Methylation of the beta-positions of the furan ring in F-acids

A bacterial biosynthetic pathway for methylated furan fatty acids

Fatty acids play many important roles in cells and also in industrial processes. Furan fatty acids (FuFAs) are present in the lipids of some plant, fish, and microbial species and appear to function as second messengers in pathways that protect cells from membrane-damaging agents. We report here the results of chemical, genetic, and synthetic biology experiments to decipher the biosynthesis of the monomethylated FuFA, methyl 9-(3-methyl-5-pentylfuran-2-yl) nonanoate (9M5-FuFA), and its dimethyl counterpart, methyl 9-(3,4-dimethyl-5-pentylfuran-2-yl) nonanoate (9D5-FuFA), in two α-proteobacteria. Each of the steps in FuFA biosynthesis occurs on pre-existing phospholipid fatty acid chains, and we identified pathway intermediates and the gene products that catalyze 9M5-FuFA and 9D5-FuFA synthesis in Rhodobacter sphaeroides 2.4.1 and Rhodopseudomonas palustris CGA009. One previously unknown pathway intermediate was a methylated diunsaturated fatty acid, (10E,12E)-11-methyloctadeca-10,12-dienoic acid (11Me-10t,12t-18:2), produced from (11E)-methyloctadeca-11-enoic acid (11Me-12t-18:1) by a newly identified fatty acid desaturase, UfaD. We also show that molecular oxygen (O₂) is the source of the oxygen atom in the furan ring of 9M5-FuFA, and our findings predict that an O₂-derived oxygen atom is incorporated into 9M5-FuFA via a protein, UfaO, that uses the 11Me-10t,12t-18:2 fatty acid phospholipid chain as a substrate. We discovered that R. palustris also contains a SAM-dependent methylase, FufM, that produces 9D5-FuFA from 9M5-FuFA. These results uncover the biochemical sequence of intermediates in a bacterial pathway for 9M5-FuFA and 9D5-FuFA biosynthesis and suggest the existence of homologs of the enzymes identified here that could function in FuFA biosynthesis in other organisms.

Valuable furan fatty acids in soybeans and soy products

Furan fatty acids (FuFAs) are valuable minor compounds in our food with excellent antioxidant properties. Naturally occurring FuFAs are characterised by a central furan moiety with one or two methyl groups in β-/β’-position of the heterocycle (monomethyl- or M-FuFAs and dimethyl- or D-FuFAs). Comparably high concentrations of D-/M-FuFAs were reported in soybeans, but soy is often consumed as a processed product, such as full-fat soy flour and flakes, soy drink, tofu and texturised soy protein (TSP). Due to the chemical lability of D-/M-FuFAs, e.g. in the presence of light or oxygen, a degradation during the processing is possible. For this purpose, freshly harvested soybeans (n = 4) and differently processed soybean products (n = 22) were analysed on FuFAs. Three FuFAs, i.e. 11-(3,4-dimethyl-5-pentylfuran-2-yl)-undecanoic acid (11D5), 9-(3,4-dimethyl-5-pentylfuran-2-yl)-nonanoic acid (9D5), and 9-(3-methyl-5-pentylfuran-2-yl)-nonanoic acid (9M5), were identified and quantified in all fresh soybeans and most of the processed soy products (n = 20). A trend towards lower D-/M-FuFA contents in higher processed products was observable. Lower FuFA concentrations were usually accompanied with a decrease of the share of the less stable D-FuFAs (9D5, 11D5) in favour of the M-FuFA 9M5. Furthermore, one or two 3,4-nonmethylated furan fatty acids (N-FuFAs), i.e. 8-(5-hexylfuran-2-yl)-octanoic acid (8F6) and partly 7-(5-heptylfuran-2-yl)-heptanoic acid (7F7), were detected in all processed products, but not in the freshly harvested soybeans. Our results indicate that D-/M-/N-FuFAs may serve as suitable markers for both, careful manufacturing processes and adequate storage conditions of soy products.

