Course description:

The aim of the course is to complete the study of thechemical constituents of drugs containing: Glycosides andAlkaloids. The course will study some narcotic plants andtoxic plants, especially those present in the Kingdom,aiming to provide students with information about theiridentification and treatment of their poisoning. Examplesfrom marine natural products derived drugs will bediscussed. The course will also cover the herb-druginteractions.

Alkaloids1 1Ramzi Moth

Alkaloids

They are nitrogenous heterocyclic compounds occurring in

Plants, formed biosynthetically from amino acids

1- True Alkaloids

are basic compound nitrogen atom is a part of

heterocyclic system derived from amino acids

3- Protoalkaloids

nitrogen atom is not a2- Pseudoalkaloids

are not derived from

amino acids, such as

terpenoid alkaloids

partof a heterocyclic ring, e.g.colchicine, ephedrine and

cathinone

Ramzi Mothana Alkaloids1 2

Distributionrarely in bacteria, fungi and pteridophytes,

essentially found in Angiosperms e.g. Liliaceae,

Amaryllidaceae, Ranuncolaceae, Papaveraceae,

Solanaceae, Berberidaceae, Rubiaceae,

Apocynaceae and Buxaceae

LocalizationAs soluble salts (citrates, malates, tartrates,

benzoate, meconates) or in combination with

tannins, and localized in peripheral tissues e.g.

external layers of the bark of the stems and roots

Function in PlantsPoisonous agent for protecting the plants

against insects and predator.

Detoxification products.

Reserve materials capable of supplying nitrogen

especially for protein synthesis.

Regulatory growth factors

1-

2-

3-

4-

Detection and Characterization

• A detection technique ought to be, to the extent possible, rapid, simple, reproducible, and sensitive; it must be applicable to small sample.

• The detection methods currently in use are preceded by an extraction and consist, most generally, in precipitating the alkaloids by using fairly specific reagents: the " general reagents of alkaloids".

• The preliminary extraction can be a "classic" alkaloid extraction or an alcoholic maceration, which takes less time: the alcoholic solution is evaporated and the residue redissolved in acidic water; after filtering, the alkaloids are characterized in the filtrate.

• The general reactions of precipitation are based on the fact that alkaloids form combination with metals and metalloids: bismuth, mercury, tungsten, and iodine.

• In practice, what is used is a solution containing iodine and iodide, or a solution containing potassium iodide and mercuric chloride- known as Mayer's reagent-

• or a reagent containing bismuth nitrate and potassium iodide, better known as Dragendorff's reagent. I

• t is also possible to use silicotugestic acid (a mixture of tungsten and silicon oxide), or alkaline solution of iodoplatinates.

• The specificity of these reagents is not absolute: proteins, α-pyrones, some coumarins, hydroxyflavones, lignans, and other compounds can give false positive reactions with Dragendorff's reagent.

Ramzi Mothana Alkaloids1 4

Detection and characterization:

A- Precipitation by certain reagents

Mayer’s reagent (potassium-mercuric iodide)

Yellowish-white precipitate

Dragendorff’s reagent(potassium-bismuth

iodide) give orange color

Wagner’s reagent (potassium triiodide)

red color

1-

2-

3-

B- Color reactions with certain reagents

1- Froehd’s reagent (sulphomolybdic acid)

2- Marqui’s reagent (formaldehyde + H2SO4)

3- Mandalin’s reagent (sulphovanadic acid)

4- Mecke’s reagent (selenic acid + H2SO4)

5- Erdmann’s reagent (HNO3 + H2SO4)

Extraction of Alkaloids

• The extraction of alkaloids is based, as a

general rule, on the fact they normally

occur in the plant as salts and on their

basicity, in other words on the differential

solubility of the bases and salts in water

and organic solvents.

A. Extraction per se

• Solvents Extraction in Alkaline Medium

* First step. The powdered defatted drug is

mixed with an alkaline aqueous solution

which displaces the alkaloids from their

combinations as salts; the free bases are

then extracted with an organic solvent.

• Second step.

• The organic solvent containing alkaloids as bases is separated from the residue and if necessary, partially concentrated by distillation under reduced pressure.

