carbohydrates - Carbohydrates (glycans) have the following...

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Monosaccharides - simple sugars with multiple OH groups. Based on number of carbons (3, 4, 5, 6), a monosaccharide is a triose, tetrose, pentose or hexose. Disaccharides - 2 monosaccharides covalently linked. Oligosaccharides - a few monosaccharides covalently linked. Polysaccharides - polymers consisting of chains of monosaccharide or disaccharide units. I (CH 2 O) n or H - C - OH I Carbohydrates (glycans) have the following basic composition:
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Monosaccharides Aldoses (e.g., glucose) have an aldehyde group at one end. Ketoses (e.g., fructose) have a keto group, usually at C2. C C OH H C H HO C OH H C OH H CH 2 OH D -glucose O H C H HO C OH H C OH H CH 2 OH CH 2 OH C O D -fructose
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D vs L Designation D & L designations are based on the configuration about the single asymmetric C in glyceraldehyde. The lower representations are Fischer Projections. CHO C CH 2 OH HO H CHO C CH 2 OH H OH CHO C CH 2 OH HO H CHO C CH 2 OH H OH L-glyceraldehyde D-glyceraldehyde L-glyceraldehyde D-glyceraldehyde
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Sugar Nomenclature For sugars with more than one chiral center, D or L refers to the asymmetric C farthest from the aldehyde or keto group. Most naturally occurring sugars are D isomers. O H O H C C H – C – OH HO – C – H HO – C – H H – C – OH H – C – OH HO – C – H H – C – OH HO – C – H CH 2 OH CH 2 OH D - glucose L -glucose
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D & L sugars are mirror images of one another. They have the same name, e.g., D-glucose & L-glucose. Other stereoisomers have unique names, e.g., glucose, mannose, galactose, etc. The number of stereoisomers is 2 n , where n is the number of asymmetric centers. The 6-C aldoses have 4 asymmetric centers. Thus there are 16 stereoisomers (8 D-sugars and 8 L-sugars). O H O H C C H – C – OH HO – C – H HO – C – H H – C – OH H – C – OH HO – C – H H – C – OH HO – C – H CH 2 OH CH 2 OH D - glucose L -glucose
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An aldehyde can react with an alcohol to form a hemiacetal. A ketone can react with an alcohol to form a hemiketal. R' O H R C H O O C O R H R' H alcohol aldehyde hemiacetal (C-O-C-O-H) R' O H R C R'' O O C O R R'' R' H alcohol ketone hemiketal (C-O-C-O-H)
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Ring Closure in glucose… hemiacetal formation CH 2 OH O OH O H OH OH C CH 2 OH O OH OH OH O H O OH OH OH OH CH 2 OH
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From Fischer to Haworth OH on the right appear below the ring OH on left appear above ring
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Ring Closure in Fructose… hemiketal formation CH 2 OH C C CH 2 OH O O H OH O H CH 2 OH C C CH 2 OH O O H OH OH C O C CH 2 OH CH 2 OH OH O H OH
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Anomers Anomeric carbon is carbonyl carbon Depending on orientation during nucleophilic attack, can get two orientations If ring closes with OH below ring, then is called α If ring closes with OH above ring, then is called β
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Anomer formation in glucose CH 2 OH O OH O H OH OH H C CH 2 OH O OH OH OH O H H O OH OH OH OH CH 2 OH H CH 2 OH O OH O H OH OH H C CH 2 OH O OH OH OH O H H O OH OH OH OH CH 2 OH H alpha glucose beta glucose
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This note was uploaded on 12/28/2011 for the course STEP 1 taught by Professor Dr.aslam during the Fall '11 term at Montgomery College.

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carbohydrates - Carbohydrates (glycans) have the following...

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