Part 3. Dienoic Fatty Acids

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Maximilian Brooks
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1 MASS SPECTRA OF 3-PYRIDYLCARBIOL ESTERS Part 3. Dienic Fatty Acids This sectin describes mass spectra f 3-pyridylcarbinl ester derivatives under the headings Methylene-interrupted dienic fatty acids Cnjugated dienic fatty acids Bis-methylene-interrupted dienic fatty acids Plymethylene-interrupted dienic fatty acids Here, the electrn-impact mass spectra f 3-pyridylcarbinl esters f thse dienic acids that are mst likely t be encuntered in nature, tgether with sme useful mdel cmpunds, are described. The widely used term 'piclinyl ester' is inaccurate and shuld nw be avided see ur webpage n the saturated derivatives). There is a separate dcument dealing with Mass spectrmetry f allenic fatty acids. Methylene-Interrupted Dienic Fatty Acids The mass spectra f 3-pyridylcarbinl esters f dienic fatty acids, like thse f mnenes, tend t be distinctive and permit lcatin f the duble bnd. As an example, the mass spectrum f 3-pyridylcarbinyl 9,12-ctadecadienate (linleate r 18:2(n-6)), the mst imprtant dienic fatty acid in nature, is illustrated belw (Harvey, 1982) As with 3-pyridylcarbinl esters f saturated and mnenic fatty acids, interpretatin is easiest if we start with the mlecular in and wrk dwn the chain. Ins crrespnding t cleavage n either side f the terminal duble bnd are seen at = 0 and (26 amu apart), there is then a gap f 14 amu t = 2, then ne f 26 amu fr the internal duble bnd t = 234. When examining the spectra f unknwns, hwever, it is ften easier t lcate gaps f amu fr the duble bnd and the assciated methylene grup n the carbxyl side, i.e. in this instance between = 0 and 2, and between 2 and 2. Regular series f ins 14 amu apart n either side f the duble bnd cnfirm that there are n further functinal grups in these regins f the mlecule. W.W. Christie lipidlibrary.acs.rg 1

2 Similar series f ins are seen in spectra frm 3-pyridylcarbinl esters f mst methyleneinterrupted dienes, but it is advantageus t have access t spectra f authentic standards when the duble bnds are clse t either end f the mlecule when cnfusin is mst likely t arise. Details f the spectra f the cmplete series f ismeric methylene-interrupted ctadecadienates have been published (Christie, Brechany and Hlman, 1987a), but nly a few f the spectra were depicted in the paper fr practical reasns. All are nw illustrated belw, but please cnsult the riginal reference fr tabulated data. Sme f these may nt ccur in nature, but a surprising number d. Spectra f ther hmlgus fatty acid ismers displaying the same diagnstic features may have been described elsewhere. Spectra fr the cmplete C 18 series fllw. 3-Pyridylcarbinyl 2,5-ctadecadienate (2,5-18:2) (Christie et al., 1987a) The mlecular in is the base peak, presumably because f the duble bnd in cnjugatin with the carbxyl grup. Ins that identify the psitin f the duble bnd are nt apparent, but the dublet f ins at = 214 and 2 are a useful indicatr (see the web pages n 3- pyridylcarbinl esters f mnenes). The regular series f ins 14 amu apart between = 214 and the mlecular in cnfirm that there are n functinal grups in this part f the alkyl chain. 3-Pyridylcarbinyl 3,6-ctadecadienate (3,6-18:2) In this spectrum, the gaps f 26 amu between = and 177, and 1 and 216 serve t lcate the duble bnds in psitins 3 and 6, respectively. W.W. Christie lipidlibrary.acs.rg 2

3 3-Pyridylcarbinyl 4,7-ctadecadienate (4,7-18:2). Sme f the marked ins that lcate the duble bnds wuld be difficult t identify frm first principles, s a mdel spectrum is essential Pyridylcarbinyl 5,8-ctadecadienate (5,8-18:2) this fatty acid is a majr cmpnent f human sebum lipids. As the distance f duble bnds frm the carbxyl grup increases, the expected fragmentatin patterns fr the duble bnds emerge as marked Pyridylcarbinyl 6,9-ctadecadienate (6,9-18:2). Here, and with many f the subsequent spectra in this series, the duble bnds are easily lcated W.W. Christie lipidlibrary.acs.rg 3

4 3-Pyridylcarbinyl 7,-ctadecadienate (7,-18:2) Pyridylcarbinyl 8,11-ctadecadienate (8,11-18:2) - 2 CH 2 OOC Pyridylcarbinyl 9,12-ctadecadienate - see the start f this sectin. 3-Pyridylcarbinyl,13-ctadecadienate (,13-18:2) W.W. Christie lipidlibrary.acs.rg 4

