Biochemistry Carb. Lecture 4

Chemical Reaction of Monosaccharide 1- Oxidation: oxidation at aldehyde group in aldohexose form (Aldomic acid) there are three products occur through oxidation. if oxidation occur with weakly oxidizing agent (glucouronic acid) will be formed. CHO H C OH HO C H H C OH COOH (Glucouronic acid) CHO H C OH HO C H CH2OH (Glucose) Oxidation Weak oxidizing agent

b) if aldo group is oxidize at C1 (gluconic acid) will be formed. CHO H C OH HO C H CH2OH (Glucose) COOH H C OH HO C H CH2OH (Gluconic acid) Oxidation Weak oxidizing agent

c) If oxidation occur with strong oxidizing agent (saccharic acid) will be formed. COOH H C OH HO C H (Saccharic acid) CHO H C OH HO C H CH2OH (Glucose) Oxidation strong oxidizing agent

2) Reduction: the carbonyl group of an aldose sugar be reduced with reducing agent such as H2 and metal catalyst to form alditol (alcohol). Glucose reduction glucitol Mannose reduction Mannitol

3) Osazone formation: The carbonyl group of aldehyde or ketone react with phenylhydrazine to form phenylhydrazone. The intial product react with more phenylhydrazine, the α hydroxy group of the initial product is easily oxidized to carbonyl group by a second molecule of phenyl hydrazine, the new carbonyl group then react with a third molecule of phenylhydrazine to form osazone. Phenylhydrazine react with C1 and C2 of the monosaccharide.

• Osazone have been used to identify the sugar, the reason for that is that most sugar are very difficult to crystallize, they tend to remain as syrups. If sugar is treated with excess phenylhydrazine a crystalline osazone will be formed, the crystal has a characteristic multing point and precipitating time and the characteristic crystal shape used to identify the sugar. • Glucose, fructose and mannose form the same osazone, while galactose form different osazone shape. Maltose and lactose have osazone. Sucrose have no osazone. All polysaccharides have no osazone.

Osazone formation:

Glycoside: It is the important derivative of monosaccharide. Glycoside is the reaction of α or β glucose with alcohol or phenol or dteroid. It is formed of two parts: 1- Sugar part called (glycone). 2- Non sugar part (aglycone). 1- The sugar part may be: Glucose glucoside Galactose galactoside Mannose mannoside

2- Non sugar part (aglycone) it may be phenol methyl group or steroid, many glycoside are important compound at plants and animals tissue. A number of those substances are important drugs, and have been used for treatment of many serious diseases. Like: 1- Digoxine used in treatment of heart disease. 2- Salicine used in treatment of malaria. CH2OH H H H OH OH H OCH3 H OH - H2O + CH3OH

Haworth Projections • In the terminology of carbohydrate chemistry, b means that the -OH on the anomeric carbon is on the same side of the ring as the terminal -CH2OH a means that the -OH on the anomeric carbon is on the side of the ring opposite from the terminal -CH2OH • a six-membered hemiacetal ring is called a pyranose, and a five-membered hemiacetal ring is called a furanose .

Haworth Projections D-Glucose forms these cyclic hemiacetals

Chair Conformations in both a Haworth projection and a chair conformation, the orientations of groups on carbons 1- 5 of b-D-glucopyranose are up, down, up, down, and up

D-ketohexose L-aldopentose This sugar has D configuration because OH is to the right of the last stereocenter This sugar has L configuration because OH is to the left of the last stereocenter

This is D-aldohexose because OH (circled) islocated to the right of the last stereocenter carbonIt is an aldohexose becausethere are 6 carbons, which gives it the suffixhexose and it contains an aldehyde, which givesit the prefix aldo. This sugar is L-aldohexose because OH (circled) islocated to the left of the last stereocenter carbonIt is an aldohexose becausethere are 6 carbons, which gives it the suffixhexose and it contains an aldehyde, which givesit the prefix aldo.

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