Strecker methionine

Hydantoinases belong to the E.C.3.5.2 group of cyclic amidases, which catalyze the hydrolysis of hydantoins [4,54]. As synthetic hydantoins are readily accessible by a variety of chemical syntheses, including Strecker reactions, enantioselective hydantoinase-catalyzed hydrolysis offers an attractive and general route to chiral amino acid derivatives. Moreover, hydantoins are easily racemized chemically or enzymatically by appropriate racemases, so that dynamic kinetic resolution with potential 100% conversion and complete enantioselectivity is theoretically possible. Indeed, a number of such cases using WT hydantoinases have been reported [54]. However, if asymmetric induction is poor or ifinversion ofenantioselectivity is desired, directed evolution can come to the rescue. Such a case has been reported, specifically in the production of i-methionine in a whole-cell system ( . coli) (Figure 2.13) [55]. 

Creatine was first isolated in 1835 by Chevreul 20 years later Dessaignes showed it to contain a methyl group. Choline was obtained from lecithin in bile by Strecker in 1849 and methionine isolated by Mueller in 1922. That methionine contained a methyl group linked to sulfur was demonstrated by Barger and Coyne in 1928. 

Problem 21.4 Outline the preparation of (a) methionine from acrolein by the Strecker synthesis (Problem 21.2(e)), (b) glutamic acid by the phthalimidomalonic ester synthesis (Problem 21.2(c)]. ... 

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. 

Maillard products which were identified in methionine/ reducing sugar model experiments, result predominantly from the Strecker aldehyde (methional) and methylmer-captan, respectively. Figure 10 summarizes compounds... 

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. 

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). 

Fig. 7.11. Synthesis of racemic methionine by means of the Bucherer modification of the Strecker synthesis. The first step of the reaction does not stop at the stage the step of the a-aminonitrile but yields a hydantoin (B mechanistic details Figure 7.12). The second step—via the anion C of a hydantoin acid—leads to the formation of the anion E of methionine, which can be pro-tonated during workup to yield the uncharged methionine (D).

Fig. 7.12. Mechanism for the formation of hydantoin from 3-(methylthio)propional-dehyde, ammonium hydrogen carbonate and sodium cyanide, the initial reaction of the Strecker/Bucherer synthesis of methionine according to Figure 7.11.

Also MTP increases likely for a degradation of methionine via Strecker mechanism (Ribereau-Gayon et al., 1998). Furthermore, EtSH and DES show opposite changing in the time resulting for DEDS a similar increasing tendency as for DES thus a shift towards the oxidized form... 

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. 

Methional results from a Strecker degradation of methionine. It is at the origin of formation of methanethiol (Q.2), dimethyl disulfide (Q.14) and acrolein (C.16). 

Ballance P.E. (1961) Production of volatile compounds related to the flavour of foods from the Strecker degradation of DL-methionine. J. Sci. Food Agric. 12, 532-6. 

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]. 

Methionai [3-(methylthio)propanal]. H3CS-(CH2)2-CH0, C4H8OS, Mr 104.17, bp. 165 °C LD50 (rat p. o.) 0.75 g g. A Strecker aldehyde formed thermally or enzymatically from methionine with an odor resembling, when diluted, bouillon and boiled potatoes olfactory threshold 0.2 ppb. M. occurs in many foods prepared thermally or by fermentation and is important for, e. g., the flavor of bread, meat, potatoes (boiled, chips), cheese, and tomato (paste). It is used as a flavor substance especially for meat and cheese flavors. 

The D isomer produced by racemic scission is subsequently racemized. The methionine synthesis proceeds via an aldehyde Strecker reaction ... 

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. 

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

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. 

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

Scheme 12.50. A synthesis of methionine (Met, M) via the Strecker process (after Catch, J. R. Cook, A. H. Graham, A. R. Heilbron, I. M. /. Chem. Soa, 1947,1609).

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