One-step production of a biologically active novel furan fatty acid from 7,10-dihydroxy-8(E)-octadecenoic acid

Furan fatty acids (F-acids) gain special attention because they are known to play important roles in biological systems including humans. Specifically, F-acids are known to have strong antioxidant activitis such as radical scavenging activity. Although widely distributed in most biological systems, F-acids are trace components and their biosynthesis is complicated and quite different by sources. On the basis of biochemical study, they are considered to be an essential nutritional factor for mammals and should be provided through the diet. Hence, several studies reported the chemical synthesis of F-acids using chemical catalysts. However, chemical synthesis required complicated multiple steps. In this study was developed a simple one-step synthesis of a novel F-acid, 7,10-epoxyoctadeca-7,9-dienoic acid (EODA), from a dihydroxyl fatty acid, 7,10-dihydroxy-8(E)-octadecenoic acid (DOD), by heat treatment. The structure of EODA was confirmed by GC-MS, NMR, and FTIR analyses, and maximum production yield under the reaction conditions of 90 °C and 24 h reached 80%.

Furan fatty acids: occurrence, synthesis, and reactions. Are furan fatty acids responsible for the cardioprotective effects of a fish diet?

Furan FA (F-acids) are tri- or tetrasubstituted furan derivatives characterized by either a propyl or pentyl side chain in one of the alpha-positions; the other is substituted by a straight long-chain saturated acid with a carboxylic group at its end. F-acids are generated in large amounts in algae, but they are also produced by plants and microorganisms. Fish and other marine organisms as well as mammals consume F-acids in their food and incorporate them into phospholipids and cholesterol esters. F-acids are catabolized to dibasic urofuran acids, which are excreted in the urine. The biogenetic precursor of the most abundant F-acid, F6, is linoleic acid. Methyl groups in the beta-position are derived from adenosylmethionine. Owing to the different alkyl substituents, synthesis of F-acids requires multistep reactions. F-acids react readily with peroxyl radicals to generate dioxoenes. The radical-scavenging ability of F-acids may contribute to the protective properties of fish and fish oil diets against mortality from heart disease.

GC-MS structural characterization of fatty acids from marine aerobic anoxygenic phototrophic bacteria

The FA composition of 12 strains of marine aerobic anoxygenic phototrophic bacteria belonging to the genera Erythrobacter, Roseobacter, and Citromicrobium was investigated. GC-MS analyses of different types of derivatives were performed to determine the structures of the main FA present in these organisms. All the analyzed strains contained the relatively rare 11-methyloctadec-12-enoic acid, and three contained 12-methyl-octadec-11-enoic acid, which has apparently never been reported before. High amounts of the very unusual octadeca-5,11-dienoic acid were present in 9 of the 12 strains analyzed. A FA containing a furan ring was detected in three strains. Analytical data indicated that this FA was 10,13-epoxy-11-methyloctadeca-10,12-dienoic acid. A very interesting enzymatic peroxidation of the allylic carbon 10 of cis-vaccenic acid was observed in three strains. Deuterium labeling and GC-MS analyses enabled us to demonstrate that this enzymatic process involves the initial dioxygenase-mediated formation of 10-hydroperoxyoctadec-11(cis)-enoic acid, which is then isomerized to 10-hydroperoxyoctadec-11(trans)-enoic acid and converted to the corresponding hydroxyacids and oxoacids. Different biosynthetic pathways were proposed for these different compounds.

Biosynthesis of furan fatty acids (F-acids) by a marine bacterium, Shewanella putrefaciens

A mutant derived from Shewanella putrefaciens 8CS7-4 treated with N-methyl-N'-nitro-N-nitrosoguanidine was found to produce 15-20 mg of a furan fatty acid (F-acid), 10,13-epoxy-11-methyloctadeca-10,12-dienoic acid (F18), per liter of growth medium (10-15% of total fatty acids). Capillary gas chromatography-mass spectrometry and proton nuclear magnetic resonance analysis of the fatty acid methyl esters of the mutant revealed the presence of other F-acids, 8,11-epoxy-9-methylhexadeca-8,10-dienoic acid (F16), 6,9-epoxy-7-methyltetradeca-6,8-dienoic acid (F14), and methyl branched unsaturated fatty acids, 11-methyl-12E-octadecenoic acid (11-me-18:1) and 11-methyl-10E,12E-octadecadienoic acid (1-me-18:2). About 90% of F-acids were present in phospholipids, in which the F-acids were found to be exclusively linked at the sn-1 position. 11-me-18:1 and 11-me-18:2 were also detected in the sn-1 position. Firstly, 11-me-18:1 increased and reached a maximum at 12 h, and then decreased rapidly. Secondly, the 11-me-18:2 content reached a maximum at 24 h, when 11-me-18:1 was little detected, and then decreased. Finally, the amount of F18 began to increase after 20 h and reached a plateau at 36 h. These results suggest that 11-me-18:1 and 11-me-18:2 are precursors of F18.