1. Chapter 25 Carbohydrates [Cn(H2O)n]
Bioorganic Chemistry
Spring 2006
Chapter 25 Carbohydrates [Cn(H2O)n]
Importance of carbohydrates in nature
DNA and RNA: genetic code;  1163 & 1164 top
cellulose/chitin: structure & protection; 
glycoconjugates: lipids; blood type; 
classification by the number of sugars
monosaccharides: glucose, fructose;  1086 top
disaccharides: sucrose, lactose;  1111 top
polysaccharides: cellulose, amylose; 
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5. monosaccharides
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6. disaccharides
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7. polysaccharides
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8. Classification of Carbohydrates (II)
Bioorganic Chemistry
Spring 2006
Classification of Carbohydrates (II)
Classification by the number of carbons
hexose: C6H12O6; glucose, fructose;  1089
pentose: C5H10O5; ribose, tetrose: C4H8O4; erythrose
Classification by the C-1/2 functional group
aldose vs ketose: aldehyde vs ketone;  1088 bottom
glucose: aldohexose / fructose: ketohexose (carbohydrates)
ribose (xylose): aldopentose / ribulose (xylulose): ketopentose
pyranose vs furanose: 6- vs 5-ring;  1091 top
glucopyranose vs glucofuranose
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9. tetroses
pentoses
hexoses
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12. Stereochemistry of Carbohydrates
Bioorganic Chemistry
Spring 2006
Stereochemistry of Carbohydrates
Stereochemistry: Fischer projection;  1087 top
Section 7.8: vertical chain down & horizontal FGs up
Haworth projection: from the edge;  1092 bottom
correlation to D-(+)-glyceraldehyde:  1088 top
small capitals for D/L: large capitals for R/S (italic)
a penultimate carbon: amino acids, a-hydroxyacids
irrespective of other configurations;  1089
irrespective of optical rotation: D-(+)-glucose vs D-(–)-ribose
d vs l: dextrorotatory (+) vs levorotatory (–)
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16. Cyclization of Monosaccharides
Bioorganic Chemistry
Spring 2006
Cyclization of Monosaccharides
Favorable hemiacetals:  1090 bottom
intramolecular vs intermolecular: favorable DS
6- vs 5-ring: thermodynamic (DH) vs kinetic;  1091 top
equilibrium depends on monosaccharides:  1089
Anomers: a- & b-OH at C-1;  1092 top
equilibrium ratio: relative stability;  1093 bottom
mutarotation: [a]D at equilibrium;  1094 Prob. 25.1
anomeric effect: unusual stability of an axial alkoxy group
configuration assignment by Karplus correlation
Jax-ax (8-10 Hz), Jax-eq (eq-eq) (2-3 Hz);  1096 bottom
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17. conf:  747 Table 18.1 & 775 bottom
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19. (diastereomers; epimers)
(anomeric carbons)
(diastereomers; epimers)
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20. (equatorial) (axial) (36.4%) [a]D +112.2 mp 146 oC (63.6%) [a]D +18.7
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21. ‘A’ value (axial strain energy): DGOH = – RT lnK ( 204)
K = [eq]/[ax] = e(900/1.987x298) = 4.572; [eq]:[ax] ≈ 82:18
EWGs at C-1 (anomeric carbon): axial position favored
origins of the anomeric effect: other examples
reduced dipole-dipole repulsion & p-s* resonance
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23. vicinal coupling
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25. Reactions of Monosaccharides
Bioorganic Chemistry
Spring 2006
Reactions of Monosaccharides
Oxidations & Reductions: aldehydes & alcohols
oxidation: HNO3 at low temp, a,w-diacid;  1095 top
oxidation: Br2 in H2O, only C-1 acid;  1097 top
oxidation: reducing sugars (ketoses);  1097 bottom
reduction: aldehydes to alcohols:  1098 top
Nucleophilic OH: peracetylation;  1099 mid
Enolization: acidic or basic;  1098 bottom
Gylcoside formation: acidic;  1099 bottom
natural glycosides: salicin, disaccharides
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26. (not optically active)
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27. (citrate)
(tartrate)
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28. (no D form)
(sugarless gum)
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30. [mechanism]
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31. MeOH
(b-glucoside)
Conf: Figure 18.5, p 776
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32. Structure Proof of Monosaccharides
Bioorganic Chemistry
Spring 2006
Structure Proof of Monosaccharides
Configuration of (+)-glucose (aldohexose)
Kiliani-Fischer synthesis: two isomeric one-C higher aldoses form lower aldoses;  1095 top
K-F synthesis of D-glucose and D-mannose from D-arabinose: 4 possible sets;  1107
