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Strecker cysteine

The Strecker reaction has been performed on the aldehyde 182 prepared from L-cysteine [86] (Scheme 28). The imine was formed in situ by treatment with benzylamine, then TMS cyanide was added to afford prevalently in almost quantitative yield the syn-diamine 183, which is the precursor of (-l-)-biotin 184. The syn selectivity was largely affected by the solvent, toluene being the solvent of choice. Since the aldehyde 182 is chemically and configurationally unstable, a preferred protocol for the synthesis of 183 involved the prehminary formation of the water-soluble bisulfite adduct 185 and the subsequent treatment with sodium cyanide. Although in this case the syn selectivity was lower, both diastereomers could be transformed to (-l-)-biotin. [Pg.33]

Hydrogen sulphide is a key intermediate in the formation of many heterocyclic sulphur compounds. It is produced from cysteine by hydrolysis or by Strecker degradation ammonia, acetaldehyde and mercaptoacetaldehyde are also formed (Scheme 12.4). All of these are reactive compounds, providing an important source of reactants for a wide range of flavour compounds. Scheme 12.6 summarises the reactions between hydrogen sulphide and other simple intermediates formed in other parts of the Maillard reaction. [Pg.278]

Probably the most important reactant in the formation of volatile meat flavor compounds is hydrogen sulfide. It can be formed by several pathways during meat cookery, but one mechanism is Strecker degradation of cysteine in the presence of a diketone as established by Kobayashi and Fujimaki (29). The cysteine condenses with the diketone and the product in turn decarboxylates to amino carbonyl compounds that can be degraded to hydrogen sulfide, ammonia and acetaldehyde. These become very reactive volatiles for the formation of many flavor compounds in meat and other foods. [Pg.173]

Figure 3. Formation of 2-acetyl-2-thiazoline by Strecker degradation of cysteine. (Reproduced from Ref. 40. Copyright 1971, American Chemical Society.)... Figure 3. Formation of 2-acetyl-2-thiazoline by Strecker degradation of cysteine. (Reproduced from Ref. 40. Copyright 1971, American Chemical Society.)...
This important flavor compound was identified in the head-space volatiles of beef broth by Brinkman, et al. (43) and although it has the odor of fresh onions, it is believed to contribute to the flavor of meat. This compound can be formed quite easily from Strecker degradation products. Schutte and Koenders (49) concluded that the most probable precursors for its formation were etha-nal, methanethiol and hydrogen sulfide. As shown in Figure 5, these immediate precursors are generated from alanine, methionine and cysteine in the presence of a Strecker degradation dicarbonyl compound such as pyruvaldehyde. These same precursors could also interact under similar conditions to give dimethyl disulfide and 3,5-dimethyl-l,2,4-trithiolane previously discussed. [Pg.178]

In roasted coffee similar reactions seem to be involved forming methylmercaptan by the Strecker degradation of free methionine and forming H S from peptide cysteine. Figure 8 presents additional flavor contributing constituents of roasted coffee. 3-Thiolanone 6 and 2-methyl-3-thiolanone 1 were identified by Stoll et al. (19) and patented as coffee flavors. The two thiolanones 6, T are formed as major constituents in erythrose and xylose/ cysteine model systems, respectively. [Pg.296]

Probably the most important reactant in the formation of volatile meat flavor compounds is hydrogen sulfide. It can be formed as a Strecker degradation product of cysteine in the presence of a diketone (37). [Pg.413]

Heterocyclic compounds are dominant among the aroma compounds produced in the Maillard reaction, and sulfur-containing heterocyclics have been shown to be particularly important in meat-like flavors. In a recent review, MacLeod (6) listed 78 compounds which have been reported in the literature as possessing meaty aromas seven are aliphatic sulfur compounds, the other 71 are heterocyclic of which 65 contain sulfur. The Strecker degradation of cysteine by dicarbonyls is an extremely important route for the formation of many heterocyclic sulfur compounds hydrogen sulfide and mercaptoacetaldehyde are formed by the decarboxylation and deamination of cysteine and provide reactive intermediates for interaction with other Maillard products. [Pg.443]

Cysteine can undergo the Strecker degradation, transamination, and -elimination, as shown by Tressl et al.247 using [1- or 6-13C]glucose (equimolar aqueous solution, 160 °C, 1.5 h). 2-Furylmethanethiol (T 0.005 ppb), very important in providing the aroma of roasted coffee and roasted meat, is formed as shown in Scheme 5.14 from [l-13C]glucose via the 3-deoxy-l,2-dicarbonyl, which loses... [Pg.76]

For the thiophen mentioned above, all the carbon atoms stemmed from cysteine, carbohydrate apparently not having a role. On the other hand, theoretically, thiophens can be derived from furans simply by reaction with H2S. Belitz and Grosch251 postulate derivation from 2-mercaptoethanal (Strecker aldehyde from cysteine) and acrolein or butenal (aldol condensation product from acetaldehyde). Vemin and Parkanyi216... [Pg.78]

Figure A shows a proposed mechanism for the formation of 2,A,5-trlmethyloxazole and A,5-dlmethyloxazole from the Strecker degradation of cysteine with 2,3-butanedlone (Al). Figure A shows a proposed mechanism for the formation of 2,A,5-trlmethyloxazole and A,5-dlmethyloxazole from the Strecker degradation of cysteine with 2,3-butanedlone (Al).
By employing thiolactone 8 as an intermediate for (+)-biotin (1), as well as availability of functionalities and a stereogenic center of L-cysteine as a starting material, synthetic schemes have successfully been devised. Our second approach investigates. The use of Strecker method I to obtain 8 from L-cysteine (Fig. (20)) [73]. [Pg.283]

