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The Carbohydrates

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The Carbohydrates Title The Carbohydrates [C(H2O)]n Emil Hermann Fischer (1852-1919) F-R Convention The Fischer-Rosanoff Convention CHO CHO CHO H OH H OH C2-OH H OH H OH C3-OH H OH H OH C4-OH H OH H OH C5-OH CH2OH CH2OH C6-CH2OH Fischer Projections Rosanoff Modification D/L Series Fischer-Rosanoff D- and L-Series OH on the right of the highest OH on the left of the highest numbered chiral carbon = D-series. numbered chiral carbon = L-series. D-Aldohexoses The D-Aldohexoses C5 8 right C3 2 right 2 left 2 right 2 left C4 4 right 4 left C2 right left right left right left right left Allose Glucose Gulose Galactose Altrose Mannose Idose Talose All altruists gladly make gum in gallon tanks [L. Fieser] Rxn of Aldoses Reactions of Aldoses CHO =N-NHPh CHO HO OH 3 equiv. PhNHNH2 =N-NHPh 3 equiv. PhNHNH2 OH OH OH OH OH HNO3 OH HNO3 OH OH OH osazone NaBH4 NaBH4 CH2OH CH2OH CH2OH Br2/H2O + PhNH2 + NH3 Br2/H2O CO2H CH2OH CO2H CO2H CH2OH CO2H OH OH OH HO HO HO OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH CH2OH CH2OH CO2H CO2H CH2OH CH2OH aldonic acid alditol aldaric acid aldaric acid alditol aldonic acid achiral achiral Osazones More on Osazones CHO CH2OH CHO O Ca(OH)2 OH Ca(OH)2 HO HO HO HO OH OH OH (Lobry de Bruyn- OH OH Alberda van Eckenstein OH rearrangement, 1895) CH2OH CH2OH CH2OH D-glucose D-fructose D-mannose 1 equiv. 3 equiv. 1 equiv. PhNHNH2 PhNHNH2 PhNHNH2 =N-NHPh =N-NHPh 2 equiv. 2 equiv. =N-NHPh PhNHNH2 HO OH =N-NHPh PhNHNH2 HO HO HO OH OH OH OH OH OH CH2OH CH2OH CH2OH D-glucose phenylhydrazone + PhNH2 + NH3 D-mannose phenylhydrazone F-K and Ruff Chain Lengthening and Shortening of Aldoses CN CHO CN OH HCN OH HCN HO OH OH OH OH Fischer-Kiliani OH Fischer-Kiliani OH OH Synthesis Synthesis OH CH2OH CH2OH CH2OH Fe+++ Pd/BaSO4 H O Pd/BaSO4 pH 4.5, H 2 2 pH 4.5, H 2 Ruff 2 Degradation CHO CO2Ca1/2 CO2Ca1/2 CHO Br2/H2O OH OH HO Br2/H2O HO OH OH OH OH OH OH OH OH OH OH OH OH CH2OH CH2OH CH2OH CH2OH Aldonic acid as Ca salt D-Series Interrelationship Interrelationship of the D-Series of Aldoses via Chain Lengthening and Degradation Which one is Glucose? The Aldohexoses But which one is (+)-glucose? D-series L-series Aldaric Acids/Alditols Rosanoff Formulation of C6 Aldaric Acids and Alditols Terminal groups identical; CO2H or CH2OH Fischer Proof: 1 Fischer’s Proof: Part 1 (+)-Glucose forms an optically active aldaric acid and optically active alditol. •1, 7, 9, 15 eliminated: plane of symmetry, achiral 1 2 3 4 5 6 7 8 X X X X 9 10 11 12 13 14 15 16 Fischer Proof:2 Fischer’s Proof: Part 2 (+)-Glucose and (+)-mannose form the same osazone. If 1, 7, 9, and 15 are not related to (+)-glucose, then they are not related to (+)-mannose nor are 2, 8, 10, and 16 related to (+)-glucose. 1 2 3 4 5 6 7 8 X X X X X X X X 9 10 11 12 13 14 15 16 Fischer Proof:3 Fischer’s Proof: Part 3 (+)-Arabinose affords (-)-glucose and (-)-mannose by Kiliani-Fischer synthesis. (+)-Arabinose must be of the opposite series (D/L)as (+)-glucose and have the same absolute configuration at C3-5 as (-)-glucose and (-)-mannose. What is the structure of arabinose? F P:3, con’t •Arabinose is either or X •Arabinose forms an optically active aldaric acid (arabinaric acid) and optically active alditol X X (arabitol) as its borax complex. •Arabinose is X X and not •(+)-Glucose