Jain Kavita, Siddam Anjaiah, Marathi Archana, Roy Uzzal, Falck J R, Balazy Michael
New York Medical College, Valhalla, NY 10595, USA.
Free Radic Biol Med. 2008 Aug 1;45(3):269-83. doi: 10.1016/j.freeradbiomed.2008.04.015. Epub 2008 Apr 20.
Fatty acid nitration is a recently discovered process that generates biologically active nitro lipids; however, its mechanism has not been fully characterized. For example, some structural details such as vinyl and allyl isomers of the nitro fatty acids have not been established. To characterize lipids that originated from a biomimetic reaction of *NO(2) with oleic acid, we synthesized several isomers of nitro oleic acids and studied their chromatography and mass spectra by various techniques of mass spectrometry. LC/MS analysis performed on a high resolution micro column detected molecular carboxylic anions of various oleic acid nitro isomers (NO(2)OA). Esterification of NO(2)OA with pentafluorobenzyl bromide and diisopropylethylamine as a catalyst produced a unique isoxazole ester derivative exclusively from allyl NO(2)OA isomers via dehydration of the nitro group at ambient temperatures. This new analytical procedure revealed that *NO(2) generated two vinyl and two allyl isomers of NO(2)OA. The vinyl isomers showed high regioselectivity with the 1.8:1 preference for the 10-NO(2)OA isomer that was absent among allylic isomers. The nitration also generated elaidic acid via cis-trans isomerization and diatereoisomers of vicinal nitro hydroxy, nitro keto and alpha-nitro epoxy stearic acids with high stereo and regioselectivity. Nitration of small unilamelar phospholipid vesicles resulted in several phospholipids containing nitro lipids and elaidic acid amenable to hydrolysis by phospholipase A(2).
脂肪酸硝化是最近发现的一种产生生物活性硝基脂质的过程；然而，其机制尚未完全明确。例如，一些结构细节，如硝基脂肪酸的乙烯基和烯丙基异构体尚未确定。为了表征源自二氧化氮与油酸的仿生反应的脂质，我们合成了几种硝基油酸异构体，并通过各种质谱技术研究了它们的色谱和质谱。在高分辨率微柱上进行的液相色谱/质谱分析检测到了各种油酸硝基异构体（NO₂OA）的分子羧酸阴离子。以五氟苄基溴和二异丙基乙胺为催化剂对NO₂OA进行酯化反应，在室温下通过硝基脱水，仅从烯丙基NO₂OA异构体中产生了一种独特的异恶唑酯衍生物。这种新的分析方法表明，二氧化氮产生了两种乙烯基和两种烯丙基NO₂OA异构体。乙烯基异构体表现出高区域选择性，对10-NO₂OA异构体的偏好为1.8:1，而烯丙基异构体中不存在这种偏好。硝化反应还通过顺反异构化以及邻位硝基羟基、硝基酮和α-硝基环氧硬脂酸的非对映异构体，以高立体选择性和区域选择性生成了反油酸。对小单层磷脂囊泡进行硝化反应，产生了几种含有硝基脂质和反油酸的磷脂，这些磷脂易于被磷脂酶A₂水解。
