980 Eur. J. Lipid Sci. Technol. 2011, 113, 980–984 Research Article Fatty acids of Thespesia populnea: Mass spectrometry of picolinyl esters of cyclopropene fatty acids* Gerhard Knothe1, Umer Rashid2, Suzana Yusup2 and Farooq Anwar3,4 1 National Center for Agricultural Utilization Research, Agricultural Research Service, U.S. Department of Agriculture, Peoria, IL, USA 2 Chemical Engineering Department, Universiti Technologi PETRONAS, Bandar Sari Iskandar, Tronoh, Perak, Malaysia 3 Department of Chemistry and Biochemistry, University of Agriculture, Faisalabad, Pakistan 4 Faculty of Food Science and Technology, Universiti Putra Malaysia, Serdang, Selangor, Malaysia Thespesia populnea belongs to the plant family of Malvaceae which contain cyclopropane and cyclopropene fatty acids. However, previous literature reports vary regarding the content of these compounds in Thespesia populnea seed oil. In this work, the content of malvalic acid (8,9-methylene- 9-heptadecenoic acid) in the fatty acid profile of Thespesia populnea seed oil was approximately 7% by GC. Two cyclopropane fatty acids were identified, including dihydrosterculic acid. The methyl and picolinyl esters of Thespesia populnea seed oil were also prepared. The mass spectrum of picolinyl malvalate was more closely investigated, especially an ion at m/e 279, which does not fit the typical series of ions observed in picolinyl esters. It is shown that this ion is caused by cleavage at the picolinyl moiety and contains the fatty acid chain without the picolinyl moiety. This type of cleavage has previously not been observed prominently in picolinyl esters and may therefore be diagnostic for picolinyl esters of cyclopropene fatty acids. The NMR spectra of Thespesia populnea methyl esters are also discussed. Practical applications: The work reports the fatty acid composition of Thespesia seed oil whose derivatives have not yet been extensively utilized for industrial purposes, for example, biodiesel. Knowing this composition is essential for understanding potential uses and, for example, in case of biodiesel the fuel properties. Besides this issue, some data (mass spectrometry and NMR) crucial for obtaining the composition information are analyzed in detail. The biodiesel properties of methyl esters of Thespesia populnea will be reported separately. Keywords: GC / MS / Nuclear magnetic resonance / Thespesia populnea Received: January 4, 2011 / Revised: March 24, 2011 / Accepted: April 12, 2011 DOI: 10.1002/ejlt.201100004 1 Introduction malvalic acid (8,9-methylene-8-heptadecenoic acid) in its seed oil [9]. Thespesia populnea belongs to the Malvaceae Several plant families whose oils contain cyclic fatty acids are family and, accordingly, its seed oil is known to contain known. Prominent representatives containing cyclopropene cyclopropane and cyclopropene fatty acids [5, 6, 10]. Both and/or cyclopropane fatty acids are Sterculaceae, malvalic acid and sterculic acid (9,10-methylene-9-octade- Bombacaceae, and Tiliceae, Sapindaceae besides Malvaceae cenoic acid) as well as dihydrosterculic acid (9,10-methylene and others as well as some bacteria [1–7]. Eight cyclopropyl octadecanoic acid) have been reported in Thespesia populnea fatty acids, including several novel compounds, were ident- [10], while an earlier report [11] does not mention the pres- ified by GC–MS in walnut oil [8]. One species, Gnetum ence of cyclic fatty acids and another gives them combined as gnemon, was even reported to contain approximately 39% sterculic acid [3]. Correspondence: Dr. Gerhard Knothe, USDA/ARS/NCAUR, 1815 N. à Disclaimer: Mention of trade names or commercial products in this University St., Peoria, IL 61604, USA publication is solely for the purpose of providing specific information and E-mail: [email protected] does not imply recommendation or endorsement by the US Department of Fax: þ1-309-681-6524 Agriculture. USDA is an equal opportunity provider and employer. ß 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.ejlst.com Eur. J. Lipid Sci. Technol. 2011, 113, 980–984 Fatty acids of Thespesia populnea 981 During our ongoing investigation of potential feedstocks for equipped with a Agilent 5973 mass selective detector. biodiesel [12, 13], defined as the mono-alkyl esters of veg- Components were identified by comparison of retention etable oils or animal fats although other lipid feedstocks can times and mass spectra with authentic samples. also be used, we also became interested in Thespesia populnea. High-resolution MS was carried at the University of The fatty acid profile of a feedstock for biodiesel is generally Minnesota MS Facility (Minneapolis, MN) using a DB-5 identical with that of the biodiesel fuel and is largely respon- column on a Hewlett-Packard Series II 5890 gas chromato- sible for the fuel properties. Therefore, the fatty acid profile is graph and Finnigan MAT 95 double-focusing high-resol- essential when considering suitability of a feedstock for bio- ution mass spectrometer. diesel production. Here we report on the fatty acid profile