Synthesis of 9(12)-oxy-8, 11, 15-trihydroxyeicosa-5, 13-dienoic acid from arachidonic acid by soybean lipoxygenase-2

Emergence of 2,3,5-trisubstituted tetrahydrofuran natural products and their synthesis

The emergence of various 2,3,5-trisubstituted tetrahydrofuran natural products in the recent literature and their synthesis is the focus of this review. These molecules exhibit varied bioactivities and have garnered the interest of several synthetic chemists owing to their efficient synthesis. A few of them have been synthesized and their absolute stereo structure has been confirmed for the first time. These will be appealing candidates in future synthetic investigations along with the untouched molecules. Thus, this compilation will reveal these molecules for expansion of their diversity within the realm of both synthesis and bioactivity studies.

A nomenclature system for isofurans

Recently, the isolation of a new class of human arachidonic acid oxidation products, the isofurans, was reported. These are produced in vivo by a free radical mechanism independent of the cyclooxygenase enzymes. Because these compounds are tetrahydrofuran derivatives that are related biosynthetically to the isoprostanes, they were termed isofurans. There are eight different isofuran regioisomers, each of which can exist as 16 racemic diastereomers. Thus, 256 enantiomerically-pure isofurans can be formed. These molecules are of interest as measurement of isofurans provides a sensitive index of free-radical induced lipid peroxidation in vivo under conditions of elevated oxygen tension. They also, in analogy to isoprostanes, may have potent biological activity. To explore this, the chemical synthesis of the IsoFs has been initiated. As a result, there is a need for a systematic nomenclature for this class of natural products. A facile system that will allow the ready differentiation of each of the isomeric structures comprising the family of isofurans is presented.

Characterization of the cytosolic epoxide hydrolase-catalyzed hydration products from 9,10:12,13-diepoxy stearic esters

In a previous report we hypothesized that diepoxy fatty methylesters are metabolized to tetraols and/or tetrahydrofurandiols through an epoxydiol intermediate. In this study, p-nitrophenyldiepoxystearate was incubated with affinity-purified liver cytosolic epoxide hydrolase and product formation was monitored by reverse phase HPLC. The diepoxystearate was converted to the corresponding 9,10,12,13-tetraol using a concentrated enzyme (greater than or equal to 100 micrograms/ml). When lower concentration of the enzyme was used, simultaneous elevation of 9,10-epoxy-12,13-dihydroxy and 12,13-epoxy-9,10-dihydroxystearate along with disappearance of tetraol was observed. The epoxydiols were intermediates which could be isolated and cyclized quantitatively to form two chromatographically distinct tetrahydrofurandiols (A with a low Rf value and B with a high Rf value on TLC). Gas chromatographic analysis on a cyclodex-beta capillary column revealed that each compound was composed of two different isomers. The structure of these isomers was 9(12)-oxy-10,13-dihydroxystearate and 10(13)-oxy-9,12-dihydroxystearate using mass spectrometry. Stereochemistry of the aliphatic chain across the tetrahydrofuran moiety was determined by nuclear Overhauser effect spectroscopy. Chemically and enzymatically generated tetrahydrofurandiols had similar retention time on GC and HPLC, and identical mass spectra using the electron impact mode.

Comparative study of the in vitro synthesis of prostaglandins and thromboxanes in plants belonging to Liliaceae family

1. Homogenates of garlic (Allium sativum), onions (Allium cepa) and Allium porum were in vitro incubated with [14C]arachidonic acid. 2. Separation of labelled prostaglandins and thromboxanes were accomplished by thin-layer chromatography (TLC) and the Rf values were compared with those of authentic standards. 3. The prostaglandins identified were 6-keto-PGF1 alpha, PGF2 alpha, TXB2, PGE2 and PGD2. 4. PGE2 and PGD2 were the major metabolites of arachidonic acid among all the members of the Liliaceae family studied. 5. Garlic was found to have the highest capacity to metabolize the [14C]arachidonic acid into prostaglandins and thromboxanes. 6. The synthesis of prostaglandins and thromboxanes, was inhibited by preincubation of homogenates with indomethacin or was completely destroyed by boiling the plant extract prior to incubation with arachidonic acid. This confirmed the presence of cyclooxygenase in these plants.