My attention has been taken over by the molecule of one fungi toxin. It exists as a mixture of epimers. And even after you separate this diastereomeric mixture both compounds turn into a mixture over time at any circumstances (in solution and in solid state). The reason for it isn't obvious for me and I've never met similar examples.
All I can say, that epimerization probably occurs through sp2-hybridised carbon atom and may be connected with long chain of conjugation (see the picture).
Does anyone have a clue of what's going on here?
And what is more important - is there any method to clarify the mechanism of this phenomena?
Hi Anatoly, can you add the substance into D2O (possibly from a DMSO stock solution, if it should dissolve readily), and record NMR kinetics?
Wolfgang Schechinger I'm afraid it's not possible. Because separation of the epimers demands C18 HPLC. And the sample preparation (evaporation of methanol-water eluent, dilution and secondary evaporation for transfer to NMR laboratory) is a time-consuming process. And after several hours every relatively pure epimer equilibrates into the initial mixture. We were able to catch this event only using analytical HPLC by analyzing the solutions of freshy separated epimers.
Could you please give a short explanation of how can kinetics help us to solve this puzzle?
Anatoly, I thought about a possible H-D exchange in excess D2O and the resulting change of NMR signals.
Wolfgang Schechinger It is definitely worth trying. Thank you for the advice!
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