Question

Naturally occurring pilocarpine is:

• A. 2R,4R (+) Pilocarpine
• B. 3S,5R (−) Pilocarpine
• C. 2S,4R (−) Pilocarpine
• D. 3R,4S (+) Pilocarpine

Hint:

Remember: Natural pilocarpine is the 3R,4S (+) enantiomer, derived from \textit{Pilocarpus} species and used for glaucoma management.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
We are asked to name the exact stereoisomer of pilocarpine that occurs naturally in the Pilocarpus jaborandi plant and is used medicinally.

Step 2: Key Formula or Approach:
Pilocarpine's gamma butyrolactone ring carries two stereocenters, numbered 3 and 4 in the standard structure, and the compound rotates plane polarized light. We need the option whose ring position numbers and rotation sign both match the real molecule.

Step 3: Detailed Explanation:
The imidazole-bearing side chain sits on carbon 3 and the ethyl group sits on carbon 4 of the lactone ring, so any option numbering the centers as 2 and 4, or as 3 and 5, is describing the wrong skeleton and can be set aside.
That leaves the two remaining options that correctly use positions 3 and 4.
Of these, the naturally occurring, pharmacologically active isomer rotates light in the positive direction, matching the (+) sign.
Combining the correct ring positions with the correct rotation sign points to the 3R,4S configuration.

Step 4: Final Answer:
The naturally occurring form is 3R,4S (+) pilocarpine.