Anthranilic acid is not an amino acid because it lacks a crucial element found in all amino acids: a carboxyl group directly attached to the alpha carbon.

Here's a breakdown:

* Amino acids: These are the building blocks of proteins. They have a central carbon atom (the alpha carbon) with four substituents:

* An amino group (-NH2)

* A carboxyl group (-COOH)

* A hydrogen atom (-H)

* A side chain (R group)

* Anthranilic acid: This molecule has an amino group (-NH2) and a carboxyl group (-COOH) but the carboxyl group is not directly attached to the carbon that carries the amino group. The carboxyl group is attached to the benzene ring, not the alpha carbon.

Therefore, anthranilic acid lacks the specific structural requirement of a carboxyl group directly bonded to the alpha carbon, making it ineligible to be classified as an amino acid.

Instead, anthranilic acid is categorized as an aromatic amine. It's a building block for some important molecules like indigo dye and is used in various industrial applications.