Trimethylamine oxide reduction

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

Metabolism of trimethylamine oxide in fish muscle involves an enzyme-catalyzed oxidation-reduction reaction. The enzyme responsible for the conversion of trimethylamine oxide to trimethylamine is known as trimethylamine-W-oxide reductase. This enzyme acts on nicotinamide adenine dinucleotide (NADH) and TMAO to produce NAD+, trimethylamine and water (Fig. 13.13.1). TMAO acts as the oxidizing agent and is reduced, while NADH undergoes oxidation as the reducing agent. 

Figure 13.13.1 The reduction of trimethylamine oxide by nicotinamide adenine dinucleotide NADH.

Figure 13.13.2 Alternative reduction pathway of trimethylamine oxide to dimethy-lamine and formaldehyde.

Beside BAs, low-molecular-weight alkylamines, commonly used as indicators of food quality, can also be present in fish muscle. Tri- and dimethylamine (TMA and DMA) are produced by bacterial reduction of the osmoregulatory substance trimethylamine oxide (TMAO) in fresh marine fish and by enzymatic reduction in frozen storage of gadoid fish (cod, cusk, hake, pollack), with concurrent formation of formaldehyde. 

All plants depend on nitrate reductase to accomplish the seemingly trivial reaction of nitrate reduction to nitrite, often the first step of nitrogen assimilation into compounds required for growth (5, 22). Many bacteria use molybdenum or tungsten enzymes in anaerobic respiration where the terminal electron acceptor is a reducible molecule other than oxygen, such as nitrate (2, 50), polysulfide (51), trimethylamine oxide (33, 52) or dimethyl sulfoxide (DMSO) (2, 29, 30). 

Pace, C. P., and Stankovich, M. T., 1991, Oxidation-reduction properties of trimethylamine dehydrogenase effect of inhibitor binding. Arch. Biochem. Biophys. 287 9711104. 

Steenkamp, D. J., and Singer, T. P, 1976, On the presence of a novel covalently bound oxidation-reduction cofactor, iron and labile sulfur in trimethylamine dehydrogenase, Biochem. Biophys. Res. Commun. 71 1289nl295. 

In general, the acetylenic triple bond is highly reactive toward hydrogenation, hydroboration, and hydration in the presence of acid catalyst. Protection of a triple bond in disubstituted acetylenic compounds is possible by complex formation with octacarbonyl dicobalt [Co2(CO)g Eq. (64) 163]. The cobalt complex that forms at ordinary temperatures is stable to reduction reactions (diborane, diimides, Grignards) and to high-temperature catalytic reactions with carbon dioxide. Regeneration of the triple bond is accomplished with ferric nitrate [164], ammonium ceric nitrate [165] or trimethylamine oxide [166]. 

Trimethylamine and other amines have often been variously associated with the aromas of fish (2, 19, 41). Much of the trimethylamine found in fresh fish arises from the microbial reduction of trimethylamine oxide (42-44) which is found abundantly in only marine fish (45-47). On the other hand, dimethylamine is an abundant product of an endogenous enzymic action on trimethylamine oxide in marine fish muscle, and it is readily produced even under high-sub-freezing conditions in marine fish (48). Both trimethylamine and dimethylamine... 

The fishy OF is primarily due to the generation of Irimethylamine via bacterial action [130,131]. Trimethylamine is formed from trimethylamine oxide, which is a natural constituent of fish muscle. This reduction is accomplished through bacterial enzymes and involves a coupled oxidation of lactic acid to acetic acid and CO2 [ 132], The latter stages of fish spoilage involve the production of various nitrogen- and sulfin-containing compounds. These componnds prodnce pntrid, sulfury notes in the fish. 

Stansby, M.E., Speculations on fishy odors and flavors. Food TechnoL, 16, p. 28,1962. Watson, D.W., Studies on fish spoilage the bacterial reduction of trimethylamine oxide, J. Fish Res. Bd. (Canada), 4, p. 252, 1939. 

Secondary and tertiary amines are formed from precursors other than amino acids. Dimethylamine results from degradation of choline (which is present in some phospholipids), some alkaloids (e.g. in beer it is produced from gramine (see 10-198) present in germinating barley grains and also in non-enzymatic browning reactions from methylamine and formaldehyde or by decarboxylation of sarcosine. Trimethylamine, together with dimethylamine, methylamine and ammonia, is an odorous compound of fish and other aquatic animals. It is formed by reduction of the sensory indifferent trimethylamine oxide (trimethylaminoxide, 8-143) in tissues post mortem. 

The characteristic essential flavour-active components of fish and other aquatic animals are amines and other nitrogenous compounds. Trimethylamine arises by reduction of sensorially indifferent trimethylamine oxide (acting in the regulation of osmotic pressure in cells) in the tissue post mortem. The amount of trimethylamine oxide, as well as the amount of a number of simultaneously produced biogenic amines, depends primarily on the species, type and time of storage. Its content in fresh water fish is about 5 mg/kg, and in seafood is 40-120 mg/kg. Other important compounds are dimethylamine and ammonia. 

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