Asparagine

Asparagine is one of the 20 most common natural amino acids on Earth. It has carboxamide as the side chain's functional group.

A byproduct of the breakdown of asparagine (asparagine-amino-succinic-acid monoamide) is also blamed for the smell in some people's urine after they have eaten asparagus. (Some scientists disagree and implicate other substances in the smell, especially methanethiol.)