Arachidonic acid preparation

The first step in the biosynthesis of eicosanoids from arachidonic acid is generally a lipoxygenation reaction. The resulting hydroperoxides (HPETE s) can undergo reduction to the corresponding alcohols (HETE s). Preparative routes to the 5-, 11-, and 15-HETE s and HPETE s have been developed as oudine below. 

Compounds 111 having structural features of the dual cyclooxygenase (COX)/5-lipooxygenase (5-LO) inhibitor tepoxalin and the 5-LO inhibitor ABT-761 were prepared. Many of these hybrid compounds are potent COX and 5-LO inhibitors two compounds (111, r =McO, R = R" = R = H, R = NH2, R = Me and r = MeO, R = R = Me, R" = R = H, R = Cl) inhibited eicosanoid biosynthesis in an ex vivo assay, but neither improved on the main deficiency of tepoxalin, duration of 5-LO inhibitory activity (99BMCL979). Compounds 111 inhibit the production of arachidonic acid products associated with 5-lipoxygenase and cyclooxygenase and are useful in the treatment of inflammatory disorders (99USP5925769). 

A series of 4-arylpyrimidines that arc amine substituted at pyrimidine C-2 was prepared. FK360 was most effective from this group on both arachidonate-induced cerebral oedema in rats and as an in vitro inhibitor of lipid peroxidation. The authors link effects of FK360 to the arachidonic acid cascade (Kuno et al., 1992). This is an unusual structure. 

A thiazole core has also been utilised by Solvay Pharmaceuticals [309] in the search for a novel bioisosterie replacement of the rimonabant (382) pyrazole core. The affinity of several compounds for the human CBi receptor was determined in transfected CHO cells using tritium-labelled CP 55940. Antagonism was determined in the same cell line by WIN 55212-2-induced release of arachidonic acid. The pK[ of (456) was found to be 6.9, while the p 2 value was measured as 8.7. A series of six 1,2,4-triazole analogues has been prepared by Jagerovic et al. [310], via their corresponding A-acylbenzamides (Table 6.39). 

Methyl and other alkyl esters were prepared in THF, also in high yields.[130] b) Arachidonic acid was converted via its tetrazolide with the aid of oxalyldi(l,2,3,4-tetrazole), prepared in situ, into the methyl ester.[1113... 

Additional hypotheses concerning prostaglandin biosynthesis in P. homomalla resulted from isolation of 11R-HETE (76) from the polar lipid fraction [95]. Apparently, 11R-HETE (76) is also a minor product of incubations of arachidonic acid with acetone powder preparations of P. homomalla [95], In this alternate hypothesis (Scheme 8), an 11-hydroxy or 11-hydroperoxy-8,9-allene oxide intermediate is formed from a sequence of oxidations at C8 and Cll. Opening of the allene oxide to a transient C8 earboeation induces eycli-zation with a consequent addition of water to C15. This proposed pathway leads initially to formation of PGE2 (16 or 38), which following acetylation, elimination of acetic acid from Cl 1-12, and esterification, forms the observed major natural product in the coral, 15-acetoxy methyl PGA2 (36 or 54). Notably, if... 

Microwave heating has also been employed for performing retro-Diels-Alder cycloaddition reactions, as exemplified in Scheme 6.94. In the context of preparing optically pure cross-conjugated cydopentadienones as precursors to arachidonic acid derivatives, Evans, Eddolls, and coworkers performed microwave-mediated Lewis acid-catalyzed retro-Diels-Alder reactions of suitable exo-cyclic enone building blocks [193, 194], The microwave-mediated transformations were performed in dichloromethane at 60-100 °C with 0.5 equivalents of methylaluminum dichloride as catalyst and 5 equivalents of maleic anhydride as cyclopentadiene trap. In most cases, the reaction was stopped after 30 min since continued irradiation eroded the product yields. The use of short bursts of microwave irradiation minimized doublebond isomerization. 

