title: Synthesis and nuclear magnetic resonance properties of all geometrical isomers of conjugated linoleic acids.
abstract: Pure geometric isomers of conjugated linoleic acid were prepared from castor oil as the primary starting material. Methyl octadeca-9Z,11E-dienoate (2) and methyl octadeca-9Z,11Z-dienoate (4) were obtained by zinc reduction of methyl santalbate (1, methyl octadec-11E-en-9-ynoate) and methyl octadec-11Z-en-9-ynoate (3), respectively, as the key intermediates. Methyl octadeca-9E,11E-dienoate (8) and methyl octadeca-9E,11Z-dienoate (9) were prepared by demesylation of the mesyloxy derivative of methyl ricinelaidate (6, methyl 12-hydroxy-octadec-9E-enoate). A study of the nuclear magnetic resonance spectral properties was carried-out, and the shifts of the olefinic carbon atoms of 18:2(9Z,11E) (2) and 18:2(9E,11Z) (9) were readily identified by a combination of incredible natural abundance double quantum transfer experiment, heteronuclear multiple bond correlation, and 1H-13C correlation spectroscopy correlation techniques. Doubts remain in the absolute identification of the individual olefinic carbon atoms of the 18:2(9Z,11Z) (4) and 18:2(9E,11E) (8), except the fact that the shifts of the "inner" (C-10 and C-11) and "outer" (C-9 and C-12) positioned olefinic carbon atoms of the conjugated diene system are distinguishable.
authors.affiliation: Department of Chemistry, University of Hong Kong. hrsclkj@hkucc.hku.hk
authors.forename: M S
authors.initials: MS
authors.lastname: Jie
authors.forename: M K
authors.initials: MK
authors.lastname: Pasha
authors.forename: M S
authors.initials: MS
authors.lastname: Alam
mesh_terms: D007536:Isomerism; D019787:Linoleic Acid / Q000138:chemical synthesis* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet
chemical_list: D019787:Linoleic Acid