Supplementary Data Average Monosaccharide Composition Calculations
Pharmacognosy- 1 PHG 222 · • A monosaccharide containing three ... Carbohydrates that give...
Transcript of Pharmacognosy- 1 PHG 222 · • A monosaccharide containing three ... Carbohydrates that give...
Prof. Dr. Amani S. Awaad
Professor of PharmacognosyPharmacognosy Department,
College of Pharmacy Salman Bin Abdulaziz
University,
Al-Kharj. KSA.
Email: [email protected]
Pharmacognosy- 1
PHG 222
To know what is carbohydrates
To Recognize Classification of
carbohydrates
To Identify types Monosaccharides
To know Structural formulas for
Monosaccharides
To understand Reactions of
Monosaccharides
To know Polysaccharides
To understand and identefiy Carbohydrate
Antibiotics
• Carbohydrates [CX(H2O)Y] are usually defined as polyhydroxy aldehydes and ketones or substances that hydrolyze to yield polyhydroxy aldehydes and ketones.
• Simple carbohydrates are known as sugars or saccharides (Latin saccharum, sugar) and the ending of the names of most sugars is –ose. For example:
1. Glucose (for the principle sugar in blood)
2. Fructose (for a sugar in fruits and honey)
3. Sucrose (for ordinary table sugar)
4. Maltose (for malt sugar)
Carbohydrates
• Monosaccharide (C6H12O6)
it is a simple carbohydrate, one that one attempted hydrolysis is not cleaved to smaller carbohydrates. e.g. glucose
• Disaccharide on hydrolysis is cleaved to two monosaccharide, which may be the same or different. e.g. sucrose
• Oligosaccharide (oligos is a Greek word that means “few”) yields 3 10 monosaccharide unit on hydrolysis. e.g. raffinose
• Polysaccharides are hydrolyzed to more than 10 monosaccharide units. Cellulose is a polysaccharide molecule that gives thousands of glucose molecules when completely hydrolyzed.
Classification of carbohydrates
Carbohydrates
• Over 200 different monosaccharidesare known.
• Monosaccharides are classified according to:
1. The number of carbon atoms present in the molecule.
2. Whether they contain an aldehyde or ketone group.
• A monosaccharide containing threecarbon atoms is called a triose; one containing four carbon atoms is called a tetrose.
• A monosaccharide containing an aldehyde group is called an aldose; one containing a keto group is called a ketose.
Monosaccharaides
Carbohydrates
Classification of carbohydrates
Monosaccharaides
Carbohydrates
Classification of carbohydrates
• The simplest monosaccharide is glyceraldehyde, which contains a stereocenter. Therefore, it exist in two enantiomeric forms.
• In 1906, (+)-glyceraldehyde is designated D-(+)- glyceraldehyde
• and ()- glyceraldehyde is designated L-()- glyceraldehyde.
• These two compounds serve as configurational standards for all
monosaccharides.
Monosaccharaides
Carbohydrates
Classification of carbohydrates
• A monosaccharide whose highest numbered stereocenter (the penultimate carbon) has the same configuration as D-(+)-glyceraldehyde is designated as a D sugar; one whose highest numbered stereocenter has the same configuration as L-()-glyceraldehyde is designated as an L sugar.
• D and L designations are not related to the optical rotations of the sugars to which they are applied.
• One may encounter other sugars that are D-(+)- or D-()- and ones that are L-(+)- or L-()-.
Monosaccharaides
Carbohydrates
Structural formulas for Monosaccharides
• Fisher projection
• Haworth formulas
• anomer or anome
Not all carbohydrates exist in
equilibrium with six-membered
hemiacetal rings, in several instances the
ring is five membered.
If the monosaccharide ring is six
membered, the compound is called a
pyranose (e.g. -D-glucopyranose );
if the ring is five membered, the
compound is designated as a furanose.
(e.g. -D-ribofuranose).
O
O
Pyran
Furan
• The spontaneous change that takes place in the optical rotation of and anomers of a sugar when they are dissolved in water. The optical rotations of the sugars change until they reach the same value.
• the explanation for this mutarotationlies in the existence of an equilibrium between the open-chain form of D-(+)-glucose and the and forms of the cyclic hemiacetals.
• the concentration of open-chain D-(+)-glucose in solution at equilibrium is very small.
