Stereoselectivity

Preliminary experiments shows, that [3+2] cycloadditions reactions proceeds with full regioselectivity and high stereoselectivity. In consequence, 3,4-trans-2-methyl-3-(3,4,5-trimethoxyphenyl)-4-halo-4-nitroisoxazolidines are forming as predominantly (or sole) products. Additionally, prognosis for the synthesized compounds to be potential ingredients of drugs is good.

6p tocectocec 26-05-2020 20 1   Download

Một tổng hợp stereoselective cao của đoạn tubuphenylalanine (9) của tubulysin được mô tả với các bước quan trọng của Phản ứng ngưng tụ Wittig và hydro hóa chọn lọc của liên kết đôi. Sản phẩm mong muốn đã được xác nhận bởi Quang phổ 1D và 2D-NMR.

4p bautroibinhyen211 26-11-2018 19 3   Download

Phản ứng của Michael của enolates là một trong những phản ứng hình thành liên kết C-C quan trọng nhất trong tổng hợp hữu cơ. Gần đây sự phát triển của hệ thống chất xúc tác chiral (chất xúc tác kim loại và chất xúc tác) cho phép phản ứng của Michael của enolates được thực hiện trong điều kiện nhẹ cho các sản phẩm bổ sung mong muốn ở năng suất cao và enantioselectivity. Trong bài đánh giá này, Một số khía cạnh quan trọng liên quan đến stereoselectivity và enantioselectivity được thảo luận chi tiết.

12p lamtan3547 04-11-2018 133 5   Download

We have determined the nucleotide sequence of a DNA fragment covering the flanking region of the R-stereoselective amidase gene, ramA, from the Pseudomonassp. MCI3434 genome and found an additional gene, bapA, coding for a protein showing sequence similarity to DmpA aminopeptidase from Ochrobactrum anthropiLMG7991 (43% identity).

10p fptmusic 11-04-2013 32 3   Download

NAD + -dependent (R)-2-hydroxyglutarate dehydrogenase (HGDH) cata-lyses the reduction of 2-oxoglutarate to (R)-2-hydroxyglutarate and belongs to the D-2-hydroxyacid NAD + -dependent dehydrogenase (D-2-hydroxyacid dehydrogenase) protein family. Its crystal structure was determined by phase combination to 1.98 A˚ resolution. Structure–function relationships obtained by the comparison of HGDH with other members of theD-2-hydroxyacid dehydrogenase family give a chemically satisfying view of the substrate stereoselectivity and catalytic requirements for the hydride trans-fer reaction.

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Kinetic experiments with a substrate series of phenylacetyl-arylamides reveal that at least one polar group in the amine moiety is required for the proper orientation of the substrate in the large nucleophile-binding subsite of penicillin acylase ofEscherichia coli. Quantum mechanical molecular model-ling of enzyme–substrate interactions in the enzyme active site shows that in the case of substrates lacking local sym-metry, the productive binding implies two nonsymmetrical arrangements with respect to the two positively charged guanidinium residues of ArgA145 and ArgB263....

8p dell39 03-04-2013 43 3   Download

A novel amidase acting on (R,S)-piperazine-2-tert-butyl-carboxamide was purified fromPseudomonassp. MCI3434 and characterized. The enzyme acted R-stereoselectively on (R,S)-piperazine-2-tert-butylcarboxamide to yield (R)-piperazine-2-carboxylic acid, and was tentatively named R-amidase. The N-terminal amino acid sequence of the enzyme showed high sequence identity with that deduced from a gene named PA3598 encoding a hypothetical hydrolase in Pseudomonas aeruginosaPAO1.

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An amidase acting on (R,S)-piperazine-2-tert-butylcarbox-amide was purified fromPseudomonas azotoformansIAM 1603 and characterized. The enzyme actedS-stereoselec-tively on (R,S)-piperazine-2-tert-butylcarboxamide to yield (S)-piperazine-2-carboxylic acid. N-terminal and internal amino acid sequences of the enzyme were determined. ThegeneencodingtheS-stereoselective piperazine-2-tert-butylcarboxamide amidase was cloned from the chromo-somal DNAof the strain and sequenced.

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We addressed the ability of various organophosphorus (OP) hydrolases to catalytically scavenge toxic OP nerve agents. Mammalian paraoxonase (PON1) was found to be more active than Pseudomonas diminutaOP hydrolase (OPH) and squidO,O-di-isopropyl fluorophosphatase (DFPase) in detoxifying cyclosarin (O-cyclohexyl methylphosphonofluoridate) and soman (O-pinacolyl methylphosphonofluoridate).

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The effect of pH and temperature on structure, stability, activity and enantioselectivity of haloalkane dehalogenase DbjA from Bradyrhizobium japonicum USDA110 was investigated in this study. Conformational changes have been assessed by circular dichroism spectroscopy, functional changes by kinetic analysis, while quaternary structure was studied by gel filtration chromatography.

11p cosis54 05-01-2013 56 4   Download