Question

Neuroprotectin D1 (NPD1) is synthesized in the body from highly unsaturated essential fatty acids. NPD1 is a potent natural anti-inflammatory agent.

a. Label each double bond as conjugated or isolated.

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b. Label each double bond as E or Z.

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c. For each conjugated system, label the given conformation as s-cis or s-trans.

Answer 1

(a)

Each double bond in neuroprotectin D1 (NPD1) are labelled as isolated or conjugated as shown below:

• Isolated double bonds are double bonds separated by more than one sigma bond whereas conjugated double bonds are separated only by one sigma bond.

• In isolated double bonds, there will be one or more hybridized carbon atoms in between the diene whereas the carbon atoms of a conjugated double bond are hybridized.

The functional group of the given molecule is carboxylic acid. Hence, the numbering for the carbon chain is started from the acid group.

The double bond between 4-5, 7-8 and 19-20 are isolated as they contain sp³ hybridized carbon atom to both sides of the double bond.

The double bonds between 11-12, 13-14 and 15-16 are conjugated as they are all sp² hybridized carbon atoms.

(b)

A double bond can be labelled as Z when the two higher priority groups are on the same side of the double bond and if the two higher priority groups are on different sides of the double bond, then it can be labelled as E.

The double bonds between 4-5, 7-8, 15-16 and 19-20 have Z conformation as it places the higher priority carbon atoms and the lower priority hydrogen atoms on the same side of the double bond.

The double bonds between 11-12 and 13-14 have E conformation as it places the higher priority carbon atoms and the lower priority hydrogen atoms on the opposite side of the double bond.

(c)

The s-cis and s-trans conformation can only be assigned for conjugated dienes.

• If the two double bonds are on the same side of the single bond joining the two double bonds, then it is known as s-cis conformation.

• If the double bonds are on the opposite side of the single bond joining the two double bonds, then it is known as s-trans conformation.

The conjugated double bonds are 11-12, 13-14 and 15-16.

The double bonds between 11-12 and 13-14 are on same side of the single bond 12-13 and thus, have s-cis conformation.

The double bonds between 13-14 and 15-16 have the double bonds on the opposite side of the single bond 14-15 and thus, have s-trans conformation.