Elucidation of the physiological role of arachidonic acid 13 and other polyunsaturated fatty acids, particularly the role of all Z-4,7,10,13,16,19-decosahexaenoic acid 14, found in brain, required the corresponding stable-isotope labelled material1011. The deuteriated phosphonium salt 15, the key intermediate used in the synthesis of title compound 16 (equation 8), has been prepared in 19% overall yield12 starting with ethanol-D6 (equation 7). 

Platelet Inhibition Ginger extract has been found to inhibit platelet aggregation induced by arachidonic acid, epinephrine, ADP, and collagen (Srivastava 1984). The extract s ability to inhibit cyclooxygenase activity and thromboxane levels correlated well with inhibition of platelet aggregation (Srivastava 1984 Mustafa et al. 1993). The type of preparation used also affects platelet inhibition, because roasted and charcoal of ginger were effective, while ether extracts of raw and dried ginger were not (Wu et al. 1993). 

Much early effort in 5-LO inhibition centered on substrate and product analogues. One goal, especially of the Corey group at Harvard, was to study the 5-LO reaction by creating mechanism-based irreversible inhibitors, or by removing the substrate protons which are abstracted by the enzyme. These approaches, which included preparation of acetylenic, methylated, cyclized, or thia-analogues of arachidonic acid, and cyclopropyl analogues... 

A common problem with gap junction measurements is a rundown of gj in these preparations, for example in neonatal rat heart cells Schmilinsky-Fluri et al. [1990] found a decrease in g, of 16.4% in 6 min which could be antagonized by addition of a phospholipase inhibitor, 20 pmol/l bromophenacyl bromide, to 1.8% within 6 min. They suggested that endogenous arachidonic acid is involved in spontaneous uncoupling. Others favored a washout of ATP and cyclic nucleotides as a possible cause and prevented their preparations from spontaneous uncoupling by addition of ATP, GTP or cAMP to the pipette solution [Miiller et al., 1997a, b]. 

Lynch M. A. and Voss K. L. (1990). Arachidonic acid increases inositol phospholipid metabolism and glutamate release in synaptosomes prepared from hippocampal tissue. J. Neurochem. 55 215-221. 

This strategy to prepare rran.r,as-configurated functionalized dienes like 34 has elegantly been exploited for syntheses of HETEs (hydroxyeicosatetraenoic acids) and leukotrienes 27). These metabolites of arachidonic acid have received much attention due to thek biological activity. Syntheses of HETEs, for instance, follow the principle outlined in Eq. 12 with the acid catalysed ring opening of homofuran derivatives 36 to 37 as the stereoselective key step. 

This reagent does not react with double bonds, as demonstrated when fluorooleic acids were prepared from the corresponding hydroxyoleic acids and incorporated by enzymes into living cells163. Acetylenes do not react with DAST either, but ynones do and produce difluoroacetylenes164. The reaction was used by Kobayashi and coworkers to prepare difluoroleukotriene 16 with similar biological effects to arachidonic acid (equation 91)165. 

Measurement of Arachidonic Acid Release. The prelabeled platelet preparation above is preincubated with 10 p,M indomethacin (added to prevent conversion of arachidonic acid to prostanoids) for 1-2 min at 37°C and with 1 mM CaCl2 for an additional 1 min. Then platelet activating factor, usually at 1 x 10 8 to 1 x 10 9 M (final concentration), dispersed in 0.005% BSA, is added and the incubation is allowed to continue for 2 min. At this point, sufficient chloroform and methanol are added to make a final concentration of chloroform-methanol-water of 1 2 0.8, v/v. Then 0.5 ml of chloroform and 0.5 ml of 0.5 mM EGTA in 2M KC1 are added. The entire mixture is... 

Calibration Standard curves are prepared for added linoleic acid, linolenic acid, arachidonic acid and internal standards. Results are calculated using the ratio of the peak-height of the 18 2(9-cis,l 1-trans) biological isomer to that of the internal standard and multiplying by the concentration of the internal standard added. 

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