This week we have a guest blog by Sean Patrick McGinley a law student at Boston College. Sean Patrick explains the scientific reasoning behind the Ninth Circuit’s decision in Lorenzo v. Sessions. Thank goodness for engineers and chemists. Please enjoy!
In response to the Lorenzo case (and just general scientific curiosity), I researched how geometric, positional, and optical isomers differ. If you bear with me through the science part, I think the importance of different methamphetamine isomers will make more sense.
Geometric and optical isomers differ because they have a different chemical arrangement within a compound. In a broad sense, the arrangement can impact how a compound transfers heat or reacts with a protein. For methamphetamine, the two isomers arrangements create significantly different reactions and end products in the body.
Please bear with me through this as I am trying to make it as digestible as possible. “Isomer” refers to a chemical compound that has the same chemical formula but a different chemical structure. Essentially, each isomer will have the same atoms, but the atoms will be arranged differently. If you are curious, optical isomers are mirror images of each other and refract light differently. Think of a hand in a mirror. If you put your hand to the mirror, there is no way for you to have the exact same image reflected. What you see is always an exact, reverse copy. Or, as another example, one isomer may cause light to reflect at a 90° angle where another causes the light to refract in multiple different directions. This may seem minor, but it can dramatically impact how proteins bond to the structure.
Positional or geometric isomers are the same carbon chain but place the functional group in a different location. A boiled down definition of “functional group” is essentially all non-carbon atoms clumped together. Typically, positional isomers are not referred to because it is a much more specific and flexible definition than geometric isomers.
For those of you who like visuals, here is the difference between the different types:
The different structures can have huge impacts. For example, in the 1950s, German pharmacists accidentally sold the wrong optical isomer of Thalidomide. The R enantiomer helped cure morning sickness during pregnancy. The S enantiomer cause significantly birth defects. The pharmacists intended to sell R-Thalidomide but instead sold S-Thalidomide. As a result, a significant number of infants either died or were born without limbs.
It is also important to note that not all isomers cause different reactions. It is heavily compound dependent. This means that a compound could have two differ isomers that both cause the same reaction. The different structures will have no effect on the end reaction.
As for the DEA’s line about being easy to tell which isomer is which, a chemist would easily be able to tell the difference between isomers. Although a lay person would probably not be able to, one skill in the art would be capable.
Application to Methamphetamine:
As the court in Lorenzo acknowledged, methamphetamine’s isomers do cause different reactions. The main difference is between the “l” and “d” forms. They are optical isomers, but my research shows that other isomers may exist as well. L-methamphetamine is the lesser of the two compounds. This is the compound commonly found in Vicks and is a known metabolite (a molecule necessary for metabolic reactions). D-methamphetamine, however, is much more dangerous. This is what we typically are thinking about in the context of controlled substances. D-methamphetamine is a known stimulant. Since they are optical isomers, they have the same chemical reaction, solubility, and melting points, but they reflect light differently. It is possible that they do, however, have different smells.
In my opinion, from the research I conducted, it does not seem like a common usage for any geometric or positional methamphetamine isomers exists. But that does not exclude the possibility of chemists discovering such a compound.
Fun fact: The International Olympic Committee also bans all forms of methamphetamine without distinguishing between what type of isomers, just like California.
Geometric and Optical Isomers, Weird Chemist (last visited Sept. 26, 2018 at 6:54 P.M.), http://www.wiredchemist.com/chemistry/instructional/an-introduction-to-chemistry/structure/geometric-and-optical-isomers
Positional Isomers, OChemPal (last visited Sept. 26, 2018 at 6:54 PM), http://www.ochempal.org/index.php/alphabetical/o-p/positional-isomers/
Simon Cotton, Methamphetamine (And Its Isomers), The Molecule of the Month (March 2007), http://www.chm.bris.ac.uk/motm/methamphetamine/methh.html