5 3-Pyridylcarbinyl 11,14-ctadecadienate (11,14-18:2) (Christie et al.,1987a) Pyridylcarbinyl 12,15-ctadecadienate (12,15-18:2) Pyridylcarbinyl 13,16-ctadecadienate (13,16-18:2) W.W. Christie lipidlibrary.acs.rg 5

6 3-Pyridylcarbinyl 14,17-ctadecadienate (14,17-18:2). It is pssible even with this last f the ismers t lcate the duble bnds by the specific fragments marked, especially if we lk fr the gaps f amu as well as thse f 26 amu Spectra f 3-pyridylcarbinl esters f many mre methylene-interrupted dienic fatty acids f this type f differing chain lengths are illustrated in ur Archive sectin, but withut interpretatin. Many f these have nt been frmally published elsewhere. Cnjugated Dienic Fatty Acids 3-Pyridylcarbinl esters may nt be the best derivatives fr fatty acids with cnjugated duble bnd systems, and fr example, DMOX derivatives may be better in this instance (see Mass spectra f DMOX derivatives dienic fatty acids), r MTAD adducts f methyl esters are uniquely valuable (see Mass spectra f methyl esters f fatty acids. Part 6. Further derivatizatin), especially fr the cmplex mixtures fund in cmmercial cnjugated linleic acid (CLA) and sme natural samples. Hwever, 3-pyridylcarbinl esters can be useful if authentic standards are available fr cmparisn, especially when ismers are well reslved n the GC clumn. The mass spectrum f 3-Pyridylcarbinyl 9-cis,11-trans-ctadecadienate, the mst abundant natural ismer (e.g. in cws' milk fat), fllws W.W. Christie lipidlibrary.acs.rg 6

7 There is a gap f 52 amu between = 234 and at either end f the cnjugated duble bnd system, with intervals f 14 amu n either side fr cleavage at successive methylene grups. The mlecular in at = is the base peak. 3-Pyridylcarbinyl -trans,12-cis-ctadecadienate In this instance, the diagnstic ins are shifted up by 14 amu frm the previus spectrum, but nt very cnvincingly if a definitive identificatin were t be required. These spectra d nt appear t have been published frmally elsewhere. Bis-Methylene-Interrupted Dienic Fatty Acids It is becming apparent that bis- and plymethylene-interrupted dienic fatty acids are mre cmmn in nature than may have been suppsed. In particular, fatty acids with a 5,9-duble bnd system and their chain elngatin prducts are cmmn in seed ils frm Gymnsperms r in certain marine invertebrates such as spnges. The spectrum f 5,9-18:2 and f sme synthetic fatty acids with the bis-methylene-interrupted duble bnds (useful fr cnfirming fragmentatin mechanisms) fllw next (Christie et al., 1987b). 3-Pyridylcarbinyl 5,9-ctadecadienate (5,9-18:2) (Hierr et al., 1996) W.W. Christie lipidlibrary.acs.rg 7

8 The truly distinctive feature is the in at = 219 (unusual in being dd-numbered) representing cleavage at the centre f the bis-methylene-interrupted duble bnd system. In additin, gaps f 26 amu, between = and 6 and = and 258 help t lcate the duble bnds in psitins 5 and 9, respectively. 3-Pyridylcarbinyl 2,6-ctadecadienate (2,6-18:2) In this spectrum (unpublished), the in at = 177 representing cleavage at the centre f the bismethylene-interrupted duble bnds is the base peak in fact. The expected in at = is missing, but the ins at = 1 and 216 lcate the duble bnd in psitin 6. 3-Pyridylcarbinyl 6,-ctadecadienate (6,-18:2) (Christie et al., 1987b) All the ins that lcate the duble bnds (marked) are easily lcated, and the same is true fr the 7,11-ismer (nt illustrated). It appears that ins diagnstic fr the psitins f the duble bnds becme easier t lcate as they mve further frm the carbxyl grup. With 3-pyridylcarbinyl 8,12-ctadecadienate (8,12-18:2) (ver page) (Christie et al, 1987b), the in representing cleavage at the centre f the bis-methylene-interrupted duble bnds is nw even numbered ( = 2). The same is true f the 9,13-ismer as in 3-pyridylcarbinyl 9,13- eicsadienate illustrated in the Archive pages f this website. W.W. Christie lipidlibrary.acs.rg 8

