• Bulletin of the Korean Chemical Society
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• 제17권4호
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• pp.380-384
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• 1996

Lithium trimethylalkynylaluminates, prepared conveniently by reacting trimethylaluminum with lithium alkynide, readily react with aldehydes and ketones to give the corresponding propargyl alcohols in 70-95% yields. The reaction is highly chemoselective; thus many other functional groups such as amides, nitriles, epoxides and halogen compounds are inert under the reaction conditions. The reagents also show an excellent 1,2-regiospecificity in the reactions with cyclic or acyclic α,β-unsaturated carbonyl compounds.

• 한국환경과학회지
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• 제3권1호
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• pp.65-76
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• 1994

자연호소의 혐기성 저질을 특정한 chlorophenol(CP)에 적응시킨 후 다른 구조물 가진 CP에 대한 탈염소 특성을 검토하였다. CP에 노출되지 않는 혐기성 저질에서는 mono-CP의 경우 ortho > meta > para-염소의 손으로 di-CP의 경우는 ortho > par > meta- 염소의 순서로 짧은 지체기를 거친 후 탈염소가 발생하였다. Mono-CP 중 2-CP에 적응된 저질은 4-CP와 3,4DCP를 제외하고, 3-CP에 적응시킨 저질은 4-CP를 제외한 모든 시험물질에 대하여 지체기 없이 탈염소 특성을 나타내었다. DCP에 적응된 모든 저질은 2-CP, 2,3,-, 2,4-, and 3,4-DCP를 지체기 없이 탈염소가 발생하지 않았다. 이 결과에서 볼 때 mono-와 di-CP를 탈염소시키는 혐기성 미생물의 종류가 다양함을 알 수 있다.

• 대한방사성의약품학회지
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• 제3권1호
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• pp.3-14
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• 2017

Nucleophilic aromatic fluorination has been one of the most explored methods in fluorin-18 based radiochemistry. Unlike electrophilic $[^{18}F]$fluorination methods, no-carrier-added nucleophilic radiofluorination with cyclotron-produced $[^{18}F]$fluoride ion offers better specific radioactivity which is essential aspect to obtain good quality images from positron emission tomography. Contrary to amenable aliphatic radiofluorination, the development of reliable aromatic $[^{18}F]$fluorination methods has been pursued by many research groups; however, no viable method has yet been established. Recently, hypervalent iodine compound draws increasing attention as versatile radiolabeling precursor for various $[^{18}F]$fluoroarenes, since it bears the capacity to introduce fluorine-18 either on electron-deficient or electron-rich aryl ring with enhanced regiospecificity. Other classes of hypervalent iodine congeners often utilized in radiochemistry are iodylarenes, iodonium ylides, and spirocyclic iodonium ylides. Recently developed spirocyclic iodonium ylides have already been avidly employed to provide various $[^{18}F]$aryl fluorides with high labeling efficiency. This metal-free protocol would afford efficient routes, replacing the traditional approaches to $[^{18}F]$fluoroarenes, from prosthetic labeling synthons to complex PET radiotracers.

• Journal of Microbiology and Biotechnology
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• 제15권1호
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• pp.188-191
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• 2005

Abstract Cyclosporins are a family of clinically-important immunosuppressive cyclic peptides produced by Tolypocladium inflatum. The structural modification of cyclosporins via hydroxylation at various positions of N-methyl leucines in cyclosporin A leads to a dramatic change of their bioactive spectra. Among over 100 soil actinomycetes screened, two actinomycetes species, Sebekia benihana and Pseudonocardia autotrophica, were identified to contain superior cyclosporin A hydroxylation activities. A HPLC-based cyclosporin A hydroxylation assay revealed that each strain possesses distinctive hydroxylation specificity and regiospecificity; mono-hydroxylation at the 4th N-methyl leucine of cyclosporin A by S. benihana, and di-hydroxylations at both 4th and 9th N-methyl leucines of cyclosporin A by P. autotrophica. The conversion yields for cyclosporin A hydroxylation by both S. benihana and P. autotrophica were significantly improved from less than 10% and 18% up to 58% and 45%, respectively, in the optimized culture containing molybdenum with 0.05 g/l of cyclosporin A concentration. An ancymidol-specific inhibition of cyclosporin hydroxylation also suggested that the regiospecific cyclosporin hydroxylation might be catalyzed by a putative cytochrome P450 mono-oxygenase enzyme.

