The Alkaloids

Typical (True) alkaloids:

Basic nitrogenous comp. of plant origin having physiological effects on man or animals (The nitrogen atom(s) is usually in a heterocyclic ring, biosynthesized from amino acid, they are precipitated by alkaloidal reagents.

N atom in side chain e.g:ephedrine.

Colchicine w is not basic.

Some nitrogenous physiological active comp. of animal origin (e,g: Aclrenaline) also termed alkaloids.

Synthetic comp. (Not found in plants) e.g: Homatropine closely related to the natural alkaloids.

The nitrogen atom in alkaloids:

The alk. Must have at least one N atom in their structure.

OH OH

NO2 NMeH

Me o

H

NMe

OH

H

Ne2M

H

Me

(-)- Norpseudo ephedrine (-)- Ephedrine

Alk. Sec. alk.

Tubocurarine

Auaternary alk.

H2C CH CH2

NMe

H2C CH CH2

C

H

O C

O

C

H

CH2OH

Hyoscyamine tertiary alk.

or (Alk. N-oxides) as Hyoscines N-oxide

The nature of the N atom affects the properties, The derivatisation and the method of isolation of the alk. From plants.

Occurrence and distribution in plant kingdom:

The family Apocyanaceae (Richest source of alkaloids) followed by the:

1) Papaveraceae

2) Fabaceae

3) Solanaceae

4) Rutaceae

5) Boraginaceae

6) Loganiaceae …….. etc

In the plant: barks, leaves and fruits are often rich in alkaloids.

Tropane alk. Of A.belladonna synthesized in the root

Leaves (site of storage), Also Nicotine in tobacco plant.

transported

While lupin alk. Formed in the stem transferred to the root.

Role of alkaloids in the plants:

1) Alk. Can serve to protect the plant against insect, microorganism or virus attacks (Solanine in potatoes when plant is attacked by microorganisms).

2) Alk. Protect the plant from being eaten by grazing cattle (Most of alk. have bitter taste and may be toxic).

3) Reserve nutrition for the plant storing nitrogen.

4) As growth regulators.

Alkaloids may exist in the free state, as salt, as amines or alk. N-oxides.

Alk. Are oftenly occur in the form of salt e common a, e.g: acetic, citric, oxalic or tannic.

Salts of special acids, examples:

1) Meconic a (Opium alk.)

2) Cinchotannic a (Cinchona)

3) Aconitic a (Aconite)

4) Gluco – alk e.g:Solanine

General properties:

1) Most alk. are crystalline comp. odorless, colorless, non volatile.

they contain C, H, N, O few oxygenated alk. Volatile liquid.

e.g: Pilocarpine, pelletierine.

non

2) Alk. Lack oxygen in their struc. Usually occur as volatile liquid.

e.g: coniine, nicotine.

3) Very rare colored alk. e.g: Berberine, Colchicine (yellow).

4) Being basic, alk. Salts e

Alkali hydroxi

NH4

or nNa.CO3

Free base

7) Weak basic alk. e.g: caffeine, narcotine, papaverine, piperine from salts

Are unstable.

W

5) Some alk. Neutral or slight acidic reaction can not form salts.

e.g: Ricinine, Theophylline.

6) Amphoteric alk. Contain-COOH gp. A narceine or-OH gp. as morphine.

Solubility of alkaloids:In fact, the differences in sdubility between alks. And their salts strongly facilitate the process of isolation and separation of the alks. From plant and from non-alkaloidalsubst.

The general role of solubilily of alks. :

Free bases are sol. In organic sol., sparingly soluble in H2O.

Alk. Salts are sol. In H2O but sparingly sol. In organic solvent.

Exception to this generalization:

1) Caffeine (base) extracted from tea by H2O.

2) Colchicine (base) sol. In acid, neutral or alkaline H2O.

3) Morphine (base) is sparingly sol. In ether.

4) Ephedrine and pilocarpine (base) are sol. In H2O.

5) (Labeline HCL salt) and apoatropine HCL (salt) are sol. In CHCL3.

