Which of the following statement(s) is correct?

Question

BlackTom AI · Accepted Answer

Esters are rapidly hydrolysed by esterases, so they are common liabilities in drug leads, and CYP‑450 enzymes typically perform oxidative Phase I reactions (often adding an OH) that can be followed by Phase II conjugation — this is the core correct idea.

1) Relevant knowledge points and concepts
- Metabolic phases: Phase I (functionalisation) commonly involves cytochrome P450 (CYP‑450) enzymes introducing polar groups (e.g., hydroxylation). Phase II (conjugation) attaches polar moieties (e.g., glucuronic acid via UDP‑glucuronosyltransferases, sulfation) to those functional groups to increase water solubility and elimination.
- Ester chemistry in biology: Esters are cleaved rapidly by ubiquitous esterases (e.g., carboxylesterases), producing acids and alcohols; this instability makes esters frequent targets for replacement during lead optimisation (bioisosteres, amides, or steric blocking).
- Amines and metabolism: Amines are often metabolised (N‑dealkylation, N‑oxidation, conjugation), so they are not impervious to metabolic enzymes.

2) Step‑by‑step reasoning
- Statement about esters: True — hydrolysis by esterases is rapid in vivo, hence medicinal chemists often replace ester moieties to improve stability and half‑life.
- Statement about CYP‑450 adding OH: True — CYPs perform hydroxylation (add OH) as a common Phase I transformation.
- Fate of that OH: True — the added hydroxyl can be a site for Phase II reactions such as glucuronidation or sulfation, facilitating elimination.
- Statement that CYP‑450 directly adds glucuronide: False — glucuronidation is a Phase II reaction catalysed by UGT enzymes, not CYP‑450.
- Statement that amines are impervious: False — amines undergo many metabolic changes.

3) Calculations
- None required.

4) Why the correct answer is correct
- Option d combines two accurate, linked statements: esters are rapidly hydrolysed and CYP‑450 often hydroxylates drugs, with those hydroxyls frequently entering Phase II metabolism. Both parts are factually correct and complementary.

5) Why other options are incorrect (brief)
- a: True but incomplete (only the ester part). d is the best combined correct choice.
- b and e: Incorrect because they state CYP‑450 directly adds glucuronide (false; glucuronidation is Phase II by UGTs).
- c: False; amines are metabolised.
- f: True as a standalone, but d includes f plus the ester statement, so d is the most complete correct choice.

Conclusion: The combined, accurate choice is d. This matches the provided answer.

Which of the following statement(s) is correct?单项选择题

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