Complex structure generation

Obviously, this procedure is an approximation, since it uses a trans-lationally invariant medium as a model for very complex structures generated by short-distance configurations such as impurity aggregates. 

In the future, the ideas that underpin DOS, such as maximal chemical space coverage and efficient complex structure generation, will remain. However, we may also see DOS being used in a more focused way, directed toward the synthesis of novel or unusual chemical structures and architectures, and used more in the field of fragment-based drug discovery. Whatever directions DOS takes in the future, it is likely that solid-phase synthesis will remain integral to the field. 

In contrast to carbenes of the AX2 type, which contain three atoms, generation of carbenes with a more complex structure under photolysis or vacuum pyrolysis conditions may be accompanied by intramolecular rearrangements. Thus, the matrix isolation study of the vacuum pyrolysis... 

Conformation analysis methods. In many cases in the process of building a 3D structure from scratch, decisions have to be made between multiple alternatives with similar energy. A typical example is an sp -sp torsion angle with similar energies for the alternatives of -i-60°, -60° and 180°. In many cases, rules are used to decide (e.g. stretch an open chain portion as much as possible to avoid clashes). Sometimes, the best result cannot be determined without a conformation analysis (e.g. complex ring systems with exocycHc substituents). Despite conformation analysis being a topic of its own covered in the next chapter, many automatic 3D structure generators have to fall back in certain situations to a limited conformation search in order so solve a specific problem and to come up with a reasonable solution. 

The OEt-substituted Zr(IV)-boratabenzene complex has been employed in an interesting dual-catalyst approach to the synthesis of branched polyethylene.47 Capitalizing on the ability of this boratabenzene complex to generate 1-alkenes (Scheme 25) and the ability of the titanium complex illustrated in Scheme 27 to copolymerize ethylene and 1-alkenes, with a two-catalyst system one can produce branched polyethlene using ethylene as the only monomer (Scheme 27). The structure and properties of the branched polyethylene can be altered by adjusting the reaction conditions. 

One advantage of whole-cell biotransformation that has not been addressed adequately in this chapter is the ability to modify compounds with complex structure, such as natural products. Natural products are ideal substrates for biotransformation reactions since they are synthesized in a series of enzymatic reactions by the whole cells. The modification of natural products by biotransformation has been reviewed recently by Azerad [ 13] and a majority of the modifications were carried out by whole-cell biotransformations. Additional examples of modification of natural products by whole-cell biotransformations can also be found in the review article by Patel [2]. Natural products are an important source of new drugs and new drug leads [53]. The use of biotransformation, especially whole-cell biotransformation, in modification of natural products for lead optimization and generating libraries of derivatives for S AR and screening studies is important for the pharmaceutical industry. 

The bis(phthalocyaninato) lanthanide (III) complexes have generated a great deal of interest because they are found to show electrochromic and semiconducting properties [87, 203]. They have been characterized by a range of spectroscopic methods, but much research interest has been directed towards understanding the f-electronic structures and their magnetic properties. In order to understand... 

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