Optical Isomerism:

Alks are optically active comp.(many of them contain at least one asymmet C-atom).

The pharmacological activities are usually more e laevorotatory isomers than e the dextrorotatory e,g: D(-)- ephedrine 3 fold stronger than D(+)-ephedrine (3:1) arterial B.p.

Some exceptions:

d-tubocurarine (dextrorotatory) is the medicinally active.

General tests for alkaloids:

1) Alkaloidal precipitating reagents:

A) Mayer’s reagent. B) wagner’s reagent.

C) Hagar’s reagent D) Gold chloricle

E) Dragendoeff’s reagent.

2) Alkaloidal coloring reagents:

(The rough dehydration or oxidation of the alks)

A) Marquis reagent. B) Mandalin R.

C) Froehed’s r D) Erdmann’s R.

3) Special tests for alks:

Used to identify or to confirm the identity of the alks.

Examples for the isolation procedures for AlkaloidsProcedure I

Ground plant

Extract with alcohol and concentrate to aqueous layer

Marc Aqueous (Alkaloid salts and bases)

1- Alkalinize with NH3

2- Extract with CHCL3,…..etc.

CHCL3 extract (Alkaloid bases) + impurityAquous layer

(test to N-Oxides) Extract with diluted HCL

CHCL3 Aq.Layer (Alkaloid at )

Add NH4OH and extract with CHCL3

Aq.LayerCHCL3

(Alkaloid bases; to be separatedchromatography)

Procedure III

General plant material

Extract with water or aqueous alcohol containing acid

MarcAqueous (alkaloid salts)

Shake with CHCL3

Aqueous layer CHCL3 extract(Alkaloid salts) (pigments and impurities)

1- Alkalinize with NH4OH.

2- Extract with CHCL3

CHCL3 Aq.Layer(Alkaloid bases;

separate by chromatography)

Quantitative Determination of Alkaloids:

If the total alks. Are to be determined togathe. “ Proximate assays”.

If the individual alks. “Ultimate assays”.

1) Volumetric methods.

a) (Acid base titration).

Add measured volume of stand acid, exces acid = stand alkali using methy red.

B) (Non aqueous titration).

In non aqueous meduim using glacial acetic a , anhydrous CHCL3or ether.

Requirements for the volumetric methods:1) The alks. Should be basic enough to be neutralized by the stand acid toform salts.

2) The Mol.Wt. of the alks must be know.

3) Basic impurities, coloring matter, fatty mat. Must be removed.

Advantages:

1) It is rapid (compared to the gravimetric methods).

2) Sensitive as it can determine alks. In trace amounts.

2) Gravimetric methods:Plant material alks. Weighed until a constant Wt. is obtained. Ext. dried

This method is restricted to the following:

A) The alks. must be present in high amounts.

B) When the alks. Are so weakly basic they can not be determined volumetrically. e.g: caffeine, theobromine, theophylline, colchicine.

3) Chromatographic methods:

A) PC, TLC, CC.

B) Advanced GLC (for thermostable volatile alk. or volatile derivative of non-volatile alks.)

C) HPLC ( for non volatile or thermolabile alks.

Extraction and isolation of Alks. From their natural sources:

1) The plant material should be reduced to coarse powder (this will permit efficient contact of the solvent e tissues containing the alks.

2) Plants e high % of fats (Should be defatted before extraction).

3) The extraction procedures are depend on:

A) The ability of the alks. (Sol. In organic solvent), to from salts e acids (of higher solubility in H2O).

B) The ability of alkaloidal salts to free bases in alkaline medium.

4) Volatile liquid alks. e.g: nicotine or coniine isolated steam distillation.

(Plant material + KOH or Ca(OH)2 then steam distilled.

4) Colorimetric and spectrophotometric methods:

Alk + specific reagent

Color produced is measured by colorimeter or spectrophotometer at a definite wave length.

Examples of the coloring reagent:

Nitrous acid for determination of morphine.

P. Dimethyl amino benzaldehde for Ergoto alk.

Vitali morin reaction for Solanaceous alks.

