Yurawecz M P, Roach J A, Sehat N, Mossoba M M, Kramer J K, Fritsche J, Steinhart H, Ku Y
U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition, Washington, DC 20204, USA.
Lipids. 1998 Aug;33(8):803-9. doi: 10.1007/s11745-998-0273-z.
The identity of a previously unrecognized conjugated linoleic acid (CLA) isomer, 7 trans, 9 cis-octadecadienoic acid (18:2) was confirmed in milk, cheese, beef, human milk, and human adipose tissue. The 7 trans, 9 cis-18:2 isomer was resolved chromatographically as the methyl ester by silver ion-high-performance liquid chromatography (Ag+-HPLC); it eluted after the major 9 cis, 11 trans-18:2 isomer (rumenic acid) in the natural products analyzed. In the biological matrices investigated by Ag+-HPLC, the 7 trans, 9 cis-18:2 peak was generally due to the most abundant minor CLA isomer, ranging in concentration from 3 to 16% of total CLA. By gas chromatography (GC) with long polar capillary columns, the methyl ester of 7 trans, 9 cis-18:2 was shown to elute near the leading edge of the major 9 cis, 11 trans-18:2 peak, while the 4,4-dimethyloxazoline (DMOX) derivative permitted partial resolution of these two CLA isomers. The DMOX derivative of this new CLA isomer was analyzed by gas chromatography-electron ionization mass spectrometry (GC-EIMS). The double bond positions were at delta7 and delta9 as indicated by the characteristic mass spectral fragment ions at m/z 168, 180, 194, and 206, and their allylic cleavages at m/z 154 and 234. The cis/trans double-bond configuration was established by GC-direct deposition-Fourier transform infrared as evidenced from the doublet at 988 and 949 cm(-1) and absorptions at 3020 and 3002 cm(-1). The 7 trans, 9 cis-18:2 configuration was established by GC-EIMS for the DMOX derivative of the natural products examined, and by comparison to a similar product obtained from treatment of a mixture of methyl 8-hydroxy- and 11-hydroxyoctadec-9 cis enoates with BF3 in methanol.
一种此前未被识别的共轭亚油酸（CLA）异构体——7反式，9顺式-十八碳二烯酸（18:2）在牛奶、奶酪、牛肉、人乳和人体脂肪组织中得到了确认。7反式，9顺式-18:2异构体通过银离子高效液相色谱法（Ag+-HPLC）以甲酯形式进行色谱分离；在分析的天然产物中，它在主要的9顺式，11反式-18:2异构体（瘤胃酸）之后洗脱。在通过Ag+-HPLC研究的生物基质中，7反式，9顺式-18:2峰通常归因于最丰富的次要CLA异构体，其浓度占总CLA的3%至16%。通过使用长极性毛细管柱的气相色谱法（GC），7反式，9顺式-18:2的甲酯显示在主要的9顺式，11反式-18:2峰的前沿附近洗脱，而4,4-二甲基恶唑啉（DMOX）衍生物使这两种CLA异构体得到部分分离。通过气相色谱-电子电离质谱法（GC-EIMS）分析了这种新CLA异构体的DMOX衍生物。双键位置在δ7和δ9处，如m/z 168、180、194和206处的特征质谱碎片离子及其在m/z 154和234处的烯丙基裂解所示。顺式/反式双键构型通过气相色谱-直接沉积-傅里叶变换红外光谱确定，988和949 cm(-1)处的双峰以及3020和3002 cm(-1)处的吸收证明了这一点。通过GC-EIMS确定了所检测天然产物的DMOX衍生物的7反式，9顺式-18:2构型，并与通过在甲醇中用BF3处理8-羟基-和11-羟基十八碳-9顺式烯酸甲酯混合物得到的类似产物进行了比较。
