Carbohydrates hydrates of carbon: general formula C n ( ) n Plants: photosynthesis hν 6 C + 6 C 6 6 + 6 Polymers: large molecules made up of repeating smaller units (monomer) Biopolymers: carbohydrates (Chapter ) peptides and proteins (Chapter 7) nucleic acids (Chapter 8) Monomer units: monosaccharides amino acids nucleotides 6
.: Classification of Carbohydrates. I. Number of carbohydrate units monosaccharides: one carbohydrate unit (simple carbohydrates) disaccharides: two carbohydrate units (complex carbohydrates) trisaccharides: three carbohydrate units polysaccharides: many carbohydrate units C C 7
II. Position of carbonyl group at C, carbonyl is an aldehyde: aldose at any other carbon, carbonyl is a ketone: ketose III. Number of carbons three carbons: triose four carbons: tetrose five carbons: pentose six carbons: hexose seven carbons: heptose etc. IV. Cyclic form (chapter.6 and.7) C C C C C C C C C C glyceraldehyde (triose) threose (tetrose) ribose (pentose) glucose (hexose) (aldohexose) fructose (hexose) (ketohexose) 8
.: Fischer Projections and the D-L Notation. Representation of a three-dimensional molecule as a flat structure. Tetrahedral carbon represented by two crossed lines: horizontal line is coming out of the plane of the page (toward you) substituent (R)-(+)-glyceraldehyde carbon vertical line is going back behind the plane of the paper (away from you) C C C C C C C (S)-(-)-glyceraldehyde C C C C C C C 9
before the R/S convention, stereochemistry was related to (+)-glyceraldehyde C C C C D-glyceraldehyde R-(+)-glyceraldhyde (+)-rotation = dextrorotatory = D L-glyceraldehyde S-(-)-glyceraldhyde (-)-rotation = levorotatory = L D-carbohydrates have the - group of the highest numbered chiral carbon pointing to the right in the Fisher projection as in R-(+)-glyceraldhyde For carbohydrates, the convention is to arrange the Fischer projection with the carbonyl group at the top for aldoses and closest to the top for ketoses. The carbons are numbered from top to bottom. 0
Carbohydrates are designated as D- or L- according to the stereochemistry of the highest numbered chiral carbon of the Fischer projection. If the hydroxyl group of the highest numbered chiral carbon is pointing to the right, the sugar is designated as D (Dextro: Latin for on the right side). If the hydroxyl group is pointing to the left, the sugar is designated as L (Levo: Latin for on the left side). Most naturally occurring carbohydrates are of the D-configuration. highest numbered "chiral" carbon C 6 C C C highest numbered "chiral" carbon D-Glucose L-Arabinose highest numbered "chiral" carbon C C L- glucose C C D-Arabinose highest numbered "chiral" carbon
.: The Aldotetroses. Glyceraldehyde is the simplest carbohydrate (C, aldotriose,,-dihydroxypropanal). The next carbohydrate are aldotetroses (C,,,-trihydroxybutanal). aldotriose C C C C D-glyceraldehyde L-glyceraldehyde highest numbered "chiral" carbon aldotetroses C C C C D-erythrose L-erythrose highest numbered "chiral" carbon C C highest numbered "chiral" carbon C C highest numbered "chiral" carbon D-threose L-threose
.: Aldopentoses and Aldohexoses. Aldopentoses: C, three chiral carbons, eight stereoisomers C C C C C C C C D-ribose D-arabinose D-xylose D-lyxose Aldohexoses: C 6, four chiral carbons, sixteen stereoisomers C C C C C C C C C C C C C C C C D-allose D-altrose D- glucose D-mannose D-gulose D-idose D-galactose D-talose
Manipulation of Fischer Projections. Fischer projections can be rotate by 80 (in the plane of the page) only! C C 80 80 C C C C C C (R) (R) (S) (S) 80 80 Valid Fischer projection Valid Fischer projection
a 90 rotation inverts the stereochemistry and is illegal! 90 C C C C (R) (S) 90 90 This is not the correct convention for Fischer projections Should be projecting toward you Should be projecting away you This is the correct convention for Fischer projections and is the enantiomer
