Substrate isopropanol

The NADP-dependent TBADH was used for the laboratory-scale preparation of several chiral aliphatic and cyclic hydroxy compounds by reduction of the corresponding ketones. For the regeneration of NADPH, this reduction reaction can be coupled with the TBADH catalyzed oxidation of isopropanol. For the reduction of some ketones it was observed that the reaction rate was increased in the presence of the regenerating substrate isopropanol, for instance in the presence of 0.2 v/v isopropanol, the reduction rate of butanone or pentanone was increased 3-4-fold [57], In some cases, the enantiomeric excess of the reduction reaction is not very high, especially when small molecules are converted, but also for compounds such as acetophenone [138]. 

In photosynthetic bacteria, HgA is variously HaS (photosynthetic green and purple sulfur bacteria), isopropanol, or some similar oxidizable substrate. [(CH2O) symbolizes a carbohydrate unit.]... 

The reverse reaction, the so-called Oppenauer oxidation, is carried out by treating a substrate alcohol with aluminum tri-r-butoxide in the presence of acetone. By using an excess of acetone, the equilibrium can be shifted to the right, yielding the ketone 1 and isopropanol ... 

The hydrogen transfer reaction (HTR), a chemical redox process in which a substrate is reduced by an hydrogen donor, is generally catalysed by an organometallic complex [72]. Isopropanol is often used for this purpose since it can also act as the reaction solvent. Moreover the oxidation product, acetone, is easily removed from the reaction media (Scheme 14). The use of chiral ligands in the catalyst complex affords enantioselective ketone reductions [73, 74]. 

Two studies have been performed by Littler on the oxidation of cyclohexanol by Hg(II), the second leading to more detailed and reliable data. The reaction is first-order in both oxidant and substrate but the rate is independent of acidity. E is 24.8 kcal.mole AS is 1 eu, Ath/Acd is 3.0 and ko ol HzO 1-30-At 50 °C di-isopropyl ether is attacked at about one-half the rate of isopropanol, which implies that hydride ion abstraction is occurring in both cases. This is supported in the case of cyclohexanol by the isotope effects. 

Transfer hydrogenation of aldehydes with isopropanol without addition of external base has been achieved using the electronically and coordinatively unsaturated Os complex 43 as catalyst. High turnover frequencies have been observed with aldehyde substrates, however the catalyst was very poor for the hydrogenation of ketones. The stoichiometric conversion of 43 to the spectroscopically identifiable in solution ketone complex 45, via the non-isolable complex 44 (Scheme 2.4), provides evidence for two steps of the operating mechanism (alkoxide exchange, p-hydride elimination to form ketone hydride complex) of the transfer hydrogenation reaction [43]. 

Other substrates which can be utilized as reducing agents by various photosynthetic bacteria are hydrogen, isopropanol, thiosulfate, and selenium/ ... 

In a study looking at solvent stability [424], various aqueous-miscible solvents (tetrahydrofuran, acetonitrile, isopropanol, methanol, and A,A-dimethylformamide) were used with pinacyanol chloride as substrate. Although a PAH was not used as a substrate, the results may be extrapolated to PAH reactions. The greater impact of peroxide as compared to the solvent on biocatalyst stability was reported in this study and the need to control peroxide concentration was noted. 

The nylon or glass substrate on which the probe solution is deposited must be pretreated with coupling agents such as lysine or acrylamide functional groups. Coupling agents bind the probe cDNA to the substrate. After hybridization, the array is washed in heated isopropanol and water to remove any unhybridized sample DNA. It is essential... 

Dense membranes are a special type of polymeric membranes. Jacobs et al. published on the use of polydimethylsiloxane (PDMS) dense membranes in the hydrogenation of dimethylitaconate and acetophenone using standard homogeneous catalysts (see Section 4.6.1)[48]. The membranes were homemade from a PDMS solution in hexane, which was cross-linked in a vacuum oven at 100°C. The membranes were able almost completely to retain unmodified Ru-BINAP dissolved in isopropanol. However, as mentioned earlier, these applications will strongly depend on the size, i.e. molecular weight, of the substrate to be converted in order to guarantee a sufficient difference in size of the product and the catalyst to be retained. 

STM-BJ experiments were performed to extract single-junction conductances of 44-BP bridged between a gold STM tip and an Au (111) substrate in non-polar solvents, such as mesitylene, isopropanol, and 1,2,4-trichlorobenzene, as well as under full electrochemical potential control in aqueous solutions of HCIO4 and LiClOq at various pH. 

