bioassay-guided purification of active extracts … filebioassay-guided purification of active...

Research Laboratory Manual for Natural Product Chemistry

Dr. Abdullahi Mann, Department of Chemistry,

Federal University of Technology, Minna

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BIOASSAY-GUIDED PURIFICATION OF ACTIVE EXTRACTS AND

STRUCTURE ELUCIDATION OF PHYTOCONSTITUENTS

EXTRACTION METHODS FOR NATURAL PRODUCTS CHEMISTRY

Before beginning the extraction process, the plants under investigation are often obtained

from ethnobotanical survey (Mann et al., 2003) and should be scientifically identified by

a plant taxonomist. The voucher specimens of these plant samples must be kept in the

laboratory for future reference.

The shade air-dried (plant parts i.e. leaves, root, stem – state the amount in Kg) of plant

(provide the scientific name of the plant e.g. Terminalia avicennioides) will be chopped

into small pieces, crumbled and grind (pulverized) to a fine powder. The fine powdered

materials should be the range of 0.1-10 mm or (0.2 mm sieve). The degree of

comminutation of the plant material should provide sufficient particulate surface areas for

the solvent to contact.

Several extraction methods are available in the literature, such as include percolation,

Soxhlet extractor (Soxtec Avanti 2055 apparatus, Foss Tecator AB, Hoganas, Sweden),

vent extraction, counter-current extraction, etc. Studies have shown that methanol

extractions of plant materials often provide high yield of the active extracts, and an

easier-to-handle sample than aqueous extraction (Eloff, 1998). The pulverized material

(state the amount in Kg) are macerated by soaking in methanol (70% v/v) (3 x 1L) in a

percolator (state the make and where manufactured, e.g. Quickfit, England) at room

temperature for 72 h for the first extraction (also known as 1st cropping). The steps were

followed again for 3 times for the complete transfer of organic compounds (metabolites)

from the plant organs into the desired solvent. Therefore, the left over solid residue is

again soaked in 70% methanol fresh solvent for better extraction for second and third

extractions (also called 2nd

and 3rd

croppings). All the organic compounds (metabolites)

extracted into methanol is then separated using filter paper or suction filter to obtain filtrate.

All the filtrates (extracts) for each set will be collected and spray-dried, freeze-dried or

concentrated in vacuo using rotary evaporator (state the make and where manufactured,

e.g. Büchi Rotavapor, R-205; Quickfit, England) at 35o

C (Mann, 2007) to obtain the

plant extracts, sometimes referred to as crude extracts. These crude extracts are further

air-dried into powdered materials and then packed in glass bottles with proper labeling

and kept under refrigeration at 4o

C and away from light (by wrapping with aluminium

foil) prior to further processing. At this stage biological testing as well as phytochemical

analyses will be carried out on the crude extracts. Thus, changing the extraction solvent

may provide greater amounts of the active compounds. For example, methanol extracts

of certain plant species have been shown to result in greater antibacterial and anti-

inflammatory chemical activity than aqueous extracts.




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CHEMICAL TESTS IN NATURAL PRODUCT CHEMISTRY

Phytochemical tests have been developed as a means of identifying what functional

groups are present in unknown compounds or metabolites. In order for a chemical

reaction to work as a chemical test, it must

1) create a visible result (a color change, a precipitate, etc)

2) work in a short amount of time (instantly to 5 minutes)

3) only work with one functional group.

PHYTOCHEMICAL TESTS

Phytochemical test is carried out on extracts of each plant organ were analysed

qualitatively for secondary metabolites, namely alkaloids, anthraqunoids, carbohydrates,

flavonoids, glycosides, polyphenols, saponins, steroids, tannins, terpenoids, etc using

standard methods (Brain and Turner, 1975; Harborne, 1973; Trease and Evans, 1989) as

follows:

Chemical Test for Carbohydrates Mono-saccharides are the building blocks of carbohydrates. Di, oligo and

polysaccharides on hydrolysis in presence of mineral acid yield monosaccharide units.

Monosaccharides are soluble in water and practically insoluble in organic solvents like

chloroform, ether and in absolute alcohols. These are optically active compounds and

respond to various color reactions and identification tests.

1. Charring test: Carbohydrates on heating in test-tube or in presence of Conc. H2SO4,

produces charring with smell like burning sugar.

2. Molish test: 0.02 g of each extract is dissolved in 1 ml of water. Aqueous solution of

carbohydrate mixed three drops of Molish reagent (α–naphthol) and Conc. H2SO4

was added gently along side of the test-tube. Formation of purple coloured ring at

junction (interface) indicates presence of carbohydrate. When the amount of

carbohydrate is high in an extract the pink colour spreads over the upper layer.

3. Iodine test: It is specific for polysacchrides. Few drops of Iodine solution was added

to aqueous solution of drug/polysaccharide. Formation of blue colour, which

disappears on heating and reappears on cooling, indicates the presence of starch.

4. Barford test: This test is used to distinguish between monosacchride and disacchrides.

Two ml of Barford reagent (Cupric acetate, acetic acid and water) was added to 1

ml aqueous solution of drug and boil. Formation of brick red precipitate in 5

minutes indicates presence of monosacchride while in 7 minutes indicates

disaccharide.

5. Seliwanoff’s test: This test is used for identification of keto-hexoses or to distinguish

between ketoses and aldoses. To 1 ml aqueous solution of drug, 5 ml of

Seliwanoff’s reagent (resorcinol in 6M HCl) was added and boiled. Formation of

cherry red colour in presence of ketose (Fructose) due to formation of hydroxyl

methyl furfural, which condensed with resorcinol to produce cherry red colour.