• The solvent is then stirred with an acidic aqueous solution: the alkaloids go into solution in the aqueous phase as salts, whereas the neutral impurities remain in the organic phase.

• The operation is repeated as many times as necessary until the organic phase no longer contains any alkaloids.

* Third step.

• The aqueous solution of the alkaloid salts, combined, and if necessary, "washed" with an apolar solvent (hexane, diethyl ether) are alkalinized with a base in the presence of an organic solvent not miscible with water.

• The alkaloids as bases precipitate and dissolve in the organic phase.

• The extraction of the aqueous phase continues until the totality of the alkaloids has gone into the organic phase (which is easy verified as Mayer's reaction on the aqueous phase becomes negative).

• The purification step may be carried out, like the previous one and depending on the quantity, in an separation funnel, or in more or less complex apparatuses: centrifugal extractors and other types of on-line set ups.

* Finally,

• the organic solvent containing the alkaloid

as bases is decanted, freed from possible

traces of water by drying over an

anhydrous salt (for example, sodium

sulfate),

• and evaporated under reduced pressure.

• A dry residue is left: the total basic

alkaloids.

Extraction of alkaloids

A- Solvent extraction on alkaline medium

Powdered defatted drug

+ NH3 or Na2CO3

+ organic solvent (CHCl3)

Residue CHCl3-Phase

(Alkaloid-Bases)evaporation

d (HCl)

Organic phase

(CHCl3-Phase containing

impurities)

Aqueous phase

(Alkaloid- salts)

+ NH3 or Na2CO3

+ organic solvent

Organic phase

(Purified alkaloid-bases)Aqueous phase

B- Solvent extraction on acidic medium

+ dilt. Aci

+ NH3 or

+ organic

Extraction in Acid Medium

• Two approaches are possible: in the first one, the pulverized drug is extracted directly with acidified water; in the second case, it is extracted with an acidified alcoholic or hydroalcoholic solution.

• In the latter case, the extraction is followed by a distillation under vacuum which eliminates the alcohol and leaves behind an acidic aqueous solution of the alkaloid salts.

• In both cases, the result is an aqueous solution of alkaloid salts requiring purification. This can be accomplished by:

1. Alkalinizing the solution and extracting the bases

with an immiscible organic solvent, this leads

back to the above step;

2. Selectively adsorbing the alkaloids contained in

the solution on an ion-exchange resin, then

eluting them with a strong acid;

3. Precipitating the alkaloids as iodomercurates.

The resulting complex is recovered by filtration,

dissolved in a mixture of water, alcohol, and

acetone, and decomposed by passing it through

an ion-exchange resin. This technique can be

used to extract quaternary ammonium salts.

Powdered Drug

Extracted marcorganic extract

(alkaloids, lipids, pigments)

base(NH4OH, Na2CO3, etc.)

organic solvent

not miscible with water

(CHCl3, CH2Cl2, Et2O, etc.)

extracted solvent(neutral alkaloids)

concentrationextraction by

a dilute acid

(HCl, H2SO4, etc)

acidic aqueous solution(alkaloid salts)

Priciples of alkaloid

extraction in

alkaline medium

extraction by an organic solvent

not miscible with water

(CHCl3, CH2Cl2, Et2O, etc.)

extractedaqueous solution

(quaternary alkaloids)

organic alkaloidsolution

TOTAL (basic)ALKALOIDS

Ramzi Mothana Alkaloids1

Alkaloids Derived from Phenylalanine and Tyrosine

The following groups of alkaloids belong to this class:

1- Phenylalkylamine group

2- Isoquinoline group

3- Tropolon group

4- Amarylidaceae group

7

1- Phenylalkylamine group

1.1. Benzylamine type 1.2. Phenylethylamine type

1.3. 2-Aminophenylpropan type

8

2

N

R R

N

R R

N

R R

Ramzi Motha

Papaver somniferum

Llkalaoitdse1x (Opium) 16

Morphine:

First isolation in 1805 by Surtner

Crystallize from dilute ethanol as colorless prisms, stable in air

Morphine base is springly soluble inCHCl3, insoluble in ehter

It dissolves in caustic alkali

It is a pentacyclic molecule with five asymmetric centers

Methylation of morphine

Acetylation of morphine

Chemical tests:

codeine

heroin

1- Iodic acid test: morphine + H2SO4 + IO3, the color disappears

2- aqueous solution of morphin + K3[Fe(CN)6] + FeCl3

deep blue color

then shake with CHCl3 violet color is produced

3- Morphine solution + conc. HNO3

then yellow color, then destroy after a period.

