In situ regeneration

Shimomura, O., and Inouye, S. (1999). The in situ regeneration and extraction of recombinant aequorin from Escherichia coli cells and the purification of extracted aequorin. Protein Expression and Purification 16 91-95. 

The homocoupling of aryl halides and triflates can be made catalytic in nickel by using zinc as a reductant for in situ regeneration of the active Ni(0) species. 

Adsorption. Adsorption of VOCs is most often carried out using activated carbon with in-situ regeneration of... 

Burch, R., Fornasiero, P. and Southward, B.W.F. (1999) An investigation into the reactivity, deactivation and in situ regeneration of Pt-based catalysts for the selective reduction of NOx under lean burn conditions, J. Catal. 182, 234. 

Rupprath, C., Kopp, M., Hirtz, D. et al. (2007) An enzyme module system for in situ regeneration of deoxythymidine 5 -diphosphate (dTDP)-activated deoxy sugars. Advanced Synthesis Catalysis, 349, 1489-1496. 

Except for those catalysts subjected to the previously mentioned conditions, which lead to irreversible transformation of the active phase and/or the support material, the HDT catalysts are regenerable [37], Through a systematic and careful procedure, the spent catalyst is unloaded from the reactor and regenerated by specialized companies. The possibility of in situ regeneration is also commercially offered and the decision, on which method would be used, is typically based on economical considerations [38],... 

The reported procedure for the selective oxidation of natural glycosides is mild, convenient and easily reproducible. The biotransformations are performed in mildly acidic water solutions therefore, this method is complementary to other chemical approaches for the in situ regeneration of the oxidized form of TEMPO, such as sodium hypochlorite, that require alkaline pH. 

As is implicit in the fact that the products of the (stoichiometric) 1,6-cuprate addition - the lithium allenyl enolate and the organocopper compound - are formed as independent species, it is also possible to conduct the reaction catalytically through in situ regeneration of the cuprate. The reaction can thus be run in a continuous mode, with only catalytic amounts of the preformed cuprate being necessary (with simultaneous addition of the substrate and the organolithium compound) enabling the desired allenes to be prepared even on larger scales (Eq. 4.17) [3oj. 

Acetate Acetyl-P Pyr PEP poly P)n-i poly(P) Scheme 4.7 General scheme of the kinase-dependent phosphorylation of DHA with in situ regeneration of ATP. 

UDP-a-D-Gal UDP-a-D-GlcNAc GDP-a-D-Man GDP-P-l-Fuc CMP-Neu5Ac In situ regeneration systems for nucleotide sugars UDP-a-D-Glc combinatorial biocatalysis [44-49]... 

In summary, the synthesis and in situ regeneration of nucleotide sugars by combinatorial biocatalysis suffers from the main disadvantage that each enzyme has to be produced in sufficient amounts. This affords efficient recombinant protein produchon hosts being a bottleneck for some genes [25]. However, once a multi-enzyme system has been developed, the productivity can be improved by repetitive use of the biocatalysts as demonstrated for repetitive batch syntheses with soluble enzymes [25, 38] or with immobilized enzymes [48]. The advantage... 

Scheme 5.5 In situ regeneration of dTDP-sugars. (A) SuSy module, (B) deoxy sugar module and (C) glycosyltransferase module [33]. 

C.-H. Wong, S. L. Haynie, and G. M. Whitesides, Enzyme catalyzed synthesis of IV-acetyl-lactosamine with in situ regeneration of uridine 5 diphosphate glucose and uridine 5 -diphos-phate galactose, J. Org. Chem. 47 5416 (1982). 

Y. Ichikawa, G.-I. Shen, and C.-H. Wong, Enzyme-catalyzed synthesis of sialyl oligosaccharide with in situ regeneration of CMP-sialic acid, J. Am. Chem. Soc. 113 4698 (1991). 

CMP-Neu5NAc and by irreversible in situ regeneration of the nucleoside triphosphate. 

The in situ regeneration of Pd(II) from Pd(0) should not be counted as being an easy process, and the appropriate solvents, reaction conditions, and oxidants should be selected to carry out smooth catalytic reactions. In many cases, an efficient catalytic cycle is not easy to achieve, and stoichiometric reactions are tolerable only for the synthesis of rather expensive organic compounds in limited quantities. This is a serious limitation of synthetic applications of oxidation reactions involving Pd(II). However it should be pointed out that some Pd(II)-promoted reactions have been developed as commercial processes, in which supported Pd catalysts are used. For example, vinyl acetate, allyl acetate and 1,4-diacetoxy-2-butene are commercially produced by oxidative acetoxylation of ethylene, propylene and butadiene in gas or liquid phases using Pd supported on silica. It is likely that Pd(OAc)2 is generated on the surface of the catalyst by the oxidation of Pd with AcOH and 02, and reacts with alkenes. 

Table 4 summarizes the enzymes which have been used for the synthesis and in situ regeneration of primary and secondary nucleotide sugars as well as recombinant enzyme sources which are available but have not yet been utilized. Enzymes from natural sources were not completely incorporated in Table 4 since they are already reviewed in other publications [189,195,260, 261]. 

Nat. native enzyme rec. recombinant enzyme In situ Reg. in situ regeneration of nucleotide sugar. 

GDP-ot-D-mannose (23) is the donor substrate for mannosyltransferases [139, 146, 338-340] and the precursor of GDP-(3-L-fucose (13) [173,197, 243, 341], Based on the work of Munch-Petersen [342, 343], only crude extracts from yeast have been used for the enzymatic synthesis of labeled and unlabeled 23 and GDP-deoxymannose derivatives (Table 4) [303-305, 307, 308, 344-346] as well as for the in situ regeneration of 23 (Table 4). Common to all these approaches is the use of chemically synthesized sugar-1-phosphates as substrates for GDP-Man PP. An obvious disadvantage of using crude yeast enzyme preparations is the poor quality of the enzyme source since only fresh cells or certain batches of baker s yeast are suitable for synthesis [304, 307], GDP-Man PP was purified from pig liver and used for the synthesis of 8-Azido-GDP-Man however, the enzyme lacks absolute specificity for GDP-Man in the pyrophos-phorylysis reaction [309]. 

Fig. 16. Enzymatic synthesis of GDP-a-D-mannose (23) from D-mannose (20) via a-D-mannose-6-phosphate (21) and ot-D-mannose-1 -phosphate (22) with in situ regeneration of ATP. A Hexokinase (EC 2.7.1.1), B Pyruvate kinase (EC 2.7.1.40), C Phosphomannomutase (EC 5.4.2.8), D GDP-Man pyrophosphorylase (EC 2.7.7.13), E inorganic pyrophosphatase (EC 3.6.1.1) [311]...

However, nucleoside diphosphates (NDP) are still expensive substrates, which can be obtained from much more cheaper nucleoside monophosphates (NMP). In this respect we have combined the SuSy-catalyzed cleavage of sucrose with the enzymatic formation of NDPs from NMPs catalyzed by nucleoside monophosphate kinase (NMPK, EC 2.7.4.4) or myokinase (MK, EC 2.7.4.3), including in situ regeneration of ATP with pyruvate kinase (PK, EC 2.7.1.40) (Fig. 20) [272]. Testing the substrate spectrum of four different kinases disclosed that none of them accepted dTMP as substrate [272], However, dUMP was well accepted by NMPK and dUDP-activated glucose could also substitute dTDP-activated glucose as precursor for the synthesis of activated deoxysugars (see below). The excellent enzyme stabilities under synthesis... 

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