Enzymatic Extension

SCHEME 19.9 Endo-A-catalyzed glycosylation of glycoproteins bearing unnatural linkages. 

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Immunocapture-polymerase chain reaction (IC-PCR) is a synthesis of two commonly used diagnostic tools. This method exploits the high-affinity binding of antibodies to provide a facile method of purification, usually from a complex matrix, supplying the substrate for PCR detection. PCR exponentially amplifies a deoxyribonucleic acid (DNA) template in a temperature-dependent fashion by the annealing of oligonucleotide primers, enzymatic extension of bound primers by a heat-stable polymerase, followed by denaturation of... 

A different experimental approach to SNP detection combines mass spectrometric detection with enzymatic extension of primers hybridized to immobilized DNA taiget aiiays. Tlie advantage of this combination is high specificity and high accmacy of allele identification. 

Figure 35.7 Enzymatic extension of DNA-synthetic polymer hybrids and preparation of DNA-synthetic polymer graft architectures. (a) Schematic representation of enzymatic extension of ss DNA diblock copolymer using TDT and dNTP. P denotes the phosphate group(s) of the nucleotide ...

Figure 8.22 Neri s DNA-recorded library synthesis scheme. The encoding is done by enzymatic extension. Reprinted, with permission, from Buller et al 2008 Elsevier.

Aldol Additions. These reactions catalyzed by lyases are perhaps the most synthetically useful enzymatic reactions for carbon—carbon bond formation. Because of the broad synthetic utiUty of this method, the enzymatic aldol reactions have received considerable attention in recent years and have been extensively covered in a number of books and reviews (10,138—140). 

Mention should also be made here of the extensive use of poly(vinyl alcohol) in potentially biodegradable applications. At appropriate hydroxyl contents these polymers will dissolve in water (see Chapter 14) and can apparently be conveniently washed away after use as a water-soluble packaging. Biodegradation does, however, appear to be slow and first requires an oxidative step involving enzymatic attack to a ketone such as polyenolketone, which then biodegrades more rapidly. 

The enzymatic cleavage of esters is a vast and extensively reviewed area of chemistry. Recently, several new esters have been examined primarily for the preparation of peptides and glycopeptides. 

Two appendices are included at the end of this chapter. The first is intended to serve as a reminder, for those of you who might need it, of the nomendature and representation of stereoisomers. The second appendix contains descriptions of various chemo-enzymatic methods of amino acid production. This appendix has been constructed largely from the recent primary literature and includes many new advances in the field. It is not necessary for you to consult the appendix to satisfy the learning objectives of the chapter, rather the information is provided to illustrate the extensive range of methodology assodated with chemo-enzymatic approaches to amino add production. It is therefore available for those of you who may wish to extend your knowledge in this area. Where available, data derived from die literature are used to illustrate methods and to discuss economic aspects of large-scale production. 

See if you can come up with an extensive range of possible applications of biological transformations that may facilitate separation and use of the racemates. (Think of the application of enzymatically mediated transformations which we describe earlier, this should help you to come up with several ideas). 

The list of possibilities you could have come up with is quite extensive. You might, for example, have suggested that enzymatic processes may be used to resolve the racemic mixture. 

Typical single-substrate enzymatic reactions can be described by the kinetic scheme (see Refs. 1 and 2 for more extensive discussions). 

Figure 10.18 Enzymatic in situ generation of dihydroxyacetone phosphate from fructose 1,6-bisphosphate (b), with extension to an in vitro artificial metabolism for its preparation from inexpensive sugars alongthe glycolysis cascade (a), and utilization for subsequent stereoselective carbon-carbon bond formation using an aldolase with distinct stereoselectivity (c).

Figure 10.19 Oxidative enzymatic generation of dihydroxyacetone phosphate in situ for stereoselective aldol reactions using DHAP aldolases (a), and extension by pH-controlled, integrated precursor preparation and product liberation (b).

Figure 10.32 Applications of bidirectional chain extension for the synthesis of disaccharide mimetics and of annulated and spirocyclic oligosaccharide mimetics using tandem enzymatic aldol additions, including racemate resolution under thermodynamic control.

Metal polysulfido complexes have attracted much interest not only from the viewpoint of fundamental chemistry but also because of their potential for applications. Various types of metal polysulfido complexes have been reported as shown in Fig. 1. The diversity of the structures results from the nature of sulfur atoms which can adopt a variety of coordination environments (mainly two- and three-coordination) and form catenated structures with various chain lengths. On the other hand, transition metal polysulfides have attracted interest as catalysts and intermediates in enzymatic processes and in catalytic reactions of industrial importance such as the desulfurization of oil and coal. In addition, there has been much interest in the use of metal polysulfido complexes as precursors for metal-sulfur clusters. The chemistry of metal polysulfido complexes has been studied extensively, and many reviews have been published [1-10]. 

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