Furan fatty acids

Three pro-inflammatory steryl esters of furan fatty acids (11-13) have recently been isolated from the Mediterranean sponge Dictyonella incisa [30]. The furan moiety was clearly established by H and 13C NMR signals corresponding to... 

Scheme 1. Proposed biogenesis of furan fatty acids 12 and 13, modified from Ciminiello and coworkers [30]...

COOCH3 Scheme 2. Chemical conversion of peroxyketal 1 to a furan fatty acid [24]... 

Teixeira A, Cox RC, Egmond MR (2013) Furan fatty acids efficiently rescue brain cells from cell death induced by oxidative stress. Food Funct 4 1209-1215... 

CMPF in humans remain unknown (Gil). Furan fatty acids have yet to be found in human lipids. However, urofuranic acids are present in the urine of babies and adults who have not consumed fish products for months (S3). Consequently, ingestion of fish does not appear to be the source of these furanoid fatty acids. Although the metabolic role of these compounds remains to be elucidated, substituted furan substances may be involved in the metabolism of uronic acid and carbohydrates (M40). 

Sand, D. M., Schlenk, H., Thoma, H., et al.. Catabolism of fish furan fatty-acids to urofuran acids in the rat. Biochim. Biophys. Acta 751, 455-461 (1983). 

Two rather interesting racemic syntheses for allylic methylated fatty acids have been recently accomplished [15]. One of these corresponds to the intriguing (12 )-11-methyl-12-octadecenoic acid (6), a marine bacterial fatty acid that in most reported identifications from natural sources has been shown to have the E double bond stereochemistry, but both Z,E isomers have been synthesized [15]. This mainly bacterial fatty acid was initially isolated from Byrsocarpus coccineus seed oil [16], but later it was reported in a bacterium associated with cat scratch disease [17], in Mycobacterium fallax [18], and most recently in a Pseudomonas sp. (.Alteromonas) associated with both the toxic dinoflagellate Ostreopsis lenticularis and several Caribbean Palythoa species [15]. More recently, acid 6 has been identified as an intermediate in the biosynthesis of the bacterial acid 10,13-epoxy-l l-methyloctadeca-10,12-dienoic acid, a furan fatty acid identified in several marine bacteria such as Shewanella putrefaciens [19-20]. 

F-acids (furan fatty acids, furanoid fatty acids). The F-a., first isolated in 1966 from Exocarpus seed oil and then in 1974 from fish oils, are multiply substituted furan derivatives of fatty acids. 

Glass, R.L., Krick,T.P., Olson, D.L., andThorson,R.L. (1977) The Occurrence and Distribution of Furan Fatty Acids in Spawning Male Freshwater Fish, Lipids 12, 828-836. 

The synthesis of furan fatty esters containing a phenyl substituent at the 3- or 4-position of the furan ring was reported these involved methyl 9,10-epoxy-12-oxostearate as a key intermediate (85). The mono-, di-, and triacylglycerols of a Cj g furan fatty acid were prepared by chemical and enzymatic means (86). Furanoacety-lene phytoalexins (wyerone [19] and dihydro-wyerone [20]) were prepared in multigram quantities from furfural (87). The synthesis route of compound [19] is presented in Scheme 6. 

The total synthesis of a naturally occurring furan fatty acid [21] has been described recently in which mercury (ll)-catalyzed isomerization of 2-(l,2-oxiranylcyclododecyl)-3-nonyn-2-ol was used as presented in Scheme 7 (88). 

Fatty acid composition linoleic acid (C18 2) is generally the most important with 40 to 50% of the fatty acids, followed by oleic acid (C18 l), stearic acid (C18 0) and furan fatty acid. These latter fatty acids each account for approximately 10 15% of the fatty acids. For a specific clone, furan fatty acid (see structure in Figure 9.5.7)... 

The mixture of bis- and tr/s-furan fatty-acid products were then DA-polymerised with BM. The corresponding polycondensations are shown in Schemes 7.6 and 7.7,... 

GC-MS has been apphed to studying the nature of the oxidation products of CLA (86-89). The subject has been reviewed by Yurawecz and colleagues (86,89). Furan fatty acids were major products that could be oxidized further to give, for example, oxofuran fatty acids. Similar to the analysis of CLA, long polar capillary GC columns were employed. Other than methyl esters, no special derivatives have been used. 

Yurawecz, M.P., Hood, J.K., Mossoba, M.M., Roach, J.A.G., and Ku, Y. (1995) Furan Fatty Acids Determined as Oxidation Products of Conjugated Octadecadienoic Acid, Lipids 30, 595-598. 

In the autoxidation of CLA, which yields identified products likely produced by a singlet oxygen pathway, i.e., furan fatty acids, the identified products are not exceptionally stable relative to the reactants (12). The reason that this reaction proceeds is then more likely due to the presence of initiators. Few reports that identify the products of CLA autoxidation are available in the literature (8-13). The results of an experiment performed in our laboratory are presented below to illustrate the effect of initiators. 

Among less volatile breakdown products, furan fatty acids were reported when air was bubbled through CLA dissolved in a mixture of methanol and water at 50°C. (20). Furanoid fatty acids might also arise in preparation of fatty acid methyl esters (FAME) for GC. To our knowledge, furan fatty acids have not been reported as an oxidative breakdown product in dry oil preparations of CLA. 

Furan Fatty Acids. These occur in fish liver oil in a range of 1-6% and up to 25% in some freshwater fish. Furan fatty acids are also part of the minor constituents of some plant oils and butter (Table 3.10). They are also present in fruits (lemon, strawberry), vegetables (cabbage, potato) and mushrooms (champignons). 

Table 3.10. Examples for the occurrence of furan fatty acids I and II...

Fig. 3.25. Side reaction of a branched furan fatty acid with singlet oxygen (R (CH2)iCOOH)...

Preparation and storage of products from both oilseeds is often inhibited by rancidity and bitter aroma defects caused mostly by volatile aroma active carbonyl compounds, e. g., (Z)-3-hexenal, (Z)-l,5-octadien-3-one and 3-methyl-2,4-nonan-dione. The rancidity-causing compounds are formed through peroxidation of linolenic acid, accelerated by the enzyme lipoxygenase and/or by hem(in) proteins (cf. 3.T.2.2). Furan fatty acids are the precursors in the case of the dione (cf. 14.3.2.2.5). Lipid peroxidation is also involved in the formation of another very potent odorant, 2-pentylpyridine, which produces grassy aroma defects in soybean products. Defatted soybean protein isolates contained 60-510 pg/kg of this compound, which with an odor threshold... 

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