• Bulletin of the Korean Chemical Society
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• v.8 no.6
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• pp.471-475
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• 1987

Benzotriazol-1-yl Diethyl phosphate and benzotriazol-1-yl diphenyl phosphate were conveniently prepared in essentially quantitative yields by the reaction of diethyl chlorophosphate and diphenyl chlorophosphate with equal amounts of 1-hydroxybenzotriazole and triethylamine in tetrahydrofuran at room temperature, respectively. Benzotriazol-1-yl diethylphosphate was effective for the preparation of amides from carboxylic acids amines. Young test and Anderson test for racemization studies using benzotriazol-1-yl diethyl phosphate were investigated and practically no racemization occurred. However, racemization occurred to some extent during coupling of Z-Phe-Val-OH with Pro-OBu. Several dipeptides and tripeptides were prepared without little racemization using benzotriazol-1-yl diethyl phosphate. Benzotriazol-1-yl diphenyl phosphate was less effective than benzotriazol-1-yl diethyl phosphate in terms of the degree of racemization.

• Macromolecular Research
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• v.14 no.5
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• pp.510-516
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• 2006

Lactide was produced from oligomeric PLA by back-biting reaction of the OH end groups. For optimization of the reaction conditions, the effects of temperature, pressure, PLA molecular weight, and catalyst type on the lactide synthesis were examined. The fraction of D,L-lactide decreased with increasing temperature. Among the various Sn-based catalysts, the D,L-lactide fraction was maximized when SnO was used. A higher yield with lower racemization was observed at lower pressure. The conversion of PLA was maximized at an oligomeric PLA molecular weight of ca. 1380. The yield of lactide increased but the fraction of D,L-lactide decreased with increasing molecular weight. The highest conversion with the lowest racemization degree was obtained at a catalyst concentration of 0.1 wt%. The lactide was more sensitive to racemization because of the entropic effect.

• Archives of Pharmacal Research
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• v.22 no.6
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• pp.614-618
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• 1999

A reversed-phase high-performace liquid chromatographic method was developed to determine the optical purity of metoprolol enantiomers. The enantiomers were converted to diastereomeric derivatives using (-)-menthyl chloroformate reagent. Separation of the enantiomers as diastereomers was achieved by reversed-phase HPLC within 30 min using Inertsil C8 column. This method allowed determination of 0.05% of either enantiomer in the presence of its stereoisomer and method validation showed adequate linearity over the required range. Owing to the reaction condition during the derivatization with (-)-menthyl chloroformate, the possibility of racemization had to be established. Different ratios of (S)-(-)-metoprolol and (R)-(+)-metoprolol were prepared. Enantiomeric separation of these mixtures took place on a chiralcel OD column or, after derivatization with (-)-menthyl chloroformate, on a C8 column. The results form the these two independent separation systems were compared with trace racemization and were in very good agreement. No racemization was found during the experiment.

• Journal of the Korean Chemical Society
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• v.30 no.4
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• pp.377-382
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• 1986

Racemic tris-oxalatocobaltate (III) complex ions were optically resolved by an optical active complex, ${\Delta}$-tris-ethylenediamine cobalt (III), and then racemization of ${\bigwedge}-[Co(ox)_3]^{3-}$ obtained was investigated in various mixed solvent such as water-organic solvent (organic solvents=ethanol, iso-propyl alcohol, acetone, and dioxane). The rate of racemization was increased with following order; water < ethanol < acetone < isopropyl alcohol < dioxane; which is the same order for polarizability of organic solvent added. Considering ${\Delta}H^{\neq},\;{\Delta}S^{\neq}$ and above facts for the racemization of ${\bigwedge}-[Co(ox)_3]^{3-}$, it seems to be twist mechanism of plausible mechanisms.

