Part 1. Nicotinate Derivatives

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Pamela Ellis
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1 Mass spectra f fatty alchls. Part 1. ictinate derivatives. MASS SPECTRA OF FATTY ALCOHOLS Part 1. ictinate Derivatives Fatty alchls can be characterized by GC-MS mst readily as the nictinate derivatives, first described by Vetter and Meister (1981). These are structurally analgus t 3-pyridylcarbinl esters and fragment in much the same way. Indeed, with alkyl mieties f the same basic structure, nictinates and 3-pyridylcarbinl esters have identical mlecular weights. The tw mst abundant ins at = 7 and crrespnd t fragmentatin at the carbxyl miety. Thereafter, interpretatin f spectra is very similar t that fr 3-pyridylcarbinl esters. ictinates are als very useful fr structural determinatin f diacylglycerls and related lipids. a 7 a D.J. Harvey was respnsible fr much f the early wrk n nictinates, and his review article is mst valuable (Harvey, 1992). The preparatin prcedure used in ur labratry is described belw. The mass spectra f the nictinates f fatty alchls illustrated belw were btained in a study f fish waxes (Jh et al., 1995). Saturated and Branched-Chain Fatty Alchls The mass spectrum f the nictinate derivative f hexadecanl is illustrated first As with 3-pyridylcarbinl esters, interpretatin is easiest if we start with the mlecular in and wrk backwards (see the web pages n 3-Pyridylcarbinl esters f saturated and branched-chain fatty acids ). There is a gap f 15 amu fr lss f the terminal methyl grup t = 332, and then a series f ins 14 amu apart fr fragmentatins at successive methylene grups, until the characteristic ins at = and 7 are reached. W.W. Christie lipidlibrary.acs.rg 1

2 Mass spectra f fatty alchls. Part 1. ictinate derivatives. The same features are seen in the mass spectrum f the nictinate derivative f ctadecanl Branched fatty alchls can als be identified by this means in a similar manner t 3- pyridylcarbinl esters, thus in the spectrum f the nictinate derivative f 14-methyl-hexadecanl (anteis-) the gap f 28 amu between = 4 and 332 reflects cleavage n either side f the carbn carrying the methyl grup. As might be expected, this gap is shifted t between = 318 and 346 in the spectrum f the is-ismer (15-methyl-hexadecanl) next W.W. Christie lipidlibrary.acs.rg 2

3 Mass spectra f fatty alchls. Part 1. ictinate derivatives. Mnenic Fatty Alchls The mass spectrum f the nictinate derivative f ctadec-9-en-1-l fllws Again, the spectrum resembles that fr a 3-pyridylcarbinl ester (see the web pages n 3-Pyridylcarbinl esters f mnenic fatty acids ). The duble bnd is lcated by the gap f 28 amu between = 234 and 2, while the dublet at = 274 and 288 are invaluable guides (identical ins are present in the spectrum f 3-pyridylcarbinyl leate). The mass spectrum f the nictinate derivative f ctadec-11-en-1-l Here, the diagnstic ins are shifted upwards by 28 amu, i.e. fr the duble bnd t between = 262 and 288, with the dublet at = 392 and 316. A further shift upwards f 28 amu fr the diagnstic ins is then seen in the spectrum f the nictinate f eics-13-en-1-l (ver page) - W.W. Christie lipidlibrary.acs.rg 3

4 Mass spectra f fatty alchls. Part 1. ictinate derivatives Di- and Plyenic Fatty Alchls The spectra reprted here were frm the first definitive finding f such fatty alchls in a fish il (Jh et al. (1995)). The mass spectrum f the nictinate derivative f ctadeca-9,12-dien-1-l (the analgue f linleic acid) is The duble bnds in psitins 9 and 12 can be lcated by the gaps f 26 amu between = 234 and 2, and 274 and, respectively. On the ther hand, the limited infrmatin available suggests that a gap f 12 amu, analgus t that fund with DMOX derivatives may be mre useful with nictinates, i.e. frm = 234 t 246, and 274 t 286, respectively. W.W. Christie lipidlibrary.acs.rg 4

5 Mass spectra f fatty alchls. Part 1. ictinate derivatives. In the mass spectrum f the nictinate derivative f ctadeca-11,14-dien-1-l, the diagnstic ins are again shifted upwards by 28 amu frm the previus example The mass spectrum f the nictinate derivative f eics-5,8,11,14,17-pentaen-1-l Here, nly the terminal duble bnds can be lcated with cnfidence, and these by the gaps f amu fr the methylene grups fllwed by the duble bnd, i.e. frm = 284 t 324, and 324 t 364, fr the duble bnds in psitins 14 and 17 respectively. The mass spectrum f the nictinate derivative f dcs-7,,13,16,19-pentaen-1-l W.W. Christie lipidlibrary.acs.rg 5

