**Core Concept**
Enalapril, a prodrug of enalaprilat, is metabolized to its active form in the liver. Sulphasalazine is a prodrug that is cleaved to release sulfapyridine and 5-aminosalicylic acid (5-ASA) in the colon. Cyclophosphamide is a prodrug that undergoes hepatic metabolism to form its active metabolites. These prodrugs rely on metabolic conversion to exert their therapeutic effects.

**Why the Correct Answer is Right**
Imipramine is a tricyclic antidepressant that is metabolized to its active form but is not considered a prodrug in the classical sense. It directly exerts its therapeutic effects without undergoing significant metabolic conversion to an active form. Unlike the other options, imipramine does not require metabolic activation to produce its therapeutic effects.

**Why Each Wrong Option is Incorrect**
**Option A:** Enalapril is indeed a prodrug that is metabolized to enalaprilat, which is the active form that inhibits angiotensin-converting enzyme (ACE).
**Option C:** Sulphasalazine is a prodrug that is cleaved to release sulfapyridine and 5-aminosalicylic acid (5-ASA) in the colon, which are responsible for its therapeutic effects.
**Option D:** Cyclophosphamide is a prodrug that undergoes hepatic metabolism to form its active metabolites, which are responsible for its therapeutic effects.

**Clinical Pearl / High-Yield Fact**
When evaluating a medication, it is essential to consider its pharmacological properties, including whether it is a prodrug or exerts its effects directly. This knowledge can inform dosing regimens, potential interactions, and the development of resistance or tolerance.

**✓ Correct Answer: B. Imipramine**