 Organic Organic Lecture Series 41 ...
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This note was uploaded on 11/21/2011 for the course CH 51455 taught by Professor Colapret during the Spring '11 term at University of Texas.

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