NATURAL COMPOUNDS DERIVED FROM
SUGARS
TWO BASIC GROUPS
1. Mono-, oligo- and polysaccharides
2. Sugars as parts of heteroglycosides
HETEROGLYCOSIDES
HETEROGLYCOSIDES
• Organic substances in majority of natural origin
• Through hydrolysis (acids, enzymes) it is cleaved
• sugar (usually reducing)
• non-sugar component - AGLYCON – GENIN
• Sugars usually in cyclic form
• Sugar is bound on aglycon usually via atom of oxygen (acetals),
less often via atom of sulphur, nitrogen, eventually carbon
HETEROGLYCOSIDES
Group of aglycon + sugar → product designation
entering the glycoside (glycoside)
---------------------------------------------------------------------------------------------------
R-O-H H-O-C6H11O5 R-O-C6H11O5 O-glycoside
R-S-H H-O-C6H11O5 R-S-C6H11O5 S-glycoside
R-N-H H-O-C6H11O5 R-N-C6H11O5 N-glycoside
R-C-H H-O-C6H11O5 R-C-C6H11O5 C-glykoside
R = alkyl or aryl
CHEMISTRY OF SUGARS
Spontaneous intramolecular addition of one of hydroxyl groups (primary or
secondary hydroxyl groups) on karbonyl group formats cyclic hemi-acetals
(pyranoses, furanoses). Formation of new chiral centre.
O
H
H
OH
OH
H
H
OH
CH2
OH
H
OH
O
H
OH
H
H
OH
CH2
OH
OH H
H OH
C OHH
C
C
C
C
CH2
OH
OH
OH
H
OH
O
H
H
H
C OHH
C
C
C
C
CH2OH
OH
OH
H
O
H
H
OH HC
C
C
C
C
CH2
OH
OH
OH
H
OH
OH
H
H
H
H O
-D-glucopyranose -D-glucopyranose
cis = anomer trans =anomer
1
1
1 1
D-glucose
1
GLYCOSIDES α- a βGlykosidic
bond is formed
• Semi-acetal hydroxyl (at anomeric carbon of monosacharide) and
• whichever hydroxyl aglycone (genine), or SH, NH group
O
CH2OH
O R
O
CH2OH
O R
-D-glucoside-D-glucoside (trans) (cis)
All natural glycosides are D-sugars of typ L-sugars
(for example L-Rha) are bonded via - glycosidic bond
SUGAR COMPONENT OF GLYCOSIDES
MONOSACCHARIDES
• glucose glukosidy
• rhamnose rhamnosidy
• arabinose arabinosidy
• xylose xylosidy
• mannose manosidy
• galactose galaktosidy
• cymarose cymarosidy
OLIGOSACHARIDY
• rutinose (disaccharide)
• ramified oligosaccharides
(saponins)
ACCORDING TO THE NUMBER OF
SUGAR MOLECULES
• mono-glycosides
• di-glycosides
• tri-glycosides
• tetra-glycosides
SUGARS AT TWO DIFFERENT C-OH
• bidesmosides
TYPES OF GLYKOSIDES AND VARIABILITY OF
AGLYCONS
O
H
H
OH
OH
H
H
OH
CH2
OH
H
O OH
O
H
H
OH
OH
H
H
OH
CH2OH
H
O
O O
OH OH
O
H
H
OH
OH
H
H
OH
CH2
OH
H
S C
OSO2
OK
N CH2
-CH=CH2
O
H
H
OH
OH
H
H
OH
CH2OH
H
CH2
OH
OH OH
N
N
NH2
N
N
OOH OH
arbutine
gitorine
sinigrine
(S-glycoside) adenosine
(N-glycoside)
barbaloine
(C-glycoside)
CLEAVAGE – HYDROLYSIS OF GLYCOSIDES
• Mineral acids
• Enzymes (glycosidases)
Specificity of enzymes
α-glycosides cleaved only by α-glycosidases
β-glycosides cleaved only by β-glycosidases
O
H
H
OH
OH
H
H
OH
CH2
OH
H
O
OH O
H
OH
OH
OH
CH2OH
OH
OH
OH
arbutine
emulsin
(-glycosidase)
glucose
+
hydroquinone
maltasa
(-glycosidase)
x x x
ENZYMATIC CLEAVAGE OF GLYCOSIDES
Specific enzymes cleave
• D-glucosides
• L-glucosides
• D-galactosides
• L-rhamnosides
Thioglycosides are cleaved by myrosinase (thioglucosidase).
Enzyme and glycoside is in plant stored separately.
BIOLOGICAL EFFECT OF GLYCOSIDES
• At majority of glycosides based on aglycone, but sugar component
can effect strongly affect and modify (cardioactive glycosides)
• Some glycosides are ineffective, effect is triggered after release of
aglycone (mustard essential oil, coumarins, HCN from amygdaline)
• Effect of some glycosides is based whole glycoside (glycosidic
bitter substances, streptomycine)
Glycosides are distributed in whole plant kingdom. Some species of
glycosides are typical for certain plant families:
• cyanogenic – Rosaceae
• thioglycosides - Brassicaceae
• In one drug more glycosidic species, for example Digitalis lanatae
folium – cardioactive, flavonoid, saponin
BIOSYNTHESIS OF GLYCKOSIDES
1. Formation of aglycon (four basic biosynthetic pathways)
2. Connection of aglycon with activated sugar
UTP + sugar-1-P
uridilyltransferase
UDP-sugar + P-P
UDP-sugar + acceptor (genin)
glycosyltransferase
acceptor-sugar + UDP
(glycoside)
PROPERTIES OF GLYCOSIDES
• Colorless, crystal compounds
• Soluble in water and diluted EtOH and MeOH
• Optically active
• Possess bitter taste
• Many of them are valuable therapeutics