Pharmacognosy and Plant Chemistry: Carbohydrates and Derived Products

Carbohydrates

• Derived from the German word "kohlenhydrates" meaning hydrates of carbon
• Consist of Carbon, Hydrogen, and Oxygen, with Hydrogen and Oxygen generally in a 2:1 ratio
• Classified into two broad groups: Sugars and Polysaccharides

Sugars

• Mostly simple sugars
• Classified into:
  • Monosaccharides (e.g. Glucose, the principal unit of sugar in the blood)
  • Disaccharides (e.g. Sucrose, table sugar)
  • Oligosaccharides (e.g. Raffinose)

Monosaccharides

• Classified based on the number of carbon atoms in a molecule
• General formula: Cn H2n On
• Examples:
  • Bioses (2 carbon atoms)
  • Trioses (3 carbon atoms)
  • Tetroses (4 carbon atoms)
  • Pentoses (5 carbon atoms)
  • Hexoses (6 carbon atoms)
  • Heptoses (7 carbon atoms)
• Classified based on functional group present in a molecule:
  • Aldose (contains an aldehyde group)
  • Ketose (contains a ketone group)

Pentoses and Hexoses

• Pentoses: a class of simple sugars with 5 carbon atoms, with a chemical formula C5H10O5
• Hexoses: the most important monosaccharides in plants, with 6 carbon atoms
• Examples of hexoses:
  • D-Fructose (Levulose)
  • D-Glucose (Dextrose)

Glucose

• An aldohexose, a polyhydroxy alcohol with an aldehyde group
• Identified as a reducing sugar due to its free aldehyde group
• Generally forms a 6-membered ring

Fructose

• A ketonic simple sugar
• Has 2 cyclic forms:
  • Fructopyranose (crystalline sugar)
  • Furanose (as part of oligosaccharides and polysaccharides)
• Commonly found in fruits

Sucrose and Derivatives

• Sucrose: the only disaccharide that occurs abundantly in the free state in plants
• Uses:
  • Nutrient
  • Ingredient in several dextrose-containing preparations
• Liquid Glucose:
  • A product obtained by the incomplete hydrolysis of starch
  • A colorless or yellowish thick syrupy liquid that is nearly odorless and tastes sweet
  • Contains primarily dextrose, together with dextrin, maltose, and water
  • Uses:
    • Pharmaceutic necessity
    • Used in the manufacture of candy, carbonated beverages, ice cream, bakery products, and food canning industry

Calcium Gluconate

• Calcium salt of gluconic acid
• Uses:
  • As a diagnostic aid
  • As an osmotic diuretic

Sorbitol

• Also known as D-glucitol and D-Sorbitol
• A hexitol that was originally obtained from the ripe berries of the mountain ash
• Taste is half as sweet as sucrose
• Uses:
  • Ingredient in toothpaste and chewing gums
  • Urologic irrigation
  • Used in conjunction with saccharin in dietetic beverages
  • Acts as an osmotic laxative when taken in large amounts

Polysaccharides and Related Compounds

• Starch:
  • The most widely distributed organic compound in plants
  • Occurs in seeds, pith, medullary rays, cortex of stems and roots of plants
  • Generally a mixture of two structurally different polysaccharides namely amylose and amylopectin
• Cellulose Derivatives:
  • Uses:
    • Surgical dressing
    • Textiles industries
  • Examples of cellulose derivatives:
    • Methylcellulose
    • Hydroxypropyl Methylcellulose (HPMC)
    • Microcrystalline Cellulose
    • Pyroxylin (Soluble Guncotton)