1) A chemist working in a pharmaceutical lab synthesized a new drug as a racemic

Question

1) A chemist working in a pharmaceutical lab synthesized a new drug as a racemic mixture. Why is it important that they separate the two enantiometers and test each for its biological activity?

2) My lab partner synthesized an experimental compound that I'd like to test in my research. the problem is, my lab partner didn't label the bottle properly, and I have no idea wheather this substance- which has a chiral center-was synthesized to be in an R or S conformation or as a racemic mixture. How can I experimentally determine the chirality of my sample?

Explanation / Answer

1) Often only one enantiomer of the drug may be active, the other isomer can have adverse effect or biologically inactive.

For example, in cases like salbutamol and thalidomide, the other enantiomer may be harmful. The (R) enantiomer of thalidomide is effective against morning sickness, while the (S) enantiomer is teratogenic, causing birth defects. Since the drug racemizes, the drug cannot be considered safe for use by women of child-bearing age, and its use is tightly controlled when used for treating other illness.

R- enantiomer of thalidomide= effective againstmorning sickness

S- enantiomer of thalidomide= teratogenic, causes birth defects      

Methamphetamine is available by prescription under the brand name Desoxyn. The active component of Desoxyn is dextromethamphetamine hydrochloride. This is the right-hand isomer of methamphetamine. The left-handed isomer of methamphetamine, levomethamphetamine, is an OTC drug that is less centrally-acting and more peripherally-acting.

So it is important to separate both the isomers and check the biological activity of each isomer. Biological assay of racemic mixture is not accurate because only one isomer of it is active, the isomer being inactive or toxic.

2) Chiral compounds rotate plane polarized light. Each enantiomer will rotate the light in a different sense, clockwise or counterclockwise. Molecules that do this are said to be optically active.

One chiral 'object' that interacts differently with the two enantiomers of a chiral compound is circularly polarised light: An enantiomer will absorb left- and right-circularly polarised light to differing degrees.

A polarimeter is a scientific instrument used to measure the angle of rotation caused by passing polarized light through an optically active substance.

Some chemical substances are optically active, and polarized (unidirectional) light will rotate either to the left (counter-clockwise) or right (clockwise) when passed through these substances. The amount by which the light is rotated is known as the angle of rotation.

So Polarimeter is a solution to check which isomer is present. Output comes with positive or negative value. R and S isomers of same compound have same alphaD value with opposite sign. So you can run polarimeter experiment to find which isomer is present.

Related Questions

Navigate

• Browse (All)
• Browse 1
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.