6. Fehling solution test: 0.02 g of the extract is heated on a water bath with 1 ml of

dilute sulphuric acid for 2-3 minutes. Sodium hydroxide solution is added drop wise




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until the solution becomes distinctly alkaline to litmus. It is generally used for

reducing sugars and composed of two solutions, which are mixed in situ. Fehling

solution A composed of 0.5% of copper sulphate whereas Fehling solution B

composed of Sodium potassium tartarate. Equal volumes of Fehling A and Fehling

B solutions were mixed (1 ml each) and 2 ml of aqueous solution of the extract was

added followed by boiling for 5-10 minutes on water bath. Formation of reddish

brown coloured precipitate due to formation of cuprous oxide indicates presence of

reducing sugar. Di-, oligo and polysaccharides having reducing sugars can be

tested by first boiling in dilute acid solution followed by neutralization with

ammonia. This neutralized aqueous is used for testing.

7. Benedict’s test: It is used for reducing sugars and composed of mainly Copper

sulphate and sodium hydroxide. To the 4 ml of aqueous solution of drug, 1 ml of

Benedict’s solution was added and heated almost to boiling. Formation of green,

yellow, orange, red or brown colour in order of increasing concentration of simple

sugar in the test solution, that is due to formation of cuprous oxide.

8. Tollens test: Tollens reagent (Silver Nitrate, NaOH and Ammonia) is Ammonical

Silver Nitrate (diaminesilver (I) complex), an oxidizing agent, which is itself

reduced to silver metal in a clean glass reaction vessel and forms a "silver mirror",

when raects with aldehydes to form carboxylic acids. Add few drops of freshly

prepared Tollens reagent to 2 ml of aqueous solution of drug in clean testube and

heat gently. Formation of black mirror on the sidewall of testube indicates the

presence of aldehydic group.

9. Bials test: It is used to distinguish between pentoses and hexoses. Pentoses reacts with

Bial’s reagent (Orcinol in Conc. HCl and traces of FeCl3 as catalyst) to form

furfural, which condenses with orcinol to produce blue-green product. Aqueous

solution of drug (2 ml) was mixed with 4 ml of Bial’s reagent and heat to boiling, it

produces blue-green colour in presence of pentose sugar.

10. Osazone test: The osazone test was developed by Emil Fischer to identify aldose

sugars differing in configuration only at the alpha-carbon. These sugars react with

2, 4-dinitro-phenyl hydrazine effecting only alpha-carbon with formation of pink-

red coloured bis-phenylhydrazone, known as an osazone. Application of the

osazone reaction to D-glucose and D-mannose demonstrates that these compounds

differ in configuration only at C-2.

Chemical test for Starch

It is soluble in hot water, gives positive test for Molish reagent and some specific tests

like Jelly test and Lugol’s iodine test.

1. Jelly test: To 0.5 gm of starch in a test-tube add 5 ml of distilled water and boil

on water bath. Formation of translucent jelly indicates presence of starch.

2. Lugol's iodine test: It is also known as iodine – KI reagent and composed of

aqueous Iodine solution in presence of KI. Few drops of iodine – KI reagent was

added to the aqueous solution of starch, which produces deep blue to bluish black

colour due to presence of amylase. The colour developed disappears on warming

and reappears on cooling. Starch amylopectin, disacchrides and cellulose do not

produce any colour.




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Chemical tests for lipids: 1. Solubility in Polar and Nonpolar Solvents: Lipids are insoluble in polar solvents

like water and soluble in nonpolar solvents like petroleum ether, benzene and

mineral oil.

2. Sudan IV test: Lipids stain red when Sudan IV (a common stain) is added.

Sudan IV is a lipid soluble dye. When Sudan IV is added to a mixture of lipids

and water, the dye will move into the lipid layer and makes it red.

3. Grease Spot Test: A simplest test for lipid is based on the ability of lipids to

produce a translucent spot on paper.

4. Emulsification test: If emulsifiers like bile salts, tween or soap solution is mixed

with lipids and water; the lipids broken down into smaller fragments, which

remained suspended for long periods of time in water.

Chemical Test for Proteins and Amino Acids:

Proteins are high molecular weight polymers of amino acids. Amino acids are colourless

ionic compounds, more or less soluble in water and present in acid hydrolysates of plant

and animal proteins. The presence of proteins and amino acids can be detected by

following chemical tests:

1. Biuret test: To the aqueous solution of protein in hot water, few drops of Biuret

reagent (KOH, CuSO4

and sodium potassium tartarate) is added, which turns blue

reagent to violet. In laboratory, it is usually done by adding few drops of 0.5%

CuSO4

solution to the alkaline aqueous protein solution. At least one peptide

linkage is necessary for this test; individual amino acids do not produce violet

colour.

2. Millons test: Any compound containing a phenolic hydroxyl group gives Millon’s test

positive. Consequently, any protein containing phenolic hydroxyl group (like

tyrosine and phenyl alanine etc) will give a positive test of a pink to dark-red colour

due to formation of a mercury salt of nitrated amino acid. The Millon reagent is a

solution of mercuric and mercurous ions in nitric and nitrous acids. Take 1 ml of

protein solution in a test tube and add few drops of Millons reagent. White

precipitate is produced, which turns red after heating for 5 minutes on water bath.

3. Ninhydrin test: The Ninhydrin test is used to detect the presence of alpha-amino acids

and proteins containing free amino groups. Protein solution when heated with

ninhydrin molecules, it gives characteristic deep blue or pale yellow colour due to

formation of complex between two ninhydrin molecule and nitrogen of free amino

acid.

4. Lead sulphid test: Sulfur-containing amino acids like cysteine can be determined by

converting the sulfur of amino acid to inorganic sulfide by using base. The resulting

sulfide when reacts with lead acetate, a black precipitate of lead sulfide is formed.

Take 1 ml of protein solution in a test-tube and add 2 ml of 10% NaOH solution

followed by few drops of lead acetate solution. Shake the solution and boil on water

bath for few minutes; it produces black precipitate in presence of sulfur containing

amino acids.




