Third year lecture 8
Transcript of Third year lecture 8
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Medicinal ChemistryLecture 8
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Exam Revision
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Receptors and Receptor Site
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Continue…• Receptor down-regulation:A phenomenon whereby an agonist, after binding
to a receptor, actually induce a decrease in the number of these receptors available for binding
• Receptor Up-regulation:The opposite of the above, involves an agonist-
induced increase in the number of receptors.
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Continue…• Affinity:The ability of the drug to combine with a receptor.
A ligand of low affinity requires a higher concentration to produce the same effect as a ligand of high affinity. Both agonists and antagonists have affinity for the receptor.
Efficacy:Describe the relative intensity with which agonist
vary in the response they produce when occupying the same number of receptors and with the same affinity
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Continue…• Potency:Refers to the dose of a drug required to produce
effect of given magnitude as compared to a standard reference. Potency is dependent on both affinity and efficacy.
• Tolerance: Decrease of the intensity of the response to a
given dose over time
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Stereochemistry of Drug Action
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Structurally Rigid Groups
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The influence of configuration on ADME•Absorption:
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Active Transport:• (-)Norgestrel is absorbed at twice the rate of
(+)Norgestrel• L-Dopa is more rapidly absorbed in comparison
to D-Dopa
• Passive diffusion:• No difference in absorption between
enantiomers
• Racemates may be absorbed at a rate that is different to their pure individual enantiomers
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Distribution• Stereoselectivity appears to have little influence
on the transport of stereoisomers through the circulatory system.
• Some enantiomers prefer to bind to a specific plasma protein (R-Propanalol prefers to bind to human albumin while S-Propanalol prefers alpha-acid glycoproteins)
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Metabolism
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• S-Indacrinone plasma half-life is 2-5 hours• R-Indacrinone plasma half-life is 10-12 hours
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Extraction• Modest stereoselectivity has been reported in
the renal excretion of these drugs
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Next Lecture
•Drug Metabolism
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THE END