How do you do anti dihyrdroxyl addition to an aromatic hydrocarbon?

Question

I am familiar with how to turn an alkene into an anti/trans diol but via epoxidation followed by water and a base (or acid). However I am writing a paper on the carcinogenic effects of polycyclic aromatic hydrocarbons (PAHs) in smoking products. I haven't taken biochemistry and don't really understand what metabolizing IS (it turns some sort of compound into "energy" does that mean it just harvests the energy of an exogernic rxnof a compound for an endergonic rxn?). Anyways so I found a resource that says PAHs can react with P450s and Epoxide Hydrolase to turn into a diol- but it under goes an addition rxn? I Don't understand how addition is possible with aromatics, unless maybe theres some sort of enzyme catalyst involved that I am not understanding? If you could explain in terms of someone who knows nothing about biochemistry, I would appreciate that.

Answer 1

Hi John, I don't know the specifics of the enzymes acting on the PAHs in smoking products, but it sounds like you know your organic chemistry. P450 and epoxide hydrolase are both enzymes. Understand that many limitations in what we can do in organic chemistry simply do not apply in biochemistry. Enzymes can do things we generally think of as difficult to do in organic chemistry. Two ways the enzyme gets away with it is by having a high-energy bond, like a phosphoryl group (think like a chemical battery, there is a net energy release even for unfavorable reactions because a phosphoryl group somewhere else was so highly powered that it released more energy than it took to react with the aromatic ring) or by having a high-energy shape (think like a spring, the enzyme is in a temporarily stable place, but when it reacts it undergoes a conformational change and the spring is released to power the reaction). All of this is to say, don't fret that an enzyme is doing something that you were taught in organic chemistry not to try to do. From the names of the enzymes involved, it sounds like it is a two-step epoxidation and then ring opening with water. This is similar to what you learned in organic chemistry using mCPBA on an alkene and then reacting that with water (basic or acidic). Here, the enzymes are doing it but in a much more advanced way than we do it in the lab. I hope that is helpful.