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5. Xanthoprotic test: It is used for detection of presence of aromatic ring in amino acids

or aromatic ring containing amino acid in proteins. To the aqueous solution of

amino acid/protein (2 ml) in a testube add 2 ml of 65% HNO3. Formation of yellow

precipitate due to nitration of aromatic ring indicates presence of aromatic ring

containing amino acid like tyrosine, tryptophane etc.

Chemical Test for Gelatin:

It can be identified using following chemical tests:

1. Solubility test: Soluble in hot water whereas insoluble in cold water.

2. Soda lime test: It produces ammonia gas on heating with soda lime solution.

3. Precipitation test: Aqueous solution of gelatin produces crystalline yellow precipitate

on addition of saturated solution of picric acid whereas buff precipitate on addition

of saturated solution of tannic acid.

Chemical Test for Alkaloids:

The chemical tests are performed from neutral or slightly acidic solution of extracts

following type of chemical test given by alkaloids:

About 0.05 g of each extract is stirred with 4 ml of 1% HCl on a steam bath and then

filtered; 1 ml of the filtrate is treated with a few drops of Mayer’s (K2HgI4), Wagner’s

and Dragendorff’s reagents. A creamy white precipitate with Mayer’s reagent, few drops

of Hagers reagent (saturated aq. solution of picric acid) formed crystalline yellow

precipitate, and few drops of Wagner’s reagent (dilute Iodine solution), formulation of

reddish-brown precipitate and Dragendorff’s reagent (Potassium bismuth iodide), and

few drops of tannic acid solution, formation of buff coloured precipitate are taken as

preliminary evidence for the presence of alkaloids. Confirmatory test for alkaloids were

performed. The procedure involved using 1 ml of the acidic aqueous extract, prepared as

described above and treating it with 28% ammonia solution until the solution is distinctly

alkaline to litmus paper and then extracted several times with chloroform (ethanol free).

The chloroform extracts are then combined and concentrated in vacuo to about 2 ml, and

then extracted with an equal volume of 1% HCl. The 1% HCl extract is divided into

three equal parts and each is treated with a few drops of Mayer’s, Wagner’s and

Dragendorff’s reagents respectively. Formation of a creamy white or reddish-brown

precipitate is taken as confirmatory evidence for the presence of alkaloids.

Chemical tests for tannins: Tannins show specific chemical reaction like solution of

tannins precipitate gelatin, alkaloids, salt of Copper, Lead and Tin etc. and shows color

reaction with K2Cr2O7, chromic acid and iron salts.

1. Test with Iron salts: It show color reaction with iron salt like FeCl3 and potassium

ferrrocyanide K4Fe(CN)6 in presence of ammonia. Addition of FeCl3

solution to the

solutions of hydrolysable tannins forms bluish black precipitate whereas with

condensed tannins it forms greenish brown coloured precipitate.

2. Goldbeater’s skin test: Goldbeater’s skin is the membrane prepared from ox intestine

and behaves like untanned hide. Small piece of ox-intestine is dipped in 2% dilute

HCl, rinse with distilled water then soaked in test solution for few minutes again

rinsed with distill water and transfer to 1% solution of Ferrous sulphate. Formation




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of brownish black color indicates the presence of tannin. This is positive for all true

tannins but negative for pseudo tannins.

3. Gelatin test: To the aqueous solution of gelatin (1% w/v) solution of gelatin 0.5-1.0%

solution of tannin was added, formation of buff coloured precipitate indicates

presence of tannins. Pseudo tannins also show this test positive if tannin is present

in sufficient amount.

4. Phenazone test: Aqueous extract of drug (5 ml) was mixed with 0.5 gm of solid

sodium acid phosphate (NaHPO4), heated the solution to boiling, cooled and

filtered. Filtrate was treated with 2% solution of phenazone drop wise to form bulky

precipitate of all tannins.

5. Test for catechin (Matchstick test): Catechins forms phlorogluecinol when heated in

presence of acids and can be detected by reaction with lignin forming woody red to

magenta colour. The paste of test extract (tannin) was applied on the rear end of

matchstick and moistened with conc. HCl. Formation of woody pink to magenta

colour on heating near the flame indicates presence condensed tannins.

6. Test for Chlorogenic acid: Extracts of drug containing chlorogenic acid on treatment

with aqueous ammonia converted to green color after exposing with air.

7. Vanillin HCl test: Solution of test drug was mixed with few drops of vanillin HCl.

Development of pink colour in presence of tannins due to conversion of

phloroglucinol from catechin.

8. Bromine water test: Condensed tannins are precipitated in presence of bromine water.

Chemical Tests of Glycosides:

Glycosides are the compounds with organic molecules having attached glucose or any

mono-oligo sacchride unit. Usually, these are crystalline or amorphous solids; optically

active, soluble in water and alcohol but insoluble in organic solvents like ether,

chloroform and benzene etc. Generally, aqueous or alcoholic extracts of crude drugs are

tested with specific reagents for presence of various types of glycosides.

Chemical tests for anthraquinone glycosides a. Borntragor’s Test: The test is used to identify the presence of free anthraquinones.

0.05 g of each plant extract is shaken with 5-10 ml CCl4/benzene and then filtered

and 5 ml of 10% ammonia solution added to the filtrate. The mixture is shaken and

the presence of pink, red or violet colour in the ammoniacal (lower) phase indicates

the presence of free anthraquinones or anthraquinone moiety.

b. Modified Borntragor’s Test: Combined anthraquinones are simply referred to as

anthraquinone glycosides; they are identified as follows: 1 gm of each plant extract

add 5 ml dilute HCl followed by 5 ml ferric Chloride (5% w/v) or 0.05g of each

plant extract is boiled with 5 ml aqueous sulphuric acid for 10 minutes on water

bath, cool and filtered while hot. The filtrate is shaken with 3 ml carbon

tetrachloride or benzene, the benzene layer separated and half its own volume of

10% ammonia solution added. Formation of a pink, red or violet colouration in the

ammonia phase (lower layer) indicates the presence of anthraquinone derivatives in

the extract.




