Question

Question: Isotretinoin, a fatty acid, is a medication used to treat severe acne that has not responded to other drugs. Because it causes fetal abnormalities, it cannot be taken by pregnant women, and its prescription and use are carefully monitored.(a) Label each C=C as E or Z.(b) Label each $\mathbf{\sigma }$ bond joining two C=C’s as s-cis or s-trans.

Short answer

Answer

a.

E-Z configuration

b.

Configuration of single bonds

Step-by-step solution

Step-by-Step Solution Step 1: Isotretinoin

Isotretinoin is a fatty acid that belongs to the first generation of vitamin A acid. It is a stereoisomer of all-trans vitamin A acid.

The oral administration of isotretinoin has an anti-oil effect and is therefore used to cure severe acne.

It is also called 13-cis retinoic acid.

Assigning E-Z values

E and Z notations are used to classify alkenes that are geometrical isomers.

Cis–trans notation cannot be given to alkenes when the substituents on the carbon atoms are different.

Therefore, the groups are ranked according to their priority on each carbon of the double bond in such molecules. If the higher priority groups on the two carbons are on the same side, it is called Z configuration. If they are on the opposite side, the double bond has an E configuration.

The Cahn Ingold Prelog system decides the priority of the group.

Assigning s-cis and s-trans configuration to sigma bonds

In the case of compounds containing more than 1 double bond in conjugation, a sigma bond connects two adjacent double bonds.

These sigma bonds are classified based on the arrangement of double bonds.

If the individual double bonds are on the same side of the single bond, then the single bond has an s-cis conformation. If the double bonds are on the opposite side, the sigma bond has an s-trans configuration.

Classifying bonds on isotretinoin

(a) Isotretinoin has five C=C double bonds. Based on the position of functional groups on each carbon, the E and Z configuration of double bonds in isotretinoin can be given as follows:

E-Z configuration of Isotretinoin

(b) Four sigma bonds connect five C=C double bonds in isotretinoin. Based on the position of double bonds around these sigma bonds, the configuration of single bonds can be given as follows:

Configuration of sigma bonds.