oxidation of D-glucose and D-mannose with HNO3: optically active aldaric acids;  1106 bot & 1108 top
HNO3 oxidation of D-arabinose: active;  1108 bot
HNO3 oxidation of L-gulose & D-glucose → 13 vs only one aldohexose 8 (16)→ 15;  1109
All altruists gladly make gum in a gallon tank:  1089
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33. cyanohydrin
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35. (not optically active)
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36. (not optically active)
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37. / H
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38. Other Reactions of Monosaccharides
Bioorganic Chemistry
Spring 2006
Other Reactions of Monosaccharides
Ruff-Fenton degradation: OH-CH-CHO → CHO
one-C less aldose: H-O-O-H, Fe3+; radical (•OH)
Osazone formation with 3 eq. of PhNHNH2
the same bis(phenylhydrzone) from 2-epi-aldose
Conversion of an aldose into its 2-epimer
epimerization of aldonic acids with pyridine
Correlation of absolute configuration: chemical
D-(-)-glyceraldehyde with D-(-)-tartaric acid
X-ray structure of Na/Rb L-(+)-tartrate: Bijvoet (1951)
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40. D-(-)-ribose
D-(-)-arabinose
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41. D-(+)-glucose
D-(+)-mannose
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42. meso-tartaric acid
D-(-)-tartaric acid
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43. Disaccharides (I) (+)-maltose: hydrolysis of starch, C12H22O11
Bioorganic Chemistry
Spring 2006
Disaccharides (I)
(+)-maltose: hydrolysis of starch, C12H22O11
reducing sugar, mutarotation, osazone: hemiacetal
2 glucose & a-glycosidic bond: hydrolysis & maltase
(+)-cellobiose: from cellulose, C12H22O11
2 glucose & b-glycosidic bond: hydrolysis & emulsin
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44. 4-O-(a-D-glucopyranosyl)-D-glucopyranose
4-O-(b-D-glucopyranosyl)-D-glucopyranose
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45. Disaccharides (II) (+)-lactose: in milk & by-product of cheese
Bioorganic Chemistry
Spring 2006
Disaccharides (II)
(+)-lactose: in milk & by-product of cheese
into lactic acid by Lactobacillus bulgaricus
galactose-glucose by a b-glycosidic bond: emulsin
(+)-sucrose: sugar cane, non-reducing sugar
a-glucopyranoside & b-fructofuranoside: acetal
synthesis of sucrose by R. U. Lemieux in 1953: the Mount Everest of organic chemistry
hydrolysis & invertase: (+) → (-); inversion of sucrose
(+)-sucrose → inverta sugar [(+)-glucose +52.7, ‘dextrose’ & (-)-fructose -92.4, ‘levulose’]
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46. 4-O-(b-D-galactopyranosyl)-D-glucopyranose
a-D-glucopyranosyl b-D-fructofuranoside
b-D-fructofuranosyl a-D-glucopyranoside
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47. Polysaccharides Cellulose: (C6H10O5)n; wood and plant fibers
Bioorganic Chemistry
Spring 2006
Polysaccharides
Cellulose: (C6H10O5)n; wood and plant fibers
hydrolysis of permethylated cellulose: 2,3,6-tri-O-methyl-D-glucose; 4-O-b-glucoside; non-reducing
MW 250,000 – 1,000,000: > 1500 glucose units
insoluble & tasteless, > 1015 kg from CO2 & H2O: biomass
Starch: (C6H10O5)n; food reserve of plants
20% amylose (soluble), 80% amylopectin (insoluble)
hydrolysis to dextrin → (+)-maltose → (+)-glucose
> 1000 (amylose) to 106 glucose units (amylopectin)-every branch/20-30 glucose
glycogen: food reserve in animals;  1113 top
similar to amylopectin but every branch/8-10 glucose units
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48. cellulose [4-O-(b-D-glucoopyranosyl)]
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50. Other Carbohydrates Cyclodextrins: oligosaccharides of > 6 glucose
Bioorganic Chemistry
Spring 2006
Other Carbohydrates
Cyclodextrins: oligosaccharides of > 6 glucose
by amylase of Bacillus macerans: a-(6), b-(7), g-(8)
cyclic pail-shaped 1,4-a-linkage (4.5 Å across): host-guest complex; polar outside/non-polar inside
enzyme models: binding and then reaction of substrates
Amino sugars: -NHR;  1114 top & chitin
Deoxy sugras: -H;  1114 bottom
Glycoproteins: sugar-protein;  1115 top
glycolipids: sugar-lipid;  1113 top
Sweeteners: with adjacent OHs (glycol)
artificial sweeteners:  1104 top
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51. a-cyclodextrin (6 glucose units)
top view
side view
a-cyclodextrin (6 glucose units)
[18-crown-6: 2.7 Å (K+: 2.66 Å)]
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52. (chitin) O-2-deoxy-2-(methylamino)-a-L-glucopyranosyl-
(1→2)-O-5-deoxy-3-C-formyl-a-L-lyxofuranosyl-
(1→4)-N,N’-bis(aminoiminomethyl)-D-streptamine
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