• Bulletin of the Korean Chemical Society
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• 제18권8호
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• pp.874-880
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• 1997

Various classes of phospholipids were investigated for the structural determination of fatty acyl groups by fast atom bombardment tandem mass spectrometry (FAB-MS/MS). Phospholipids were desorbed by FAB as molecules chelated with sodium ion (or ions). Collision-induced dissociation (CID) of intact sodium adduct molecular ions ([M+Na]+, [M-H+2Na]+ or [M+Na-2H]-) produced a series of homologous fragment ions via the charge-remote fragmentation along the fatty acid chains. These ions were found useful to locate the double bond positions even for the polyunsaturated fatty acid chains. The regiospecificity of the acyl chain linkages in phosphatidylcholine (PC) could also be determined based on the ratio of relative abundance of the product ions (i.e., [M+Na-85-R2COOH]+ vs [M+Na-85-R1COOH]+) in CID-MS/MS of [M+Na]+. These are generated by the loss of fatty acyl groups at sn-1 and sn-2, respectively, together with the choline group. In all the phospholipid compounds investigated, loss of the fatty acid at the sn-2 position was dominant. The present method was applied to the structural determination of molecular species of phosphatidylglycerols (PG) isolated from cyanobacterium Synechocystis sp. PCC 6803.

• Journal of Microbiology and Biotechnology
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• 제19권12호
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• pp.1547-1556
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• 2009

A novel thermostable $\alpha$-glucosidase (TtGluA) from Thermoanaerobacter tengcongensis MB4 was successfully expressed in E. coli and characterized. The TtgluA gene contained 2,253 bp, which encodes 750 amino acids. The native TtGluA was a trimer with monomer molecular mass of 89 kDa shown by SDS-PAGE. The purified recombinant enzyme showed hydrolytic activity on maltooligosaccharides, p-nitrophenyl-$\alpha$-D-glucopyranide, and dextrin with an exotype cleavage manner. TtGluA showed preference for short-chain maltooligosaccharides and the highest specific activity for maltose of 3.26 units/mg. Maximal activity was observed at $60^{\circ}C$ and pH 5.5. The half-life was 2 h at $60^{\circ}C$. The enzyme showed good tolerance to urea and SDS but was inhibited by Tris. When maltose with the concentration over 50 mM was used as substrate, TtGluA was also capable of catalyzing transglycosylation to produce $\alpha$-1,4-linked maltotriose and $\alpha$-1,6-linked isomaltooligosaccharides. More importantly, TtGluA showed exclusive regiospecificity with high yield to produce $\alpha$-1,6-linked isomaltooligosaccharides when the reaction time extended to more than 10 h.

• 대한화학회지
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• 제26권1호
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• pp.7-17
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• 1982

Diels-Alder 반응의 배향성에 대한 치환기 및 산촉매 효과를 예측하기 위해 또 Lewis산이 diene, dienophile과의 착물 형성의 경쟁성을 예측하기 위해서 Diels-Alder 반응의 열 또는 촉매반응에 FMO이론을 적용하여 CNDO/2 방법으로 고찰하였다. (1)Acetoxy로 치환된 diene의 카르보닐 산소는 dienophile보다 더 큰 음 전하를 갖기 때문에 Lewis 산이 dienophile보다는 diene에 우선적으로 배위하였다. (2) 본 연구의 대부분의 반응은 Neutral electron demand 반응형태를 가지므로 4-c, 2-c 및 정량적인 SOI방법이 일반적으로 실험적인 주 배향체와 일치함을 알았다. (3) 황은 빈 d-궤도 함수의 참여로 인해서 산소에 비해 치환기의 인접된 말단 탄소원자의 LUMO를 크게 활성화 시켜 Neutral electron demand 반응에서의 diene LUMO-dienophile HOMO 상호작용을 크게 해주어 배향성 결정에 주도적 역할을 하게 되었다.