. If one group of a Fischer projection is held steady, the other three groups can be rotated clockwise or counterclockwise. hold steady C C (R) C (R) C C hold steady C (S) C C (S) QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. 0 0 QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. hold steady hold steady hold steady QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. 0 QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. 0 QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. hold steady hold steady hold steady 6
Assigning R and S Configuration to Fischer Projections. Assign priorities to the four substitutents according to the Cahn-Ingold-Prelog rules. Perform the two allowed manipulations of the Fischer projection to place the lowest priority group at the top or bottom.. If the priority of the other groups is clockwise then assign the carbon as R, if priority of the other groups is counterclockwise then assign the center as S. N hold steady rotate other three groups counterclockwise C C place at the top C N C -- counterclockwise = S C N C N C C C N C -- clockwise = R 7
Fischer projections with more than one chiral center: C C C Threose C C C S old Steady C C (S, R) old Steady C C C R S C 8
.: A Mnemonic for Carbohydrate Configuration. (please read).6: Cyclic Forms of Carbohydrates: Furanose Forms. R + R + R R +, R R R R (Ch. 7.8) hemiacetal acetal R +, R Ch.. cyclic hemiacetal mixed acetal (glycoside) 9
In the case of carbohydrates, cyclization to the hemiacetal creates a new chiral center. * C C * + * D-erythrose Converting Fischer Projections to aworth formulas 60
.7: Cyclic Forms of Carbohydrates: Pyranose Forms. C D-ribose C ribopyranose new chiral center C 6 C D-glucose C 6 C 6 C 6 C 6 C C 6 glucopyranose new chiral center 6
.8: Mutarotation and the Anomeric Effect. The hemiacetal or hemiketal carbon of the cyclic form of carbohydrates is the anomeric carbon. Carbohydrate isomers that differ only in the stereochemistry of the anomeric carbon are called anomers. Mutarotation: The α- and β-anomers are in equilibrium, and interconvert through the open form. The pure anomers can be isolated by crystallization. When the pure anomers are dissolved in water they undergo mutarotation, the process by which they return to an equilibrium mixture of the anomer. C C C Cis β-d-glucopyranose (6%) (β-anomer: C- and C are cis) C D-glucose C C Trans α-d-glucopyranose (6%) (α-anomer: C- and C are trans) 6
.9: Ketoses. Ketoses are less common than aldoses C C C C C C C C dihydroxyacetone D-ribulose Dxylulose C D-fructose C D-sedohepuloase Fructofuranose and Fructopyranose C 6 C C 6 C C 6 C 6 C furanose C 6 C C 6 C C 6 C 6 pyranose C 6
.0: Deoxy Sugars. Carbohydrates that are missing a hydroxy group. C C C C C C D-ribose -Deoxy-D-ribose 6 C C 6 C 6 C C 6 C L-Galactose 6-Deoxy-L-Galactose (fucose) 6
.: Amino Sugars. Carbohydrates in which a hydroxyl group is replaced with an -N or -NAc group C N N-acetyl-D-glucosamine (GlcNAc or NAG) C C N C N-Acetylmuramic acid (MurNAc).: Branched-Chain Sugars. (Please read) 6
.: Glycosides. Acetals and ketals of the cyclic form of carbohydrates. R + R + R R +, R R R R C C D-glucose C pyranose (hemiacetal) R + hemiacetal C R + Glycoside (acetals) acetal C R Note that only the anomeric hydroxyl group is replaced by R 66
.: Disaccharides. A glycoside in which R is another carbohydrate unit (complex carbohydrate). maltose (,'-α-glycoside) cellobiose (,'-β-glycoside).: Polysaccharides. Cellulose: glucose polymer made up of, -β-glycoside linkages Amylose: glucose polymer made up of, -α-glycoside linkages Lactose (,'-β-glycoside) sucrose (,'-glycoside) 67
Amylopectin:.6: Reactions of Carbohydrates. Glycoside formation is related to acetal formation..7: Reduction of Monosaccharides. C of aldoses are reduced with sodium borohydride to the alcohol (alditols) C Reacts like A carbonyl C C NaB C C D-glucose D-glucitol 68
Reduction of ketoses C C NaB C C + C C D-fructose D-glucitol D-mannitol.7: xidation of Monosaccharides. C of aldoses can be selectively oxidized to the carboxylic acid (aldonic acids) with Br or Ag(I) (Tollen s test). C C C Br Ag(I) N, Ag(0) C C C aldonic acid C C Reducing sugars: carbohydrates that can be oxidized to aldonic 69 acids.
