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October 26, 2005
The Latest in Pharmaceutical Technology
I've been spending some time with a batch of compound recently, boiling it in ethyl alcohol all day long. I distill out the ethanol, then add more and boil it up again. And again. Why am I being so darn productive, you ask? Well, this is some material we received from a contract synthesis company, and while it's the right stuff, it came to us with nearly 10% chloroform in it. You find these things out by taking NMR spectra of the outsourced stuff as soon as you get it in, and preferably in more than one solvent. Trust but verify and all that, particularly from the low bidder.
Deuterated chloroform is a common solvent for NMR spectra, and it always shows a greater or lesser peak for the plain stuff. If we'd only run the spectrum in that, we might have just written it off as an ugly bottle of NMR solvent, but it's rather more difficult to explain its presence in a sample run in, say, DMSO. As it turns out, it's a contaminant left over from the last step of the synthesis, and it's the sort of thing you'd think that a day or two on the vacuum pump would take care of. After all, it's pretty volatile stuff, right?
Well, not in this case. This is one of those times when the solvent seems to have decided to work its way into the crystal lattice of a compound, because that chloroform's not going anywhere without a fight. This compound is not the most soluble stuff in the world, but hot ethanol gradually does the trick. Thus the repetitive distillation. Of course, now the compound is cut with ethyl alcohol instead of chloroform, but that's a much more benign thing to feed the rodents come assay time. Drunken mice we can allow for, but not ones that have been chloroformed from the inside out.
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