Selected hydrolysis concept

The most promising new approaches to using enzymes in the pulp and paper industry, however, are based either on the idea of selected hydrolysis of certain components or limited hydrolysis of several components in the fibre. This concept is apparently in accord with both the technical and economic demands of a feasible process. By limiting the extent of hydrolysis... 

Bayer improved upon this concept with the selective hydrolysis of racemic acetamide 3 using C. antarctica lipase B (Figure 14.3) [6]. In this case, the (1 ) acetamide was deacylated, forming the (U) amine 4. Although the enantioselectivities obtained were excellent, the process was not used industrially due to low space time yields. 

On the basis of these three cross coupling reactions, it is probably fair to say that using the OSSOS concept is highly compatible with palladium catalysis but probably not limited to it. For example, a lipase can be used for the kinetic resolution of a racemic ibuprofen ester supported on an imidazolium salt. In a DMSO/phosphate buffer mixture and in the presence of the lipase isolated from Candida antartica, the, V-(+(-supported ibuprofen ester is hydrolyzed selectively (87% ee) in 87% yield. Noticeably, during workup, the support can easily be recovered and reused for another cycle while the other enantiomer can be obtained by hydrolysis using K2CQ3 [137] (Fig. 48). 

Intraligand asymmetric induction. An instructive introduction to intraannular alkylations is the self-regeneration of chirality centers concept introduced by Seebach [62-66]. Scheme 3.9 illustrates the concept and Table 3.1 lists several representative examples. A chiral educt, such as an amino acid derivative, is condensed with pivaldehyde. This derivatization creates a new stereocenter selectively, and this second stereocenter then controls the selectivity of the subsequent alkylation by directing the electrophile to the face of the enolate opposite the tert-butyl group, a good example of intraannular 1,3-asymmetric induction. After purification of the alkylation product, hydrolysis affords enantiomerically pure products. 

The displacement of the heavy ligand by the lighter molecule HCN yields an increase in the sensitivity, a concept identified as "mass amplification", and was not applied to piezoelectric detectors before. As mass is lost from the coated crystal when exposed to HCN, the frequency increases whereas a decrease in frequency is expected if moisture is absorbed by the coating. The effect of humidity was studied over the range of 40-92% RH, and it was shown that humidity plays a part in the reacation. Since the reaction is irreversible and the nickel complex is prone to hydrolysis, the coated crystal could be used once only. Substitution of other ligands in nickel complexes, including dibenzoylmethane, dipivaloyl-methane, formate and acetate, did not improve the selectivity towards HCN. 

Nettekoven has devised an interesting combinatorial approach to diverse libraries of indole derivatives <01BMCL2169>. In this approach, 2-aminobenzonitriles 134 arc treated with acid chlorides affording the amides 135 which upon treatment with various a-bromoketones yield the corresponding indoles 136. Taking advantage of the libraries from libraries concept, the original library could be subjected to selective amide hydrolysis to produce a companion library of N-H indole derivatives. 

Apart from catalysis, supported IL membranes have also been investigated for a variety of separation applications [23], which ranged from the separation of isomeric amines [24] to the enzyme-fadlitated transport of (S)-ibuprofen through a supported liquid membrane [25], The latter study demonstrated the selective separation of the (S)-enantiomer from the racemic mixture (see Figure 3). The concept was that by employing certain enzymes, such as lipase, it would be possible to catalyze the hydrolysis or the esterification ofibuprofen enantioselectively. In this investigation... 

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