Structure madness & NMRs from hell

 

mytotoxin2

I know I cheated a little bit, but there was no way I was going to equal this gem. And for all the structure aficionados, here’s the proper structure:

maitotoxin structure
Colour coded structure from this paper: http://pubs.acs.org/doi/abs/10.1021/ja103708j

When @LouisRedux mentioned I should try my luck and draw mytotoxin for my next #chemdoodle it was meant as a joke; but a quick glance at this molecule had me instantly fascinated: 32 rings, no aromatics, non carbonyl groups but instead a whole array of fused cyclic ethers as well as 98 stereocenters, a molecular weight of more than 3400 g/mol and a proton NMR straight from hell. It also seems to have, despite its size, no known repeating units such as amino acids or sugars – nice going, biosynthesis. Always there to make the chemists’ life more difficult.

1H NMR from hell
1H NMR from hell. Taken from here: http://jb.oxfordjournals.org/content/104/2/184.full.pdf

Mytotoxin is the largest known non-peptide, non-polisaccharide compound synthesised by any organism. And just to make things perfect, the stuff is toxic, really toxic with an LD50 in the area of nanograms per kg body weight (at least for mice but I suppose other mammals shouldn’t be far off), outperformed only by certain protein toxins.

Mytotoxin is produced by a tiny marine plankton. The heck I know what it is using that lethal toxin for cause it doesn’t seem to help him not getting eaten: it is mainly found in coral reef fish, causing a whole lot of food poisoning by people eating them. Now, do we need another reason to save the coral reefs? After all, they are awesome synthetic chemistry labs we could learns thing or two from.

Finding Mytotoxin’s structure was (and still is) an adventure. I usually don’t tend to enjoy structure elucidation papers, but these ones here were actually quite a read. Using a combination of NMR, degradation, mass spectrometry and other (for me) exotic techniques, they pieced together the clues to get an idea of the structure.

And there are actually people crazy brave enough to attempt a total synthesis, cause why wouldn’t you want to make something super toxic with a ridiculous amount of stereocentres? They admit though that at times it’s some pretty adventurous chemistry – not something you read in a publication every day (but maybe would like to read more frequently!).

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