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Chemical tests for saponin glycosides a. Haemolysis test: A drop blood on slide was mixed with few drops of aq. Saponin

solution, RBC’s becomes ruptured in presence of saponins.

b. Foam test or Frothing test: 0.05 g of each extract is shaken with 1 ml distilled water in a test-tube for 1 min. It

is kept aside and observed for persistent frothing for 60-120 seconds. If the frothing

persists this indicates the presence of saponins.

Chemical tests for steroid and triterpenoid glycosides a. Libermann Bruchard test: Alcoholic extract of steroid was evaporated to dryness

and extracted with CHCl3, add few drops of acetic anhydride followed by conc. H2

SO4 from side wall of test tube to the CHCl3

extract. Formation of violet to blue

coloured ring at the junction of two liquid, indicate the presence of steroid moiety.

b. Salkovaski test: Alcoholic extract of steroid was evaporated to dryness and extracted

with CHCl3; add conc. H2SO4 from sidewall of test tube to the CHCl3

extract.

Formation of yellow coloured ring at the junction of two liquid, which turns red

after 2 minutes, indicate the presence of steroid moiety.

c. Antimony trichloride test: Alcoholic extract of drug was evaporated to dryness and

extracted with CHCl3, add saturated solution of SbCl3 in CHCl3 containing 20%

acetic anhydride. Formation of pink color on heating indicates presence of steroids

and triterpenoids. .

d. Trichloro acetic acid test: Triterpenes on addition of saturated solution of trichloro

acetic acid forms colored precipitate.

e. Tetranitro methane test: It forms yellow colour with unsaturated steroids and

triterpenes.

f. Zimmermann test: Meta dinitro benzene solution was added to the alcoholic solution

of drug containing alkali, on heating it forms violet colour in presence of keto-

steroid.

Chemical tests for cardiac glycosides a. Keller Killiani test: 0.05 g of each extract is boiled with 5 ml of 70% ethanol for 2-3

mins and filtered. The filtrate is diluted with an equal volume of water. This

solution is shaken with 1-2 drops of strong lead acetate solution to precipitate

other pigments and filtered. The filtrate is shaken with 5 ml of chloroform in a 50

ml separatory funnel and the chloroform layer transferred into a porcelain dish

and gently evaporated to dryness on a water-bath. The cooled residue is dissolved

in 3 ml of glacial acetic acid containing 2 drops of 5% ferric chloride solution.

This solution is transferred into a test-tube containing 2 ml of concentrated

sulphuric acid, a reddish-brown ring at the interface between the two liquid

indicates the presence of deoxy sugar, a pale green or blue colour at the upper

layer indicates the presence of a steroidal ring as the aglycone portion of the

cardiac glycosides.

b. Legal test: To the alcoholic extract of drug equal volume of water and 0.5 ml of strong

lead acetate solution was added, shaked and filtered. Filtrate was extracted with




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equal volume of chloroform and the chloroform extract was evaporated to

dryness. The residue was dissolved in 2 ml of pyridine and sodium nitropruside 2

ml was added followed by addition of NaOH solution to make alkaline.

Formation of pink colour indicates presence of glycosides or aglycon moiety. OR

a small portion of the extract is dissolved in pyridine; and few drops of 2%

sodium nitroprusside together and few drops of 20% sodium hydroxide solution

are added. A deep red colour which faded to brownish-yellow indicates the

presence of cardenolides.

c. Kede test: 1 ml of 8% solution of the extract in methanol is mixed with 1 ml of 2%

methanolic 3, 5-dinitrobenzoic acid and 1 ml of 6% aqueous sodium hydroxide. A

reddish- brown to brownish-yellow colour indicates the presence of cardenolides

and the presence of a whitish crystalline solid in solution indicates the presence of

a lactone ring in the cardenolides.

d. Baljet test: Thick section of leaf of digitalis or the part of drug containing cardiac

glycoside, when dipped in sodium picrate solution, it forms yellow to orange

colour in presence of aglycones or glycosides.

e. 3,5-dinitro benzoic acid test: To the alcoholic solution of drug few drops of NaOH

followed by 2% solution of 3,5-dinitro benzoic acid was added. Formation of pink

colour indicates presence of cardiac glycosides.

Chemical tests for Coumarin glycosides a. FeCl3

test: To the concentrated alcoholic extract of drug few drops of alcoholic FeCl3

solution was added. Formation of deep green colour, which turned yellow on

addition of conc. HNO3, indicates presence of coumarins.

b. Fluorescence test: The alcoholic extract of drug was mixed with 1N NaOH solution

(one ml each). Development of blue-green fluorescence indicates presence of

coumarins.

Chemical tests for Cynophoric glycoside a. Sodium picrate test: Powdered drug moistened with water in a conical flask and few

drops of conc. Sulphuric acid was added. Filter paper impregnated with sodium

picrate solution followed by sodium carbonate solution was trapped on the neck of

flask using cork. Formation of brick red colour is due to volatile HCN in presence

of cynophoric glycosides.

Chemical tests for flavonoid glycosides a. Ammonia test: Filter paper dipped in alcoholic solution of drug was exposed to

ammonia vapor. Formation of yellow spot on filter paper. Specific tests can be

carried out on extracts to determine the nature of flavonoid present.

b. Shinoda test: i. To the alcoholic extract of drug Magnesium turning and dil. HCl was added, formation

of red colour indicates the presence of flavonoids.




