Topological Beauty

In nearly two decades, challenging structured of phomactins coupled with the interesting biological activity has elicited an impressive amount of synthetic efforts [16-18]. (+)-Phomactin D was first synthesized by Yamada in 1996 [19], and Wulff [20] reported the synthesis of ( )-phomactin B2 in 2007. However, (+)-phomactin A has been the most popular target because of its unique topology. To date, two monumental total syntheses have been accomplished Pattenden s [21] racemic synthesis and Halcomb s [22] asymmetric synthesis in 2002 and 2003, respectively. Both syntheses are beautifully done but also mimicked Yamada s synthesis of D, thereby underscoring the remarkable influence of Yamada s earlier work on the phomactin chemistry. Upon completing their synthesis of ( )-phomactin A, Pattenden [23] completed ( )-phomactin G via a modified route used for A. 

Whatever the beauty of the resolved systems discussed above, it should be noticed that the enantiomers obtained after resolution are not topological enantiomers but classical geometrical diastereomers. In each case, a rigid chiral function... 

After the very early achievements due to the real pioneers of chemical topology who forty years ago first acceeded to that intriguing molecule that is a catenane (by statistical threading approach Wasserman, 1960 or by a directed approach Liittringhaus and Schill, 1964), this peculiar field of research concerned with molecules whose prime feature rests without doubt on beauty and non trivial spacial arrangement, has in the beginning of the 80 s literaly exploded with the apparition of various templated approaches. 

This is particularly true, since rotaxanes and catenanes have entered a stage in their development, in which they have undergone the transition from beautiful structures with ever-new topologies to those which possess function. Many so-called molecular devices have been synthesized and studied with respect to a controlled motion of the two components relative... 

Likewise, three-dimensional renderings of MIMs remind us instantly of some of the ordinary objects we encounter in our everyday lives (see Sect. 2.3). Take olympiadane [82], for example (Fig. 13), with its five interlocked rings unmistakably sharing the same topology as the Olympic logo Most catenanes bear resemblance at least to the links of a chain, as their name implies. Regardless of their resemblance to familiar objects, hundreds of beautiful crystal structures of MIMs have been produced since their debut in 1985, when Sauvage [83] published the first solid-state structure of a [2]catenane (Fig. 14a). It would be impossible to do justice to all of the beauty contained in the databank of solid-state mechanically interlocked structures. In Fig. 14 we simply present a few examples that we find noteworthy [84—88]. See Fig. 23 in Sect. 4.2 for more beautiful crystal structures of some particularly novel MIMs. 

Fig. 18 Different representations of the same donor-acceptor [2]catenane. Line drawings (a) and condensed structural formulas (b) were the order of the day until the modem era of MIMs gave way to structural diagrams (c) and crystal structures (d). Graphical representations, also called cartoons (e), can be a helpful compromise between these representations when attempting to emphasize the topology, noncovalent bonding interactions, shape, beauty, or function of a MIM...

There is no lack of beautifully simple MIMs. The quintessential example is SchilFs all-hydrocarbon [2]catenane [167], the simplest non-trivial topology composed of the simplest atoms and bonds (Fig. 24). Other MIMs are simplified by highly symmetrical structures that make them easy on the brain , such as the... 

Liquid extraction was used to make diastereomers, exploiting the high solubility of potassium triflate in water compared with the binaphthylphosphate salts. The two diastereomers have different solubilities and the (+) isomers of knot and anion crystallise together [49, 50], while the laevorotatory knot remains soluble. Counterion exchange with hexafluorophosphate gave the pure topological enantiomers. The optical rotatory power of the copper knots is very high At the sodium D-line (589 nm), the optical rotatory power was 7.000 mol 1 L dm They are beautiful molecules with a remarkable property ... 

This book assumes no mathematical competence on the part of the reader (although the authors are distinguished geometers) and offers a good entree into the field of surface geometry and topology for those who find standard mathematical texts bidding. Filled with beautiful pictures ... 

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