is one of these structures X Fischer Proof:4 Fischer’s Proof: Part 4 The pentose (+)-xylose affords optically inactive xylaric acid and optically inactive xylitol as its borax complex. • (+)-Xylose can only be one of the following: X X Fischer-Kiliani synthesis of (+)-xylose leads to two new hexoses, (+)-gulose and (+)-idose, both of which form optically active aldaric acids. • These enantiomers cannot be (+)-xylose because their Fischer-Kiliani hexoses (already eliminated) would lead to one optically active and one optically inactive aldaric acid. • (+)-Xylose must be one of the remaining two structures. Fischer Proof:5 Fischer’s Proof: Part 5 •(+)-Arabinose •(+)-Glucose/(+)-Mannose •(+)-Xylose •(+)-Gulose/(+)-Idose Fischer Proof:5, con’t Fischer’s Proof: Part 5 (+)-Glucose and (-)-gulose form the same optically active aldaric acid, glucaric acid. identical or identical • (+)-Glucose must be either Fischer Proof:5, con’t-2 Fischer’s Proof: Part 5 • (+)-Mannose must be one of these hexoses, the C2 epimer of (+)-glucose. identical rotate 180o mannaric acid rotate 180o identical • Mannaric acid is formed from a single hexose. Fischer Proof:6 Fischer’s Proof: Part 6 But which enantiomer of glucose is (+)-glucose? Just Guess! D-glucose L-glucose • Fischer arbitrarily assigned the D-series to the dextrorotatory enantiomer. • Sixty years later (1951), he was proved correct when Bijvoet related (+)-glucose to (+)-tartaric acid. • Fischer: All sugars related to D-(+)-glucose by chemical correlation belong to the D-series. Fischer’s Flaw A Flaw in the Fischer Scheme (+)-Glucose (-)-Glucose Identical Achiral Mucic Acid (An Aldaric Acid) (+)-Galactose (-)-Galactose "Two aldoses can produce the same dibasic acid only if they belong to the same stereochemical family. That this, however, is erroneous as a general proposition, may be readily seen from the fact that the two enantiomorphous galactoses - plainly belong to the opposite families - yield the same mucic acid.” A. M. Rosanoff-1906 Rosanoff’s Wheel Rosanoff’s Reorganization of the Carbohydrates •Arranged by successive Kiliani syntheses • The D- and L- assignments were Fischer’s based on chemical correlation with D-(+)-glucose, an unreliable scheme. 2 4 8 16 λ-series δ-series mirror plane Evolution of Signage Evolution of Signage Optical Activity Configuration Fischer-1891 +/- d,l Rosanoff-1906 +/- δ,λ Today +/- = d,l D,L D-Aldohexoses The D-Series of Aldoses aldotriose (+)-glyceraldehyde aldotetrose (-)-erythrose (+)-threose aldo pentose (-)-ribose (-)-arabinose (+)-xylose (-)-lyxose aldo hexose (+)allose (+)-altrose (+)-glucose (+)-mannose (-)-gulose (-)-idose (+)-galactose (+)-talose All altruists gladly make gum in gallon tanks [L. Fieser] Fischer Projections Fischer Projections of Glucose CHO CHO 2 OH OH HO 3 HO = 4 OH OH form hemiacetals between 5 OH HOH2C C5-OH and C1 CH2OH OH o D-(+)-Glucose rotate C5 about C4 by 120 Anomers Fischer Projections of Glucopyranose Anomers right left HO C C OH beta alpha OH OH HO HO OH OH O O CH2OH CH2OH β-D-(+)-Glucopyranose α-D-(+)-Glucopyranose Haworth Haworth Projections of Glucopyranose Anomers up (top) beta CH OH down (bottom) CH2OH 2 OH alpha O O OH OH OH OH OH OH OH β-D-(+)-Glucopyranose α-D-(+)-Glucopyranose Conformational Glucopyranose Chair Conformations of Glucopyranose Anomers up (top) down (bottom) beta alpha OH OH O O HO H O OH HO HO OH OH OH β-D-(+)-Glucopyranose