Question

How many optical isomers does isoleucine have?

Answer 1

There are four optical isomers of isoleucine.

The structure of isoleucine is

Its chemical name is 2-amino-3-methylpentanoic acid.

We see that `"C2"` and `"C3"` are chiral centres.

The maximum number of stereoisomers is `2^n`, where `n` is the number of chiral centres.

Since `n = 2`, there are `2^n = 4` stereoisomers.

The most important stereoisomer is

This is L-isoleucine or (`2S,3S`)-2-amino-3-methylpentanoic acid.

It is the only form that is found in nature.

The enantiomer of L-isoleucine is D-isoleucine or (`2R,3R`)-2-amino-3-methylpentanoic acid.

Another stereoisomer is L-`allo`-isoleucine or (`2S,3R`)-2-amino-3-methylpentanoic acid.

The fourth stereoisomer is D-`allo`-isoleucine or (`2R,3S`)-2-amino-3-methylpentanoic acid.