Anthranilate pathway

The shikimate pathway — the major pathway that makes every aromatic ring in plants — splits into two branches at a fork.

One branch leads to phenylalanine, and from there to eugenol, cinnamaldehyde, anethole and vanillin. That is the phenylpropanoid group, the group of rich spices.

The other branch leads to anthranilic acid and then to tryptophan. This is the only branch that brings nitrogen into the aromatic ring, because anthranilic acid has an amino group attached directly to the ring.

Nitrogen changes everything. This group has only two representatives in the library, and the two sound unrelated: indole gives a faecal note at high concentration and a white-flower note at low concentration, while methyl anthranilate gives the smell of Concord grapes and ripe kumquat. Nobody would put them side by side judging by nose alone.

But they are chemical siblings, and both carry a nitrogen atom that none of the other five groups has. It is the clearest example of a biosynthetic pathway grouping compounds by lineage rather than by smell.

This library classifies compounds along three axes, and each answers a different question.

Boiling point tells you when you smell a compound — early or late on the smelling strip. Chemical family tells you how it behaves — stable or fragile, and how to recognise it on an analysis. Biosynthetic pathway tells you where it comes from.

The third axis is the explanatory one. The other two describe how compounds cluster into groups; this one says why they cluster that way.