Mutarotation
Monosaccharaides
Carbohydrates
Structural formulas for Monosaccharides
H2OH2O
Glycoside Formation
Carbohydrates
Monosaccharaides
Structural formulas for Monosaccharides
Hemiacetal: a functional group, consisting of a carbon atom bonded to an alkoxy group
and to a hydroxyl group. Hemiacetals are synthesized by adding one molar equivalent of
an alcohol to an aldehyde or a ketone.
The reactions of aldehydes and ketones with alcohols parallel their reactions
with water.
• Carbohydrate acetals, generally, are called glycosides, and an acetal of glucose is called a glucoside.
• The methyl D-glucosides have been shown to have six-membered ring, so they are properly named methyl -D-glucopyranoside and -D-glucopyranoside.
• Glycosides are stable in basic solutions because they are acetals.
• In acidic solutions, glycosides undergo hydrolysis to produce a sugar and an alcohol (aglycone).
Glycoside Formation
Carbohydrates
Monosaccharaides
Structural formulas for Monosaccharides
Carbohydrates
Sugars that contain nitrogen
1. Glycosylamines
Glycosylamines are a class of biochemical compounds consisting of an amine with a β-N-glycosidic bond to a carbohydrate, forming a cyclic hemiaminal ether bond (α-aminoether).
Adenosine is an example of a glycosylamine that is also called a nucleoside.
2. Amino sugars
A sugar in which an amino group replaces a nonanomeric OH group. e.g. D-glucosamine.
•D-glucosamine can be obtained by hydrolysis of chitin, a polysaccharide found in the shells of lobsters and crabs and in the external skeletons of insects and spiders.
Glucosamine (C6H13NO5) is an amino sugar and a prominent precursor in the
biochemical synthesis of glycosylated proteins and lipids.
Reactions of MonosaccharidesCarbohydrates
1. Enolization, Tautomerization, and Isomerization
Dissolving monosaccharides in aqueous base
causes them to undergo enolizations and a
series of keto-enol tautomerizations that lead to
isomerizations.
Enols are in equilibrium with an isomeric aldehyde or ketone, but are normally much less stable than aldehydes and ketones.
Enolate ion is the conjugate base of an enol. Enolate ions are stabilized by electron delocalization.
Tautomerizm is a process by which two isomers are interconverted by a movement of an atom or a group. Enolization is a form of tautomerism
RC
OH
CR2
RC
O
CR2 RC
O
CR2
Enol
Enolate ion
Tautomerization creates structural isomers
D-Glucose to D- Fructose
Note: Formation of a glycoside prevents enolization
Reactions of Monosaccharides
Carbohydrates
2. Formation of Ethers
The hydroxyl groups of
monosaccharides are more acidic than
those of ordinary alcohols because the
monosaccharide contains so many
electronegative oxygen atoms, all of
which exert electron-withdrawing
inductive effects on nearby hydroxyl
groups.
In aqueous NaOH, the hydroxyl
groups are converted to alkoxide ions
and each of these in turn, reacts with
dimethyl sulfate to yield a methyl
ether.
Formation of Ethers
– Exhaustive Methylation
• SN2 Mechanism
• Base-catalyzed
Reactions of Monosaccharides
Carbohydrates
3. Conversion to Esters
Treating a monosaccharide with excess acetic anhydride and a weak base
(such as pyridine or sodium acetate) converts all of the hydroxyl groups,
including the anomeric hydroxyl, to ester groups
O
H
H3CCO
H
H3CCO
H
H
OCCH3
OCCH3 OCCH3
O
O
O
O
O
O
H
HO
H
HO
H
H
OH
OH OH
(CH3CO)2O
°Pyridine,0 C
Reactions of Monosaccharides
Carbohydrates
4. Oxidation Reactions of Monosaccharides
A. Fehling’s solution or Benedict’s reagent
A characteristic property of an aldehyde
function is its sensitivity to oxidation.
Carbohydrates that give positive tests with
Fehling’s or Benedict’s reagents are termed
Reducing Sugars.
Ketoses are also reducing sugars, since under
the conditions of the test, ketoses
equilibrate with aldoses by way of enediol
intermediates, and the aldoses are oxidized
by the reagents
CH
O
2Cu2+ R CO
O
Cu2O 3H2O
Aldehyde From copper(II)sulfate
Hydroxide ion
Carboxylateanion
Copper(I)oxide
Water
R 5HO
Fehling’s
Benedict’s
Reactions of Monosaccharides
Carbohydrates
B. Bromine Water: the synthesis of aldonic acids
4. Oxidation Reactions of Monosaccharides
Bromine water is a general reagent
that selectively oxidizes the - CHO
group to α-CO2H group
Bromine Water:
The Synthesis of Aldonic Acid
Selectively oxidizes Aldehydes,
Gives a positive Test for Aldose,
and
Gives a negative test for Ketose.
