5. Biological action of opiods
• depends on
1. Phenolic hydroxyl group
2. 6 hydroxyl
3. Double bond between 7 & 8 c
4. N-methyl group
5. Ether (E) bridge
6. Aromatic ring
6. Phenolic hydroxyl group
• is needed for binding of μ & κ receptors;
• seen in all potent µ agonist.
• Changing -OH to just –H or -OCH3 lowers activity.
R= C3 substituent Activity effect
-H Decrease
-OH Morphine
-OCH3 (codeine) Decrease (1/3)
7. R= Nitrogen substituent Effect
3-5 Carbons
(with double bond/ small cyclic or
aromatic rings) eg. CH2CH=CH2
µ antagonist
>5c (in chain or ring ) µ agonist
Aralkyl
CH2CH2Ph
(Total 8 C)
µ agonist (10X
morphine)
N-methyl group
• Interacts hydrophobically with μ receptor.
• Size of substituent on Nitrogen dictates
potency and agonist/antagonist activity.
9. 14 β H/OH moiety
• Addition of OH at 14 β position
1. Increases activity (2-3X)
2. Increases penetration of BBB
3. Decrease in antitussive action
10. 7,8 double bond
Reduction of 7,8 double bond increases activity
Activity
increases
Activity
increases
OH at C14
7,8 Reduction of double bond
to single bond
11. Hydroxyl at 6
• Modifications at 6 OH which increases activity
1. Removal of Hydroxyl at 6 increases lipophylicity
2. Oxidation of Hydroxyl to keto group at 6 + reduction of 7,8
double bond eg Hydrocodone
3. Acetylation of Hydroxyl at 6 (eg. Heroin)
R= C6 substituent Effect in activity
H Increase 10X
=O (keto)
=O (keto) with 7,8 reduction
decrease (1/3)
Increases (6X )
H3CC=O (acetyl) Increase
13. Hydroxyl at 6
• Associated with mast cell degranulation
Histamine release allergic response
(eg . Codeine – so not given parentrally)
14. Ether linkage
• Removal of Ether linkage produces
compounds called Morphinans that has
increased activity
Activity increases
No ether linkage
Levorphanol
(10X )
18. Codeine
• Methyl morphine (Weak µ agonist )
• OCH3 loss of activity less potent (1/3) .
Thus, used in mild to moderate pain only.
• 6OH- release of Histamine allergic responses.
Thus not used parenterally.
• Lack of 14 β OH- Used as antitussive drug
• Metabolite is Morphine abused by addicts
19. Heroin
• Weak μ agonist
• 3,6-diacetyl derivative of morphine
• Two factors make it more potent than morphine
a. Diacetyl form - increases its lipophilicity
enhances its penetration into brain
b. Metabolite, 6 acetyl morphine, is more active than
morphine
These two factors work together to provide a intense
and quick occuring ‘euphoric rush’ that addicts seek
20. Buprenorphine
• Mixed Agonist/antagonist effect
• N- cyclopropyl methyl group μ antagonist
overcome by
• Additional hydrophobic & H bonding at C7
– High μ affinity highly Potency (25X)
– Highly lipid soluble cross BBB
21. Pentazocine
• Benzomorphine (tricyclic)
• 1st agonist-antagonist to be used as analgesic
(κ agonist & µ antagonist)
• 5C N substitution μ antagonist
• Missing 6 &7 carbons compromises its
ability to interact with Receptors weak
analgesic effect (1/5X)
22. Tramadol
• Atypical opiod analgesic
•
• Dual action opiods
(-) isomer blocks norepinephrine reuptake
(+) isomer blocks serotonin reuptake
analgesic activity. But effect is weak
• Metabolite is active - 1/35X
23. Naloxone
• N-allyl nor oxy morphone
• N –substituent CH2CH=CH2 Strong opiod
antagonist
Tetrazoline polar group ( strong electron withdrawing ring system)
↓pKa ↓ratio of ionised- unionised form better BBB penetration
↓ratio of ionised- unionised form maintained at receptor surface ↓ cation available for ion- ion anchoring with recptor ↓μ Receptor affinity