Sulfur-Containing Heterocyclic Compounds

A heterocyclic sulfur-containing compound, 2-methyl-thiophene, was identified in boiled crayfish tail meat and pasteurized crabmeat. Thiazole and 3-methylthiopropanal were identified in the crayfish hepatopancreas. Heterocyclic sulfur-containing compounds play important roles in generating meaty aromas in a variety of meat products and are considered important volatile aroma components of marine crustaceans (12— 14). The 2-methylthiophene could be an important flavor cemponent in boiled crayfish tail meat. Both thiazole find 3-methylthiopropanal were important contributors to the desirable meaty aroma associated with crayfish hepatopancreas. The 3-methyl-thiopropanal, identified in boiled crayfish hepatopancreas, is derived from Strecker degradation of methionine (15), and has been considered to be an important cemponent in basic meat flavor (16). Pyridine was detected in the headspace of the hepatopancreas from freshly boiled crayfish. Pyridine and 2-ethylpyridine have been previously reported as components in the atmospheric distillate from a sample of crayfish hepatopancreas frozen for three months (2). 

Sulfur Heterocyclics. Sulfur containing compounds (thiols, thiophenes, thiazoles,. .. etc.) play a major role in the flavor of raw and processed foods. These compounds have characteristic flavor notes and the flavor thresholds are mostly low. Several reviews (ill, 112, 113) demonstrate the important role of sulfur compounds in food flavors. Organoleptic properties of these compounds may be pleasant, strong nut-like odor of U-methyl-5-vinylthiazole which is present in cocoa (llU) objectionable pyridine-like odor of thiazole (115) quinoline-like odor of benzothia-zole (ll6) strong tomato leaf-like odor of isobutylthiazole (117) and bread crust flavor of acetyl-2-thiazoline (ll8). A mixture of oxazoles, thiazoles, thiazolines, imidazoles, trithiolanes and... 

There are those happy users who dissolve their sample in the mobile phase and inject right away. If you are one of these and you also have isocratic conditions with acetonitrile/water, you can forget about sample preparation for now. There are however those users who need to quantify minor unknown impurities of a metabolized metabolite from bile fluid and others who hunt after heterocyclic sulfur-containing compounds in crude oil residue from Iran and compare it with Iraqi oil. They all have my sympathy. In the following table, a few typical errors occurring in a normal sample preparation are listed. 

Numerous different types of heterocyclic compounds containing sulfur are produced via the Maillard reaction [61,62], These include thiophenes, dithioles, dithianes, dithiins, trithiolanes, trithanes, tetrathianes, thiazoles, thiazolines, and thiazolidines. The major heterocyclic sulfur-containing compounds produced via the Maillard reaction are thiazoles and thiophenes (Figure 5.6d and Figure 5.6e, respectively). 

Boron, D. J. Atlas, R. M. Johnson, A. R., et ah, Method for removing organic sulfur from heterocyclic sulfur containing organic compounds. Patent No. USH1986H. 

Of particular interest is the identification of five different types of heterocyclic sulfur-containing flavor components, the preponderance of which were furans and thiophenes substituted with sulfur in the 2- and 3-position. The bulk of these flavor compounds had not been identified in meat and had not been reported in the literature so far. These sulfur-substituted heterocyclic flavor components will be further discussed below. 

Dihydro-277-l-benzothiopyran-4-ol has been used as a model sulfur-containing compound in a study of molecular metal sulfide cluster substrate binding to oil-refinery hydrodesulfurization catalysts <2002IC1336> and also as a model compound in an evaluation of the removal of heterocyclic S-containing compounds from oil precursors by supercritical water <1995MI1485>. 

MNDO calculations have been reported for the heterocycle (7) in order to predict its HOMO energy and ionization potential <89SM179>. Compound (7) is a derivative of tetrathiafulvalene (8) and sulfur-containing compounds related to heterocycle (8) are of intense current interest as organic metals. CNDO calculations on 3,6-dithioxo-l,2,4,5-tetrathiapentalene (9) have been reported and there is agreement between experimental and calculated 13C NMR data <84ZC418>. 

