Oxygen, heterocyclic compounds furan

Figure 8 presents a selected part of a gas chromatogram recorded for the extracts A and B. The extract B consisting of furan derivative contains more oxygen heterocyclic compounds compared to extract A. The excess of 0-heterocycles is responsible for the observed (better) antioxidant activity of extract B (Figure 9). Careful analysis of GC, FT-IR, and NMR results let to identify more than 50 compounds which conld be accounted to the compounds potentially exhibiting antioxidant activity. Some of them are listed in Table 3 which contains names, formulas and information on most typical MS ions observed during the GC-MS identification. In general, most of the identified compounds may be seen as derivatives of the three basic structures (Figure 10) (A) cumarol alcohol, (B) coniferyl alcohol, and (C) synapine alcohol.

Heterocycles Both non-aromatic unsaturated heterocycles and heteroaromatic compounds are able to play the role of ethene dipolarophiles in reactions with nitrile oxides. 1,3-Dipolar cycloadditions of various unsaturated oxygen heterocycles are well documented. Thus, 2-furonitrile oxide and its 5-substituted derivatives give isoxazoline adducts, for example, 90, with 2,3- and 2,5-dihydro-furan, 2,3-dihydropyran, l,3-dioxep-5-ene, its 2-methyl- and 2-phenyl-substituted derivatives, 5,6-bis(methoxycarbonyl)-7-oxabicyclo[2.2.1]hept-2-ene, and 1,4-epoxy-l,4-dihydronaphthalene. Regio- and endo-exo stereoselectivities have also been determined (259). 

The formation of oxygen-containing heterocyclic compounds is also a consequence of the Maillard reaction. Amines and amino acids have a catalytic effect upon the formation of 2-furaldehyde (5), 5-(hydroxy-methyl)-2-furaldehyde (11),2-(2-hydroxyacetyl)furan (44),2 and 4-hy-droxy-5-methyl-3(2//)-furanone (111) (see Ref. 214). This catalytic effect can be observed with several other non-nitrogenous products, including maltol. The amino acid or amine catalysis has been attributed to the transient formation of enamines or immonium ions, or the 1,2-2,3 eno-lization of carbohydrates. Of interest is the detection of A -(2-furoyl-... 

Heating of carbohydrates produces a number of aromatic compounds Including aldehydes, ketones, and dicarbonyls as well as oxygen containing heterocyclic compounds such as furans, dihydrofuranones, and pyrans through caramelizatlon and dehydration reactions. 

Food, flavors consist of numerous compounds, none of which alone is characteristic of specific food. Classes of compounds which emcompass food flavors are - hydrocarbons (aliphatic, ali-cyclic, aromatic) carbonyls (aldehydes, ketones) carboxylic acids, esters, imides, anhydrides alcohols, phenols, ethers alkylamines, alkylimines aliphatic sulfur compounds (thiols, mono-, di- and tri-sulfides) nitrogen heterocyclics (pyrroles, pyrazines, pyridines) sulfur heterocylics (thiophenes, thiazoles, trithiolane, thialidine) and oxygen-heterocyclics (lactone, pyrone, furan). Discussion will be limited to striking developments in heterocyclics. 

The most important sugars may exist in an open-chain form, as a five-membered oxygen heterocycle (called a furanoside after the aromatic furan) or a six-membered oxygen heterocycle (called a pyranoside after the compound pyran). 

Heterocyclic compounds— The polarity of heterocyclic compounds is due to the formation of ionic valence bond structures. Thus in furan, 7, structures, similar to those in esters occur, 77, as well as a structure with a trivalent, positive oxygen atom, 777, and the moment is 0 71, D. 

Oxygen, nitrogen and sulfur are most commonly found in heterocyclic compounds, but there is no fundamental limitation to these particular elements. Examples of heterocyclic compounds include pyridine and furan. 

With this large group of heterocycles, ring strain is of little or no importance. Ring-opening reactions are, therefore, rarer than in three- and four-membered heterocycles. The crucial consideration is rather whether a compound can be regarded as a heteroarene or whether it has to be classified as a heterocycloalkane or heterocycloalkene (see p 2). Various aromaticity criteria apply to heteroarenes, and as a consequence, different opinions have been expressed on this matter [1]. As will be shown by means of examples of the various systems, the nature and number of heteroatoms are the critical factors. The parent compound of the five-membered heterocycles with one oxygen atom is furan. 

The heterocyclic compounds of oxygen that are largely used as solvents, tetrahydro-furan and 1,4-dioxane, are an irritant to the eyes and respiratory tract, a depressant to the central nervous system, and exhibit a low order of toxicity. Exposure to high concentrations, however, may cause injury to the kidney and liver in humans. 

The most common oxygen-containing heterocyclic alcohol is furfuryl alcohol, which is a degradation product of sugars. Furfuryl alcohol results primarily from furan-2-carbaldehyde by reduction or a Cannizzaro reaction. A large number of other alcohols derived from furan, pyran and other heterocyclic compounds are products of the Maillard reaction. 

Propylene oxide Tetramethylethylene oxide Heterocyclic Compounds, Oxygen, Furans Euran... 

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