Compounds with Topological Bonds

Further developments in this field led to the elaboration of an alternative approach that envisaged the creation of temporary bridges which forcefully held together the parts of the future catenane or rotaxane. Quite a number of catenane and rotaxane systems were synthesized via this route. As a rule, though, these syntheses were too cumbersome to be of any preparative importance. It became obvious that the non-trivial character of the target structures necessitates the elaboration of equally non-trivial approaches for their syntheses. 

The main problem of catenane or rotaxane synthesis can be formulated as follows how to hold together the non-reacting partners, like 104 and 105, or 107a and 108, in an orientation to secure the formation of catenane or rotaxane, respectively Below we will consider several examples illustrative of the modern approach to solving this problem. 

Often in this book we refer to selectivity as the most burning problem of organic synthesis and mentioned that complexation may be employed as an efficient tool to deal with this problem. This same principle was successfully applied to the elaboration of the directed synthesis of catenane structures. 

The observed ease of formation of [3]catenane 117 is especially remarkable in view of the complete failure to achieve the formation of the parent tetracationic macrocycle from 115 and 116, in the absence of crown ether 114. This result prompted the following important conclusion in the cited paper, it is easier to construct molecular assemblies than it is to create one of their components by itself. The message is a simple but exciting one — the prospects for self-assembly, as a synthetic paradigm, are extremely encouraging .  

For A and B f and g designate functional groups capable of forming f-g bond f-f moiety is capable of serving as a bidentate ligand for the transition metal (circle) 

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The non-trivial character and the structural peculiarities of compounds with topological bonds stimulates the elaboration of equally non-trivial approaches to the solution of synthetic problems in this field. In this respect it seems... 

Our definitions of the stereoisomeric center, line, and plane all stipulate the existence of bonds between the ligating element and its ligands. The exclusive use of these elements limits our analysis to classical stereochemistry and thus does not encompass the so-called topological isomerism (47) of interlocked rings—catenanes (48)—or of knots. As there is no bond between the rings of the catenanes we cannot expect to handle such compounds with a system based on connectedness. At the present stage of development, this limitation in scope... 

Strategies based on some special topological features, such as the presence of "strategic bonds" and/or "common atoms" which apply preferentially to sesquiterpene compounds (as, for instance, longifolene, patchouli alcohol, seychellene, sativene, etc.) and non-natural compounds with a high degree of internal connectivity as, for example, twistane, bullvalene, etc. 

Cabrera et al. pursued a topological substructural approach for the prediction of P-gp substrates. A linear discriminant model classified 163 compounds with an accuracy of 81% based on standard bond distance, polarizability, and the Casteiger-Marsilli atomic charge [35]. Furthermore, the predictive potential ofthis TOPS-MODE approach was demonstrated for a set of 6-fluoroquinolones not included in the training set. 

All authors descrilung one or another compound with a nonchemical bond often employ the terms topological corrpound and topological bond "phese... 

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