of NMR spectra were acquired on a on a Bruker (Billerica, Thespesia populnea seed oil, also in light of the aforementioned MA) Avance 500 spectrometer operating at 500 MHz 1 13 inconsistent results. ( H-NMR) or 125 ( C-NMR) with CDCl3 as solvent. The mass spectra of picolinyl esters of cyclopropene fatty acids, namely malvalic and sterculic acids, have been dis- 3 Results and discussion cussed in the literature [14, 15]. However, there are discrep- ancies in this literature regarding some aspects of these Fatty acid profile: Previous literature on the fatty acid profile of spectra. In the course of identifying the various fatty acids Thespesia populnea seed oil shows some disagreements or in Thespesia populnea oil and its methyl esters, we analyzed the variations. While one report [11] does not even mention corresponding picolinyl esters by GC with a FID (GC) and cyclopropene or cyclopropane fatty acids, another report GC–MS. In light of the aforementioned discrepancies in the indicates 2.5% malvalic and 1.6% sterculic acid with 0.9% literature, we also report on the mass spectrum of picolinyl combined dihydrosterculic acid/C18:3v3 [12] while another malvalate. As a third aspect of this work, the essential features 1 13 [3] reports up to 8% cyclopropenoid acids (given as sterculic of the H- and C-NMR spectra of the methyl esters of acid). The fatty acid profile of Thespesia populnea oil as Thespesia populnea are briefly discussed. obtained here is given in Table 1 and shows malvalic acid at approximately 7% (6.8% as determined by GC). 2 Materials and methods Furthermore, two cyclopropane fatty acids were identified here which contrasts with another report [12] in which two The seeds from fully ripened Milo (Thespesia populnea L.) cyclopropene fatty acids (malvalic and sterculic) and one fruits were collected in the vicinity of the University of cyclopropane fatty acid (dihydrosterculic) were reported. Karachi, Karachi, Pakistan. The oil from the seeds was With the exception of a greater amount of palmitic acid found extracted with hexane in a Soxhlet extractor. The oil content here and malvalic acid as discussed above, the fatty acid of the seeds determined from this procedure is approximately profile determined in this work largely agrees with that dis- 20 wt%. cussed in the literature. Thespesia populnea methyl esters (TPME) were synthes- MS: Figure 1 shows the EI mass spectrum of picolinyl ized by a conventional transesterification procedure at 608C malvalate as obtained by GC–MS analysis. It largely agrees with a 6:1 molar ratio of alcohol/vegetable oil and 1% sodium methoxide as catalyst for 1 h. The product was purified by washing with water until the wash water showed a neutral pH, Table 1. Fatty acid profile of Thespesia populnea as determined by removing the methanol by rotary evaporation and drying with GC. Components are given in order of elution. The order of elution is magnesium sulfate. the same for picolinyl esters when using the same GC conditions Picolinyl esters of Thespesia populnea and standard fatty (however, analysis time extended) acids (palmitic, stearic, oleic, linoleic) were synthesized by a procedure available at the Lipid Library [16]. The picolinyl Fatty acid Amount (%) esters of the standard fatty acids were used to verify identity Tetradecanoic (Myristic) 0.5 and retention times of the components of picolinyl esters of Hexadecanoic (Palmitic) 26.8 Thespesia populnea. 9(Z)-Hexadecenoic (Palmitoleic) 0.7 GC for fatty acid profile analysis was carried out with an 9,10-Methylenehexadecanoic 0.9 Agilent 6890 gas chromatograph equipped and a Supelco Octadecanoic (Stearic) 4.1 (Bellefonte, PA) SP–2380 capillary column (30 m  8,9-Methylene-8-heptadecenoic (Malvalic) 6.8 0.25 mm inner diameter  0.2 mm film thickness). The oven 9(Z)-Octadecenoic (Oleic) 15.7 temperature ramp program was 1508C for 15 min, 150– 11(Z)-Octadecenoic (Asclepic) 1.8 2108Cat28C/min, and then ballistic heating to 2208C with 9(Z),12(Z)-Octadecadienoic (Linoleic) 39.2 9.10-Methyleneoctadecanoic (Dihydrosterculic) 1.5 a 5 min hold with He flow rate of 0.8 mL/min and 15 psi Eicosanoic (Arachidic) 0.5 (217.6 bar) pressure. For mass spectrometric analysis by Tetracosanoic (Lignoceric) 0.5 electron ionization (EI) of the picolinyl esters, analysis was Other 1.2 carried out using the same column in an Agilent 6890 GC ß 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.ejlst.com 982 G. Knothe et al. Eur. J. Lipid Sci. Technol. 2011, 113, 980–984 92 have been virtually no reports on such a fragment being observed prominently in the mass spectra of the picolinyl esters of fatty compounds. Therefore, the question arises if m/z 279 corresponds to C H NO (cleavage between the Abundance 17 29 2 cyclopropenyl moiety and the terminal CH3)orC18H31O2 108 (cleavage of the picolinyl moiety; in case of picolinyl malva- 164 þ 55 67 81 late 279 ¼ 371 (M ) – 92). To clarify this issue, high-resol- 272 279 ution MS was carried out on a sample of picolinyl esters of 370 121 151 206 286 328 Thespesia populnea oil.