Medicinal Chemistry

Step 1: Understanding the structure.
Salvarsan is an antibiotic that contains an As=As linkage, which distinguishes it from other antibiotics. This unique structure contributed to its effectiveness against syphilis.
Step 2: Analyzing the options.
(A) Sulphapyridine: Incorrect. Sulphapyridine is an antibiotic, but it does not contain an As=As linkage.
(B) Prontosil: Incorrect. Prontosil is another early antibiotic but does not have an As=As linkage.
(C) Salvarsan: Correct — Salvarsan contains an As=As linkage, which is important for its biological activity.
(D) Sulphanilamide: Incorrect. Sulphanilamide does not contain an As=As linkage.
Step 3: Conclusion.
The correct answer is (C) Salvarsan, as it contains the As=As linkage.