Molecule of the Day

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:

A few things this ends up in are compounds like carvone, limonene, and menthol, shown below:

You’ll notice they all have ten carbons. We’ve talked about carvone, which can smell minty or licorice-like. Limonene, as one reader remarked, has the stereoisomeric smell phenomenon as well - one isomer smells like citrus, the other, pine. Menthol, finally, you’re familiar with. I wouldn’t ascribe any particular taste to it, more of just a cooling sensation.

These are called “monoterpenes.” All chemicals built up from IPP can be termed terpenes of some sort. The monoterpenes come from two molecules of IPP. A fifteen carbon terpene is called a sesquiterpene, and a twenty carbon terpene is called an diterpene. And so on. IPP ends up in stuff as diverse as ginger oil, Vitamin A, rubber, and your very own cholesterol. As I alluded to yesterday, the enzyme pathway leading up to IPP is a drug target for cholesterol reduction. Here is the structure of cholesterol:

If you are particularly observant, anal, or both, you will note that cholesterol is only a C₂₇ compound. This is because some carbon is lost in the conversion of its precursor; it is still a triterpene (six IPPs involved in its production). Its C₃₀ precursor in vivo is lanosterol.

So, the same biosynthetic pathway produces rubber; aromas as diverse as rye, citrus, and mint; cholesterol; and Vitamin A. Neat, huh? See you tomorrow.