摘要:

AbstractReactions of 4,6‐dimethyl‐2β‐hydroxy‐8‐oxo‐3,5,7‐trioxatetracyclo‐[7.2.1.0.4,11.06,10]dodecane 1 with nucleophiles have been studied. Reaction of 1 with alcohols, triethylsilane, allyltrimethylsilane, and methylthiotrimethylsilane in CH2Cl2in the presence of TiCL4, gave the substitution products 2,7a, 7b, and 7c in 80‐90% yields. The substitution reaction took place chemoselectively on the hemiacetal group of I. Reaction of 1 with cyanotrimethylsilane in CH2C12in the presence of TiCL4, gave compound 8 and the rearranged product 9. The structure of 9 was proven

ISSN:0009-4536    

DOI:10.1002/jccs.199700011

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

Abstractα‐Arylthioalkyl esters can be prepared by the addition reactions of vinyl esters with arylthiols in the presence of Pseudomonas lipase (PSL) as catalyst. In the toluene, the reaction mixtures were stirred at 60 °C for three days, the chemical yields up to 85% were obtai

ISSN:0009-4536    

DOI:10.1002/jccs.199700012

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA sweet almond β‐glucosidase (EC 3.2.1.21) isozyme was purified from commercial crude product. The process of purification consisted of a Protein‐Pak Q anion exchange chromatography following by a Superdex 75 HR gel filtration separation. The purified enzyme is a monomeric glycoprotein with molecular weight of 58 kDa and pI=4.55 which is distinguished from reported isozymes. The enzyme has apH optimum in the range of 5.2‐5.6 whenp‐nitrophenyl‐β‐D‐glycopyranosides are used as substrate and is stable up to 50 °C at that pH range. The purified protein also exhibits profound β‐galactosidase and σ‐L‐arabinosidase activity. The study of substrate specificity revealed that lacking of hydroxymethyl group at C‐5 of glycosides resulted in higher affinity for substrate binding to enzyme, whereas the chemical step of hydrolysis (kcst) was prevented significantly. The pH activity profile displayed a bell‐shaped curve for all measuredp‐nitrophenyl‐β‐D‐glycopyranosides with apparent pK1and pK2values of 4.4‐4.7 and 6.2‐6.4, respectively. This isozyme was strongly inhibited by δ‐gluconolactone (Ki= 160 μM) and 4‐phenylimidazole (Ki= 17.8 μM) reversibly at pH 6.2. Among the tested glycoses, the binding affinity of N‐acetyl‐β‐D‐glucosamine to the enzyme (Kl= 52 mM)

ISSN:0009-4536    

DOI:10.1002/jccs.199700013

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY