Chemistry Forums for Students > Organic Chemistry Forum for Graduate Students and Professionals
Phenylfluorenyl PG removal + isolation of small aminoacid
rolnor:
I repeat also, this compound with the amino group as free base is not stable.
kriggy:
--- Quote from: rolnor on November 05, 2021, 05:44:12 AM ---I repeat also, this compound with the amino group as free base is not stable.
--- End quote ---
Why do you think so? Im fine with it being whatever kind of salt that allows subsequent amide bond formation or even deprotecting it in-situ before the coupling
Babcock_Hall:
I like to think of the proton as a poor man's protecting group.
rolnor:
--- Quote from: rolnor on November 04, 2021, 04:36:09 PM ---The amino group can be oxidized if its unprotected I think, I guess you use hydrogen peroxide to get the selen oxide before elimination? Also the unsaturated product is a Michael addition substrate so a free amino group can add to the double bond. Its also a di ester so it can ringclose or polymerize via aminolysis.
--- End quote ---
As I wrote here, the free base is problematic but it depends on the timescale, it could be stable for short time.
kriggy:
So I did run the NMR experiment and after addition of TFA the double bond signal shifted towards lower ppm. Im not sure if its because of the N protonation or because of the deprotection is happening but after about hour or so, the double bond signals dissapeared completely. I dont have much idea whats going on but seems I need to do the deprotection quick.
Im running the same sequence with trityl and for some reason, the Phenylselenyl derivative is decomposing to something which is neither alkene nor selenoxide and for some reason, it does not get oxidized using same condition as the Pf derivative..
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