xidation of aldoses to aldaric acids with N. C C N C C Glucaric acid Uronic Acid: Carbohydrate in which only the terminal -C is oxidized to a carboxylic acid. C C [] C C Gluronic acid C 70
Reducing sugars: carbohydrates that can be oxidized to aldonic acids. reducing end Ag(I) [] + Ag(0) cellobiose and maltose are reducing sugar lactose (,'-β-glycoside) glucose ' reducing end sucrose (,'-glycoside) α ' β fructose Ag(I) [] No reducing end [] No reaction Ag(I) sucrose is not a reducing sugar lactose is a reducing sugar + Ag(0) 7
.9: Cyanohydrin Formation and Chain Extension. Kiliani-Fischer Synthesis- chain lengthening of monosaccharides 7
Determination of carbohydrate stereochemistry ) CN ), Pd/BaS ) C C D-(-)-erythrose N, heat C C tartaric acid C C Killiani-Fischer synthesis D-(+)-glyceraldehyde ) CN ), Pd/BaS ) C C D-(-)-threose N, heat C C D-(-)-tartaric acid 7
C ) CN ), Pd/BaS ) C C D-(-)-ribose N, heat C C ribonic acid Killiani-Fischer synthesis C D-(-)-erythrose ) CN ), Pd/BaS ) C C N, heat C C D-(-)-arabinose arabonic acid 7
) CN ), Pd/BaS ) C N, heat C C C C D-(+)-xylose xylonic acid Killiani-Fischer synthesis C D-(-)-threose ) CN ), Pd/BaS ) C C N, heat C C D-(-)-lyxose lyxonic acid 7
C C C C C C C C D-ribose D-arabinose D-xylose D-lyxose C C C C C C C C C C C C C C C C D-allose D-altrose D- glucose D-mannose D-gulose D-idose D-galactose D-talose C C C C C C C C C C C C C C C C optically inactive optically active optically active optically active optically active optically active optically inactive optically active enantiomers 76
.0: Epimerization, Isomerization and Retro-Aldol Cleavage. C 6 C C C, C 6 C C C, C 6 C C C C (R), C, C (S) C D-glucose C C D-mannose, C C D-fructose Fructose is a reducing sugar (gives a positive Tollen s test) 77
Retro-aldol reaction of carbohydrates C C D-fructose :B C C + C D-Glyceraldehyde C -B C C Dihydroxyacetone Glycolysis C C P - D-glucose-6-phosphate phosphoglucose isomerase C C P - D-fructose-6-phosphate phosphoglucose isomerase - P C C α-d-fructofuranose- 6-phosphate - P C phosphofructokinase D-fructose-,6-bisphosphate C P - C P - aldolase aldolase C P - + C Dihydroxyacetone C P - phosphate D-fructose-,6-bisphosphate C triose phosphate isomerase C P - D-glyceraldehyde- -phosphate 78
.: Acylation and Alkylation of ydroxyl Groups Acylation (ester formation): β-d-glucopyranose C C pyridine Alkylation (ether formation): C C C C C β-d-glucopyranose C C Ag, C I + C C C C C C C C C C C C C C.: Periodic Acid xidation. The vicinal diols of carbohydrate can be oxidative cleaved with I. 79