[Babcock_Hall]

We are having a little trouble purifying compounds of the forms 1 and 2 in the drawing.  We used to purify compound 1 using two extractions, but we now use silica with a mobile phase that includes small portions of methanol and acetic acid.  The column successfully removes the side product 4-nitrophenol, but strangely there is sometimes a small amount of DMF, the solvent from the original reaction.  Most of the DMF was removed prior to running the column by repeatedly adding water and performing rotary evaporation (would anyone care to comment on why the DMF is present?).

Presently, we purify compounds similar or identical to pyridinium salt 2 by precipitating them in MTBE or diethyl ether.  We are interested in obtaining material that would be suitable for elemental analysis or high-resolution mass spectrometry.

We have also tried to purify the deprotected versions of compounds 1 and 2 using ion-exchange on Dowex-1; recently we have tried using gels such as SP-Sephadex C25 and DE-52 (cellulose-based).  We have had mixed success, often seeing low recovery with Dowex-1.  Our hope was to improve recovery by replacing the matrix with carbohydrate gels, but we have not used these two ion-exchange gels enough times for me to form a strong opinion about them yet.

I have been thinking about using Sep Pak or other C18 systems, preferably as syringe-based systems, as opposed to columns for purifying compounds either related to 1 or 2.  Does anyone have any suggestions about how to do method development?  This would be a new area for us.  A previous thread which covered related issues is here:  http://www.chemicalforums.com/index.php?topic=65872.msg237067#msg237067