215%20F08-carbohydr-10-31-08

215%20F08-carbohydr-10-31-08 - Chem 215 F08 Notes M...

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Chem 215 F08 Notes – M. Koreeda (subbing for Dr. Brian Coppola) October 31, 2008 Chapters 14.8; 23-1, 2, 5, and 7: Carbohydrates Carbohydrate nomenclature: http://www.chem.qmul.ac.uk/iupac/2carb/ Carbohydrates: • Polyhydroxylated aldehydes and ketones and their equivalents • Important constituents of both plants and animals • D-glucose: The primary source of energy in the human body (CHOH)n CH 2 OH O H e.g., Hexoses: Sugars possessing six carbon atoms. • Pentoses: Sugars possessing five carbon atoms. • Aldoses: Sugars containing an aldehyde group. • Ketoses: Sugars containing a ketone group. • Monosaccharides: Carbohydrates that do not undergo cleavage on hydrolysis (treatment with water) to smaller molecules. I. Stereochemistry O H HO H HO H H HO H OH OH OH H HO H HO H H HO H O OH O OH HO H HO H H HO H H OH equatorial anomeric carbon axial 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 anomeric carbon opn-chain form of D-glucose another hemiacetal form of D-glucose one hemiacetal form of D-glucose These are anomers and (C-1) epimers. Glucose reacts like an aldehyde since small amounts of the open-chain form are present at equilibrium. Glucose has 4 stereocenters 2 4 = 16 stereoisomers possible 8 pairs of enantiomers (1) Fischer projection formulas (a) (+)-Glyceraldehyde: configurational reference compound for all monosaccharides H CH 2 OH O H D- (+)-glyceraldehyde vertical bonds go in and horizontal bonds come out small upper-case D configurational designation sign of optical rotation at the sodium D-line (589 nm) C H OH CH 2 OH O H HO H O H CH 2 OH R R - (+)-glyceraldehyde This stereochemistry is defined as "D" if the OH is projected to the right. S -(-)-Glyceraldehyde has an L-configuration. • D-Stereochemistry and the sign of optical rotation have no direct correlation, although many D sugars are dextrorotatory ( d or +).
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Chem 215 F08 - Notes [M. Koreeda – October 31, 2008] Page 2. I. Stereochemistry (1) Fischer projection (cont’d) The configurational relatioship was established between D -glyceraldehyde and the naturally occurring positive-rotating grape sugar, (+)-glucose. HO H HO OH HO OH O 1 2 3 4 5 6 D HO OH HO OH HO O 1 2 3 4 5 6 D HO H HO OH O 1 2 3 4 5 D D -glucose D-fructose (found in many fruits) D-2-deoxyribose (found in DNA) [an aldohexose] [a ketohexose] [a deoxyaldopentose] (in its open-chain (in its open-chain (in its open-chain aldehyde form) aldehyde form) keto form) ------------------------------------------------------------------------------------------------------------------------ The Fischer projection of (+)-glucose • The more oxidized end of the chain (i.e., the aldehyde in this case) on top of the Fischer chain. • The first chiral center from the bottom of the chain determines the configuration (i.e., D or L ). CH 2 OH OH H H OH HO H H OH O H HO H HO OH HO OH O 1 2 3 4 5 6 D 1 2 3 4 5 6 OH H H HO OH H OH H CH 2 OH all eclipsed! not a natural, stable conformation!
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215%20F08-carbohydr-10-31-08 - Chem 215 F08 Notes M...

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