6 Mass spectra f fatty alchls. Part 1. ictinate derivatives. Again, the duble bnds in psitins 13, 16 and 19 nly can be lcated frm the gaps f amu between = 272 and 312, 312 and 352, and 352 and 392 respectively. There has been a suggestin in the literature that rather than preparing 3-pyridylcarbinl esters f fatty acids fr structural analysis, better results might be btained by reducing them t the aliphatic alchls and then preparing nictinates fr mass spectrmetry. Frm my admittedly limited experience f nictinates relative t piclinyl esters, I have t disagree. Alkan-2-ls Frm the limited number f mass spectra available t us, thse f nictinates f alkan-2-ls are almst indistinguishable in terms f which ins are frmed frm thse f alkan-1-ls. Fr example, the mass spectrum f the nictinate f hexadecan-2-l is illustrated next CH 3 COOCH Essentially the same ins are present in the spectra f bth ismers, but their relative abundances in the spectrum f the 2-alkanl derivative are lwer in the high mass range. In cntrast, 1- and 2- alkanls are readily distinguishable as the trimethylsilyl ether derivatives (see the apprpriate web page). Diacylglycerls Derived frm Phsphlipids A cmmn apprach t the analysis f phsphlipids cnsists in enzymatic hydrlysis t the diacylglycerls fllwed by cnversin t UV-absrbing derivatives fr separatin by liquid chrmatgraphy. While mst such derivatives ffer little useful structural infrmatin when subjected t mass spectrmetry, nictinates are an imprtant exceptin. t nly d they permit identificatin f which fatty acid is esterified t each psitin, but they allw lcatin f the duble bnds in the fatty acyl chains. Separatins can als be mnitred by UV absrptin. The fllwing spectra were btained by separatin f mlecular species by reversed-phase HPLC n a basedeactivated ODS clumn, with particle-beam electrn-impact mass spectrmetry (Dbsn et al., 1998). The spectra belw have been adapted frm this paper, where much mre detailed interpretatin is ffered than is apprpriate here. W.W. Christie lipidlibrary.acs.rg 6

7 Mass spectra f fatty alchls. Part 1. ictinate derivatives. Fr example, the mass spectrum f the nictinate derivative f 1,2-dilein is illustrated first H C OOC x There is an abundant mlecular in, tgether with the ins at = 6/7 and fr fragmentatins at the nictinyl miety. Ins at = 444 ([M-RCOO] + ) and 462 ([M-RCO+2] + ) establish the size f the acyl mieties. The distinctive fragments shwn serve t lcate the duble bnds in the chain. It is ntewrthy that there is n dubiety abut the mlecular in. ext fllw the mass spectra f the nictinate derivatives f bth 1-palmityl-2-leyl-glycerl and 1-leyl-2-palmityl-glycerl H C OOC x / H 198 C OOC / x W.W. Christie lipidlibrary.acs.rg 7

8 Mass spectra f fatty alchls. Part 1. ictinate derivatives. The spectra are qualitatively similar, but differ in the relative abundance f specific ins that serve t determine the nature f the acyl-chains, specifically at = 436 (M-RCO+2), and 461 (M-R CO+1; nt at = 462 as fr dilein). Mass spectrum f nictinate derivative f 1,2-palmityl/linleyl-glycerl, in which the reverse ismers may be present, althugh nly ne frmula is illustrated H C OOC x and lastly, this may be true als fr the nictinate f 1,2-linleyl/linlenyl-glycerl H C OOC C OOCH x / 648/ /7 4/2 458/ 512/4 499/ Preparatin f ictinates The fllwing methd was used t prepare the nictinate derivatives fr the abve spectra (Dbsn et al. (1998)). It was adapted frm a prcedure by Zllner and Schmid (1996). Prtcl: At ºC,, -dicyclhexylcarbdiimide (Cautin carcingenic!) ( mg) was added t a slutin f fatty alchls (up t 2 mg), nictinic acid ( mg) and 4- dimethylaminpyridine (2 mg) in dichlrmethane (3 ml). After 5 minutes, the mixture was allwed t warm t rm temperature and left vernight. Hexane (2 ml) was then added and the prduct filtered thrugh a cttn wl plug pre-washed with hexane. After taking t dryness, the prduct was purified by slid-phase extractin thrugh a bnded H 2 clumn. After pre-washing the clumn with hexane, the prduct was applied in hexane and washed with hexane (8 ml). The required prduct was recvered by elutin with hexane-acetne (95:5, v/v; ml). W.W. Christie lipidlibrary.acs.rg 8

9 Mass spectra f fatty alchls. Part 1. ictinate derivatives. We have sme spectra f further nictinate derivatives f fatty alchls n file in ur Archive pages, but withut interpretatin. References Dbsn, G., Itabashi, Y., Christie, W.W. and Rbertsn, G.W. Liquid chrmatgraphy with particle-beam electrn-impact mass spectrmetry f diacylglycerl nictinates. Chem. Phys. Lipids, 97, (1998). Harvey, D.J. Mass spectrmetry f piclinyl and ther nitrgen-cntaining derivatives f lipids. In: 'Advances in Lipid Methdlgy - One', pp. 19- (edited by W.W. Christie, Oily Press, Ayr) (1992). Jh, Y.-G., Brechany, E.Y. and Christie, W.W. Characterizatin f wax esters in the re il f the amber fish Serila aurevittata, by silver in high-perfrmance liquid chrmatgraphy. J. Am. Oil Chem. Sc., 72, (1995). Vetter, W. and Meister, W. ictinates as derivatives fr the mass spectrmetry investigatin f lng chain alchls. Org. Mass Spectrm., 16, (1981) Zllner, P. and Schmid, R. Utility f nictinyl derivatives in structural studies f mn- and diacylglycerls by GC/MS. Part 3. Applicatin t acylglycerls with methyl branchings and epxy and cyclprpyl rings. J. Mass Spectrm., 31, (1996). William W. Christie James Huttn Institute (and Mylnefield Lipid Analysis), Invergwrie, Dundee (DD2 5DA), Sctland Last updated: September 2 nd, 13 W.W. Christie lipidlibrary.acs.rg 9

Part 3. Dienoic Fatty Acids

Part 3. Dienoic Fatty Acids 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