Download 2) α-D-xylose

Pentoses
In nature the following pentoses are available:
L- arabinose
D-ribose
D-xylose
Apilose
1)α-L-arabinose ( arabopyranose):
 It’s found as a common constituent of
complex polysaccharides (pectius,
gums: gum Arabica) and
hemicelluloses
 It’s a constituent of various glycosides, particularly phenolic one.
 Constituent of bacteria polysaccharides
2) α-D-xylose ( α-D-xylopyranose):
 Found in wood sugar, straw, corn cobs and
as xylan polymer
 It could be fermented
 It is absorbed orally, but not metabolized,
so it is useful in diagnosis of mal absorption
3) Ribose:
 Ribose and deoxyribose are found in RNA and
DNA ( as β-D-)-ribufuranose
 It is also found in vit.B12 as (α-D-ribose)
4) Apilose ( Apiose)
 It’s a rare pentose, found as a sugar component of the glycosides of parsley
leaves
Hexoses
1)D- glucose (Dextrose): α-D-(+)-glucopyranose, “corn ,grape, blood sugar,…”
 It’s obtained from starch (complete hydrolysis) (suspension, 15-30%) +0.03
NHCL + Autoclave (150°c), 30
 It’s found as anhydrous glucose gluc.mono.hyo (7-9.5% H2O)
 Liquid glucose: a thick syrup gained by incomplete hydrolysis of starch and
composed of Dextrin + Maltose + Glucose
 uses: Sweetening agent \ Syrup\ Prepreparation of pills
 D-glucose: uses:
*used as nutrient (food): S.C. or I.V. in dripin
*used in eitrate-dextrose solution (anticoagulant)
*used in Ca-gluconate (calcemic agent)
*Rehydration solutions: (13-50%) : if water loss > salt-Na loss
*Prevention of dehydration
*Prophylaxis of treatment of ketosis in malnutrition
 Other starch products containing glucose:
1. Maltodextrins: Mixture of polysaccharides resulting from partial
hydrolysis of starch. “ have low Dextrose Equivalent (DE) < 20”
uses: Infant food, Adhesive in bandages and in granulation.
2. Glucose syrup: DE> 20: used in agricultural food industry
3. Glucose syrups enriched in fructose:
*known also as “high frucrose corn syrups HFCSs” and as “Isoglucoses”
*contain 40-90% fructose
* used as sweetners in liquid preparations
*prepared by enzymatic conversion from glucose syrup, followed by
glucose separation “usually produces HFCSs of 80-90%”
2) Fructose (Levulose): β-D-(-)-fructofuranose:
 Found free in fruits and honey and in polysaccharides
 It’s a furanose “in polysacch.” , and pyranose in free known as fruits sugar
 Prepared from sucrose chemically and enzymatically “ by invertase
enzyme”
Sucrose
Dextro
hydrolysis
invertase
Glucose
Dextro
+
Fructose
Levo
-This mixture is Levarotatory and known as Invert sugar (gluc. + fruct. + sucrose traces )
-It’s 50% by dry wt of gluc + fruc
 Also obtained by Insulin hydrolysis.
 Uses: * parenteral feeding
*sweetner (107 times as sweet as sucrose)
*has a value in diabetes “doesn’t trigger insulin secretion and with
low intestinal reabsorption”
 Separation if fructose from invert sugar mix:
(a) by recrystallization before glucose
(b) using Ca(OH)2 : Mixture + Ca(OH)2
Glucose forms Ca-gluconate (soluble in water)
Fructose forms Ca-fructosate (insoluble in water)
Ppt. + CO2
CaCO3 + fructose
Recrystallize
 To differentiate between Glucose & Fructose:
(1) Br2 in water oxidizes only glucose
(2) Reaction with resorcinol
(3) Raction with Methylphenylhydrazine
* Note: Both are reducing sugars and form the same osazone with phenylhydrazine
3) D-mannose: “ a C2-epimer of glucose”
 Not found free in nature, but as component of polysaccharides:
Homopolysaccharides (e.g. mannosans)
Heteropolysaccharides (e.g. hemicelluloses)
 It has a sweet taste followed by bitterness
 It’s not readily metabolized and used as osmotic diuvertic by parenteral
administration.
 It’s also laxative, used for dyspepsia for colon preparation for endoscopy
(200
 Excepient in various solid dosage forms
 Source: Manna ash : Fraxinus ornus (F. Oleacea)
4) D-galactose: “C4- epimer of glucose”
 Not found free but mainly as a polysaccharide component “ gums,
mucilage,agar” and the common disaccharide Lactose
Lactose
hydrolysis
galactose + glucose
Products of reductive metabolism:
Sugar alcohols “ Alditols “
1) Sorbitol: “Glucitol, Hexitol”
 Obtained by reduction of glucose and it’s found in many fruits (e.g.
Mounain ash : Sorbus aucuparia)
 Not absorbed orally and not metabolized when given parenterally,
thus used as:
- substitute for sucrose for diabetes
-osmotic laxative “adjunctive in constipation”
-sweetening agent
 It has a sweet flavor that’s cool because of negative heat of solution,
thus used in:
-chewing gums
-tooth pastes
 In Iron Sorbitex inj.
 It is cholagogue: increases biliary flow and increases volume of biliary
secretions, thus it’s used for treatment of biliary stones
2) D-mannitol:
 Obtained after mannose or fructose reduction
 Has similar characteristics of sorbitol, but used mainly as osmotic
diuretics:
When injered I.V, it’s eliminated rapidly into urine and this removes
fluid by osmotic effect
Derivatives of polyalcohols
1) 1,5-anhydro-D-sorbitol : “polyglucitol”
 It’s prepared by heating D-sorbitol in H2SO4
 It’s the starting material for the manufacturing of sorbitan esters “
spanus, Tweeus” and polysorbates.
2) Synthetic derivatives: “Alditol nitro esters”
e.g. trinitroglycerol, mannitol hexanitrate and nitrodulcitol
 Are coronary vasodilators used in the prophylactic treatment of
angina pectoris
 Are unstable: used in explosive industry
Other monosaccharides derivatives
1) Ascorbic acid: “vit C”
2) Sorbic Acid: “2,4-hexadiennoic acid”
3) Cyclitols: “Inositol” : “ Cyclohexane hexol” .
*Sorbic Acid : “2,4- (E,E)hexadienotic acid”:
 It’s used in pharmaceutical preparations as preservative that inhibits mold
growth
 It’s produced synthetically
 Available as Lactone (parasorbic acid) in the fruits of Mountain ash
*Cyclitols : ( Cyclohexanehexol, inisitol) :
 6 of 9 isomers are naturally available
 Phytic Acid: a phosphoric ester of myo inisitol
 The sodium salts of phytic acid cause precipitation of Ca++ in intestine thus,
they are indicated in:
1) Hyper calciurias
2) Infected lathiasis involving calcium
Written by: Jomana Bakeer
3) Calcium metabolism tests
Pharmacognosy, Part 2( chemistry of
natural drugs)