Acetate as substrate

C. la Rosa, F. Pariente, L. Hernandez, and E. Lorenzo, Determination of organophosphorus and car-bamic pesticides with an acetylcholinesterase amperometric biosensor using 4-aminophenyl acetate as substrate. Anal. Chim. Acta 295, 273-282 (1993). 

T. M. Kitson, The Action of Cytoplasmic Aldehyde Dehydrogenase on Methyl p-Nitro-phenyl Carbonate and p-Nitrophenyl Dimethylcarbamate , Biochem. J. 1989, 257, 579-584 T. M. Kitson, K. E. Kitson, A Comparison of Nitrophenyl Esters and Lactones as Substrates of Cytosolic Aldehyde Dehydrogenase , Biochem. J. 1996, 316, 225-232 T. M. Kitson, K. E. Kitson, Studies of the Esterase Activity of Cytosolic Aldehyde Dehydrogenase with Resorufin Acetate as Substrate , Biochem. J. 1997, 322, 701-708. 

Using 5(3,6(3-epoxycholestan-3(3-yl acetate as substrate, other solvents were also screened in this reaction and it was observed that using MeN02, a solvent with higher dielectric constant, the preferential formation of the backbone rearranged derivative occurred, but the Westphalen-type compound was also formed (Scheme 31). 

Methanogens can use only a limited number of Ci compounds and acetate as substrates for growth and methane formation (Reactions 1-11 of Table 1). Very recently pyruvate was shown to be a methanogenic substrate [35]. The substrates can be divided into two groups CH4 is foiTned either by the reduction of CO2 (Reactions 1-4) or by the reduction of a methyl-group (Reactions 5-11) with different electron donors. For a distribution of... 

This technique was adapted to thin layer chromatography by Acker-mann (43), The substrates used were 1-naphthylacetate, 2-azobenzene-l-naphthylacetate, and indoxylacetate. Sensitivity was in the nanogram range. A later study (44) was carried out using different activation techniques in an attempt to make the procedure more sensitive. Mendoza et al, (45) used indoxyl and substituted indoxyl and naphthyl acetates as substrates. Indigo compounds produced by the hydrolysis of these... 

It has already been mentioned that there are some doubts A26) about the existence of an anionic site in human or horse cholinesterase. Comparative kinetic studies using a series of pyridylcarbinol acetates as substrates have shown that acetylcholinesterase from T. marmorata electric organ and the plasma cholinesterases from horse and man have similar esteratic sites. It was also shown that the electric eel organ enzyme has an anionic site, whereas the second site of butyrylcholine... 

Catalytic enantioselective protonations of metal enolates already published can be roughly classified into two methods carried out under basic conditions and acidic conditions. The process under basic conditions is, for example, the protonation of reactive metal enolates such as lithium enolates with a catalytic amount of chiral acid and an excess of achiral acid. The process under acidic conditions employs silyl enol ethers or ketene silyl acetals as substrates. Under the influence... 

Enol ethers are interesting substrates for epoxidations since a-hydroxy ketones or the corresponding acetals are isolated, depending on the choice of solvent. Kat-suki has used enol ethers as substrates, including the cyclic enol ether (4.67), which affords the hydroxy acetal product (4.68). ° Adam has used silyl enol ethers and silyl ketene acetals as substrates. A typical example is provided by the asymmetric oxidation of silyl enol ether (4.69), generating the oi-hydroxy ketone (4.70) after a suitable work up. ... 

The development of the new tridentate ligand-titanium complex 67, by Carreira et al. allows the use of silylketene acetals as substrates. 3-Hydroig esters were obtained in high yields and enantioselectivities (Scheme 7.40). In addition, cheap and easily available 2-methoxypropene was found to be a suitable alternative to silyl enol ethers. 

Beside the above-mentioned hydroxylation steps, oxygenation at C-9 is also presumed to occur fairly early in the pathway. A clone for the cytochrome P450 taxoid 9a-hydroxylase was tentatively identified, but testing the 5a,13a-diol, the 5a,10p-diol, and the corresponding 5a-acetates as substrates could not provide sufficient biosynthetic products to permit NMR-based confirmation of structures [251]. 

About 70% of methane is produced by aceticlastic methanogens using acetate as substrate. 

M. expansa was cytosolic and conjugated CDNB but not bromobenzene or chlorobenzene (Douch and Buchanan 1978). Similarly, glutathione-S-transferase activity in H. contortus was observed only with CDNB as substrate and not with DCNB or l,2-epoxy-3-(p-nitrophenoxy)propane (Kawalek et al. 1984). Neither M. expansa not A. suum produced glucuronides with 4-nitrophenol, 2-aminophenol or 4-methylumbelliferone (Douch and Blair 1975), or possessed measurable DDT-dehydrochlorinase activity (Douch and Buchanan 1978). Various specific (cholinesterase) and non-specific esterases have been detected in trematodes, e.g. using a-naphthyl acetate as substrate, in A laria marcianae (Dickinson and Johnson 1978) and Schistosoma mansoni and Schistosoma haematobium (Coles 1970). 

Finally, Chen s work on the direct allylation of carbonyl compounds using benzyl alcohol in the multicomponent Sakurai reaction catalyzed by selective and green solid acids, such as sihcomolybdic acid (SMA-SiO ) [92] or perchloric acid (HClO -SiOj) [93], both supported on silica gel, should be mentioned. In some cases, the use of preformed acetals as substrates provided better results. These methods allowed the synthesis of a broad number of homoallylic ethers in moderate to high yields in a short reaction time. Significantly, catalyst loading of HClO -SiOj is only 2mol%. 

The same catalytic system proved to be advantageous for the tandem hydroformylation (Wittig olefination) reaction of a more sophisticated vinyl acetate as substrate at about 10bar (Scheme 4.68) [41]. (-p)-Patulohde C, a compound exhibiting both antifungal and antibacterial activity, was obtained with 93% de (for more details and examples of stereoselective tandem reactions, see Section 5.5). 

Also of interest is the model developed by Breslow and Overman (183) where a metal ion is introduced into a cyclodextrin-subtrate complex. With p-nitrophenyl acetate as substrate the presence of Ni(II) in the cyclodextrin-substrate complex results in a further increase in rate of hydrolysis by a 1000-fold. 

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