Reactions of Monosaccharides
Carbohydrates
4. Oxidation Reactions of Monosaccharides
C. Nitric Acid Oxidation: Aldaric Acids
Dilute nitric acid – a stronger oxidizing agent
than bromine water – oxidizes both the –CHO
group and the terminal –CH2OH group of an
aldose to –CO2H group. These dicarboxylic
acids are known as aldaric acids.
(CHOH)n
CHO
CH2OH
(CHOH)n
CO2H
CO2H
Aldose Aldaric acid
HNO3
Reactions of Monosaccharides
Carbohydrates
4. Oxidation Reactions of Monosaccharides
D. Periodate oxidations: oxidative cleavage of polyhydroxy compounds
Compounds that have hydroxyl groups on adjacent atoms undergo
oxidative cleavage when they are treated with aqueous periodic acid
(HIO4).
In these periodate oxidations that for every C-C bond broken, a C-O
bond is formed at each carbon.
C
C
OH
OH
HIO42 C
O
HIO4 H2O
Stoichiometric cleavage
When three or more –CHOH groups are contiguous,
the internal ones are obtained as formic acid. For
example, glycerol
Oxidative cleavage also takes place when an –OH
group is adjacent to the carbonyl group of an
aldehyde or ketone (but not that of an acid or an
ester). For example, glyceraldehyde
Periodic acid does not cleave compounds in which the
hydroxyl groups are separated by an intervening –CH2 –
group, nor those in which a hydroxyl group is adjacent
to an ether or acetal function.
Reactions of MonosaccharidesCarbohydrates
Aldoses (and ketoses) can be reduced with sodium borohydride to
compounds called alditols. For example, D-glucitol (or D-sorbitol)
5. Reduction of Monosaccharides: Alditols
(CHOH)n
CHO
CH2OH
(CHOH)n
CH2OH
CH2OH
Aldose Alditol
NaBH4
• Disaccharides are carbohydrates that yield two monosaccharide molecules on hydrolysis.
e.g. 1)sucrose,
2)lactose,
3)maltose
• Structurally, disaccharides are glycosides in which the alkoxy group attached to the anomeric carbon is derived from a second sugar molecule.
DisaccharidesCarbohydrates
• Ordinary table sugar (C12H22O11)
• Acid hydrolysis yields D-glucose and D-fructose.
• Sucrose is a nonreducing sugar; it gives negative tests with Fehling’s solution because neither the glucose nor the fructose portion of sucrose has a hemiacetal group (both carbonyl groups are present as full acetals (i.e. as glycosides).
Disaccharides
Carbohydrates
Sucrose
• Polysaccharides, also known as glycans, consist of monosaccharides joined together by glycosidic linkages.
• Polysaccharides that are polymers of a single monosaccharide are called homopolysaccharides; those made up of more than one type of monosaccharide are called heteropolysaccharides.
• Homopolysaccharides are also classified on the basis of their monosaccharide units.
• A homopolysaccharide consisting of glucose monomeric unit is called a glucan, one consisting of galactose units is a galactan, and so on.
Polysaccharides
Carbohydrates
• Three important polysaccharides, all of which are glucans, are starch, glycogen, and cellulose.
• Starch is the principle food reserve of plant.
• Glycogen functions as a carbohydrate reserve for animals.
• Cellulose serves as structural material in plants.
Polysaccharides Carbohydrates
Carbohydrate Antibiotics
• One of the important discoveries in carbohydrate chemistry was the isolation of the carbohydrate antibiotic called streptomycin.
• Streptomycin is made up of three unusual components.
• The glycosidic linkage is nearly always .
OH
HN
NH
OH
NH2
NH
NH
H2N
OH
O
CHO
HO
H3C
O
R'R
HO
HO
R = NHCH3
R' = CH2OH
O
O
Streptomycin
Streptidine
L-Streptose
2-Deoxy-2-methylamino-L-glucopyranose
Carbohydrates
Carbohydrate antibiotics refers to microbial metabolites (mainly from
Actinomyces species) having antibacterial and antifungal properties and which
are carbohydrates or contain a carbohydrate component in their chemical
structure. Types include the aminoglycosides, macrolides, nucleoside analogs,
and glycosylated aromatic structures