9 Spectra f 3-pyridylcarbinl esters f many mre bis-methylene-interrupted dienic fatty acids are illustrated in ur Archive sectin, but withut interpretatin. Many f these have nt been frmally published elsewhere. Ply-Methylene-Interrupted Dienic Fatty Acids Fatty acids with mre than tw methylene grups between duble bnds are perhaps less cmmn in nature than bis-methylene-interrupted ismers, but sme examples f mass spectra f 3-pyridylcarbinl esters f synthetic and natural fatty acids f this type are illustrated belw. Spectra frm tw synthetic fatty acids are available (Christie et al.,1987b), and the first f these has been fund naturally in a spnge (Carballeira and Maldna, 1989). 3-Pyridylcarbinyl 6,11-ctadecadienate (6,11-18:2) has three methylene grups between the duble bnds There are prminent ins fr cleavages between the duble bnds, i.e. at = 233 and (ne dd-numbered), and the duble bnds themselves can be lcated by the usual means as marked. W.W. Christie lipidlibrary.acs.rg 9

10 3-Pyridylcarbinyl 7,12-ctadecadienate (7,12-18:2) The spectrum is very similar t the previus, except that the key ins are all shifted by 14 amu upwards, as might be expected. 3-Pyridylcarbinyl 5,11-ctadecadienate (5,11-18:2) has fur methylene grups between the duble bnds and is present in the seeds f Gingk bilba. Its mass spectrum has been published (Wlff et al., 1999)) In this instance, the duble bnds are lcated in the same way as fr islated mnenes, with that fr psitin 5 being determined by the gap f 26 amu between = and 4, and fr psitin 11 by that between = 2 and. Direct cmparisn with the mass spectrum f 5-18:1 is invaluable here, fr cnfirmatin f the psitin f the first duble bnd. 3-Pyridylcarbinyl 5,11- eicsadienate has a very similar spectrum (see the Archive sectin). W.W. Christie lipidlibrary.acs.rg

11 3-Pyridylcarbinyl 6,12-ctadecadienate (6,12-18:2). This spectrum resembles that f the 5,11- ismer except that the diagnstic ins are all 14 amu higher Pyridylcarbinyl 5,13-eicsadienate - frm (Christie et al., 1988). As with the previus, interpretatin f the spectrum is similar t thse f islated mnenes, and this is als true f the next spectrum Pyridylcarbinyl 9,19-hexacsadienate (9,19-26:2) (Christie et al., 19)) W.W. Christie lipidlibrary.acs.rg 11

12 My clleagues and I have encuntered a few lng-chain fatty acids with mre than fur (six) methylene grups between duble bnds and the last tw examples were frm marine invertebrates. Spectra f 3-pyridylcarbinl esters f many mre dienic fatty acids, including sme branchedchain ismers, are illustrated in ur Archive sectin, but withut interpretatin. Many f these have nt been published frmally elsewhere. References Carballeira,.M. and Maldna, M.E. On the islatin f the new fatty acid 6,11-eicsadienic (:2) and related 6,11-dienic acids frm the spnge Euryspngia rsea. Lipids, 24, (1989). Christie, W.W., Brechany, E.Y. and Hlman, R.T. Mass spectra f the piclinyl esters f ismeric mnand dienic fatty acids. Lipids, 22, (1987a). Christie, W.W., Brechany, E.Y., Gunstne, F.D., Lie Ken Jie, M.S.F. and Hlman, R.T. Mass spectra f the piclinyl esters f sme nn-methylene-interrupted ctadecadienic acids. Lipids, 22, (1987b). Christie, W.W., Brechany,E.Y. and Stefanv, K. Silver in high-perfrmance liquid chrmatgraphy and gas chrmatgraphy-mass spectrmetry in the analysis f cmplex fatty acid mixtures: applicatin t marine invertebrates. Chem. Phys. Lipids, 46, (1988). Christie, W.W., Brechany, E.Y., Stefanv, K. and Ppv, S. The fatty acids f the spnge Dysidea fragilis frm the Black Sea. Lipids, 27, (19). Harvey, D.J. Piclinyl esters as derivatives fr the structural determinatin f lng chain branched and unsaturated fatty acids. Bimed. Mass Spectrm., 9, (1982). Hierr, M.T.G., Rbertsn, G., Christie, W.W. and Jh, Y.-G. The fatty acid cmpsitin f the seeds f Ginkg bilba. J. Am. Oil Chem. Sc., 73, (1996). Wlff, R.L., Christie, W.W. and Marpeau, A.M. Reinvestigatin f the plymethylene-interrupted 18:2 and :2 acids f Ginkg bilba seed lipids. J. Am. Oil Chem. Sc., 76, (1999). William W. Christie James Huttn Institute (and Mylnefield Lipid Analysis), Invergwrie, Dundee (DD2 5DA), Sctland Last updated: August 7 th, 13 W.W. Christie lipidlibrary.acs.rg 12

Part 1. Saturated and Branched-Chain Fatty Acids

Mass spectra f DMX derivatives. Part 1. Saturated and branched-chain fatty acids MASS SPECTRA F DMX DERIVATIVES Part 1. Saturated and Branched-Chain Fatty Acids a 4,4-Dimethylxazline (DMX) derivatives