Aspartame has this structure below

Aspartame structure

Shouldn't the peptide group be oxidised along with the ester group?

Then why is the answer to the question below B?

EDIT : I'm sorry I misunderstood a friend's marking, the answer is A. I deeply apologise for my stupid mistake.


Thank you very much!

  • $\begingroup$ Hi I've put in a new image $\endgroup$
    – user114526
    May 20, 2016 at 16:37
  • $\begingroup$ No oxidation is taking place. It is just a hydrolysis reaction. I do agree with you though that both groups should be hydrolysed. $\endgroup$
    – bon
    May 20, 2016 at 17:47
  • 1
    $\begingroup$ Amides are much slower to hydrolyze than esters, so you could obtain the bond 2 product under mild conditions or if you limited the reaction time. However, unless the specific conditions and hydrolysis rates for this reaction were covered in the readings or lecture notes, you should get credit for answer A. $\endgroup$
    – iad22agp
    May 20, 2016 at 18:07
  • $\begingroup$ But why would the answer be B? $\endgroup$
    – user114526
    May 21, 2016 at 1:43

1 Answer 1


This looks like it's from an exam so there's a very high possibility that the person setting the question and answer intended the ester group on the right to be something else. I am largely of the opinion that the answer should be A.

However, there is one way I can imagine that you can try justify "B" being the answer (although it is a long shot):

Under alkali conditions, we can expect the acid group from aspartic acid to be deprotonated to carboxylate which can act as an intramolecular nucleophile.

We take note that intramolecular reactions are generally faster than intermolecular reactions. The carboxylate can attack either the ester group or the amide group. An attack on the amide results in a 5-membered ring transition state, and an attack on the ester results in a 9-membered ring transition state. Since 5-member rings are more stable, the carboxylate attacks and breaks bond 1, leaving bond 2 alone. Aqueous alkali then destroys the acid anhydride that is formed.

That said, this is highly unlikely given that esters are less stable to base-catalyzed hydrolysis than amides. So if Bond 1 Breaks, Bond 2 must have also broken.


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