• BMB Reports
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• v.33 no.1
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• pp.82-88
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• 2000

A homologous gene to alanine racemase was cloned from a hyperthermophilic bacterium, Aquifex pyrophilus. The cloned gene encodes a protein of 341 amino acids, which has a significant homology to alanine racemase of Bacillus stearothermophilus, Lactobacillus brevis, and E. coli. When the gene was expressed in Escherichia coli, it produced a 40 kDa protein. The purified protein contains one mole pyridoxal 5-phosphate per one mole of protein, which is essential for catalytic activity of alanine racemase. The purified protein catalyzed racemization of L-alanine to D-alanine, or vice versa, indicating that the cloned gene encoded alanine racemase. It also showed significant racemization activity against L-serine and ${\alpha}-aminobutylic$ acid. The A. pyrophilus alanine racemase showed strong thermostability, and it maintained catalytic activity in the presence of organic solvents.

• Archives of Pharmacal Research
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• v.18 no.2
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• pp.69-74
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• 1995

In order to improve physico-chemical properties and to enhance stability of drugs, amino acid salt has been widely adoptd in pharmaceutical synthesis. Acetylsalicylic acid lysinate is one of the widely used analgesics and it is a good example of t5his synthesis. In the case of bacetylsalicylic acid lysinate synthesis, racemization of natrually occurred lysine is esential because the racemic lysine salt of the drug shows better yield, crystallinity and dryness than that of the L-lysine salt. To esatablish a simple, practical and economical process for L-lysine racemization, L-lysine treatments with phosphoric acid and with acetic acid were compared and the optimum conditions for its process and derivatization were investigated by chiral separation methods using GC_MS spectroscopy.

• Bulletin of the Korean Chemical Society
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• v.25 no.6
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• pp.931-933
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• 2004

• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.677-679
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• 2013

• Journal of Oral Medicine and Pain
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• v.14 no.1
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• pp.43-55
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• 1989

The need of age estimation for identification was increased by complexity of society, and the tooth was used widely for age estimation because of less individual deviation than the other organ. The age estimation using the tooth had several methods. Recently, the one using the racemization of aminoacid in the tooth was admitted more accurate than the other methods, especially in old age. But, this study was not tried in our country, and I would report the result of experiment about age estimation using racemization of dentine. I selected 40-Whole dentine sample from extracted teeth, those were reserved in natural dried condition for 2 weeks~ 1year and calculated the estimation of age from the ratio of D-aminoacid and L-aminoacid (D/L ratio) using gaschromatography and the results were below. 1. The aminoacids showed apparent K/L ratio in dentine were aspartic acid, serine. 2. The aspartic acid showed the highest racemic rate and its rate was 0.0012$\pm$0.0003/yr. 3. The relation between the actual age and K/L ratio was very positive correlation(r+0.954) in the estimation of age using aspartic acid. 4. The deviation between the estimated age using D/L ratio of aspartic acid and actual age was $\pm$3.32.

• KSBB Journal
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• v.19 no.3
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• pp.215-220
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• 2004

A variety of solid bases such as inorganic bases, basic anion exchange resins, and resin-bound bases were tested as a catalyst for racemization of (S)-naproxen 2,2,2-trifluoroethyl thioester in isooctane at 45$^{\circ}C$. Among the various bases, DIAIOM WA30, which is a weakly basic anion exchange resin with a tertiary amine based on a highly porous type styrene-divinylbenzene copolymer, showed the highest catalytic activity. The second-order interconversion constant of DIAION WA30 was 8.6${\times}$10$\^$-4/ mM$\^$-1/h$\^$-1/ and about 3 times higher than that of trioctylamine under the same conditions. The rate of DIAION WA30-catalyzed racemization decreased with increasing an amount of water added to the reaction medium. Lipase-catalyzed kinetic resolution of racemic naproxen 2,2,2-trifluoroethyl thioester was successfully carried out under in situ racemization of substrate with DIAION WA30 in isooctane at 45$^{\circ}C$. More than 60% conversion and 99% enantiomeric excess for the desired (S)-naproxen product were obtained. Furthermore, such a solid base catalyst could be easily separated and reused in contrast to trioctylamine.