Pharmacology:

orange red color

1- Morphine exerts a depressant action on the CNS

(hypnotic, narcotic)

2- Morphine depresses the cough center.

3- It causes myosis.

4- It acts on the pituitary to decrease the secretion of FSH, LH

and ACTH.

5- Morphine can be used as starting material for the synthesis of

apomorhine (as emetic drug used),

17

Ramzi Mothana Alkaloids1 18

Codeine

Codeine is methyl morphine

It may be obtained from opium or by methylation of

morphine or from thebaine by reduction and demethylation.

Codeine and its salt occur as fine needles or as white

crystalline powders.

Pharmacology: Codeine has an antitussive activity

Codeine is also a potent analgesic, acting like morphine on

enkephalinergic receptors, but with a much less intense action.

Papaverine:

Insoluble in H2O, soluble in CHCl3, in the form of prisms

It is smooth muscle relaxant (antispasmodic)

its ability to inhibit the phosphodiestrase, which hydrolyzes

cAMP, and to decrease the intracellular Ca-concentration.

Tests:1- in H2SO4, give colorless solution, which becomes red at

2- Warren’s test

with KMnO4 mixed and by adding Marqui’s reagent, green

color appears, which rapidly changes to blue

110 C

Bisbenzyltetrahydroisoquinolines

Curare alkaloidsdried extract from the bark and stems of Strychnos species

e.g. S. castelnaei, S. toxifera, S. crevauxii (Fam. Loganiaceae)

and from Chondodendron species (Fam. Menispermaceae)

used as arrow poison by certain native tribes of the Amazon

regions of South America.

According to the containers in which the drug was packaged

there are 3 preparations:

1- Calabash (gourd) curare

-

-

-

poured into the fruits of various Bignoniaceae

originally from Colombia, Venezuela

from the genus Strychnos (Loganiaceae) including S. toxifera

and S. letails etc.

2- Tube (bamboo) curare

-

-

-

poured into bamboo tubes

from Brazil and Peru, used as arrow poison.

composed chiefly of extracts of stems of Menispermaceae

of the genus C. tomentosum

3- Pot (clay pot) curare

-

-

-

poured into clay pots of various shapes,

specific to the upper Orinoco and upper Amazon basin

contains a mixture of extracts of Menispermaceae and

Loganiaceae.

The active constituent of curares are very different

according to the plant extract used.

1- Menispermaceous curares

- 2 to 10% bisbenzyltetrahydroisoquinoline alkaloids,

(+)-tubocurarine (quaternary ammonium structure

with two ether bridges), the other alkaloids are

tertiary bases : (-) curine, (+) - isochondrodendrine

and (+) chondrocurine.

- (+)-tubocurarine

- a white or yellowish white to grayish white, odorless,

derived from tube curare and isolated in 1898,

soluble in water and in alcohol, insoluble in acetone,

chloroform and ether.,

- it is a non-depolarizing neuromuscularblocking

agent , employed i. m or i. v. as a skeletal muscle

relaxant to secure muscle relaxation in surgical

procedures.

- Its use was discontinued about ten years ago. A

semisynthetic derivative of C-toxiferine is used

N, N-diallylnortoxiferinium dichloride

(=alcuronium), which is used i. v. as adjunct in

anesthesia.

2- Loganiaceous Curares:

- are symmetrical bis quaternary ammonium

alkaloids, C-toxiferine (calabash), C-curarine,

C-alkaloid G and E, C- calebassine and other

(indole alkaloids)

- The crude extract exhibits a paralyzing effect on

voluntary muscle (curari-form effect) by

blocking nerve impulses to skeletal muscles

at the myoneural junction.

- It also produces a toxic action on blood vessels

as well as histamine-like effect.

