By Michael Breslav on Monday, March 24, 2003 - 03:01 pm:
I was asked to isolate basic ~900 DA weight compound as a very pure free base. Crude material is an impure free base. I guess that this can be done by RP either with water/ACN/TFA followed by an ion-exchange or extraction, or using ammonium acetate buffer, or using ammonium (bi)carbonate buffer. First way is reliable but time and material consuming, second way may produce acetic salt (pKa of some of the groups is 10 to 14), I am not sure about feasibility of the ammonium carbonate method. (I also doubt that NP will give me a very pure material in this case.)
What do you think? Thanks.
By Anonymous on Tuesday, March 25, 2003 - 04:21 am:
I would use classical NORMAL Phase CHROMATOGRAPHY and use pure organic MP (no salt present).
By Anonymous on Tuesday, March 25, 2003 - 08:09 am:
Normal phase on alumina-basic would probably be your best bet.
By Uwe Neue on Tuesday, March 25, 2003 - 03:57 pm:
We have done this many times using XTerraPrep columns at alkaline pH. You can either use ammonia or an ammonium carbonate buffer at pH values around 9 to 10. Carbonate decomposes around 60 degrees, if you do not want to use ammonia.
In general, the pK of basic compounds shifts to more acidic values in the presence of an organic solvent. Your compound may be completely nonionic under these conditions, which also improves the loadability in prep by a factor of 50.
I can get you more detailed information if you contact me.