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Natural Science Forum / Chemistry / Organic Synthesis / February 2004purification question
I've synthesized (3R,5S)-1-(t-butyloxycarbonyl)-3-fluoro-5-(trityloxymethyl)-2-pyrrolidinone as a precursor to L-erythro-4-fluoroglutamine, but am having trouble purifying it. My reference says use hexanes/ethyl acetate (4:1) but for some reason the entire sample binds strongly to the silica gel column. I'm baffled, the fluorination rxn (1.DiIsoPrAmine/THF, 2. NFSi/THF) went according to plan and the work up was simple. Starting material was (S)-1-(t-butyloxycarbonyl)-5-(trityloxymethyl)-2-pyrrolidinone. I'd REALLY appreciate any helpful suggestions. The sample was filtered prior to loading on the column. Thanks! Kirk  SignaturePaul J. Franklin(moderator - sci.chem.organic.synthesis) http://organicworldwide.net/sci.chem.organic.synthesis Georgia State University <chepjf@panther.gsu.edu> Atlanta, GA > I've synthesized (3R,5S)-1-(t-butyloxycarbonyl)-3-fluoro-5-(trityloxymethyl)-2-pyrrolidinone > as a precursor to L-erythro-4-fluoroglutamine, but am having trouble [quoted text clipped - 8 lines] > > Thanks! Use a more polar eluant. What did the TLC look like? Are you sure you still have your protecting groups in place? If you add a very little Et3N to the silica gel slurry before pouring the column you can controllably progressively diminish adsorption. Try dipping a TLC plate in very dilute Et3N, drying, and see if it helps move things along while retaining separation. SignatureUncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) "Quis custodiet ipsos custodes?" The Net! -- Paul J. Franklin(moderator - sci.chem.organic.synthesis) http://organicworldwide.net/sci.chem.organic.synthesis Georgia State University <chepjf@panther.gsu.edu> Atlanta, GA >I've synthesized (3R,5S)-1-(t-butyloxycarbonyl)-3-fluoro-5-(trityloxymethyl)-2-pyrrolidinone >as a precursor to L-erythro-4-fluoroglutamine, but am having trouble [quoted text clipped - 6 lines] >I'd REALLY appreciate any helpful suggestions. The sample was >filtered prior to loading on the column. Well, what does the TLC look like? One spot or many? Using what visualization technique? What are the Rf values? The usual procedure to remove something stuck to a SiO2 column is to increase the polarity of the eluant. If you're using 25% ethyl acetate, go to 50%. If that doesn't work then go to 100%, and after that you'd begin adding a few percent methanol. Steve Turner SignaturePaul J. Franklin(moderator - sci.chem.organic.synthesis) http://organicworldwide.net/sci.chem.organic.synthesis Georgia State University <chepjf@panther.gsu.edu> Atlanta, GA >I've synthesized (3R,5S)-1-(t-butyloxycarbonyl)-3-fluoro-5-(trityloxymethyl)-2-pyrrolidinone >as a precursor to L-erythro-4-fluoroglutamine, but am having trouble [quoted text clipped - 6 lines] >I'd REALLY appreciate any helpful suggestions. The sample was >filtered prior to loading on the column. Well, what does the TLC look like? One spot or many? Using what visualization technique? What are the Rf values? The usual procedure to remove something stuck to a SiO2 column is to increase the polarity of the eluant. If you're using 25% ethyl acetate, go to 50%. If that doesn't work then go to 100%, and after that you'd begin adding a few percent methanol. Steve Turner SignaturePaul J. Franklin(moderator - sci.chem.organic.synthesis) http://organicworldwide.net/sci.chem.organic.synthesis Georgia State University <chepjf@panther.gsu.edu> Atlanta, GA |
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