New arachidonate-derived lipid mediators: The "isoprostanes". Synthesis and measurement

• Main Author: Adiyaman, Mustafa
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1997
• Subjects: Biochemistry; Organic chemistry; Pharmacology
• ISBN: 9780591311471; 059131147X

Recently, a new class of compounds, the isoprostanes (IP), have been described. These isoprostanes, isomeric with biologically active prostaglandins (PGs), are produced in vivo by a cyclooxygenase (COX) independent free-radical mechanism. The isoprostanes, formed in situ on phospholipids by peroxidation of unsaturated fatty acids such as arachidonic acid (AA), are subsequently released in the free form by the action of phospholipases (PLs). Four groups of isoprostanes (I-IV) have been proposed as potential products of reactive oxygen species (ROS)-initiated peroxidation of AA. One of these isoprostanes, 8-iso-PGF$\sb{2\alpha}$, is a potent vasoconstrictor and has also been identified in minor amounts in the COX-1 and COX-2 induced oxygenation of AA. We present here the total synthesis of isoprostanes and the measurement of these novel endogenous compounds. We have developed a new methodology for the synthesis of isoprostanes which contain five asymmetric centers and have two cis oriented side chains. Our synthetic method uses a radical cyclization to construct the five-membered ring synthons. We have obtained the syn-anti-syn lactones 189 and 193 and the all-syn lactones 188 and 192 as the major products by controlling the radical cyclization process. We have successfully used these key lactone intermediates for the synthesis of IPF$\sb{2\alpha}$-I 2, IPF$\sb{2\alpha}$-II 3, IPF$\sb{2\alpha}$-III 4, IPF$\sb{2\alpha}$-IV (8-iso-PGF$\sb{2\alpha}$) 5 and 8-iso,12-iso-IPF$\sb{2\alpha}$ (12-iso-PGF$\sb{2\alpha}$) 6.* We have identified IPF$\sb{2\alpha}$-I in human urine as the major isoprostane by using the synthetic standard, in combination with gas chromatography/mass spectrometry (GC/MS). ftn*Please refer to the dissertation for diagrams.