Question

Biological activity of synthetic adrenaline is almost:

• A. 25% of S-adrenaline
• B. 25% of R-adrenaline
• C. 50% of S-adrenaline
• D. 50% of Natural R-adrenaline

Hint:

Biological activity is highly dependent on stereochemistry, as only specific enantiomers interact effectively with biological receptors.

Answer 1

The Correct Option is D

Step 1: Understanding adrenaline's stereoisomers and activity. Adrenaline exists as stereoisomers, and its biological activity is dependent on the stereochemistry. The natural adrenaline (R-enantiomer) is more biologically active compared to the synthetic mixture, which usually contains both R and S enantiomers. 

Step 2: Synthetic adrenaline's biological activity. Synthetic adrenaline is typically a racemic mixture (50% R and 50% S). Since only the R-enantiomer is biologically active, the biological activity of synthetic adrenaline is approximately 50% of the natural R-adrenaline.

Answer 2

The question is about how the biological activity of synthetic adrenaline compares with the naturally occurring hormone. This comes down to stereochemistry, since adrenaline has one chiral carbon and exists as R and S forms.

1. 25% of S-adrenaline: The S-form is the weaker enantiomer, so measuring synthetic activity against it does not reflect how this comparison is actually made, and 25% is not the figure associated with it.
2. 25% of R-adrenaline: This understates the potency. Since half of synthetic adrenaline is the fully active R-form, its overall activity is higher than a quarter of the natural hormone's strength.
3. 50% of S-adrenaline: The S-enantiomer is the biologically weaker one, so comparing synthetic adrenaline's strength to a percentage of the weak form is not how this potency ratio is defined.
4. 50% of Natural R-adrenaline: The adrenaline made in the body is almost entirely the R-enantiomer, which binds adrenergic receptors strongly. Synthetic adrenaline is manufactured as a racemic mixture, meaning it contains equal parts R and S forms. Since the S form is far weaker at the receptor and contributes very little activity, the overall potency of the racemic mixture works out to be close to half that of pure natural R-adrenaline.

Because synthetic adrenaline is a 50:50 mix of a fully active and a nearly inactive enantiomer, its overall strength lands at about half of what pure natural adrenaline produces.

So the correct answer is 50% of Natural R-adrenaline.