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ii. To the alcoholic extract of drug Zinc turning and dil. HCl was added, formation of

deep red to magenta colour indicates the presence of dihydro flavonoids.

c. Ammoniacal silver nitrate test

0.02 g of the sample is dissolved in 1 ml of water and a few drops of ammoniacal

silver nitrate are added. The colour is observed before and after heating for 5

mins. A brown, blue or black colour before heating with the blue turning black or

brownish-black and black still remains black is indicative of the presence of

flavonol glycosides. No colour before and after heating indicates flavanone

glycosides. The only exception in this class of flavonoid is hesperidin which turns

black after heating. Formation of a reddish-brown colour before heating which still

remains the same colour after heating indicates flavone aglycones. Chalcones do

not form colour before heating except 2, 3, 4-trihydroxychalcones, it forms a

reddish-brown or black colour after heating.

d. Vanillin HCl test: Vanillin HCl was added to the alcoholic solution of drug, formation

of pink colour due to presence of flavonoids.

e. 0.02 g of the extract is dissolved in 1 ml of 50% ethyl acetate solution and the colour in

the upper layer observed. Formation of a pale yellow colour in visible light

indicates the presence of flavonol glycosides.

Chemical test for terpenoids

1) Un-saturation test due to presence of double bond.

2) Addition reaction with H2 + HX and forms characteristic addition product with

NaCl and NaBr.

3) Undergoes polymerization.

4) Thermal decomposition yields isoprene

a. Liebermann–Burchard’s test

0.05 g of each plant extract is dissolved in 1 ml of acetic anhydride and cooled in ice. 2

drops of sulphuric acid are then carefully added. Formation of a colour change from blue

to green indicates the presence of a steroidal nucleus as the aglycone portion of the

cardiac glycoside. While a pink colour formation indicates the presence of terpenes.

Chemical tests for volatile oils:

Natural drugs containing volatile oils can be tested by following chemical tests:

1. Thin section of drug on treatment with alcoholic solution of Sudan IIIrd develops

red color in the presence of volatile oils.

2. Thin section of drug is treated with tincture of alkana, which produces red color

that indicates the presence of volatile oils in natural drugs.

Chemical tests of resins: a. Solubility test: Resins are insoluble in water, rarely soluble in light petroleum

(except Colophony and Dammar) soluble in alcohol, ether, acetone, chloroform,

fixed oils and volatile oils etc.




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b. Turbidity test: Resinous drug was extracted with alcohol and water is added in

excess to form turbidity, because these are insoluble in aqueous solutions.

c. HCl test: One gram of drug was extracted with few ml of acetone and 3ml of dilute

HCl was added. Formation of pink colour after heating the solution on water bath

for 30 minutes indicates presence of resins.

d. FeCl3 test: Few drops of FeCl3

solution was added to the alcoholic extract of drug.

Formation of greenish blue color indicates presence of resins.

PARTITIONING OF THE CRUDE PLANT EXTRACTS (Aqueous suspension) The crude aqueous methanolic extract (state the amount in grammes) obtained from the

extraction above is dissolved in water (1000ml) to give the Aqueous Layer. The scheme

in figure 1 below indicates the solvents to be used in order of their increasing polarities

(n-hexane, dichloromethane, ethyl acetate, n-butanol) (Mann, 2007). Apart from CH2Cl2

fraction other organic fractions had density less then water so the top layers of the

fractions are collected while bottom layers of CH2Cl2, having a density of 1.3, are

collected. All of the fractions so obtained shall be filtered twice using Whatman No. 1

filter paper sheets (state the make and where manufactured, e.g. Whatman Biometra,

Göttingen, Germany). Each extract is concentrated in vacuo by the evaporation of the

various solvent soluble extracts under reduced pressure at 35oC using Rotavapor. The

constituents in the extract can be identified and quantitatively analyzed using

conventional High Performance Liquid Chromatography (HPLC).

THIN LAYER CHROMATOGRAPHY (TLC)

Thin Layer Chromatography is the separation technique in which sample is tested for the

different constituents in it by running it on a thin silica layer (which acts as a stationary

phase) spread over a glass plate, with the help of a solvent system (which acts as a mobile

phase). If the compound is more polar, the more will be its mobility and less will be its

Rf (retardation factor) value. This trial plate technique though is time taking and

strenuous, has helped us to go directly for Preparative TLC and Column

Chromatography. Not only that but to go for long or short column i.e., if the Rf values of

the compounds are too close we have to go for long column and if they are far we have to

go for a short ones.

The mobility of the compounds can be assayed in three ways:

1. If the compound shows chromatographic effect, this can be possible only for the

compounds which show conjugated (alternate) double bonds or lone pair of electron

sunder transition. Then the compound can be observed and identified under U.V

radiation.

2. When exposed to Iodine vapours.

3. When sprayed with 10% methanolic sulphuric acid solution or with ansaldehyde.

For further clarification, the sprayed plates were kept for charring on hot plate

Therefore, the concentrated plant extract is usually chromatographed on TLC to find out

the extract’s mobile phase for clear separation (good resolution), that is to find out the

degree of mobility or Rf of a particular molecule or compound which mainly depends on

its polarity.




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The soluble fractions are usually dissolved in methanol in a concentration of 1 mg/ml. A

line is drawn 2 or 3cm from the base of each TLC plate (to serve as origin). Adopting one

dimensional and ascending technique, a fine bore glass capillary tube is used to apply a

spot volume of 3-5 μL of each fraction on the pre-coated glass TLC plates silica gel (state

the size, make and where manufactured, e.g. 60 F254 layer thickness 0.25 mm Kieselgel

60 F254, Merck, Darmstadt, Germany) of size 2 x 10 cm. Similarly eluents when collected

from column chromatography are treated in the same manner.

Selection of solvent systems for crude extracts by trial TLCs:

Several trials were made on trial TLC plates by increasing the polarity of the solvent

systems, to find out the exact mobile phase. The following solvent systems are found to

be useful as mobile phases for TLC analysis:

i. With Hexane.

ii. With ethyl acetate and hexane.

iii. With methanol and hexane.

iv. With acetone and hexane.

v. With chloroform and hexane.

