- Dynamic Kinetic Resolution for Asymmetric Synthesis of L-Noncanonical Amino Acids from D-Ser Using Tryptophan Synthase and Alanine Racemase
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L-Ser is often used to synthesize some significant l-noncanonical α-amino acids(l-ncAAs), which are the prevalent intermediates and precursors for functional synthetic compounds. In this study, threonine aldolase from Escherichia coli k-12 MG1655 has been used to synthesize l-Ser. In contrast to the maximum catalytic capacity (20 g/L) for l-threonine aldolase(LTA), d-Ser was synthesized with high yield (240 g/L) from cheap Gly and paraformaldehyde using d-threonine aldolase (DTA) from Arthrobacter sp ATCC. In order to fully utilize d-Ser and expand the resource of l-Ser, a dynamic kinetic resolution system was constructed to convert d/dl-Ser to l-Ser through combining alanine racemase (Alr) from Bacillus subtilis with l-tryptophan synthase (TrpS) from Escherichia coli k-12 MG1655, and l-ncAAs including l-Trp and l-Cys derivatives were synthesized with excellent enantioselectivity and in high yields. The results indicated l-ncAAs could be efficiently synthesized from d-Ser using this original and green dynamic kinetic resolution system, and the reliable l-Ser resource has been established from simple and achiral substrates.
- Yu, Jinhai,Li, Jing,Gao, Xia,Zeng, Shuiyun,Zhang, Hongjuan,Liu, Junzhong,Jiao, Qingcai
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p. 6618 - 6625
(2019/11/03)
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- Substituent Effects on the Spectral, Acid-Base, and Redox Properties of Indolyl Radicals: A Pulse Radiolysis Study
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Spectral and acid-base properties and reduction potentials of various substituted indolyl radicals were studied by pulse radiolysis in aqueous solutions at 20 deg C.Except for the 5-methoxyindolyl and 5-carboxyindolyl radicals, the spectra of the substituted indolyl radicals resemble the previously published 320- and 520-nm spectra of the neutral and 330- and 580-nm spectra of the cation indolyl and tryptophan radicals.The substitution of indolyl radical cation by electron-attracting groups (positive ?+) results in a blue shift of the 580-nm band by ca. 30 nm,, whereas the spectra of methylindolyl (?+ = -0.31) are similar to those of unsubstituted indolyl radicals.The 430- and 455-nm bands appearing in the spectra of the 5-carboxyindolyl and 5-methoxyindolyl radical cations, respectively, indicate even stronger interaction of the unpaired electron with the 5-substituent.The radical cations of various indole-3-acetic acids decarboxylate at pH values below their pKa to produce allyl radicals.The 5-bromoindolyl radical undergoes solvolysis to 5-hydroxyindolyl radical in acidic and alkaline media.The dissociation constants and reduction potentials of the substituted indolyl radicals correlate with the Brown substituent constants: pKr = 4.14 - 2.13Σ?+, correlation coefficient 0.987, and E0/0.059 = 22.29 + 3.5Σ?+, correlation coefficient 0.980.The ρ values from these correlations (-2.13 and 3.5) are similar to that of the Hammett correlation of the dissociation constants of the protonated indole nitrogen in various substituted indoles, ρ = -2.49, but smaller than the ρ value of the dependence on the substituent of the reduction potentials of phenoxyl radicals, ρ = 5.4.
- Jovanovic, Slobodan V.,Steenken, Steen
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p. 6674 - 6679
(2007/10/02)
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- Syntheses of Substituted L- and D-Tryptophans
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Several 5-substituted nb-methoxycarbonyl-L- and -D-tryptophan derivatives were synthesized from proline by a new route involving electrochemical oxidation, as well as by the known procedures.Removal of the Nb-methoxycarbonyl group was accomplished by treatment with Me3SiI in refluxing chloroform, then alkaline hydrolysis of the methyl esters afforded 5-substituted L- and D-tryptophans with high optical purities.Keywords - L-tryptophan 5-substituted; D-tryptophan 5-substituted; anodic oxidation; N-methoxycarbonyl group deprotection; Fischer indole synthesis; iodotrimethylsilane
- Irie, Kunihiko,Ishida, Akihiko,Nakamura, Tohru,Oh-ishi, Tokuro
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p. 2126 - 2139
(2007/10/02)
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