Hi all,
I tried an Fmoc protection on primary amine using Fmoc-Cl. Typical conditions I found were dioxane+aqueous sodium carbonate. When I tried this, I obtained little product and mostly fluorenemethanol (fluorene-CH2-OH) which appears to be a byproduct of Fmoc-Cl reaction with water (which is why I am confused that water is even included in this reaction).
Does anyone have any alternative procedures or know what I might have done wrong if anything? Or an explanation as to why water would be included if it appears to breakdown Fmoc-Cl?
Note: I recrystallized Fmoc-Cl from hexanes and confirmed its structure/purity by TLC, NMR, and IR so bad reagent is not the issue here.
I think it is important to cool for this conditions. You cant avoid the formation of fluorenemethanol (could be removed by crystallization or extraction) with this procedure, but ou should get your product.
See attachments.
http://www.rsc.org/suppdata/gc/c1/c1gc15868f/c1gc15868f.pdf
http://faculty.virginia.edu/mcgarveylab/Carbsyn/AminoAcids.html
Greg:
If you use dioxane+aqueous sodium carbonate, aqueous means you have water and aqueous sodium carbonate has OH-, both water and OH- may react with Fmoc-Cl.
Thanks for the suggestion Jürgen Wintner .
Guobing Xiang , yes I know those things react with Fmoc-Cl; I stated that in my question. My question was why have the water in the first place if it appears to breakdown the Fmoc-Cl.
Greg
haha, sorry!
If the pH is not so high, the concebtration of OH- is not high enough and the reactivity of NH2 is much higher than the reactivity of H2O.
Greg,
Based on Greene's Protective Groups, in aqueous dioxane, NaHCO3 (bicarbonate) is recommended as a base, which is much milder comparing to Na2CO3 (carbonate). Perhaps this will be helpful in your case.
Good luck,
Vladimir
I also attempted something similar as well using Fmoc N hydroxyl succinimide and an amine in DMF:Water and the reaction failed. I think it might be best to try your reaction in THF and completely avoid water or use a low temperature.
I tried Fmoc protection by 3rd paper shared by Jürgen Wintner at 60 Celsius and water ethanol mixture as solvent but no result, This method not using any base, so how to make amino acid
Amine free so that it can react with Fmoc-Cl. Is temperature the source of free amine in amino acid in this case?
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