Omega-3 Fatty Acids Nomenclature

Omega-3 Fatty Acids Nomenclature - Ralph T. Holman

Omega-3 Fatty Acids Nomenclature - Ralph T. Holman
The omega-3 nomenclature applicable to polyunsaturated fatty acids was proposed by professor Ralph T. Holman in 1964. Holman had prior to his retirement been an employee The Hormel institute, University of Minnesota. The omega nomenclature has been used ever since.
A number of articles describe the omega-3 nomenclature in detail, but fail to recognize its inventor. This might be a consequence of lack of documentation which is not readily extracted from the literature. However, one of the top Google-hits based on the key words “Omega-3 fatty acids”, furnished the answer in a -article entitled Omega-3 fatty acid. The answer was not found in the text of the article, but in the publication pointed out in reference no. 97 of a total of 142 which would be time-consuming to scrutinize for a person being unaware of Holman´s role.
Quotation from ref. no. 5 in the present article, page 428S:
“….The use of the omega nomenclature was proposed by Holman (1964)…..”
The reference “Holman (1964)” is identical to ref. no. 1 in this article.
The term “omega-3”, (ω - 3), is well-known to chemists as well as to the public worldwide, and refers to essential fatty acids which are dietary supplements. Fish oil contains predominantly two of the three essential fatty acids, EPA and DHA (vide infra) and are available as liquids, capsules, and more recently and surprisingly, as tablets. In fact “omega-3” has become synonymous with dietary fatty acids and their nutritional benefits.
The omega-3 nomenclature
The omega-3 nomenclature provides a simplified system for describing the chemical structures of naturally occurring unsaturated fatty acids. The omega-3 names of the three essential fatty acids ALA, EPA and DHA, and their corresponding systematic IUPAC-names are presented below. The latter names provide the exact chemical structures:
ALA: 18:3 (ω - 3) [(9Z,12Z,15Z) - octadeca - 9,12,15 - trienoic acid]
EPA: 20:5 (ω - 3) [(5Z,8Z,11Z,14Z,17Z) - eicosa - 5,8,11,14,17 - pentaenoic acid]

DHA: 22:6 (ω - 3) [(4Z,7Z,10Z,13Z,16Z,19Z) - docosa - 4,7,10,13,16,19 - hexaenoic acid]

<sub>
<big>Quotation from a footnote in Holman´s paper :</big>
”The notation” (20:5ω3, 22:5ω3, 22:6ω3) “used here is required to distinguish the various isomers of PUFA” (polyunsaturated fatty acids) “and indicate relationships. The first number indicates chain length, the second indicates the number of double bonds, and the number following the omega indicates the position of the last double bond, counting from the terminal methyl groups.” Holman´s notations did not have the minus sign between the omega (ω) and the figure 3.</sub>
<sub>Two prerequisites:
(1) All double bonds have the (Z)-configuration
(2) The double bonds are separated by one -CH 2 - group
(e.g. -CH 2 -CHCH-CH 2 -CHC(3)H-CH 2 -C(ω)H 3 )</sub>

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