Leukotriene A4 may be metabolized to 5(S),6(R)‐ and 5(S),6(S)‐dihydroxy‐7,9‐trans‐11,14‐cis‐eicosatetraenoic acids by enzymatic or non‐enzymatic hydrolysis. Incubation of human platelet suspensions with these dihydroxy acids led to the formation of lipoxin A4 and 6(S)‐lipoxin A4 via lipoxygenation at C‐15. Furthermore, human platelets converted the two 5(R),6(S)‐ and 5(R),6(R)‐dihydroxy‐7,9‐trans‐11,14‐cis‐eicosatetraenoic acids to tetraene‐containing trihydroxyeicosatetraenoic acids. In contrast, leukotrienes C4, D4 and E4 were not transformed to cysteinyl‐lipoxins, Time‐course studies of leukotriene A4 metabolism in human platelet suspensions indicated lipoxin formation via two pathways: (i) direct conversion of leukotriene A4, leading to formation of the lipoxin intermediate 15‐hydroxy‐leukotriene A4; and (ii) 15‐lipoxygenation of the 5(S),6(R)‐ and 5(S),6(S)‐dihydroxyeicosatetraenoic acids. The results demonstrate that lipoxygenation at C‐15 of 5,6‐dihydroxy‐7,9,11,14‐eicosatetraenoic acids may be an alternative novel pathway for platelet‐dependent lipoxin formation.
Evidence for the composition and structure of 2 is already provided by the 'H NMR spectrum and the mass spectrum. Equivalent pentamethylcyclopentadienyl(6 = 2.01) and NH (6 = 13.4) groups are found. The molecular ion (m/z 608) is observed with 100% relative intensity in the mass spectrum. In the field-ionization mass spectrum, only the signal of [ M + 1]@ (mi-. 609) appears. The IR spectrum shows two of the three ( 2 A , 1 A') absorptions (3357 and 3345 cm-') expected for C, symmetry. We assign these to the N-H valence vibrations.Single crystals suitable for an X-ray structure analysis (Fig. I)['] were obtained by recrystallization from n-hexane. 11/12. The CdrbOnatlOn of the mixture of rhreo diols 8 and 9 was simpler, since it occurred within 1.5 h at 20 "C following one addition of N,N'-carbonyldiimidazole (1 70 mg. 5.0 equiv.). Extraction and chromatographic separation of the two yellow crystalline rhreo carbonates 11 and 12 were performed as described above for 10 (I1 + 12: ll5.9mg. 85% overall yield, 11:12 = 90: 10).
Die hoch diastereoselektive Osmylierung einer C C‐Bindung in Nachbarschaft zu einem Komplexfragment ist der Schlüsselschritt des Aufbaus von 2 aus dem Butadien(tricarbonyl)eisen‐Komplex 1. Die Diole 2 lassen sich leicht in 3, Schlüsselverbindungen der Synthese von 5,6‐DiHETE und Lipoxin A4 umwandeln. R = SiPh2tBu; R′ = Me; E = CO2Me.
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