MASS SPECTRA OF DERIVATIVES OF ALICYCLIC FATTY ACIDS WITH 5- AND 6-MEMBERED RINGS

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1 MASS SPECTRA OF DERIVATIVES OF ALICYCLIC FATTY ACIDS WITH 5- AD 6-MEMBERED RIGS The dcument des nt aim t be a cmplete accunt f mass spectrmetry f all cyclic fatty acids, but rather is a persnal accunt f ur experience f thse natural fatty acids encuntered during ur research activities and fr which we have spectra available fr illustratin purpses. Spectra f methyl esters, 3-pyridylcarbinl ( piclinyl ) esters, DMOX derivatives and pyrrlidides are described in the same dcument. Where we are aware f prir illustratins f mass spectra in the literature, the apprpriate papers are cited. These ntes are a practical guide rather than a mechanistic accunt. atural fatty acids with 5- and 6-membered rings all have the ring structure in the mega r terminal psitin. The ccurrence and bilgical prperties f cyclic fatty acids have been reviewed by Sébédi and Grandgirard (1989). ω-cyclpentenyl and Cyclpentyl Fatty Acids Fatty acids with a terminal cyclpent-2-enyl miety are fund in high cncentratin in the seed ils f several species frm the plant family Flacurtiaceae, thugh the crrespnding cyclpentyl (saturated species) have been detected at lw levels nly. It is wrth nting that althugh the nitrgen-cntaining derivatives permit lcatin f mst f the structural features with varying degrees f success, nne fix the actual psitin f the duble bnd within the ring. Fr the latter purpse, chemical degradatin, perhaps allied with mass spectrmetry, is required (Christie et al., 1989). Again the mass spectra f the methyl ester derivatives have limited value nly fr characterizatin purpses, althugh the ring structure itself can be detected and cnfirmed (Christie et al., 19). Thus, the mass spectrum f methyl hydncarpate (11-cyclpentenylundecanate) is CH 3 OOC The base peak at = is presumed t be the inized cyclpentene ring per se, but n crrespnding fragment at = 199 is detectable. Instead, an in at = 185 represents the remainder f the mlecule with cleavage beta t the ring (tgether with an in at = 153 fr lss f a methxyl grup frm this in). In the high mass range, the mlecular in is small but distinct, and there is an in representing lss f a methxyl grup frm this (at = 235). W.W. Christie lipidlibrary.acs.rg 1

2 In the mass spectrum f methyl grlate (13-cyclpent-2-enyltridec-6-enate) next, the base peak is again at =, but the in representing cleavage beta t the ring (at = 2) is barely distinguishable in this instance. There is n feature that serves t lcate the duble bnd in the alkyl chain. CH 3 OOC The mass spectrum f methyl 11-cyclpentylundecanate, i.e. with a saturated ring, is smewhat different CH 3 OOC An in representing the ring fragment ( = ) des stand ut, as des an in fr the lss f the ring at = 199 (i.e. cleavage alpha t the ring). Otherwise, the spectrum resembles that f a nrmal saturated ester (ther than the fact that the mlecular in is tw units lwer), and the McLafferty in at = 74 is nw the base peak, fr example. Once mre, in my pinin, 3-pyridylcarbinl esters are by far the best fr characterizatin f fatty acids with cyclpentenyl and cyclpentyl mieties, especially when these are n the terminal carbn (Christie et al., 1989). Fr example, the mass spectrum f 3-pyridylcarbinyl 11- cyclpentylundecanate is illustrated next W.W. Christie lipidlibrary.acs.rg 2

3 92 8 CH 2 OOC In the high mass regin, the mlecular in (at = 345) is fllwed by a relatively clear gap f amu t an in at = 276, representing lss f the cyclpentane ring. Thereafter, there is a regular series f ins 14 amu part fr cleavage at the successive methylene grups. The in fr the charged cyclpentane ring ( = ) is als distinctive. In cntrast, there is the spectrum f the crrespnding DMOX derivative f 11-cyclpentylundecanate O Here, ne needs t use the eye f a true believer t see the gap f amu, between the mlecular in and that at = 238, fr a terminal cyclpentane ring (Zhang et al., 1989). The prblem is that the facile lss f methyl grups frm the DMOX ring results in series f ins in the high mass range ( = 264, 278 and 292) that cnfund the picture (Hamiltn and Christie, 00). Similarly, 3-pyridylcarbinl esters wrk best with cyclpentenyl fatty acids, as illustrated with the mass spectrum f 3-pyridylcarbinyl hydncarpate. Here the gap f amu between the mlecular in and that at = 276 is clearly diagnstic fr lss f the cyclpentene ring, while the inized cyclpentene ring ( = ) is in fact the base peak. W.W. Christie lipidlibrary.acs.rg 3

4 CH 2 OOC In cntrast, there is the spectrum f the DMOX derivative f hydncarpate. In fairness, the gap f amu ( = 238 t 5) fr lss f the terminal ring is a little mre cnvincing, althugh interpretatin is again cnfunded by ins that result frm lss f methyl grups frm the DMOX ring (c.f. = 2), a prblem with all terminally substituted fatty acids. The in representing the cyclpentene ring itself ( = ) is certainly mre abundant in this instance. O Hwever, the pyrrlidide derivative f hydncarpic acid has a much mre useful spectrum - OC W.W. Christie lipidlibrary.acs.rg 4

