Alkaloids

Question 1

What are alkaloids?

Answer 1

Products from secondary metabolism in plants

Question 2

What are alkaloids used for in plants?

Answer 2

Bitter taste to defend against herbivores
A way to store N

Question 3

Modern uses of alkaloids

Answer 3

Caffiene
Nicotine
Cocaine

Question 4

Basic amine + acid ——> ?

Answer 4

Salt of weak base

Question 5

What are most alkaloids soluble in?

Answer 5

organic solvents

Question 6

What is the isolation and extraction process of alkaloids?

Answer 6

Power plant material
Extract with dilute acid
Wash with organic solvent
Neutralise with a base
Free base may need extracted with organic solvent

Question 7

Ways to purify alkaloids?

Answer 7

Fractional Precipitation
Fractional Crystallisation
Steam Distillation
Sublimation
Column Chromatography

Question 8

How does steam distillation purify alkaloids?

Answer 8

Volatile or low BP alkaloids are carried in steam
Alkaloids will separate from water as they are immiscible

Question 9

How does sublimation purify alkaloids?

Answer 9

Solid phase to vapour phase
Cooling quickly to return to solid phase
Use cold-finger apparatus with vacuum
Material with does not sublime stay in test tube

Question 10

How does chromatography purify alkaloids?

Answer 10

Separates alkaloids based according to polarity

Question 11

Hager’s Reagent

Answer 11

Piric acid
Piccrates form
Yellow/orange colour

Question 12

Mayer’s Reagent

Answer 12

Mercuric potassium iodide solution
White/yellow

Question 13

Wagner’s Reagent

Answer 13

Potassium Iodide
Red/Brown precipitate

Question 14

Dragendorff’s reagent

Answer 14

Potassium bismuth iodide spolution
Orange precipitate

Question 15

What is transamination?

Answer 15

Substitution between amino group and ketone of neighbouring keto acid

Question 16

What is decarboxylation?

Answer 16

Carboxylic acid on the amino acid is removed in the form of CO2

Question 17

How are amino alkaloids different?

Answer 17

N is in amino group and not a member of a heterocyclic ring

Question 18

How do ephedrine and pseudoephedrine differ?

Answer 18

Pseudoephedrine has different stereochemistry

Question 19

What are the effects of ephedrine?

Answer 19

Increased BP
Vasoconstrictor
Appetite suppression

Question 20

How many enantiomers are there for 2 chiral centres?

Answer 20

4

Question 21

What type of alkaloid is methamphetamine?

Answer 21

Amino

Question 22

How do beta blockers work?

Answer 22

cardioactive b-adrenoceptor blocking agents, control the rate and force of cardiac contractions in the management of hypertension

Question 23

What are pyridine alkaloids derived from?

Answer 23

Nicotinic acid

Question 24

What are piperidine alkaloids derived from?

Answer 24

Lysine

Question 25

What are the effects of nicotine?

Answer 25

Hypertension in low doses Toxic doses can cause respiratory depression

Question 26

What is the structure of tropane alkaloids?

Answer 26

Pyrrolidine and Piperidine rings that share N and 2C atoms

Question 27

How is cocaine synthesised?

Answer 27

Mixed ester extract from plants is hydrolysied to Ecogonine Ecogonine is esterified, methylated and benzolyated to cocaine

Question 28

What is essential for anesthetic behaviour?

Answer 28

Aromatic carboxylic acid and basic amine group Must be separated by a form of chain

Question 29

What is cocaine used in now?

Answer 29

Brompton's cocktail with morphine

Question 30

Where is epibatidine found?

Answer 30

In poisonous frogs - 200-500x more potent than morphine

Question 31

What are quinoline alkaloids derived from?

Answer 31

Tryptophan

Question 32

What is the difference between quinoline and isoquinoline?

Answer 32

In isoquinoline, N is one position away from position in quinoline

Question 33

What form is the N usually in on isoquinoline alkaloids?

Answer 33

Quaternary salt form - influences solubility properties

Question 34

How is morphine biosynthesised?

Answer 34

From reticuline - single bonds rotate Transition phase has 2 radicals

Question 35

Solubility of morphine

Answer 35

Morphine is organic compound and semi polar so does not dissolve well in water Basic N will protonate in HCl to form quaternary salt - very soluble in aqueous acid

Question 36

Why is morphine soluble in aqueous base and acid but codeine only in aqueous acid?

Answer 36

Codeine has a MeO group masking OH group from morphine so will not react in aqueous base

Question 37

How is heroin synthesised?

Answer 37

Morphine + acetic anhydride ---> diacetylmorphine Esterification reaction

Question 38

How is heroin metabolised?

Answer 38

Heroin undergoes deacetylation in first pass metabolism so is a prodrug

Question 39

How does the ester group affect heroin?

Answer 39

Makes heroin more lipophilic so crosses the BBB when injected

Question 40

Why is codeine used instead of morphine?

Answer 40

Demethylated in the liver so has the same pain killing effect but with less euphoria

Question 41

What are the binding interactions with an opioid receptor?

Answer 41

Ionic bonding, Van der Walls (aromatic ring) and H-Bonding

Question 42

What are imidazole alkaloids synthesised from?

Answer 42

Histidine by decarboxylation

Question 43

What are the main actions of imidazole alkaloids?

Answer 43

Increases saliva Decreases heart rate Increases urination

Question 44

What is the structure of purine alkaloids?

Answer 44

Pyrimidine ring fused to an imidazole ring - lots of Ns

Question 45

What are common purine alkaloids derived from?

Answer 45

Xanthine structure

Question 46

What are common purine alkaloids?

Answer 46

Caffeine and theobromine

Question 47

What is the structure of indole alkaloids?

Answer 47

Benzene ring fused to a pyrolle ring

Question 48

Are indole alkaloids bases?

Answer 48

No because the N lone pair is in the π cloud of electrons

Question 49

What are indole alkaloids formed from?

Answer 49

Tryptophan amino acid

Question 50

What type of alkaloid is serotonin?

Answer 50

Indole

Question 51

What are ergot alkaloids based on?

Answer 51

Indole alkaloids with an extra chain than contains N

Question 52

What are medicinally useful ergot alkaloids?

Answer 52

LSD

Question 53

What does LSD do?

Answer 53

Mimics action of serotonin Time distortion Crawling geometric patterns

Question 54

What type of alkaloid is strychnine?

Answer 54

Indole/Ergot