Lipid Nomenclature

The nomenclature of lipids falls into two main categories: systematic names and common or trivial names. The latter includes abbreviations which are a convenient way to define acyl/alkyl chains in glycerolipids, sphingolipids and glycerophospholipids. The generally accepted guidelines for lipid systematic names have been defined by the International Union of Pure and Applied Chemists and the International Union of Biochemistry and Molecular Biology (IUPAC-IUBMB) Commission on Biochemical Nomenclature (http://www.chem.qmul.ac.uk/iupac/). The nomenclature proposal follows existing IUPAC-IUBMB rules closely and should not be viewed as a competing format. The main differences involve (a) clarification of the use of core structures to simplify systematic naming of some of the more complex lipids, and (b) provision of systematic names for recently discovered lipid classes. Key features of our lipid nomenclature scheme are as follows:

1. The use of the stereospecific numbering (sn) method to describe glycerolipids and glycerophospholipids. The glycerol group is typically acylated or alkylated at the sn1 and/or sn2 position with the exception of some lipids which contain more thane one glycerol group and archaebacterial lipids in which sn2 and/or sn3 modification occurs.
2. Definition of sphinganine and sphing-4-enine as a core structures for the sphingolipid category where the D-erythro or 2S,3R configuration and 4E geometry (in the case of sphing-4-enine) are implied. In molecules containing stereochemistries other than the 2S,3R configuration, the full systematic names are to be used instead (e.g., 2R-amino-1,3R-octadecanediol).
3. The use of core names such as cholestane, androstane, and estrane, for sterols.
4. Adherence to the names for fatty acids and acyl-chains (formyl, acetyl, propionyl, butyryl, etc) defined in Appendix A and B of the IUPAC-IUBMB recommendations.
5. The adoption of a condensed text nomenclature for the glycan portions of lipids, where sugar residues are represented by standard IUPAC abbreviations, and where the anomeric carbon locants and stereochemistry are included but where the parentheses are omitted. This system has also been proposed by the Consortium for Functional Glycomics (http://www.functionalglycomics.org/static/index.shtml).
6. The use of E/Z designations (as opposed to trans/cis) to define double-bond geometry.
7. The use of R/S designations (as opposed to α/β or D/L) to define stereochemistries. The exceptions are those describing substituents on glycerol (sn) and sterol core structures, and anomeric carbons on sugar residues. In these latter special cases, the α/β format is firmly established.
8. The common term "lyso", denoting the position lacking a radyl group in glycerolipids and glycerophospholipids, will not be used in systematic names, but will be included as a synonym.
9. The proposal for a single nomenclature scheme to cover the prostaglandins, isoprostanes, neuroprostanes, and related compounds where the carbons participating in the cyclopentane ring closure are defined and where a consistent chain numbering scheme is used.
10. The "d" and "t" designations used in shorthand notation of sphingolipids refer to 1,3 dihydroxy and 1,3,4-trihydroxy long-chain bases, respectively.
11. The LIPID MAPS glycerophospholipid abbreviations (PC, PE, etc.) are used to refer to species with one or two radyl side-chains where the structures of the side chains are indicated within parentheses in the 'Headgroup(sn1/sn2)' format (e.g. PC(16:0/18:1(9Z))). By default, R stereochemistry at the C2 carbon of glycerol and attachment of the headgroup at the sn3 position.
12. In a similar fashion, the LIPID MAPS glycerolipid abbreviations (MG,DG,TG for mono-, di- and triradyglycerols respectively) are used to refer to species with one to three radyl side-chains where the structures of the side chains are indicated within parentheses in the 'Headgroup(sn1/sn2/sn3)' format (e.g. TG(16:0/18:1(9Z)/16:0)).
13. The alkyl ether linkage is represented by the "O-" prefix, e.g. DG(O-16:0/18:1(9Z)/0:0) and the (1Z)-alkenyl ether (neutral Plasmalogen) species by the "P-" prefix, e.g. DG(P-14:0/18:1(9Z)/0:0). The same rules apply to the headgroup classes within the Glycerophospholipids category. In cases where glycerolipid total composition is known, but side-chain regiochemistry and stereochemistry is unknown, abbreviations such as TG(52:1) and DG(34:2) may be used, where the numbers within parentheses refer to the total number of carbons and double bonds of all the chains.