Identification:

1- Aq. Solution + FeCl3 faint green c.

Yellow-brown ppt2- Aq. Solution + Na2CO3

Ramzi M na Alkaloids1 32

Alkaloids Derived from Tryptophane

This group of alkaloids is classified into two main subclasses:

1- Indol alkaloids 2- Quinoline alkaloids

A- Simple Indol alkaloids B- Monoterpenoid Indol alkaloids

1- Indolalkylamine type

e.g. bufotenine,

psilocybine

2- Physostigmine-type

e.g. physostigmine

N

otha

N

H R R

Indolealkylamine-type

N N

H H

Physostigmine-type

Ramzi Mothana Alkaloids1 33

3- β- Carboline-type 4- Ergoline-type

e.g.e.g. harmaine, harman

and harmaline ergometrine, ergotamine

N

B- Monoterpenoid Indol alkaloids

In Apocynaceae, Rubiaceae and

Loganiaceae

1-

2-

3-

4-

5-

6-

7-

Ajmallicine type (e.g. Raubasine)

Eburnamine type (e.g. vincamine)

Yohimbine type (e.g. yohimbine, reserpine)

Ajmaline-type (e.g. ajmaline)

Aspidsperma type (e.g. vindoline)

Iboga type (seco form as monomer I of vincaleukocristin)

Strychnine type (e.g. strychinin, C-toxiferine)

N

H

Carboline-type

NH

NH

Ergoline-type

Ramzi Mothana Alkaloids1 37

Alkaloids of β-carboline type

The simple β-carboline alkaloids are alkyl derivatives of

pyrido (3,4-b) indols

The most important ones are the 1-methyl- β-carbolin

derivatives harmane, harmine and harmaline.

Passiflora incanata and Peganum harmala

Passiflora incanata (Fam. Passifloraceae)It is a climber plant, found in South USA

It containsabout 0.03 - 0.05% alkaloids in particular,

harmane, besides, harmine, harmol, and harmaline

Harmine (R = OCH3)N

Harmol (R = OH)R N

Pharmacology:

These alkaloids are short acting monoamino-oxydase

inhibitor , replace benzodiazepines from their receptors

High doses are acting psychosmimetic

Leaves are used as sedative

Peganum harmala (Fam. Zygophylaceae)

The seeds contain 3-4% alkaloids, harmine, harmol,

and harmaline

At first CNS-stimulant, after that sedative

Harmane (R = H)

N Harmine (R = OCH3

H

Claviceps purpurea

Ergometrine:

- a potent oxytocic,

- it increases the frequency and strength of uterine

contractions.

- methylergonovine (methylergometrine) is the

preferred medication, this is the amide of lysergic

acid and of 2-aminobutanol, a semisynthetic

derivative that is more active on the uterus and

practically devoid of alpha-adrenergic antagonist

activity;

- It is indicated for treating afterbirth delivery and

post-partum hemorrhages, after cesarean sections.

Ergotamine:

- at low doses potent vasoconstrictor acting by

stimulation of the alpha-adrenergic receptors.

- at higher doses, an adrenergic antagonist activity

appears, which is weak. , in addition ,

- Ergotamine tartrate is used for treating the acute attack

of migraine headache and related vascular headaches.

Isomerisation of ergot alkaloids:

1- Ergot alkaloids (l)-form can be converted to ergot

alkaloids (d)-form under reflux with methanolic alkali.

2- Ergot alkaloids (d)-form can be converted to ergot

alkaloids (l)-form under reflux with alcoholic acetic

acid and phosphoric acid.

3- Ergot alkaloids (l)-form produce in aqueous solution

under the influence of light, especially UV-light

Lumi-alkaloids. N-RN-R

CH3CH3 O = C

HO = C

H

NN UV H

H

HO

Lumi-alkaloid

Identification:1- Van-urk reaction

(with dimethylaminobenzaldehyde in

gives blue color)2- Keller’s reaction

acidic conditions

(with glacial acetic acid, traced of FeCl3 and H2SO4, intense

3- Aqueous solution of the alkaloids gives blue

fluorescence under UV-light (365 nm)

blue color is formed)