After the initial trials of various solvent systems as above, any one that give good

separation or resolution is adopted. If not, further clearer separation is required by

another round of trials, which is made by increasing or decreasing polarity i.e. by

changing the ratio of the solvents in the solvent system as thus:

a) Hexane: chloroform in 10:1

b) Hexane: chloroform in 9: 1

c) Hexane: chloroform in 8: 2

d) Hexane: chloroform in 7: 3

e) Hexane: chloroform in 6: 4

f) Hexane: chloroform in 5: 5

g) Hexane: chloroform in 4: 6

h) Hexane: chloroform in 3: 7

i) Chloroform: Methanol 9:1

j) Chloroform: Methanol 5:1

k) Chloroform: Methanol 4:1

l) Chloroform: Methanol: Ethylacetate 4: 1: 1

m) Chloroform: Methanol: Ethylacetate: water 28: 30: 35: 5

n) Dichloromethane: Methanol: Water 30: 10: 1

Preparative TLC With this idea the soluble fractions are then chromatographed very carefully over

preparative thin layer chromatography (20cm x 20cm). This is done by dissolving in

methanol (1 mg/ml) and applying it with the help of a fine bore glass capillary tube, a

volume of 50 μl of each fraction on the entire length of pre-coated glass TLC plates of

size (20 cm x 20 cm). The solvent systems given in the table below are used for the

development of chromatograms of the respective fractions.




12

Solvent systems for fractions

Fraction Solvent System(s)

n-Hexane fraction CH3OH: CHCl3 (3:200)

Dichloromethane fraction* i) CH3OH: CHCl3 (1:20)

ii) CH3OH: CHCl3 (3:10)

Ethyl acetate fraction n-Butanol: Acetic acid: Water (12:3:5)

n-Butanol fraction n-Butanol: Acetic acid: Water (12:3:5)

Methanol fraction n-Butanol: Acetic acid: Water (12:3:5)

*TLC plates loaded with the dichloromethane fraction were first developed to a

maximum with system (i) and then half developed with system (ii)

The major bands observed are identified and they are suspected to contain organic

compounds (metabolites). The identified bands are carefully bordered with pencil and

scraped. The organic compounds (metabolites) are then eluted from the silica gel bed by

washing it with suitable solvents (such as ethyl acetate, methanol, etc) and to separate it

from silica gel by filtration. Further bioassay directed fractionation is continued on the

active fractions in order to isolate the active compounds (Mann, 2007).

COLUMN CHROMATOGRAPHY CC The Column is usually packed using wet packing method. Slurry is prepared by shaking

one hundred grams (100 g) of silica gel (state the size, make and where manufactured,

e.g. particle size 0.040-0.063 nm; 70-230 mesh, Merck) with 200 ml of hexane and then

packed in a column (ɸ3 x 30 cm). The silica gel is first activated in the oven for 2 h at

105o

C. One gram (1g) of the extract is re-dissolved in fifty (10 ml) of methanol and 20 g

of the activated silica gel was used to absorb the dissolved extract. The dissolved extract

is kept under the fan to dry. The dried absorbent (silica gel) is then introduced to the top

of the packed column and a piece of glasswool or filter paper gently on top of the

column. Elution is then carried out using gradient mixtures of n-hexane, n-Hex-EtOAc

(100:0 → 95:5 → 20:80 → 0:100) and MeOH. Eluents may be collected in 10 or 20 or 50

or 100 ml. Eluents are then monitored by TLC behaviour (Mann, 2007).

BIOACTIVITY SCREENING

Determination of antimicrobial activity

Contact with members of staff in the Microbiology and Biochemistry Departments for the

appropriate protocols will be made. However, these are commonly encountered protocols

(Brantner et al., 1994; Mitscher et al., 1972).

Agar well diffusion method The crude extract fractions are dissolved in 10% (v/v) solution of dimethyl sulfoxide,

DMSO (state the maker and where manufactured, e.g. Fluka, Madrid, Spain) in normal

saline (0.9% w/v) to give a final concentration equal to 3.2 mg/ml. The prepared

concentrations are then filtered using sterilized Millex, 33 mm filter unit having pore size

0.22 μm (Millipore, Cork, Ireland). The bacterial strains are cultured on nutrient agar

((state the maker and where manufactured, e.g. Merck, Darmstadt, Germany) in 9 cm




13

diameter petri plates, a single isolated colony of test bacteria e.g. Staphylococcus aureus,

Escherichia coli, Bacillus subtilis, Bacillus cereus, Pseudomonas aeruginosa, and

Salmonella typhi is aseptically picked and transferred to nutrient broth (state the maker

and where manufactured, e.g. Oxoid, Hampshire, UK) and incubated in a shaker

incubator (state the maker and where manufactured, e.g. Innova 43, New Brunswick

Scientific Co., New Jersey, USA) at 150 rpm for a period of 18 hours except for the S.

typhi (4 h incubation) at 37 oC. After incubation period the turbidity of the solutions will

be adjusted to 0.5 McFarland turbidity standards, using sterile nutrient broth. Hundred

microliter of the inoculum was evenly spread over the entire area of 9 cm diameter Petri

plates containing Muller Hinton agar (state the maker and where manufactured, e.g.

Oxoid, Hampshire, UK) media, with the help of a sterile glass spreader and is allowed to

dry. With the help of a sterile cork borer, wells measuring 0.7 cm in diameter were made.

Seventy microliter of crude extract solution is transferred aseptically into the wells. 10%

(v/v) DMSO in normal saline (negative control) and standard antibiotics; 0.072% (w/v)

(state the drug, maker and where manufactured, e.g. Ciprofloxacin (Sigma-Aldrich,

Steinheim, Germany) in 0.1N HCl, that is used against Gram Negative organisms and

0.029% (w/v) (state the drug, maker and where manufactured, e.g. Clarithromycin

(Sigma-Aldrich, Steinheim, Germany) in 0.1N HCl, is utilized for Gram positive

organisms (positive controls). The plates are placed in upright position in refrigerator for

a period of 2 h in order to allow the materials to diffuse around the well area. The zones

of inhibition are measured after 24 h incubation at 37 oC, in case of all the organisms in

an upright position. All the tests are run in triplicate.