α-D-(+)-Glucopyranose Old Salt How an Old Salt Remembers port starboard left right red light green light fewer letters more letters beta alpha up down top bottom Mutarotation Mutarotation of Anomers OH OH O O HO H O OH HO HO OH OH OH β-D-(+)-Glucopyranose α-D-(+)-Glucopyranose Crystallizes above 98oC Crystallizes below 98oC equilibrium pure β-anomer mixture pure α-anomer H2O H2O mp 150oC [α] = +52.6o mp 146oC o o [α]D = +18.7 [α]D = +112.2 β/α =64/36 Ring Sizes of Hexoses Ring Sizes of Hexoses Hexose Pyranose Form (%α/%β) Furanose Form allose 92 8 altrose 70 30 glucose ~100(36.5/63.5) <1 mannose ~100(67/33) <1 gulose 97 3 idose 75 25 galactose 93(27.5/72.5) 7 talose 69 31 fructose 67 33 Periodic acid Periodic Acid Cleavage of Carbohydrates as a Diagnostic Tool OH HIO4 2 CH2=O OH OH HIO4 HIO4 CHO OH CH2=O + CH2=O + HCO2H OH OH H O HO 2 OH HIO4 OH Formaldehyde (CH2O) arises from a primary alcohols Formic acid (HCO2H) arises from a secondary alcohols Periodic Acid Diagnostic Periodic Acid Cleavage of Carbohydrates as a Diagnostic Tool OH HIO4 OH 2 CH2=O + HCO2H OH • RCH2OH CH2=O • R2CHOH HCO2H CHO • RCH=O HCO2H HIO4 OH CH2=O + 2 HCO2H • R2C=O CO2 OH OH HIO CO2H HIO 4 4 CH =O + CO O CH2=O + 2 2 OH OH Periodic on Carbohydrates Periodic Acid Cleavage of Carbohydrates CHO HCO2H OH HCO2H HO HCO2H OH HCO2H OH HCO2H CH2OH H2CO OH H2CO CO D-glucose O 2 HO HCO2H OH HCO2H OH HCO2H CH2OH H2CO CH2OH H2CO HO HCO H 2 D-fructose HO HCO2H OH HCO2H OH HCO2H CH2OH H2CO D-mannitol Methylation Methylation of Pyranoses: Pyranosides OH OH O + O CH3OH, H HO HO HO HO HO HO OH OCH3 CH3I Ag2O (CH3)2SO4 NaOH OCH3 OCH3 + O H3O O CH3O CH3O CH3O CH3O CH3O CH3O OH OCH3 Ring Size Ring Size of Pyranosides CO2H OCH3 O OCH HNO3 3 CH3O CH3O CH3O CO2H CH3O CO2H HNO3 HNO3 CO2H OCH OCH3 3 O CH3O CH3O OCH CH3O 3 CH3O OH CO2H via oxidation of the enol of the ketone Periodic on Glycosides Periodic Acid Cleavage of Methyl α-Glucopyranoside OH OH HIO O 4 OHC O HO HCO H OHC HO 2 HO OCH3 OCH3 + H3O CHO OH + OHCCHO + CH3OH OH glyoxal D-glyceraldehyde Enzymes Enzymatic Cleavage of Glucosides HO HO O O HO HO OCH HO HO 3 HO HO + OCH3 H3O Methyl α-D-glucoside Methyl β-D-glucoside maltase emulsin HO HO O O HO OH HO HO HO HO HO OH α-D-glucose β-D-glucose Tollens The Silver Mirror Test HO O Tollens reagent HO no reaction HO + - Ag(NH3)2 OH HO OCH3 Methyl -D-glucoside non-reducing sugar (a glycoside) CO2H HO OH O Tollens reagent HO HO OH o HO + - + Ag Ag(NH3)2 OH HO OH OH silver mirror CH2OH D-glucose reducing sugar (an aldose) www.chem-pics.co.uk/download.htm Tollens 2 The Silver Mirror Test HO OH CH2OH OH enediol O O + - Ag(NH3)2 OH OH HO HO OH HO OH OH OH OH OH CH2OH β-D-fructofuranose CH2OH D-fructose + - Ag(NH3)2 OH CO2H CHO OH + - OH o Ag(NH3)2 OH Ag + HO HO OH OH silver mirror OH OH CH2OH CH2OH Aldoses and ketoses are reducing sugars Intro: Di- and Polysaccharides Disaccharides and Polysaccharides Sucrose/Olestra α-D-Glucopyranosyl- β -D-fructofuranoside or β-D-Fructofuranosyl-α-D-glucopyranoside OH OOCR O O HO RCOO HO acetal RCOO HO RCOO O HO O RCOO O O ketal HO RCOO OH OOCR HO RCOO Sucrose Olestra (non-reducing sugar) (R=n-CnH2n+1; n=6-8) Woodward Sucrose is Formed from Glucose and Fructose This discussion brings to mind a wonderful story told to me by Professor Harry Wasserman (Yale), who during the late 1940's was a graduate student of Professor R.
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