Eighteen-membered rings

Fusafungine (INN), also known as fusafungin, is an active agent used in antibiotics for treatment of nasal and throat infection. It also possesses anti-inflammatory properties. Fusafungine is a mixture of enniatin cyclohexadepsipeptides made up of alternating D-α-hydroxyvaleric acid and L-N-methylamino acid residues, produced by the ascomycete Fusarium lateritium, and marketed by Servier under the trade names Locabiotal, Bioparox, and Locabiosol.

Cyclooctadecanonaene or [18]annulene is an organic compound with chemical formula . It belongs to the class of highly conjugated compounds known as annulenes and is aromatic. The usual isomer that [18]annulene refers to is the most stable one, containing six interior hydrogens and twelve exterior ones, with the nine formal double bonds in the cis,trans,trans,cis,trans,trans,cis,trans,trans configuration. It is reported to be a red-brown crystalline solid.

Cyclooctadeca-1,3,5,7,9,11,13,15,17-nonayne or cyclo[18]carbon is an allotrope of carbon with molecular formula . The molecule is a ring of eighteen carbon atoms, connected by alternating triple and single bonds; thus, it is a polyyne and a cyclocarbon.