[ Science vol. 331 pp. 1395 – 1396 (editorial) and 1429 – 1432 ’11 (18 March issue) ] is an example of the “have an idea ?”, “then build a molecule to prove it !” that organic chemistry allows you to do so elegantly. In this case it was a single molecule which produced products of different chirality depending on the conformation of the molecule. No atom of greater mass than sulfur was in the catalyst. The reaction was a simple Michael addition of a thiol anion to an alpha-beta unsaturated ketone. A thiourea part of the molecule coordinated the oxygen of the ketone, while a 2 amino pyridine moiety coordinated the thiolate anion.
The cleverness came in putting the two of them at ends of multiringed aromatic structures (each of which was effectively planar). The two aromatic structures were tied together by a double bond between two cyclopentane rings. To produce the product the aromatic structures had to be pointing the same way so each one could bind its reactant and then bring them together.
The double bond could have the two planes trans (in which case a racemic mixture of product was obtained, or cis. Trans to cis was accomplished by light. The cleverness came by using heat to change the chirality of what was basically a helix (I’m not sure how this happened) from right handed to left handed. The molecule in the right handed helical state produced enantiomeric excess of one product, while in the left handed helical state it produced enantiomeric excess of the other.
Bravo ! ! ! Brilliant, simply brilliant. Organic chemistry lets you do such things.
Hopefully more chemistry is on the way, now that the flu is winding down. No benzodiazepines or codeine were required for sleep last night. The next post will be about why we’ll never have a really good drug to fight addiction. I was grateful for the sleep, but hated the way I felt on the stuff. Not everyone does and therein lies a tale.