[uglepik]

I have a compound (a lipopeptide) where I've removed the protecting groups with TFA, meaning that I now have trifluoroacetate anions at the two amines of my compound. However, the boys over at the cell biology department would really like an acetate salt instead. Therefore, two questions arise:

1) Which is the best method for converting TFA salts to acetate salts? I have tried dissolving my compound in acetic acid and freeze-drying it. The idea was the large excess of acetate would displace the TFA. This does not seem to work at all.

2) Does anyone have experience with removing Boc- and tBu- protecting groups by acetic acid. I'm guessing this is possible, I just don't know how long it would take. I would assume elevated temperature was preferable.

- Information about the (protected compound): Dissolves in chlorinated solvents, with up to 75% TFA added. I haven't tried dissolving in AcOH. It does not dissolve in polar solvents or water. It contains two ester bonds.

Thanks for your help
Andreas

[fledarmus]

Usually I would free-base the compound by washing it with a sodium bicarbonate solution. Depending on the structure of the lipoprotein, it is possible that the unprotected compound would either be soluble enough in ethyl acetate to extract from the aqueous base solution, or insoluble enough in the aqueous base to crystallize. I've also had some success free-basing compounds by dissolving them in methanol and stirring them over solid sodium bicarbonate or sodium carbonate. If these are not possible, you might be able to use an ion-exchange resin to remove the TFA.