Methyl acetate, specific activity

Methyl a-acetamidocinnamade hydrogenation of, 42 490, 491 Methyl acetate specific activity, 31 41... 

In order to prepare C -labeled d-a-tocopherol we started from natural d-7-tocopherol (Fig. 6) and introduced the C -methyl group into the 5-position by use of the Mannich reaction. Condensation of d-y-tocopherol with radioactive paraformaldehyde in the presence of diethylamine followed by catalytic reduction gave d-a-tocopherol. This was acetylated to methyl-C Mabeled d-a-tocopherol acetate (specific activity 1.7 tc/mg Fig. 6). 

The introduction of tritium into molecules is most commonly achieved by reductive methods, including catalytic reduction by tritium gas, PH2], of olefins, catalytic reductive replacement of halogen (Cl, Br, or I) by H2, and metal pH] hydride reduction of carbonyl compounds, eg, ketones (qv) and some esters, to tritium-labeled alcohols (5). The use of tritium-labeled building blocks, eg, pH] methyl iodide and pH]-acetic anhydride, is an alternative route to the preparation of high specific activity, tritium-labeled compounds. The use of these techniques for the synthesis of radiolabeled receptor ligands, ie, dmgs and dmg analogues, has been described ia detail ia the Hterature (6,7). 

The route for the cyclization was easier to determine than the identification of the very reactive isoprene unit, and was understood in outline by 1960. Studies of labeled compounds detected within 10 min. of 14C-acetate addition to intestinal preparations showed label in squalene, lanosterol, and a further, unidentified ring compound, all with higher specific activities than cholesterol. By 75 min cholesterol was the main labeled compound. Clayton and Bloch then confirmed that lanosterol, previously known from sheep s wool, was converted to cholesterol with the extra three (methyl) carbon atoms being lost as carbon dioxide. 

Immobilisation of an Acetobacter aceti strain in calcium alginate resulted in improvement of the operational stability, substrate tolerance and specific activity of the cells and 23 g phenylacetic acid was produced within 9 days of fed-batch cultivation in an airlift bioreactor [133]. Lyophilised mycelia of Aspergillus oryzae and Rhizopus oryzae have been shown to efficiently catalyse ester formation with phenylacetic acid and phenylpropanoic acid and different short-chain alkanols in organic solvent media owing to their carboxylesterase activities [134, 135] (Scheme 23.8). For instance, in n-heptane with 35 mM acid and 70 mM alcohol, the formation of ethyl acetate and propylphenyl acetate was less effective (60 and 65% conversion yield) than if alcohols with increased chain lengths were used (1-butanol 85%, 3-methyl-l-butanol 86%, 1-pentanol 91%, 1-hexanol 100%). This effect was explained by a higher chemical affinity of the longer-chain alcohols, which are more hydrophobic, to the solvent. 

The specific activity for both methyl acetate and dimethyl ether as a function of rhodium level on the catalyst was measured and is shown in Fig. 19. Clearly, there is a marked decrease in specific activity for both products with increasing rhodium level in the range 0.5-1 wt.% Rh. The optimum in terms of catalyst efficiency was considered to occur in the range 0.25-0.5 wt.% Rh. The reaction rate was found to be zero order in both CO and CH3OH partial pressures, as has also been found for the homogeneous catalyst system (196). 

Esterases. Acetyl esterase (EC 3.1.1.6) removes acetyl esters from acetylated xylose and short-chain xylo-oligomers. It s polymeracting counterpart, acetyl xylan esterase (EC 3.1.1.72), has a similar activity, but prefers polymeric xylan.244 In addition to acetate-specific enzyme detection kits, HPLC or GC analysis of acetate release from native extracted xylan and chemically acetylated xylan, colorimetric substrates, such as p-nitrophenol acetate and /3-napthyl acetate, or the fluorometric substrate, 4-methylumbelliferyl acetate are also used to assay acetyl esterases.244,253 The third esterase, ferulic acid esterase (EC 3.1.1.73), hydrolyzes the ester bond between ferulic acid or coumaric acid and the arabinose side chain of arabinoxylan. Assays for this activity are usually carried out using starch-free wheat bran or cellulase-treated gramineous biomass as a substrate and monitoring ferulic or coumaric acid released by HPLC or TLC. When preparing enzyme-treated substrates, care must be taken to employ phenolic-acid-esterase-free cellulases.244 Other substrates include methyl and ethyl esters of the phenolic acids, as well as finely ground plant biomass.240,254,255... 