5 In the high mass regin, the gap f amu between = 238 and 5 fr cleavage f the cyclpentenyl ring can be seen unambiguusly. In all ther respects, the spectrum is very similar t that f the crrespnding DMOX derivative. We als have the spectrum f the C 18 analgue in the Archive pages. either f these spectra appears t have been published frmally elsewhere. Three main ismers with ne duble bnd in the chain are als fund in nature and the spectra f the 3-pyridylcarbinl esters are available in ur Archive pages. The nly ismer where identificatin might be prblematic is 3-pyridylcarbinyl 13-cyclpent-2-enyltridec-4-enate CH 2 OOC The cyclpentene ring is lcated by the gap f amu in the high mass regin f the spectrum as befre. The duble bnd in psitin 4 is recgnized by the fingerprint ins at = 5 and 218, tgether with the in at = 164 f lw intensity relative t that at = (see the riginal reference (Christie et al., 1989) r the sectin f the mass spectrmetry pages n 3- pyridylcarbinl esters f mnenes). Spectra f the DMOX derivatives f tw f the natural cyclpentenyl fatty acids with duble bnds in the chain acids fllw, starting with that f 13-cyclpent-2-enyltridec-4-enate. Fingerprint ins at = 152 and 166 lcate the duble bnd, while the gap f amu between = 264 and 331 defines the cyclpentene ring. O W.W. Christie lipidlibrary.acs.rg 5

6 DMOX derivative f 15-cyclpent-2-enylpentadec-9-enate r hrmelate - O With the last, definitive lcatin f the cyclpentene ring is again prblematic, thugh it shuld be recgnized that each derivative gives a distinctive fingerprint at least (Zhang et al., 1989). T define the lcatin f the duble bnd in the chain, see the sectin f this web site n Mass spectrmetry f DMOX derivatives f mnenes. Hwever, with the last example, it wuld be easy t cnclude frm an apparent gap f 12 amu between = 182 and 194 that the duble bnd was in psitin 8 rather than 9 f the chain. This des nt ccur with the 3-pyridylcarbinl ester r pyrrlidide. This des nt mean that ne derivative is better than anther, ther than in ne particular circumstance but there are times when cnfirmatry evidence is desirable by using anther derivative type. The pyrrlidide derivatives f terminal cyclpent-2-enyl fatty acids give mass spectra that resemble thse f the DMOX derivatives. Hwever, the psitin f the ring is mre clearly defined with the frmer. Fr example, in the spectrum f the pyrrlidide f 13-cyclpent-2-enyltridec-4- enate 264 OC the gap f amu between = 264 and 331 clearly lcates the terminal ring structure, and there are n ins in the regin that cnfund the picture. The duble bnd is lcated frm the fingerprint ins as in the analgus mnene (see ur web pages n Pyrrlidine derivatives f mnenic fatty acids). W.W. Christie lipidlibrary.acs.rg 6

7 Pyrrlidine derivative f 15-cyclpent-2-enylpentadec-9-enate r hrmelate OC M In this example, bth the psitins f the ring and f the duble bnd can be lcated as indicated n the spectrum. Further mass spectra f natural cyclic fatty acids in the frm f the varius derivatives are available, but withut interpretatin, in the Archive Sectins f these web pages. ω Cyclhexyl Fatty Acids ω-cyclhexylundecanic acid is a minr cmpnent f cw s milk fat, althugh it prbably riginates in rumen bacteria, and this was the surce fr the mass spectrum f methyl 11- cyclhexylundecanate (first published by Schgt and Begemann, 1965) - CH 3 OOC The in at = 199 defines the psitin f the cyclhexane ring as illustrated, via fragmentatin adjacent t the ring (as with the cyclpentyl fatty acids abve). The ther fragment in at = 83 is als prminent. The in at = 239 ([M-43] + ) is cmmn in saturated esters and represents a W.W. Christie lipidlibrary.acs.rg 7

8 cmplex rearrangement invlving expulsin f carbns C2 t C4, while that at = 251 is prduced by the lss f the methxyl grup. ω-phenyl Fatty Acids Fatty acids with a terminal phenyl miety are fund in seed ils f the subfamily Arideae f the Araceae and certain species f bacteria. Sme f the available data have been published (Christie, 03). The mass spectrum f methyl 13-phenyltridecanate, which is usually the main cmpnent, is 91 CH 3 OOC There is a distinct mlecular in at = 4, and an abundant in at = 272 reflects the lss f methanl. Hwever, the base peak at = 91 is a trpylium in, which is typical fr spectra f armatic cmpunds. The in at = 181 is presumably frmed by lss f a trpylium frm the in representing [M-32] +. 3-Pyridylcarbinyl 13-phenyl-tridecanate has the mass spectrum. + trpylium in CH 2 OOC W.W. Christie lipidlibrary.acs.rg 8