14




15

Disk diffusion method

For Bacteria The Paper disc diffusion technique described by Bauer-Kirby Method (Bauer et al., 1966)

can be used to determine the antimicrobial activities of the extracts. Stock solutions of

crude methanolic extracts are prepared by dissolving 1 mg of each extract in 100 ml of

dimethyl sulphoxide. These solutions are used in the determination of antimicrobial

activities of the extracts as well as for the determination of Minimum Inhibition

Concentration. Solution concentrations of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 mg/mL are prepared

for each extract by serial dilution. The plates containing the sterile media are seeded with

the microorganisms by the spread plate technique and are then left for half an hour to dry.

Blank disks of diameter 6 mm are punched from Whatman No. 1 filter paper sheets

((state the drug, maker and where manufactured, e.g. Whatman Biometra, Göttingen,

Germany). Filter paper discs are cut and sterilized for 1 h (Bauer et al., 1966), and then

soaked in the solution of the extract concentrations prepared and dried at 45 oC for 1 h;

disks are allowed to dry in the laminar flow. The dried paper discs are then planted on the

blood agar plates seeded with test microorganisms. The plates are placed in inverted

position in refrigerator for a period of 2 h in order to allow the materials to diffuse around

the disks area. The plates are then incubated at 37 oC for 24 h in the case of bacteria

species, before they are examined for the zone of inhibition of growth. Tetracycline (0.5

mg/mL) (state the drug, maker and where manufactured) could be used as reference or

positive control while DMSO without sample is used as negative control.

For Yeast Agar tube dilution method is usually applied for determination of the antifungal activity

against Candida albicans. Candida albicans is subcultured on sabourad dextrose agar

(state the drug, maker and where manufactured, e.g. Oxoid, Hampshire, UK) slants and

refreshed fortnightly. The slants are stored at 4 oC. C. albicans is Gram stained for

morphology and characterized by simple germ tube test. It involved pipetting 0.5 ml of

human serum into a small test tube followed by inoculation with a yeast colony and

incubated at 37 oC for 3 h. A drop of serum yeast culture is transferred to a glass slide and

covered with a cover glass and examined the preparation for characteristics sprouting

yeast cells having tube-like outgrowths known as germ tubes (Cheesbrough, 1985). A

single isolated colony is aseptically transferred to sabourad dextrose broth (state the drug,

maker and where manufactured, e.g. Oxoid, Hampshire, UK) and incubated overnight at

37 oC at 140 rpm in a shaker incubator. One hundred microliter of inoculum (ca. 5 x 105

CFU/ml) is evenly spread, with the help of a sterile glass spreader over the entire surface

area of 15 cm diameter petri plates containing sabourad dextrose agar (state the drug,

maker and where manufactured, e.g. Oxoid, Hampshire, UK). The seeded plates are

allowed to dry under laminar flow. The plates are then incubated for a period of 48 h in

an inverted position in the case of fungi species, before they were examined for the zone

of inhibition of growth. The disks containing the plant crude extracts, CHCl3 (negative

control) and (state the drug, maker and where manufactured, e.g. miconazole; Sigma-

Aldrich, Steinheim, Germany) served as positive control. The diameters of the zones of

inhibition of growth are measured and recorded in millimetres. The tests are run in

triplicate.




16

CONTACT BIOAUTOGRAPHY

For Bacteria The developed chromatograms obtained from preparative TLC are cut into pieces of 2

x10 cm size with the help of a glass cutter, wrapped twice and sealed in polythene bags.

They are then gas sterilized for a period of 18 h using an ethylene oxide sterilizer (state

the maker and where manufactured, e.g. Axis, Izmir, Turkey). Alternatively, the plates

are also sterilized by briefly dipping them into dioxane (state the maker and where

manufactured, e.g. Merck, Darmstadt, Germany) and allowing them to dry under laminar

flow. The seeded bacterial plates are similarly treated as mentioned above. The pieces of

TLC plates are then aseptically placed upon the bacterial lawn and are left for a period of

2 h, in order to allow the materials from them to diffuse on to the seeded plates.

Tetracycline and miconazole disks (prepared as given earlier) are used as positive

controls.

Determination of antimycobacterial activity

The susceptibility test is conducted using the broth microdilution method (BMM) in 96

well microtitre plates. Fifty microlitres of the medium is pipetted into wells No 2-12.

While, 50 μL of extract is pipetted into wells No 1 & 2. The content of well 2 is then

mixed thoroughly and 50 μL is transferred to well 3, repeated through out the plate and

the final 50 μL from well 12 is then discarded. Extracts are first dissolved in DMSO and

then diluted in Middlebrook 7H9 broth, to give a starting concentration of 5000 μg/mL

which is diluted out across a 96-well microlitre plate in a two-fold serial dilution to give

final testing concentrations of 2500, 1250, 625, 312, 156 and 78 μg/mL. The same

procedure is repeated for the control (Rifampicin) with the initial concentration of 32

μg/mL with the subsequent dilution to the final testing concentrations of 1, 0.5, 0.25,

0.125, 0.06, 0.03μg/mL. Appropriate DMSO, growth and sterile controls are carried out

with rifampicin as positive control. All plates are incubated initially at 37OC for14 days.

The plates were re-incubated at 37oC for further 2 weeks. After this incubation, any well

that turned cloudy are recorded as positive for growth. The minimum inhibitory

concentration (MIC) is defined as the lowest extract concentration at which no

mycobacterial growth is observed.

