(2) The activity of Procaine, a local anaesthetic, can be related to its carbony
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Question
(2) The activity of Procaine, a local anaesthetic, can be related to its carbonyl group. The more double bond character the drug has, the less active the drug is. CH2CH3 H2N -c-0-CH2CH2 CH2CH3 Procaine (a) Explain (with structures if appropriate) whether each of the following ring substituents (in place of the NH2 or a hydrogen as the case may be) will likely enhance or reduce the intrinsic activity of the corresponding analog to Procaine: (i) 4-chloro; (ii) 4-fluoro; (ii) 3,4-dichloro, (iv) 4-methyl; (v) 4-methoxy and (vi) 2,4-dimethoxy.Explanation / Answer
2a) i. In 4-chloro subsituent, Cl has more electron-withdrawing inductive effect than electron-donating resonance effect. So the electron density of benzene nucleus will be less available for conjugation with C=O. So it will have more double character and drug activity will decrease.
ii. In case of 4-fluoro, F has better +R effect due to its proper orbital matching with C. So Resonance will be more and drug activity will be enganced.
iii. The case of 3,4-dicloro will only be a more prominant effect of case i. Drug activity will further decrese.
iv. 4-methyl has electron donating inductive effect, but it does not work through so many bonds. So drug activity will decrease slightly.
v. 4-methoxy has strong +R effect, so more single bond character of C-O bond and increased activity.
vi. Two methoxy groups at ortho and para positions will further enhance drug activity.
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