9 The distinctive and diagnstic feature is a gap f 91 amu between = 2 and 381 ( ) fr lss f the terminal phenyl grup tgether with carbn-13, presumably as the stable trpylium in. Thereafter, there are sequential gaps f 14 amu fr lss f successive methylene grups in the aliphatic chain. The trpylium in per se is the base peak. When there is a duble bnd in the alkyl chain, the spectra f the methyl esters still have the trpylium in r that plus a methyl grup ( = 4) as the base in, but as might be expected, there is nthing that helps t lcate the duble bnd. This is pssible with 3-pyridylcarbinl ester, DMOX and pyrrlidide derivatives (see the web pages dealing with the mass spectra f the apprpriate mnenes fr discussin). Mass spectrum f 3-pyridylcarbinyl 15-phenyl-pentadec-9-enate CH 2 OOC M In additin t the ins that lcate the phenyl miety, the psitin f the duble bnd in the alkyl chain is easily determined frm the ins highlighted. Mass spectrum f the DMOX derivative f 15-phenyl-pentadec-9-enate O W.W. Christie lipidlibrary.acs.rg 9

10 Mass spectrum f the pyrrlidide f 15-phenyl-pentadec-9-enate OC Mass spectra f pyrrlidides and DMOX derivatives als exhibit the gap f 91 amu between the mlecular in and the next abundant in in the high mass regin (t = 278), as illustrated abve, and the trpylium in at = 91 is distinct. Hwever, the spectrum f the DMOX derivatives is cnfused in the high mass range, because f fragmentatins invlving the methyl grup n the hetercyclic ring. When there is a duble bnd in the aliphatic chain in additin t the terminal benzene ring, it can be lcated by means f the nitrgen-cntaining derivatives, r by preparing dimethyl disulfide derivatives (c.f. the spectra f the apprpriate mnenes). Hwever, in this instance the spectrum f the pyrrlidide culd be cnfusing as a gap f 12 amu between = 182 and 194 suggests a duble bnd in psitin 8 rather than 9. Again, this illustrates the value f using mre than ne derivative type fr identificatin purpses. Spectra f mre fatty acids f this type tgether with thse f derivatives f the armatic ferulic and cafeic acids are in the varius Archive pages. Cyclic Fatty Acids Frmed in Frying Oils Fatty acids with internal five- and six-membered ring structures are frmed when vegetable ils are heated t the high temperatures attained during frying r the physical refining prcess. The mechanism f cyclizatin is nw believed t invlve cncerted thermal rearrangements with lss f ne f the duble bnd.. As a hst f basic structures can be frmed frm different fatty acid precursrs, and cis-trans ismerizatin f duble bnds and/r abut the ring als takes place, the range f cyclic prducts is very great. With my clleagues and cllabratrs, we have characterized mst f these, and f curse thers have wrked n the prblem. The chemistry and analyses f these cmpunds are discussed in ur Frying Oil web pages. References Christie, W.W. 13-Phenyltridec-9-enic and 15-phenylpentadec-9-enic acids in Arum maculatum seed il. Eur. J. Lipid Sci. Technl., 5, (03). W.W. Christie lipidlibrary.acs.rg

11 Christie, W.W., Brechany, E.Y. and Shukla, V.K.S. Analysis f seed ils cntaining cyclpentenyl fatty acids by cmbined chrmatgraphic prcedures. Lipids, 24, (1989). Christie, W.W., Rebell, D. and Hlman, R.T. Mass spectrmetry f derivatives f cyclpentenyl fatty acids. Lipids, 4, (19). Hamiltn, J.T.G. and Christie, W.W. Mechanisms fr in frmatin during the electrn impact-mass spectrmetry f piclinyl ester and 4,4-dimethylxazline derivatives f fatty acids. Chem. Phys. Lipids, 5, 93-4 (00). Schgt, J.C.M. and Begemann, P.H. Islatin f 11-cyclhexylundecanic acid frm butter. J. Lipid Res., 6, (1965). Sébédi, J.L. and Grandgirard, A. Cyclic fatty acids: natural surces, frmatin during heat treatment, synthesis and bilgical prperties. Prg. Lipid Res., 28, (1989). Zhang, J.Y., Wang, H.Y., Yu, Q.T., Yu, X.J., Liu, B.. and Huang, Z.H. The structures f cyclpentenyl fatty acids in the seed ils f Flacurtiaceae species by gas chrmatgraphy-mass spectrmetry f their 4,4-dimethylxazline derivatives. J. Am. Oil Chem. Sc., 66, (1989). William W. Christie James Huttn Institute (and Mylnefield Lipid Analysis), Invergwrie, Dundee (DD2 5DA), Sctland Last updated: March 6 th, 14 W.W. Christie lipidlibrary.acs.rg 11

MASS SPECTRA OF DERIVATIVES OF CYCLOPROPYL AND CYCLOPROPENYL FATTY ACIDS

MASS SPECTRA OF DERIVATIVES OF CYCLOPROPYL AD CYCLOPROPEYL FATTY ACIDS The dcument des nt aim t be a cmplete accunt f mass spectrmetry f cyclprpyl and cyclprpenyl fatty acids, but rather is a persnal accunt