[Hand15]

In the last week organic Lab, we did this reaction:



Well... surely the alcalase (a kind of Serine Protease) is responsible for the selectivity of the reaction
But I just don't know what makes it  highly selective and what is the mechanism...

could someone tell me what is the reaction mechanism and the reason for the selectivity?

[agrobert]

The reaction is selective because the Alcalase protein/enzyme has a site specific binding pocket.  So the functionality and steroechemistry of the aromatic and amide groups direct the etser hydrolysis.  Only one of the racemic enantiomers is hydrolyzed.

[Hand15]

The reaction is selective because the Alcalase protein/enzyme has a site specific binding pocket.  So the functionality and steroechemistry of the aromatic and amide groups direct the etser hydrolysis.  Only one of the racemic enantiomers is hydrolyzed.

Yes... i already know that... but could it be more specific such as the mechanism?

I've search on the web about the mechanism of serine protease:


But the product seems to be different from the reaction I've done in the Lab as the above mechanism attack the carbonyl group... not the ester

And makes me curious... what is the role of NaHCO3?

[agrobert]

Ok, so you understand the catalytic triad of serine proteases.  This mechanism shown is for amide hydrolysis.  The mechanism for ester hydrolysis is exactly the same, except it is an oxygen instead of a nitrogen.  I don't know the structure of the alcalase enzyme but I am certain this is what is involved.  In your mechanism the SER-HIS are shown as free amino acids.  In alcalase they are residues.  Not sure becuase I don't know your exact procedure but sodium bicarbonate can be a buffer or initiation base to ensure the solution is basic.

[Hand15]

Ok, so you understand the catalytic triad of serine proteases.  This mechanism shown is for amide hydrolysis.  The mechanism for ester hydrolysis is exactly the same, except it is an oxygen instead of a nitrogen.  I don't know the structure of the alcalase enzyme but I am certain this is what is involved.  In your mechanism the SER-HIS are shown as free amino acids.  In alcalase they are residues.  Not sure becuase I don't know your exact procedure but sodium bicarbonate can be a buffer or initiation base to ensure the solution is basic.

But why would it hydrolised the ester? Not the amide just what happen in the above reaction mechanism?. Certainly the compound also has amide structure... 
Sorry, I'm not very familiar with this enzymatic chemistry