Chapter : Carbohydrates hydrates of carbon: general formula C n ( ) n Plants: photosynthesis hν C + C + Polymers: large molecules made up of repeating smaller units (monomer) Biopolymers: Monomer units: carbohydrates (Chapter ) monosaccharides peptides and proteins (Chapter ) amino acids nucleic acids (Chapter ) nucleotides Synthetic Polymers (Chapter 7) various.: 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 (oligosaccharides): many carbohydrate units C glucose C galactose glucose glucose 8
II. Position of carbonyl group the carbonyl at C is an aldehyde: aldose the carbonyl at any other carbon is a ketone: ketose III. Number of carbons three carbons: triose six carbons: hexose four carbons: tetrose seven carbons: heptose five carbons: pentose etc. IV. Cyclic form (Chapter. and.7) C C glyceraldehyde (triose) C C threose (tetrose) C C ribose (pentose) C C glucose (hexose) (aldohexose) C C fructose (hexose) (ketohexose).: Fischer Projections and the D, L Notation. Representation of a three-dimensional molecule as a flat structure (Ch. 7.7). Tetrahedral carbon represented by two crossed lines: horizontal line is coming out of the plane of the page (toward you) substituent (R)-(+)-glyceraldehyde C C C vertical line is going back behind the plane of the paper (away from you)! carbon 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-(+)-glyceraldehyde (+)-rotation = dextrorotatory = d L-glyceraldehyde S-(-)-glyceraldehyde (-)-rotation = levorotatory = l D-carbohydrates have the - group of the highest numbered chiral carbon pointing to the right in the Fischer projection as in R-(+)-glyceraldehyde. 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. 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 carbohydrate is designated as D (Dextro: Latin for on the right side). If the hydroxyl group is pointing to the left, the carbohydrate 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 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 0
.: 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 highest numbered "chiral" carbon C C C C highest numbered "chiral" carbon D-threose L-threose 7.: 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, 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 8
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 9 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 70
. If one group of a Fischer projection is held steady, the other three groups can be rotated clockwise or counterclockwise. hold steady C C C C (R) (R) C hold steady C C (S) (S) 0 0 hold steady hold steady C hold steady 0 0 hold steady hold steady hold steady 7 Assigning R and S Configuration to Fischer Projections. Assign priorities to the four substituents 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 the priority of the other groups is counterclockwise then assign the center as S. C N hold steady rotate other three groups counterclockwise place at the top C C -- counterclockwise = S N C N C C N C C -- clockwise = R C N C 7
Fischer projections with more than one chiral center: C C C C Threose 7.: A Mnemonic for Carbohydrate Configuration. (please read).: 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) 7
Cyclization of carbohydrates to the hemiacetal creates a new chiral center. 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 and designated as α and β. * C C * + * D-erythrose Converting Fischer Projections to aworth formulas 7.7: Cyclic Forms of Carbohydrates: Pyranose Forms. C D-ribose C ribopyranose new chiral center C C C C D-glucose C C C C glucopyranose Note: the pyranose forms of carbohydrates adopt chair conformations. new chiral center 7
.8: 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 C acid-catalyzed mechanism: p. 99 C β-d-glucopyranose (%) (β-anomer: C- and C are cis) C cis trans α-d-glucopyranose (%) (α-anomer: C- and C are trans) [α] D +8.7 [α] D +. 77.9: Carbohydrate Conformation: The Anomeric Effect (please read).0: Ketoses. Ketoses are less common than aldoses C C dihydroxyacetone C C D-ribulose C C Dxylulose Fructofuranose and Fructopyranose C C C C C C D-fructose C C C D-sedohepuloase C C C furanose C C C C C C 78 pyranose
