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

Answer 1

The Correct Option is D

The correct option is (D): 50% of Natural R-adrenaline.

Answer 2

Natural adrenaline made by the body exists as a single, specific spatial arrangement, the R-form, while synthetic adrenaline made in the laboratory without a chiral-selective process comes out as a 50:50 mixture of the R- and S-forms, called a racemate. The question asks how the biological activity of this synthetic mixture compares with the natural hormone. Let's check each option.

1. 25% of S-adrenaline: This choice frames the comparison against the wrong enantiomer, the S-form, which is actually the much weaker of the two, and 25% does not reflect the real ratio either.
2. 25% of R-adrenaline: This understates the activity. Since half of the racemic mixture is still the fully active R-form, the overall activity should land closer to half, not a quarter, of the natural hormone's effect.
3. 50% of S-adrenaline: Comparing against S-adrenaline is the wrong reference point, since S-adrenaline is the much less active enantiomer and is not what the body itself produces or what activity is normally measured against.
4. 50% of Natural R-adrenaline: The R-enantiomer is far more potent at adrenergic receptors than the S-enantiomer, which contributes very little activity. In a racemic (50:50) mixture, only the R-half does most of the work, so the overall biological effect of synthetic adrenaline works out to about half that of pure natural R-adrenaline.

Because only the R-form of the racemic mixture carries strong activity and it makes up half of the synthetic product, the overall potency comes out to roughly 50% that of the natural hormone.

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