Fig. 16. Electrophoretic separation of the lipase and esterase activities of porcine pancreas (146, 147). Starch columns equilibrated with 0.025 M acetate buffer, pH 5.25. The activities of the fractions have been determined (o) on emulsions of triolein and tributyrin (black circles), methyl oleate, methyl laurate, and p-nitro-phenyllaurate (black triangles), (b) On solutions of methyl butyrate and p-nitro-phenylacetate (crosses). White circles and dotted line, protein background. Figures along the first peak give the specific activity (lipase) of some fractions, determined against triolein emulsion. Ordinates and abscissas are the same as in Fig. 14.

It is known that formic acid is synthesized from H2/CO2 as ester in alcohol solvent using metal complex catalysts such as HM(CO)5 (M W,Cr,Ru) in batch reactor system.[61] However, specific activity (TOF) of these system are relatively low. Recently, Noyori et al. found a significant increase of formic acid in a supercritical mixture of H2/CO2 with N(C2H5)3 using RuH2 P(CH3)3)4 complex at the condition of 20.5 Mpa, 5013 and H2/C02=l/1.4.[62] TOF increased one order of magnitude over that of conventional process because of high miscibdity of H2 with supercritical CO2. It is also noted that methyl formate produced from H2/CO2 is easdy converted to acetic acid by isomerization reaction. 

Generator-produced (equation 165) [ Cu]copper(ll) bis (iV -methylthiosemicarbazo-ne)CuPTSM and CuPTSMj have been suggested as a Cu-62 radiopharmaceutical for evaluation of cerebral and myocardial blood flow by PET Complexes 282-387 of copper-67, a convenient radiolabel which has a half-life of 2.58 days (equation 166), have been prepared in >95% radiochemical yield by addition of NaOH solution of the ligand to an acetate-buffered ethanol solution of the ionic radiocopper [Cu(II) in 2N HCl, specific activity 5 x 10 Ci mol ). The biodistribution of each [ Cu] bis(thio-semicarbazone) complex has been determined. Methylation of the terminal amino groups was found to be essential for good cerebral uptake of tracer . ... 

The dl-a-tocopheryl acetate was labeled in the methyl group in 8-position of the chromane ring and had a specific activity of 3.5 nc/mg. The EMQ was ring-labeled in 2- and 4-position with a specific activity of 5.15 /ic/mg. 

Tuberization in potato plants is considered to be controlled by a specific active compound. The structure of an active tuber-inducing compound from potato leaves was determined to be 3-oxo-2-(5 -3-D-glucopyranbsyloxy-2 -(E)-pentenyl)-cyclopentane-l-acetic acid. The aglycone of this glucoside is 12-OH-jasmonic acid, termed tuberonic acid [53]. Jasmonic acid, methyl jasmonate and cucurbic acid were also shown to be capable of inducing tuberization in potato in vitro [53]. In addition, jasmonic acid seems to be involved in tuberization in yam [54], Jerusalem artichoke [55] and in bulb formation of garlic [56]. 

The devolatilization concept has been extended to certain commonly used isotope sources with the additional advantage of making them more stable or storable. [ H/ C]Methyl nosylate (17) has been developed as a substitute for tritiated or carbon-14-labeled methyl iodide, both of which are relatively unstable and difficult to handle (Figure 1.6). Ester 17 is a nonvolatile, easily purifiable solid that is substantially less radiolytically sensitive than the corresponding methyl halides ([ H]methyl nosylate at a specific activity of > 80 Ci/mmol suffered no appreciable decomposition after storage at 39 mCi/mL for 14 weeks at 4 °C in hexane/ethyl acetate ). This derivative is reported to possess similar reactivity to [ H/ C]methyl iodide in a variety of reactions, and to provide greater flexibUity during use in synthesis. 

Applied to 5-(l,3-dithiacyclopent-2-yl)uracil 11681 and 3/3-acetoxy-7-spiro(l, 3 -dithia-cyclopent-2 -yl)cholest-5-ene (170), Raney nickel tritiolyses furnished [5-methyl- H]-thymine 71691 and [7- H]cholesteryl acetate 71711 in moderate yields with specific activities of 11.6 Ci/mmol and 8.1 Ci/mmol, respectively. ... 

The isomeric valerianic acids have the formula C Hj O.. Normal valerianic acid does not appear to be found in any essential oils. Iso-valerianic acid, (CHg). jCH. CH. COOH, is found in valerian and other oils it is a liquid boiling at 174°, of specific gravity -947. Another isomer, also found in champaca and coffee oils, is methyl-ethyl-acetic acid, (C.,Hg)(CH3). CH. COOH. This is an optically active liquid, boiling at 175°, of specific gravity -941 at 21°. 

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