Carvone (You can smell chirality!)
12th May 2006
The other day we talked chirality. Here’s the example they give in every organic chemistry class when they’re teaching chirality. Carvone!
The two molecules are identical compositionally. The only difference is that that isopropenyl group (the < shape on the right) is coming out of the plane of the page in S-carvone (we call this a "wedged" bond), and going into the plane of the page in R-carvone (a "hatched" bond). S-(+)-carvone smells of caraway (anise-like), and R-(-)-carvone smells of spearmint. All this because of chirality!
I have tasted and smelled caraway, but never neat S-carvone. I have tasted R-carvone, apparently: Wikipedia tells me Wrigley’s Spearmint is just gum soaked in R-carvone and sugar. I don’t think the old-timey licorice/aniseed flavored Black Jack gum is flavored with S-carvone, though.
It’s also worth noting: carvones don’t just “smell like” caraway and spearmint, they are the flavors of caraway and spearmint. Also neat is that the same biochemical pathway, the HMG-CoA reductase pathway, produces molecules as diverse as carvone, cholesterol, carotene, and chlorophyll. Sundry natural products come out of this pathway and are called isoprenoids or terpenoids. Statins, the superheroes of the cholesterol-lowering drugs, target this very pathway. You will, no doubt, hear about this pathway from me again!
May 12th, 2006 at 7:00 am
I would always use limonene as the example, one enantiomer smells of oranges, the other, lemons…
May 15th, 2006 at 9:58 pm
[…] Friday, we talked about about carvone. I mentioned that it comes from the same biosynthetic pathway as cholesterol. The precursor to this, as well as a number of other natural products, is isopentenyl pyrophosphate, which we’ll refer to as IPP: […]
May 17th, 2006 at 9:41 am
[…] Carvone (You can smell chirality!) […]
July 31st, 2006 at 8:38 pm
[…] All this leads up to a truly unusual thiol: grapefruit mercaptan. You’ll notice it looks like another terpene, like carvone and damascone. Grapefruit mercaptan is such a singular compound because it is a nice-smelling thiol. It’s another one I haven’t smelled, but I’m told it’s very complex and grapefruity. It’s also unique because not many things synthesize thiols on purpose (thiols being reactive and stinky - skunks are a notable exception here). […]