.: Deoxy Sugars. Carbohydrates that are missing a hydroxy group. C C C C C C D-ribose -Deoxy-D-ribose C C L-Galactose C C C -Deoxy-L-Galactose (fucose) C.: 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) 79.: Branched-Chain Carbohydrates. (Please read).: Glycosides: The Fischer Glycosylation. 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 acetal C R acid-catalyzed mechanism: Mechanism., p. 97 Note that only the anomeric hydroxyl group is replaced by R 80 7
.: 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) 8 Amylopectin: Branched amylose polysaccaride.7: Application of Familiar Reactions to Monosaccharides. (Table., p. 97) 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 8 8
Reduction of ketoses Cyanohydrin formation C C D-arabinose β-d-glucopyranose C C D-fructose CN C C pyridine NaB CN C C, Cl C C pyridine C C C D-glucitol + C C C C C C + CN C Acylation of the ydroxyl Groups (ester formation): C C D-mannitol C C C C 8 Alkylation of ydroxyl Groups (ether formation) β-d-glucopyranose Acetal formation C C Ag, C I + C C C C C C C C K, PhC Br Furanose pyranose isomerization PhC ZnCl Ph C Ph C Ph C Ph C Ph C C C C C C C C C C D-ribopyranose D-ribose D-ribofuranose 8 9
Enolization and Epimerization C C C C, C C C C, C C C C from Ch 0. C (R) C D-glucose, C C, C (S) C D-mannose Aldose to ketose isomerization, C C D-fructose 8 Retro-aldol reaction of carbohydrates C C D-fructose :B C C + C D-Glyceraldehyde C -B C C Dihydroxyacetone.8: 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 Br C C C C C Ag(I) N, Ag(0) C C 8 aldonic acid 0
Reducing sugars: carbohydrates that can be oxidized to aldonic acids. reducing end Ag(I) [] + Ag(0) cellobiose and maltose are reducing sugar ' lactose reducing (,'-β-glycoside) end glucose sucrose (,'-glycoside) Ag(I) α [] fructose No reducing end ' β No reaction Ag(I) [] sucrose is not a reducing sugar lactose is a reducing sugar + Ag(0) 87 xidation of aldoses to aldaric acids with N. C C N C C Glucaric acid C Uronic Acid: Carbohydrate in which only the terminal -C is oxidized to a carboxylic acid. C C [] C C Gluronic acid C Periodic Acid xidation. The vicinal diols of carbohydrate can be oxidative cleaved with I. 88
Kiliani-Fischer Synthesis: chain lengthening of monosaccharides 89 Symmetry Monarch butterfly: bilateral symmetry= mirror symmetry Mirror symmetry Mirror symmetry & axis ( fold) of symmetry Whenever winds blow butterflies find a new place on the willow tree -Basho (~ - 9) Point (center) of symmetry 90
Determination of carbohydrate stereochemistry ) CN ), Pd/BaS ) C C D-(-)-erythrose C C Killiani-Fischer synthesis D-(+)-glyceraldehyde ) CN ), Pd/BaS ) C C D-(-)-threose 9 C C D-(-)-erythrose ) CN ), Pd/BaS ) Killiani-Fischer synthesis ) CN ), Pd/BaS ) C C D-(-)-ribose C C D-(-)-arabinose 9
C C D-(-)-threose ) CN ), Pd/BaS ) Killiani-Fischer synthesis ) CN ), Pd/BaS ) C C D-(+)-xylose C C D-(-)-lyxose 9 C C D-ribose C C C C C C 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 9
.: Glycosides: Synthesis of ligosaccharides Mechanism.: p. 980 Ac Ac Ac Ac Ac Br Ac Ac Ac Ac.: Glycobiology (please read) Br Ac Ac Ac Ag, base Glycoproteins: glycosides of proteins carbohydrate N serine C N X Ac Ac Ac Ac Protein Ac Ac Ac X= -- or -N- carbohydrate C N threoine C N N carbohydrate N asparagine N 9 Chapter : Lipids. ydrophobic (non-polar, soluble in organic solvent), typically of low molecular weight compounds of organic origin. fatty acids and waxes essential oils many vitamins hormones (non-peptide) components of cell membranes (non-peptide) Share a common biosynthesis that ultimately derives their carbon source from glucose (glycolysis) Glucose pyruvate lactate C C C C C C C C 9