The flavor of fish and seafoods is composed of taste-active low molecular-weight extractives and aroma-active compounds. The taste-active compoimds are more abundant in the tissues of mollusks and crustaceans than fish. The most important non-volatile taste components are fi-ee amino acids, nucleotides, inorganic salts and quaternary ammonia bases. Alcohols, aldehydes, ketones, furans, nitrogen-containing compounds, sulfur-containing compounds, hydrocarbons, esters and phenols are the most important volatiles is shellfish. Alkyl pyrazines and sulfur-containing compounds are important contributors to the cooked aroma of crustaceans. Furans pyrazines, and Lactones have been found in heat-treated seafoods. Dimethyl disulfide, dimethyl trisulfide, heterocyclic sulfiir-containing compounds (alkylthiophenes) have been found in most thermally treated crustaceans like prawn, crab, oyster, crayfish and shrimp (52). 

Two chapters deal with sulfur-containing compounds. The benzisothiazoles and other polycyclic isothiazoles are covered by M. Davis, in a sequel to earlier reviews in Advances in Heterocyclic Chemistry, Volumes 14 and 15. 1,4-Ben-zothiazines and related compounds are dealt with by C. Brown and R. M. Davidson these compounds have not been previously comprehensively reviewed. 

Katritzky, A.R., Barcock, R.A., Balasubramanian, M., and Greenhill, J.V. (1995) Aqueous high-temperature chemistry of carbo- and heterocycles, reactions of sulfur-containing compounds in supercritical water at 460 °C. Energy Fuels, 8, 498. 

This five-membered-ring (cyclic) sulfur-containing compound is another example of that group of compounds called heterocycles. Many more will be encountered. 

Biodesulfurization is a process that removes sulfur from fossil fuels using a series of enzyme-catalyzed reactions.Biodesulfurization is another alternative processing method that has some similarity to the above-mentioned oxidative desulfurization, in that both methods oxidize sulfur atoms in the sulfur-containing compounds. Certain microbial biocatalysts have been identified that can biotransform sulfur compounds found in fuels, including ones that selectively remove sulfur from dibenzothiophene-type heterocyclic compounds. " Biocatalytic sulfur removal from fuels may have applicability for producing low sulfur gasoline and diesel fuels. 

Trofimov, B.A. 2003. Pyrrolecarbodithioates Synthesis and application in design of complex heterocyclic system. In Chemistry and Biological Activity of Natural Compounds. Oxygen- and Sulfur-Containing Compounds, vol. 1, ed. V.G. Kartsev, pp. 119-135. Moscow, Russia IBS Press. 

Sulfur containing heterocycles are also common Compounds m which sulfur is the heteroatom m three four five and six membered rings as well as larger rings are all well known Two interesting heterocyclic compounds that contain sulfur-sulfur bonds are hpoic acid and lenthiomne... 

Competitive metallation experiments with IV-methylpyrrole and thiophene and with IV-methylindole and benzo[6]thiophene indicate that the sulfur-containing heterocycles react more rapidly with H-butyllithium in ether. The comparative reactivity of thiophene and furan with butyllithium depends on the metallation conditions. In hexane, furan reacts more rapidly than thiophene but in ether, in the presence of tetramethylethylenediamine (TMEDA), the order of reactivity is reversed (77JCS(P1)887). Competitive metallation experiments have established that dibenzofuran is more easily lithiated than dibenzothiophene, which in turn is more easily lithiated than A-ethylcarbazole. These compounds lose the proton bound to carbon 4 in dibenzofuran and dibenzothiophene and the equivalent proton (bound to carbon 1) in the carbazole (64JOM(2)304). 

Silylthioaldehydes 103, reactive dienophiles formed in situ from acetals according to a general method, are directly trapped with dienes to afford sulfur-containing heterocyclic compounds in good yield (Equation 2.29). Silylthioaldehydes are quite reactive in comparison with the aliphatic ones [102] which are rather inert in the cycloaddition reactions. 

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