Structure and absolute configuration of an unsaturated anteiso fatty acid from Bacillus megaterium
2010 (English)In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1217, no 10, 1683-7 p.Article in journal (Refereed) Published
Gas chromatography in combination with electron ionization mass spectrometry (GC/EI-MS) was used to determine the fatty acids of a membrane lipid from Bacillus megaterium. Special attention was put on the structure and absolute configuration of a monoenoic fatty acid previously described in this sample. GC/EI-MS operated in the selected ion monitoring mode was used to determine twelve fatty acids in the bacterium. Methyl esters were prepared to verify the presence of a 14-methylhexadecenoic acid (a17:1) isomer. The position of the double bond of the a17:1 isomer and four further monoenoic fatty acids was elucidated by means of their picolinyl esters produced by the transesterification of the phospholipid. For the a17:1 isomer, the double bond was located between C-5 and C-6. Silver ion liquid chromatography was used to verify that the double bond was in cis-configuration. The bacterial 14-methylhexadec-5-enoic acid (a17:1Delta5) is chiral due to the stereogenic C-14 carbon. Initial enantioselective measurements were carried out with isomers of a17:1Delta5 which were available in form of racemic and (S)-enantiopure cis- and trans-isomers of a17:1Delta12 previously synthesized. The cis-a17:1Delta12 enantiomers were partly resolved on a chiral stationary phase coated with 50% heptakis(6-O-tert.-butyldimethylsilyl-2,3-di-O-methyl)-beta-cyclodextrin in OV-1701 (beta-TBDM). However, resolution of the enantiomers of the trans-isomer of a17:1Delta12 failed. Only one peak was also observed for the a17:1Delta5 isomer from B. megaterium. Thus, it remained unclear whether the compound a17:1Delta5 was racemic or enantiopure in the sample. To clarify this point, we separated the cis-monoenoic fraction from the saturated fatty acids. Then, the monoenoic fraction was hydrogenated in order to transform a17:1Delta5 into 14-methylhexadecanoic acid (a17:0). This chiral fatty acid was known to be sufficiently enantioseparated on the beta-TBDM column and was found to be (S)-enantiopure in the sample. Hence, these measurements verified that the B. megaterium sample contained enantiopure (S)-a17:1Delta5.
Place, publisher, year, edition, pages
Elsevier B.V. , 2010. Vol. 1217, no 10, 1683-7 p.
Enantioselective gas chromatography, Gas chromatography–mass spectrometry, Silver ion liquid chromatography, Lipids, Branched-chain fatty acids, Bacillus megaterium
IdentifiersURN: urn:nbn:se:umu:diva-31628DOI: 10.1016/j.chroma.2010.01.036ISI: 000275132500016PubMedID: 20117788OAI: oai:DiVA.org:umu-31628DiVA: diva2:293603