the carbon skeleton being further substituted by singly-bound oxygen atoms

Full Title

Compounds containing amino and carboxyl groups bound to the same carbon skeleton > having amino and carboxyl groups bound to carbon atoms of six-membered aromatic rings of the same carbon skeleton > with amino and carboxyl groups bound to carbon atoms of six-membered aromatic rings being part of the same condensed ring system > the carbon skeleton being further substituted by singly-bound oxygen atoms