Orange Monascus pigments belong to azaphilone [3].
Azaphilones are structurally variable family of fungal polyketide
metabolites processing a highly oxygenated pyranoquinone bicyclic
core (known as isochromene) and a quaternary carbon center.
The 4-H-pyran nucleus undergoes substitution with primary amines
to form the corresponding vinylogous c-pyridines and then
changes the oxygen of pyran cycle to nitrogen, which makes the
azaphilones turn red.