The standard ruthenium arene and CATHy catalysts are insoluble in water, but are nevertheless stable in the presence of water. Reactions in the I PA system can be carried out in mixtures of isopropanol and water the net effect is a lower rate due to dilution of the hydrogen donor. The use of formate salts in water, with CATHy or other transfer hydrogenation catalysts dissolved in a second immiscible phase was shown to work well with a number of substrates and in some cases to improved reaction rates [34]. The use of water as reaction solvent will be discussed in more detail in Section 35.5. 

The catalysts are best prepared in situ by mixing a half-equivalent of the di-chloro-metal aromatic dimer with an equivalent of the ligand in a suitable solvent such as acetonitrile, dichloromethane or isopropanol. A base is used to remove the hydrochloric acid formed (Fig. 35.3). If 1 equiv. of base is used, the inactive pre-catalyst is prepared, and further addition of base activates the catalyst to the 16-electron species. In the IPA system the base is conveniently aqueous sodium hydroxide or sodium isopropoxide in isopropanol, whereas in the TEAF system, triethylamine activates the catalyst. In practice, since the amount of catalyst is tiny, any residual acid in the solvent can neutralize the added base, so a small excess is often used. To prevent the active 16-electron species sitting around, the catalyst is often activated in the presence of the hydrogen donor. The amount of catalyst required for a transformation depends on the desired reaction rate. Typically, it is desirable to achieve complete conversion of the substrate within several hours, and to this extent the catalyst is often used at 0.1 mol.% (with SCR 1000 1). Some substrate-catalyst combinations are less active, requiring more catalyst (e.g., up to 1 mol.% SCR 100 1), in other reactions catalyst TONs of 10000 (SCR 10000 1) have been realized. 

The mechanism of the Meerwein-Pondorf-Verley reaction is by coordination of a Lewis acid to isopropanol and the substrate ketone, followed by intermolecular hydride transfer, by beta elimination [41]. Initially, the mechanism of catalytic asymmetric transfer hydrogenation was thought to follow a similar course. Indeed, Backvall et al. have proposed this with the Shvo catalyst [42], though Casey et al. found evidence for a non-metal-activation of the carbonyl (i.e., concerted proton and hydride transfer [43]). This follows a similar mechanism to that proposed by Noyori [44] and Andersson [45], for the ruthenium arene-based catalysts. By the use of deuterium-labeling studies, Backvall has shown that different catalysts seem to be involved in different reaction mechanisms [46]. 

PfefFer, de Vries and coworkers developed the use of ruthenacycles, based on chiral aromatic amines as enantioselective transfer hydrogenation catalysts. These authors were able to develop an automated protocol to produce these catalysts by reacting ligand and metal precursor in the presence of base, KPFS in CH3CN. After removal of the solvent, isopropanol was added followed by the substrate, acetophenone, and KOtBu. In this way, a library of eight chiral... 

The Meerwein-Ponndorf-Verley reaction is a classic method for ketone/ aldehyde carbonyl group reduction, which involves at least 1 equivalent of aluminum alkoxide as a promoter. In this reaction, the hydrogen is transferred from isopropanol to the ketone/aldehyde substrate, so the reaction can also be referred to as a transfer hydrogenation reaction. 

The use of water-miscible organic solvent-water mixtures is a particularly attractive method for use with cofactor-dependent enzymes due to its simphcity. The high water content can allow dissolution of both enzyme and cofactor, whilst the water-miscible solvent can provide a dual role in both substrate dissolution and as a cosubstrate for cofactor recycling (substrate-coupled cofactor recycling).The asymmetric reduction of a ketone intermediate of montelukast using an engineered ADH in the presence of 50 % v/v isopropanol offers a powerful demonstration of this methodology (Scheme 1.55). 

Ketoreductase enzymes KRED-104 (120mg) and KRED-108 (30mg) and NADP+ (30 mg) were added to 0.5 m potassium phosphate buffer pH 6.5 (9.5 niL) that was stirring at 35 °C. The reaction was started with the addition of a solution of ketone substrate (100 mg) in isopropanol (0.5 mL) and aged for 12h. 

For each Codexis ketoreductase enzyme, 50 pL each of the substrate and cofactor solutions were added to 300 pL isopropanol, 100 pL 0.1 m potassium phosphate buffer pH 7 and 1 mg ketoreductase in one location of a 96-well plate. 

A large number of reports have concerned transfer hydrogenation using isopropanol as donor, with imines, carbonyls-and occasionally alkenes-as substrate (Scheme 3.17). In some early studies conducted by Nolan and coworkers [36], NHC analogues of Crabtree catalysts, [Ir(cod)(py)(L)]PF,5 (L= Imes, Ipr, Icy) all proved to be active. The series of chelating iridium(III) carbene complexes shown in Scheme 3.5 (upper structure) proved to be accessible via a simple synthesis and catalytically active for hydrogen transfer from alcohols to ketones and imines. Unexpectedly, iridium was more active than the corresponding Rh complexes, but... 

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