Chemistry Forums for Students > Organic Chemistry Forum for Graduate Students and Professionals
Phenylfluorenyl PG removal + isolation of small aminoacid
phth:
Protect the seleno compound from oxygen. It is stable to acid. Seleno compounds can oxidize during column chromatography... Why not just deprotect then do the elimination step???
rolnor:
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.
phth:
--- 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 ---
Yes MCPBA may be the wrong reagent. I would try a chlorine source under aqueous and buffered conditions.
kriggy:
--- Quote from: phth on November 04, 2021, 01:43:41 PM ---Protect the seleno compound from oxygen. It is stable to acid. Seleno compounds can oxidize during column chromatography... Why not just deprotect then do the elimination step???
--- End quote ---
Im able to purify on column without any issues - except the starting material spot is very cloes to the product as much as they are almost coeluting but its doable.
--- Quote from: phth on November 04, 2021, 07:59:43 PM ---
--- 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 ---
Yes MCPBA may be the wrong reagent. I would try a chlorine source under aqueous and buffered conditions.
--- End quote ---
The original procedure for the elimination on this cpd used mcpba, I find NaIO4 bit better and easier to do (just mix and stir) but the deprotection is then not described because they do ester reduction, dihydroxylation and deprotection later.
--- Quote from: phth on November 04, 2021, 01:43:41 PM ---Protect the seleno compound from oxygen. It is stable to acid. Seleno compounds can oxidize during column chromatography... Why not just deprotect then do the elimination step???
--- End quote ---
I did attempt that as well (one experiment) and while I observed the product in LCMS only traces were there and mostly it was some uknown which was assigned from m/z to compound having 2 SePh groups so some kind of rearrangement or transfer probably happened.
--- Quote from: Babcock_Hall on November 04, 2021, 09:36:08 AM ---I work a good deal with unsaturated amino acids, but I doubt that I can be of much help in this instance. KMnO4 dipping has worked well for visualizing our TLC plates. The amino group should not be performing a Michael addition, unless one is under basic conditions; therefore, I am puzzled. Regarding MS, if I could spare a small portion of a product with a free amino group, I would at least consider using heptafluorobutyric anhydride to make a derivative.
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Thank you. Im used to using CAM which I thought it should work but maybe KMnO4 is better in this case.
--- Quote from: rolnor on November 04, 2021, 10:37:25 AM ---OK, maybe you can run a deprotection in a NMR-tube to see what goes wrong, if the double-bond is affected this should be easy to spot.
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That is actually great idea. Dont know why I did not think of that already.
rolnor:
The seleno compound will also stain with KMnO4, it will oxidize.
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