The Carbohydrates

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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

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

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

• (+)-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

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. B. Woodward at Harvard. Apparently Woodward had received a notice of a $1,000 prize for the ﬁrst person to accomplish a chemical synthesis of sucrose. He went into the laboratory and said to his students that all they had to do was connect two molecules of glucose together [...and lose a molecule of water] and they would have themselves $1,000. One student, obviously not overwhelmed by Woodward's stature in the ﬁeld even at such a young age, replied that if you did it that way,

the prize would be $2,000! Sucralose

Sucralose

1,6-Dichloro-1,6-dideoxy-β-D-fructofuranosyl-4-chloro-4-deoxy-α-D-galactopyranoside

OH Cl OH O galacto O HO HO HO OH OH gluco HO O Cl O O O OH OH OH Cl OH OH

Sucrose Sucralose (non-reducing sugar) (600 times sweeter than sucrose) Bees Do It

Bees Do It

CHO OH OH HO O OH HO OH HO CH OH HO 2 O + HO or H3O o D-glucose [α]D = +52.7 O dextrose HO invertase OH OH HO

o O Sucrose [α]D = +66.5 (non-reducing, non-mutarotating sugar) HO OH OH

CH2OH

o D-fructose [α]D = -92.4 levulose Cellobiose

Disaccharides-Cellobiose

HO HO HO O O O HO O O Cellulose (polysaccharide) HO HO HO OH HO HO HO n β-acetal linkage

partial emulsin, β-glucosidase (termites, ruminants) hydrolysis + H3O 4-O-attachment

HO HO O O HO HO OHO OH HO HO

Cellobiose (disaccharide)

4-O-(β-D-glucopyranosyl)-D-glucopyranose Cellobiose-Str. Proof

Cellobiose-Structure Proof

HO HO O OH HO HO Br2/H2O O O HO O HO HO HO CO2H HO OHO OH HO HO HO HO

Cellobiose permethylation

•hydrolysis ----> only D-glucose MeO MeO O OMe MeO O •emulsin ----> β-glucoside MeO MeO CO2H MeO MeO

•positive Tollens test ----> reducing sugar + H3O •shows mutarotation CO2H CHO OMe OMe MeO MeO OH OMe OMe OH

CH2OMe CH2OMe tetramethoxy- tetramethoxy carboxylic acid aldehyde Cellobiose-Str. Proof

HO HO O O MeO MeO O OMe HO O OH Cellobiose-Structure Proof HO HO MeO O HO HO MeO MeO CO2H MeO MeO

CO2H OMe MeO

CO2H CHO CO2H OMe OMe MeO dimethyl MeO OMe L-tartaric acid OH OH hot hot OMe CH2OMe HNO3 HNO3 CH2OMe tetramethoxy tetramethoxy- aldehyde carboxylic acid

CO2H OMe CO2H MeO OMe OMe CH2OMe

CO2H

trimethyl dimethyl D- xylaric acid glyceric acid Maltose

Disaccharides: Maltose

Starches: poly-α-D-glucosides

Malt (barley) maltase HO O HO HO HO HO O O OH HO HO

•hydrolysis ----> only D-glucose

•maltase ----> α-glucoside

•positive Tollens test ----> reducing sugar

•shows mutarotation

•differs from cellobiose at the glycosidic anomeric center Lactose

Disaccharides: Lactose

4-O-(β-D-galactopyranosyl)-D-glucose ~5% of human and cow milk

HO HO HO O O HO OHO OH HO HO

•hydrolysis ----> D-glucose and D-galactose

•β -galactosidase (lactase) ----> β-galactoside

•lactose intolerance

•positive Tollens test ----> reducing sugar

•shows mutarotation Amygdalin

Disaccharides: Amygdalin

Laetrile (laevorotatory mandelonitrile), “vitamin 17”

1,6-β-linkage HO O HO O HO HO O HO O CN HO HO H Ph cyanohydrin of β-linkage benzaldehyde

1836 - Isolated from bitter almonds by Wohler. Demonstrated that emulsin produces glucose, benzaldehyde and prussic acid (HCN)

Touted in some circles as a treatment for cancer. Cellulose: Chain Length

Cellulose: Chain Length

HO HO HO O O O HO O O HO HO HO OH HO HO HO n permethylation

MeO MeO MeO O O O MeO O O MeO MeO MeO OMe MeO MeO MeO n

+ H3O

MeO MeO 2,3,4,6-tetra-O- O O 2,3,6-tri-O- MeO HO methyl D-glucose MeO MeO methyl D-glucose (terminal) MeO OH MeO OH (chain) 100-200 units 0.6% 99.4% Starches: Plant Polysaccharides

Starches: Plant Polysaccharides

HO O HO HO HO HO O O HO HO O HO O HO n HO OH

Amylose :

• ~20% water soluble starch; poly 4-O-(α-D-glucoside)

• forms helical structure; blue complex with iodine Starches: Plant Polysaccharides

Starches: Plant Polysaccharides

Amylopectin:

• ~80% water insoluble starch branched poly-4-O-(α-D-glucoside) • permethylation/hydrolysis • permethylation: 90% 2,3,6-tri-O-methyl-D-glucose

~5% 2,3-di-O-methyl-D-glucose

~5% 2,3,4,6-tetra-O-methyl-D-glucose

HO MeO O MeO O O HO HO MeO MeO MeO MeO MeO OH MeO OH MeO OH

chain junction terminus

Average 20 glucose units /chain Diogenes

And Finally, a True Story

In March of 1986 I was in California visiting several universities. While at Stanford University, I stopped at the health center to have a swollen foot examined. The young resident was very attentive. To assess his qualiﬁcations, I asked him where he had attended college. “M.I.T.,” he responded. “So you must have had Professor Kemp for organic chemistry,” I countered. “Yes, I did,” he said. Then I asked, “What D-aldohexose forms the same osazone as glucose?”

Like Diogenes the Cynic in search of an honest man (person), I have posed this question to many a practitioner of the medical and dental professions. Neither Diogenes nor I have fulﬁlled our quests. However, the responses to my query were often amusing.

Response: My thought:

“I really enjoyed organic chemistry!” Really?

“Organic, don’t remind me!” An honest man?

“I know the mechanism of the aldol condensation.” Wrong chapter!

“I know what a Grignard reagent is.” Wrong test!

“Wait! Give me some time.” “It’s only an hour exam.” Moral

The Moral of the Story

Somewhere,…sometime…someone might ask you this question.

What D-aldohexose forms the same osazone as D-glucose?

Your answer will be...

D-Mannose! The End

The End