Tetrahydroxanthone

Tetrahydroxanthones are natural products formally derived by partial reduction of xanthone.

One example is neosartorin, composed of 5-acetylblennolide A and blennolide C, exhibits antibacterial activity against Gram-positive bacteria, notably including Staphylococcus aureus.

[3][4] The enzyme NsrQ features a catalytic glutamic acid residue in the active site which protonates the enol produced by NsrK, leading to dearomatization.

Once the final reduction and dehydration events take place (NsrJ and NsrI), chrysophanol is accepted into monooxygenase NsrF.

NsrK, a flavin-dependent monooxygenase, the installs an alcohol ortho- to the ester and methyl groups, breaking the aromaticity of the compound.