Enzymatic conversion of DL-.ALPHA.-amino-.EPSILON.-caprolactam into L-lysine. VI. Conversion of D- and DL-.ALPHA.-amino-.EPSILON.-caprolactam into L-lysine using both yeast cells and bacterial cells.
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An enzymatic process has been proposed for producing L-lysine from DL-aminolactam by the author. Several yeasts, including Cryptococcus laurentii, have been isolated from soil and found to catalyze the selective hydrolysis of aminolactam. As well, several bacteria, including Achrornobacter obae nov. sp., have been isolated which catalyze the racemization of aminolactam. This paper reports an investigation of the conversion reaction of D- and DL-aminolactam into L-lysine using both cells of Crypt. laurentii and Achr. obae nov. sp. The optimum pH of the reaction was between 8.0 and 9.0, but most often near 8.0. An inhibitory effect of the substrates on the reaction was observed when the substrate concentration was higher than 10%, but the inhibition was slight at 5% substrate. The optimum temperature of the reaction for 3_??_6hr was around 39°C. A complete conversion reaction of 10% DL-aminolactam was carried out at 40°C for 24 hr, producing L-lysine in a conversion rate of 99.8 %. L-Lysine•HCl isolated from the reaction mixture was 99.5% optically pure.Keywords:
Racemization
Caprolactam
The degree of racemization in the several activated ester methods of the peptide synthesis was measured in using the critical racemization test, Pro-Val+Pro, with help of gas chromatography. The results were compared with that in the coupling reaction, Leu-Phe+Val, in which no racemization had been reported in the corresponding reaction conditions by F. Weygand et al., when the activated dipeptide esters had been prepared from Z-Leu+Phe-activated esters. The significantly higher racemization was observed in the methods of N-hydroxypiperidine ester and thiophenyl ester, even when the activated dipeptide esters were prepared from Z-Pro+Val-activated esters. On the other hand, almost no racemization was observed in the N-hydroxysuccinimide ester and p-nitrophenyl ester methods. A great extent of the racemization was detected when the activated dipeptide esters were prepared directly from Z-Pro-Val-OH.
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Fe and Ru pincer-type catalysts are used for the racemization of benzylic alcohols. Racemization with the Fe catalyst was achieved within 30 minutes under mild reaction conditions, with a catalyst loading as low as 2 mol %. This reaction constitutes the first example of an iron-catalyzed racemization of an alcohol. The efficiency for racemization of the Fe catalyst and its Ru analogue was evaluated for a wide range of sec-benzylic alcohols. The commercially available Ru complex proved to be highly robust and even tolerated the presence of water in the reaction mixture.
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This paper gives an overview of the available methods for racemization of amines and related derivatives, and the racemization catalysts can be coupled with enzymes to achieve the dynamic kinetic resolution, which provides enantiopure products with approximate 100% yields. Transition metal-catalyzed racemization, free radical-based racemization, racemase leading to automatic racemization and alkali-catalyzed racemization have been summarized, and their advantages and disadvantages have been discussed and compared. A purely enzymatic method would enable efficient and environmentally benign processes as a green and sustainable technique. Keywords: Racemization, Amines, Enzymes, Dynamic kinetic resolution.
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The amino acids in living organisms are optically active. However, once biologically synthesized amino acids are isolated from the biochemical processes which maintain their optical activity, racemization reactions gradually convert the amino acids into an optically inactive mixture. Racemization proceeds by a very simple reaction, the kinetics and mechanism of which can be easily elucidated. Amino acid racemization on Earth has important applications and implications. The slow racemization of amino acids in fossils and metabolically stable proteins in living mammals can be used to estimate the ages of these materials. Racemization in well-dated fossils can be used to deduce information about the temperature history of the sample. Also, racemization in metabolically stable proteins in living mammals may induce structural changes which in turn affect the functionality of the protein; thus racemization may be part of the ageing process in mammals. Finally, racemization places an important restraint on any proposed mechanisms for the origin of optically active amino acids on Earth since racemization would rapidly convert any optically active amino acids back into an optically inactive or racemic mixture.
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(+)-1,2-Epoxy-1,2-dihydrochrysene, a major initial mammalian metabolite of chrysene, has been synthesised and assigned the configuration (1R, 2S). Kinetic studies on the spontaneous thermal racemization of (+)-1,2-epoxy-1,2-dihydrochrysene gave a barrier to racemization (Ea) of 24.8 kcal mol–1. The kinetic results and activation parameters support a thermal racemization mechanism involving an oxepin intermediate.
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The degree of racemization in the several activated ester methods of the peptide synthesis was measured in using the critical racemization test, Pro-Val+Pro, with help of gas chromatography. The results were compared with that in the coupling reaction, Leu-Phe+Val, in which no racemization had been reported in the corresponding reaction conditions by F. Weygand et al., when the activated dipeptide esters had been prepared from Z-Leu+Phe-activated esters. The significantly higher racemization was observed in the methods of N-hydroxypiperidine ester and thiophenyl ester, even when the activated dipeptide esters were prepared from Z-Pro+Val-activated esters. On the other hand, almost no racemization was observed in the N-hydroxysuccinimide ester and p-nitrophenyl ester methods. A great extent of the racemization was detected when the activated dipeptide esters were prepared directly from Z-Pro-Val-OH.
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