notes for carbohydrates (1).docx

**CARBOHYDRATES** These are defined as group of compounds composed of carbon, hydrogen and oxygen in which the latter 2 elements are in the same proportion as in water and are expressed by the formula (CH~2~O)n; that is, they are considered as hydrates of carbon. However, this definition has it's d...

**CARBOHYDRATES** These are defined as group of compounds composed of carbon, hydrogen and oxygen in which the latter 2 elements are in the same proportion as in water and are expressed by the formula (CH~2~O)n; that is, they are considered as hydrates of carbon. However, this definition has it's drawback as certain compounds which contain hydrogen and oxygen in the same proportion as water are not carbohydrates (CHO). For example, formaldehyde, HCHO, OR C(H~2~O), Acetic acid CH3COOH written as C~2~(H~2~0)~2~. Equally, a large number of carbohydrates do not contain H and O in the usual proportion as in water, for example Rhamnose (C~6~H~12~O~5~), Cyamose (C~7~H~14~O~4~) and Digitoxose (C~6~H~12~O~4~). Of importance is the fact certain carbohydrates in addition to Carbon, Hydrogen and Oxygen also contain other elements such as sulphur, and nitrogen Thus CHO are now defined as polyhydroxy aldehydes and ketones or compounds which on hydrolysis will yield either of the two. CHO are of importance pharmacognostically because they interact with a wide variety of other compounds to form glycosides and other secondary metabolites. They are formed in plant as the first visible product of photosynthesis. CLASSIFICATION OF CARBOHYDRATES These are divided into simple sugars (Saccharides) and complex or polysaccharides. The simple sugars further sub-divided into Mono, Di, Tri, Tetra and so on. **MONOSACHARIDES** The term Monosaccharide is employed for those sugars which on hydrolysis yield no lower sugars. The general formula for monosaccharaides is C~n~H~2n~O~n~. The monosaccharaides are further sub-divided into Bioses, Trioses, Tetroses, Pentoses, Hexoses, Heptose.....depending on the number of carbon atom they possess. A chain form monosaccharide that have a carbonyl group ( C=O) on an end carbon forming an aldehyde is referred to as an aldose, while that with the carbonyl group in an inner carbon gives rise to a ketone, also referred to as a ketose. C:\\Users\\THIS PC\\AppData\\Local\\Microsoft\\Windows\\INetCache\\Content.Word\\Screenshot (115).png  Glucose Fructose **Bioses** These contain two carbon atoms and rarely found in nature.. The only known compound is glycoaldehyde or 2- hydroxyethanal (C~2~H~4~O~2~). **Triose** These contain 3 carbon atoms and represent the simplest form of monosaccharide sugar found in nature. e.g glyceraldehyde. C:\\Users\\THIS PC\\AppData\\Local\\Microsoft\\Windows\\INetCache\\Content.Word\\Screenshot (116).png Glyceraldehyde **Tetrose** These contain four carbon atoms, E.g, erythrose  Erythrose **Pentose** These are very common in plants and are the product of hydrolysis of polysaccharide such as hemicellulose and gum. Examples include ribose, arabinose and xylose. INSERT THE STRUCTUSES OF RIBOSE, XYLOSE AND ARABINOSE **Hexoses** These are monosaccharide containing 6 carbon atoms and are abundantly available in the plant kingdom. They are further subdivided into 2 types: aldose and ketose. They can be obtained by the hydrolysis of polysaccharide like starch, cellulose and inulin. Examples of aldose are glucose, mannose and galactose, while that of ketose are fructose and sorbose. **Heptose** These contain seven carbon atoms and play a key role in photosynthesis of plant and glucose metabolism of animals. They are rarely found accumulated in plants and glucose metabolism of animals. Example glucoheptalose, manoheptalose **OLIGOSACHARIDES** These consist of short chain monosaccharide units joined by characteristic linkages called glycoside bonds. They have their names ending in --ose and often do not exist as free entities. **DISACCHARIDES** These are CHO which on hydrolysis yield two molecules of monosaccharide. E.g, Sucrose \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- Glucose + Fructose Maltose \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- Glucose + Glucose Lactose \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- Glucose + Galactose **Trisaccharide** Examples include Raffinose and Gentianose. These will yield 3 molecules of monosaccharide on hydrolysis. Raffinose (Found in sugarcane and Beetroot \[*Beta vulgaris*, L Amaranthaceae\]) \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- Glucose + Fructose+ Galactose Gentinose (Gentian root ) \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- Glucose + Glucose+ Fructose **Tetrasaccharides** These will yield four molecules of monosaccharaides on hydrolysis and examples include; Stachyose. (will on hydrolysis yield 1 glucose unit, 2 galactose and 1 fructose units). **POLYSACCHARIDE** These are CHO which on hydrolysis give an indefinite number of monosaccharide. They are formed by condensation and the elimination of water. For example, Cellulose is composed of glucose units joined by ẞ-1,4 glycosidic linkages, whereas starch contain glucose connected by α-1,4 and α-1,6 glycosidic bonds. Most CHO found in nature occurs as polysaccharides. They differ from one another in constituent units and hence in molecular weight and other structural features. Some are linear, while others are branched. They are insoluble in water, non-sweet to taste and form colloidal suspension instead of solution. **Classification** Various indexes have been used in classifying polysaccharide however, the most popular is related to their product of hydrolysis. That is, whether these products are similar or different. Thus we have; homo-polysaccharide and hetero-polysaccharide. **Homopolysacharides** These are polysaccharides which on hydrolysis give only one type of monosaccharide unit. They include starch, cellulose and glycogen. Heteropolysacharides\-\-\-- Example includes Hemicellulose and pectin. **TESTs FOR CHO** Molisch' test Fehling's test for reducing sugar also Benedict's test Test for pentose Test for ketose Iodine test for polysacharide **Pharmaceutical Importance of CHO** They serve as excipients of importance in the pharmaceutical industry. They are used as excipients, diluents, disintegrants, granulating and coating agents, sweeteners, bulking agents, fillers and plasticizers.