Nomenclature of Lignans and Neolignans (IUPAC Recommendations 2000)

Lignans and neolignans are a large group of natural products characterized by the coupling of two C 6 C 3 units. For nomenclature purposes the C 6 C 3 unit is treated as propylbenzene and numbered from 1 to 6 in the ring, starting from the propyl group, and with the propyl group numbered from 7 to 9, starting from the benzene ring. With the second C 6 C 3 unit the numbers are primed. When the two C 6 C 3 units are linked by a bond between positions 8 and 8' the compound is referred to and named as a lignan. In the absence of the C-8 to C-8' bond, and where the two C 6 C 3 units are linked by a carbon–carbon bond it is referred to and named as a neolignan. The linkage with neolignans may include C-8 or C-8'. Where there are no direct carbon–carbon bonds between the C 6 C 3 units and they are linked by an ether oxygen atom the compound is named as an oxyneolignan. The nomenclature provides for the naming of additional rings and other modifications following standard organic nomenclature procedures for naming natural products. Provision is included to name the higher homologues. The sesquineolignans have three C 6 C 3 units, and dineolignans have four C 6 C 3 units.