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Carbohydrates

Carbohydrates. Saccharides - saccharum (Latin) - sugar. Photosynthesis. Carbohydrates are synthesized by green plants via the process of photosynthesis. This involves the chemical combination of carbon dioxide and water which results from the absorption of visible light.

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Carbohydrates

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  1. Carbohydrates Saccharides - saccharum (Latin) - sugar

  2. Photosynthesis Carbohydrates are synthesized by green plants via the process of photosynthesis. This involves the chemical combination of carbon dioxide and water which results from the absorption of visible light. The detailed mechanism of the transformation is not fully understood. There are many enzyme-catalyzed reactions which take place, the first of which involves absorption of light by the extended  system of chlorophyll.

  3. Chlorophyll-a Synthesis - R.B. Woodward, 1960

  4. Carbohydrate metabolism Carbohydrates “store” solar energy which is released when they are metabolized to give CO2 and water: Cx(H2O)y + xO2 xCO2 + yH2O + energy Much of the energy released is conserved in a new chemical form through reactions that are coupled to the synthesis of adenosine triphosphate from adenosine diphosphate.

  5. Carbohydrate metabolism Plants and animals use the conserved energy of ATP to perform energy-requiring processes such as muscle contraction. The energy is released and the ATP hydrolyzed to ADP.

  6. D-glyceric acid

  7. D-glyceric acid D???? The letter D designates the absolute configuration of this acid. This pre-dates Cahn-Prelog-Ingold by many years! This system was suggested by Rosanoff in 1906 and works as follows: the configuration is D, if the hydroxyl group of the stereogenic centre is to the right in the Fischer projection formula. If it is to the left, the letter L is used.

  8. D, L Sugars (R)-(+)-glyceraldehyde The configuration of (+)-glyceraldehyde was arbitrarily assigned as (D)! Monosaccharides have the D configuration if the OH group attached to their highest numbered stereogenic centre is to the right in the Fischer projection formula; L is used if it is to the left. In 1951, Bijvoet determined the absolute configuration of L-(+)-tartaric acid and hence that of D-(+)-glyceraldehyde. The D assignment was correct!

  9. D-Sugars Virtually all naturally occurring monosaccharides are D sugars.

  10. Epimers Examine D-(+)-glucose and D-(+)-mannose: They only differ in the configuration about one stereogenic centre, C-2. Two diastereoisomers which only differ in the configuration about one stereogenic carbon are called epimers.

  11. Epimers D-(+)-glucose D-(+)-galactose

  12. Classification of carbohydrates “sugars” - the general name used for monosaccharides, disaccharides, oligosaccharides (low molecular weight polymers) and polysaccharides. (saccharum, Latin, sugar) “monosaccharides” - sugars that cannot be hydrolyzed into smaller molecules (monomer units) “aldoses” - sugars with an aldehyde carbonyl group “ketoses” - sugars with a ketone carbonyl group

  13. (+)-Glucose • the most abundant monosaccharide • present in the free state in fruits, plants, honey, blood and urine of animals • an aldohexose • C6H12O6 • there are 4 stereogenic centres and therefore 24 (16) optical isomers are possible! All are known!

  14. (+)-Glucose Emile Fischer, at the end of the 19th century, successfully identified glucose among the 16 possible isomers! The configuration at C-5 was identical to that of D-(+)-glyceraldehyde.

  15. Reactivity of glucose Glucose reduces -Fehling’s solution (Cu(II) in Cu(I)) Tollens’ reagent (Ag(I) in Ag(0)) Glucose is an aldehyde! When it reacts with amines, it does not always form imines (C=N-R). Glucose is not an aldehyde?

  16. Reactivity of glucose Aldehydes react with two equivalents of methanol to form dimethyl acetals: Glucose does not form a dimethyl acetals! It forms two different monomethylated derivatives: methyl - and -D-glucoside

  17. Cyclic glucose

  18. Anomers There are two different D-(+)-glucose molecules! Stereoisomers which only differ in the configuration about the hemiacetal carbon are called anomers. The OH at C-1 is to the right of the chain in the  anomer and to the left in the  anomer.

  19. Haworth Projections The CH2OH is drawn above the ring for D sugars and below the ring for L sugars. In D sugars, the OH at C1 is drawn below the ring for the  anomer and above the ring for the  anomer.

  20. Conformations of monosaccharides

  21. Ring Size

  22. Mutarotation

  23. Mutarotation 64% 30%

  24. Reactions of Glucose With Amines

  25. Reactions of Glucose With Amines anomers of N-phenyl-D-glucosamine

  26. Glycosides cyclic acetals

  27. Osazones phenylosazone of glucose

  28. Osazones fructose

  29. Kiliani-Fischer Synthesis

  30. Ruff Degradation

  31. (+)-Lactose - a Disaccharide -glycosidic bonding

  32. (+)-Sucrose

  33. Cellulose Cellulose contains about 3,000 monomer units. It is essentially linear. Cotton fiber is almost pure cellulose. Wood and straw is made up of about 50% of this polysaccharide.

  34. Starch Starch is a polyglucose containing more than 1,000 units connected by  acetal bonds. It is easily hydrolyzed by acid to give glucose.

  35. Adenosine - a Nucleoside A nucleoside is a glycosylamine in which the amino residue is a pyrimidine or a purine: (a purine)

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