Pharmacognosy | Carbohydrates and Related Compounds

Carbohydrates

Polyhydroxy alcohols (either aldehyde or ketone)

Carbohydrates — functional groups

Aldehyde or ketone

Carbohydrates — composition

C, H, O

Carbohydrates — general formula

Cn(H2O)n

Carbohydrates — origin

First products of photosynthesis

Photosynthesis — reduction product

Glucose

Photosynthesis — oxidation product

Oxygen

Oxidation

Losses hydrogen; reactant is converted to higher oxidation state, becoming more unstable, e.g., from solid to liquid to gas

Reduction

Gains hydrogen; reactant is converted to lower oxidation state, becoming more stable, e.g., from gas to liquid to solid

Major carbohydrate classifications

Monosaccharides; disaccharides; polysaccharides

Polysaccharides — homoglycans

Only one type of sugar

Polysaccharides — heteroglycans

Different types of sugar

Homoglycan example — starch

Glucosan; yields glucose units

Homoglycan example — cellulose

Glucosan; yields glucose units

Homoglycan example — inulin

Fructosan; yields fructose units

Heteroglycan examples

Gums and mucilage; glycosides

Monosaccharides

Simple sugars; have 1 sugar unit; cannot be further hydrolyzed

Monosaccharides — physical properties

Crystalline, water-soluble, and sweet due to the hydroxyl group

Most important monosaccharides in plants

Hexoses

Monosaccharides — functional group classification

Aldose and ketose

Aldose

Contains an aldehyde functional group

Ketose

Contains a ketone functional group

Aldose: Diose

Hydroxyacetaldehyde; never free in nature

Aldose: Triose

Glyceraldehyde

Ketose: Triose

Dihydroxyacetone (DHA)

Aldose: Tetrose

erythrose, threose

Ketose: Tetrose

erythrulose

Aldose: Pentose

ribose, arabinose

Ketose: Pentose

ribulose

Aldose: Hexose

glucose, galactose

Ketose: Hexose

fructose (levulose)

Ketose: Heptose

sedoheptulose

Ketose: Octose

glycero-manno-octulose

Glycero-manno-octulose — occurrence

Avocado pulp and Sedum

Simplest synthetic sugar

Hydroxyacetaldehyde

Simplest natural aldose

Glyceraldehyde

Simplest natural ketose

Dihydroxyacetone

Glyceraldehyde and dihydroxyacetone

Both are seen in glycolysis

Erythrose

Shikimic path requirement

Ribose

DNA

Arabinose

Acacia gum

Ribulose

Photosynthesis and respiration

Sedoheptulose

Sedum

Fischer projection

Linear configuration

L-glucose

Less active

D-glucose

More active

Haworth projection

Cyclic configuration

Pyranose

6-member ring; example: glucopyranose

Furanose

5-member ring; example: ribofuranose

Cyclic configuration — stability

Unstable but may be stabilized on glycoside formation

Anomeric carbon

Spotted by finding a carbon with two oxygens

Alpha anomer

Anomeric OH down

Beta anomer

Anomeric OH up

Aldose carbonyl group

C1

Ketose carbonyl group

C2

Carbonyl group interaction

Interacts with the penultimate carbon

Penultimate carbon

The farthest/last chiral carbon with 4 different functional groups

Number of isomers

2n

n in the isomer formula

Number of chiral carbons

Glucose — number of chiral carbons

4

Glucose — number of isomers

16

Fructose — number of chiral carbons

3

Fructose — number of isomers

8

Diastereomer

Differ in 2 or more chiral carbons; example: arabinose and xylose (C2, C3)

Epimer

Differ in only 1 chiral carbon; examples: arabinose and ribose (C2), glucose and mannose (C2)

Enantiomer

Mirror images; all chiral carbons are switched; example: rhamnose and mannose

Glucose

Only useful sugar in the blood; most important hexose

Glucose / dextrose — classification

Aldohexose

Glucose / dextrose — functional group

Aldehyde group in C1

Glucose / dextrose — reducing property

Reducing sugar as determined by Benedict’s test

Glucose / dextrose — configurations

Occurs as linear and cyclic; D-glucose / α-D-glucopyranose

Glucose / dextrose — names

Blood sugar, physiologic sugar, grape sugar, corn sugar

Glucose / dextrose — blood

The only utilizable sugar in the blood

Glucose / dextrose — natural source

Grapes

Glucose / dextrose — source

Enzymatic hydrolysis of starch

Glucose / dextrose — use

Sweetening agent, mask unpleasant taste, flavor

Dextrose — routes (4)

PO

SC

IV

enema

Parenteral dextrose

Rigorously purified

D5W, D5NSS, D5LR

Nutrient

D50

50% glucose in 50 cc water; used in the emergency room to treat hypoglycemic patients who are unconscious, comatose, or intoxicated with alcohol

Glucose — Pharmaceutic necessity

Less rigorous purification

Liquid glucose

Syrupy liquid, almost colorless and sweet; sweetening agent

Glucose — Pharmaceutic necessity | Dextrose excipient

Crystalline sweetening agent

Glucose — Related compounds | Liquid glucose

Thick, syrupy liquid from incomplete hydrolysis of starch

Glucose — Related compounds | Calcium gluconate

Electrolyte replenisher

Calcium gluconate — ethylene glycol poisoning

Supportive treatment for hypocalcemia

Ethylene glycol — conversion

Converted to oxalic acid

Oxalic acid — effect

Gets calcium from the blood and forms calcium oxalate crystals

Calcium oxalate crystals

Can block the kidney, causing acute renal failure; crystals are found in the urine

Calcium gluconate vs calcium gluceptate

Calcium gluconate is more available than calcium gluceptate

Glucose — Related compounds | Calcium gluceptate

Calcium source; given in ethylene glycol poisoning as supportive treatment

Glucose — Related compounds | Ferrous gluconate

Hematinic; given for iron deficiency anemia

Plant sugar transport

Sugar is transported as sucrose through the phloem

Phloem

Food-conducting vessel

Xylem

Water and minerals are transported from roots to stem, leaves, etc.

Glucose in leaves

Converted to fructose through isomerase

Fructose in leaves

Undergoes dehydration to form sucrose

Sucrose in plants

Transported through the plant

Sucrose in roots

Hydrolyzed to glucose and fructose

Fructose in roots

Converted into glucose through isomerization