The target compound 8 is derived from a known carboxylic acid 54 [85], which is obtained via reductive cleavage of the carbon-sulfur bond of bicyclic amide 53 whose carboxylic acid congener is an intermediate of the Merck s approach [85]. The compound 53 is obtained through amidation and subsequent cyclization of 5y -a-amino nitrile syn-Sl. The compound syn-51 should be prepared stereoselectively by Strecker reaction of a-amino aldehyde 51 that can be readily prepared from L-cysteine. [Pg.283]

Thiols are another key group of odor compounds in coffee, these are formed due to Strecker degradation of amino acids like mediionine to give mediional and die reaction of H2S (formed by the degradation of Cysteine) with fiiraldehydes, namely the formation of 2-furylthiol (62). [Pg.18]

The latter authors also found it when serine and/or threonine reacted with sucrose. It was previously identified in other model reactions by treating furfural with hydrogen sulfide and ammonia (Shibamoto, 1977) or by heating rhamnose with ammonia (Shibamoto and Bernhart, 1978). Ho and Hartman (1982) proposed a plausible mechanism for the formation 2,4,5-trimethyloxazole from the reaction of dl-alanine or L-cysteine and 2,3-butanedione. Ho el al. (1982) also studied the formation of oxazoles and oxazolines in the Strecker degradation of dl-methionine and L-cysteine with 2,3-butanedione. In their proposed mechanisms, the authors suggested the formation of intermediate 3-oxazolines. [Pg.280]

Dawes and Edwards (1966) isolated it from the volatiles obtained by heating a mixture of D-fructose and glycine or L-3-phenylalanine. Wang et al. (1969) presented a model reaction in which the product of condensation of pyruvaldehyde with any amino acid degraded by a Strecker reaction can form an aminoketone which by subsequent steps of self-condensation and oxidation formed 2,5-dimethylpyrazine (Wang et al., 1969 Manley et al., 1974). It was found in a heated cysteine/glucose model system (Sheldon et al., 1986). [Pg.304]

Ho C.T. and Hartman G.J. (1982) Formation of oxazolines and oxazoles in Strecker degradation of DL-alanine and L-cysteine with 2,3-butanedione. J. Agric. Food Chem. 30, 793-4. [Pg.363]

The Strecker degradation involves the oxidative deamination and decarboxylation of a a-amino acid in the presence of a dicarbonyl compound. The products formed from this reaction are an aldehyde containing one less carbon atom than the original amino acid and an a-aminoketone (Table 9.2). The Strecker degradation of methionine and cystein is a source of sulfur-containing intermediates (e.g hydrogen sulfide and 2-methylthiopropanal = methional) [48]. [Pg.298]

The formation of furans, thiophenes, furanones, thiophenones etc. was investigated in a series of [l(or 6)- C]-glucose and [l- C]-arabinose/ cysteine and methionine model experiments. The labeled compounds were analyzed by capillary GC/MS and NMR-spectroscopy. From their structures the degradation pathways via different reactive intermediates (e.g. 3-deoxyaldoketose, 1-deoxydiketose) and fragmentations were evaluated. Besides the transformations to flavor compounds via identical labeled precursors, major differences in the flavor compounds result from specific Strecker reaction sequences. Major unlabeled compounds e.g. 3-mercaptopropionic acid from cysteine and 4-methylthiobutyric acid from methionine demonstrate transamination/reduction, and the formation of pyruvate and 2-mercaptopropionic acid from [l-i C]-glucose/cysteine indicates B-elimination. [Pg.224]

Strecker Degradation, fi-Eliminatton and TVansamination of Cysteine/ Methionine during Heating with [l(or 6)- C]-D-Glucose... [Pg.225]

During Strecker degradation of [l-i CJ-D-glucose with primary a-amino acids, pyrroles and pyridinols are formed as major products (6). 4-Aminobutyric acid and peptide bound lysine are transformed into [i3CHO]-2-formyl-5-hydroxymethylpyrroles (9). Amino acids like Val, He, Leu, Phe and Met are transformed into 2-[i3cjjO]-pyrrole lactones (70). Equimolar amounts of cysteine (methionine) and [l(or 6)- C]-D-glucose were heated for 1,5 h at 160°C in aqueous solution at pH 5. The volatiles were extracted with pentane/ether and analyzed as described (7). In Table I selected (unlabeled) Strecker degradation products from cysteine and methionine are summarized. Pyruvat (1), 2- and 3-mercaptopropionic acids (2, 3) from cysteine as well as 2-oxo-5-thiahexanoic acid (4) and 5-thiahexanoic acid (5) from methionine. [Pg.225]

Table I. Strecker Degradation Products from [l- C]-D-Glucose with Cysteine or Methionine... Table I. Strecker Degradation Products from [l- C]-D-Glucose with Cysteine or Methionine...

See other pages where Strecker cysteine is mentioned: [Pg.272]    [Pg.273]    [Pg.279]    [Pg.175]    [Pg.248]    [Pg.162]    [Pg.163]    [Pg.170]    [Pg.288]    [Pg.414]    [Pg.447]    [Pg.448]    [Pg.92]    [Pg.270]    [Pg.288]    [Pg.301]    [Pg.7]    [Pg.270]    [Pg.270]    [Pg.288]    [Pg.301]    [Pg.4]    [Pg.224]    [Pg.226]   
See also in sourсe #XX -- [ Pg.363 ]




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