5) Flourimetric methods:

For fluorescent alks. or alks that forms fluorescent derivative e certain reagents.

Quinine and quinine dissolved in oxygenated acid.

Reserpine in hydrogen peroxide.

Other methods for extraction:(Alkaloid adducts)

Use alkaloidal precipitating reagents

Alk. + precipitating R crystalline insol. complexesPurified by

Alkaloid free Repeated crystallization

Mager’s R (Hgcl2) complex Alk.e alk. H2s

Dragendorff’s complex free Alk.Baco3e alk.

Ammonium reineckate used for the isolation of quaternary alks.

Separation of the individual alks.:

A) Different chromatographic methods.

B) Gradient PH technique (Separation the alkaloids on basis of difference in their basic strength.

Proto alkaloids or amino alkaloids:

From amino acids but they lack a heterocyclic ring. e.g:ephedrine.

Pseudo alkaloids:

Unrelated to amino acids. They are considered as alkaloids because of their pharmacological importance and they contain nitrogen. E.g: purine alk. And colchicuie .

Most of these alk. Derived from sterols, nicotinic or purines.

False alkaloids:

W false + ve test e alkaloidal reagents but they are not alk. e.g: proteins, some amino a, conjugated = bonds.

Classification of Alkaloids:1) The botanical origin of alk.:

e.g: Solanaceous alk., Cinchona alks.,Ergot alks.

2) The pharmacological action of alks:

CNS stimutant alk, narcotic alk.

3) The amino acids from w alks. Are biosynthesized in the plants:

Ornithine – derived alk., tryptophane – derived alks., alanine derived alks.

4) The chemical structure of the alks.:

Non heterocyctic alk. heterocyctic alks.

a typical alks or proto alk. e.g: phyrrole

piperine

pyridinee.g: ephedrine

colchicine

Nomenclature of alks.:

1) Name of the plant yielding them.

e.g:atropine (Atropa belladonna), cocaine (coca), ergotamine (Ergot)

2) The name of scientist who discovered the alk. Pelletierine (after pelletier).

Non Heterocyclic Alokaloids:

A) Tropolone Alkaloids.

(Colchicum alkaloids)

Seed, corn of colchicum autumnale (liliaceae).

Main alk. Colchicum (0.6 %– 1.2%).

Smaller amount of demecolcine.

O

OMe

A

B

C

O CH3H

N

Meo

OMeMeo

Tropolone st.

Non basic alk. (very weak base alk.).

Aromaic ring A e 3 methoxyl gp.

7-membered ring B e acetylated amino gp.

Tropolone ring C hose hydroxyl gp. Methylated.is

Neutrat e litmus puper.

Pale yellow crystals.(laevo) asymmetry of C7.

Ab uvat 350 nm.

Colchicine MeOH from methoxy of ring C. Mild hydr.

HCL or dil alk.

Isolation of Colchicine:

Powdered seeds oor cotms alc. Ext. Filter (fat, resin) 90% alc. Conc.

Alk. ex. e CHCl3

Evap. To syrup. while

Small amount of alc.

While ppt. is formed

Cooled at 0C

Colchicine – CHCL3

A 60-70 C for long time

Yellowish amorphous mass of colchicine

CHCL3, hot benzene

Insol in ether

Sol. In H2O, aq. Alc.

Tests for identity:

A) Colchicine +mineral a yellow

B) e conc.HNO3 dirty violet brown yellow

Uses: Poisonous (7 mg may be fatal).

1) Prevention and cure of acute attacks of gout

W is

Deposition of uric a in the tissues of joints

Resulting in

Serve inflammatory pain

Error in the metabolism of uric acid

Dehydration of tissues (a rhiazide diuretice)

Colchicine relieving the pain of inflammation.

Not preventing ppt. of uric a cryslals.

Not help uric a not uricosuric agent as probencid.excrete

But colchicine often combined e them.

2) In plant genetics polyploidy or multiplication of chromosomes.

Demecolcine wide safety chronic myelogenic leukemia, malignant lymphomata.