For Brine Shrimp Lethality assay The brine shrimp lethality test (BST) is used to predict the presence of cytotoxic activity

in the extracts (McLaughlin et al., 1991; Meyer et al., 1982; Solis et al., 1993) with some

modifications. Brine shrimps (Artemia salina) eggs could be obtained from any standard

chemical store in Lagos and hatched in hatchery chamber made of plastic dish filled with

natural sea water from Bar Beech, Lagos. The hatchery with the eggs is placed in light for

48 h. The stock solution is prepared by dissolving 0.02 g extract in 2ml dimethyl

sulphoxide (DMSO). 1.8 ml of the brine is added to 0.2 ml of the stock to give 1000 ppm

solution. Subsequent concentrations of 100 and 10 ppm are obtained from this. Ten

nauplii are drawn through a glass capillary and placed in test tube containing 4.0 ml of

brine solution and 0.5 ml of plant extract concentration and made up to 5 ml with brine

solution. Tests for each concentration are done in triplicate. A control experiment




17

containing 5 ml of brine solution with two drops of DMSO and ten nauplii is set along

side. The experiments are maintained at room temperature for 24 h under light and the

surviving larvae counted.

Statistical analysis

The lethality of the extracts is calculated from the mean survival larvae of extract treated

and control using Finney’s probit analysis is used to determine the ED50 of each extract.

The toxicity is expressed by this ED50 which is defined as concentration of extract that

kills 50% of the shrimps within 24 h. Toxicity of the extract against the brine shrimps is

determined by a statistically significant decrease in the survival of brine shrimps exposed

to plant extract relative to the survival of shrimps in the control.

Determination of antitrypanosomal activity

Infection of Animals:

Blood is collected by cardiac puncture with EDTA coated syringe from heavily infected

mouse and immediately diluted with physiological saline to serve as inoculum. Healthy

mice were infected intraperitoneally with 0.02ml of the inoculum containing about 103

trypanosome cells. Infection was monitored every two days by microscopic examination

of blood samples taken from tails of the infected animals.

Twelve healthy (parasite free) mice are grouped into four (i.e. A-D) of three mice each.

They are intraperitoneally administered the extract at doses of 100, 200, 300 and 400mg

per kilogram body weight (kg/bw). They are all infected with trypanosomes as described

above. Three uninfected mice to which 400mgkg/bw is administered is the fifth group.

This will provide the clue of acute toxicity of the extract. The sixth group of three mice

formed the negative control (i.e. infected but not treated), while positive control is the

infected and treated with 3.5mgkg/bw of the standard drug berenil formed the seventh

group. Parasitaemia is thereafter monitored at two days interval for two weeks by

microscopic examination of wet film prepared from blood samples taken from the tail of

infected animals (Ogbadoyi et al., 2011).

REFERENCE

Bauer, A.W., Kirby, W.M., Sherris, J.C. and Turk, M. 1966. Antibiotic susceptibility

testing by standard single disc method. Am. J. Clin. Path., 45: 493-496.

Brain, K.R. and Turner, T.D. 1975. The Practical Evaluation of Phytopharmaceuticals.

Wright-Science Technical, Bristol, pp. 57-63.

Brantner, A., Pfeiffer, K.P. and Branter, H. 1994. Applicability of diffusion methods

required by the pharmacopoeias for testing antibacterial activity of natural compounds.

Pharmazie, 49: 512-516.

Cheesbrough, M. 2000. Medical Laboratory manual for Tropical countries.

Microbiology. Linacre house, Jordan Hill Oxford.

W.C. Evans, Trease and Evans Pharmacognosy, Fifth edition, Harcourt Brace and

Company Asia, Pvt. Ltd.




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Eloff, J.N. 1998. Which extractant should be used for the screening and isolation of

antimicrobial components from plants? J. Ethnopharmcol. 60:1-8.

Harborne, J.B. 1973. Phytochemical Methods: A Guide to Modern Techniques of Plant

Analysis. Chapman A & Hall. London, pp. 160-161.

Mann, A., Gbate, M. and Nda-Umar, A. 2003. Medicinal and Economic Plants of

Nupeland. Jube-Evans Books and Publications, Bida, Niger State, Nigeria. ISBN 978-

33921-9-0. 276p.

Mann, A. 2007. Survey of Ethnomedicine for the treatment of Tuberculosis: Chemistry

Perspective. Ayanwola Printing Works, ISBN 978-978-085-536-9, Minna, Niger State,

Nigeria, 117 pp.

McLaughlin, J.L., Rogers, L.L. and Anderson, J.E. 1998. The use of biological assays to

evaluate botanicals. Drug Information Journal, 32: 513-524.

Meyer, B.N., Ferrigni, R.N., Putnam, J.E., Jacobson, L.B., Nicholas, D.E. and

McLaughlin, J.L. 1982. Brine shrimp: A convenient general bioassay for active plant

constituents. Planta Medica. 45: 31–34.

Mitscher, L.A., Leu, R.B., Bathala, M.S., Wu, W.N., Beal, J.L. and White, R. 1972.

Antimicrobial agents from higher plants. 1. Introduction, Rationale and Methodology.

Lloydia, 35: 157 – 166.

Ogbadoyi, E.O., Garba, M.H., Kabiru, A.Y., Mann, A. and Okogun, J.I. 2011.

Therapeutic evaluation of Acacia nilotica (Linn) stem bark extract in experimental

African trypanosomiasis. International Journal of Applied Research in Natural Products,

4 (2): 11-18.

Solis, P.N., Wright, C.W., Anderson, M.M., Gupta, M.P. and Phillipson, J.D. 1993. A

microwell cytotoxicity assay using Artemia salina (brine shrimp). Planta Med., 59(3):

250-252.

Trease, G.E. and Evans, W.C. 1989. Text book on Pharmacognosy. 13rd Ed., Bailiere-

Tindall, London, pp. 343-383.




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