Macrocyclic cavitands

The chiral cavitands 3.109 have been developed by combining the amino acid residue L-alanine with macrocyclic cavitands (calixarenes - Section 3.14).51 These ammonium ion receptors are able to complex a range of amino acids and their methylester hydrochloride salts, all of which contain an -NH3+ functionality capable of interaction with the carboxylate residues of the host. In general amino acids are bound only very weakly in aqueous solution, while association constants with the chiral methyl esters range from 620 M-1 for L-tryptophan methylester to 110 M-1 for L-alanine methylester. The methylester of glycine is not bound at all. Receptors related to 3.109 with variable four peptide loops arrayed around a central calixarene core have been used to bind to the surfaces of proteins. The... 

Cucurbituril is a hexameric macrocyclic compound with the formula (C6H6N402)6 shaped like a pumpkin which belongs to the botanical family Cucurbitaceae. This macrocyclic cavitand has idealized symmetry Z>6h with a hydrophobic internal cavity of about 0.55 nm. The two portals, which are each laced by six hydrophilic carbonyl groups, have a diameter of 0.4 nm [Fig. 20.4.8(a)],... 

Cucurbituril is a macrocyclic cavitand (Figure 9). Several comprehensive reviews on cucurbituril are available [24]. Preparation of cucurbituril first appeared in the literature by Behrend et al. in 1905 [25]. Those German chemists reported that glycoluril, which can be obtained from urea and glyoxal, reacts with an excess of... 

Scheme 1 Typical examples of phosphorylated cryptands A [12, 13], B [14, 15], C [16], macrocycle [17], hemispherand [18], and cavitand [19]...

As stated above, systematic names of macrocyclic host molecules were absurdly complicated for routine discussions [22]. Therefore Vogtle proposed the name coronand for crown ethers, and that of coronates for their complexes while cryptand complexes were called cryptates . The corresponding noncyclic analogues are podands such as 64 [23] and podates, respectively. The cumbersome name podando-coronands (and correspondingly podando-coronates ) was proposed for lariat ethers [24] having at least one sidearm like 65. Examples of hemispherands 66 [25], cavitands 25 [26] and those of some other hosts are discussed in Chapter 7 in some detail, whilst the exceptional stability of fragile guests 4 [2a] and 67 [27] in the hemicarcerand 5 cavity are discussed in Chapters 1 and Section 7.3. 

An additional nuance in the nomenclature of these compounds concerns their complexes. The open-chained compounds are often referred to as podands and their complexes as podates. The cyclic ethers may also be called coronands and their complexes are therefore coronates. Complexed cryptands are cryptates. The even more complicated structures known as spherands, cavitands, or carcerands are called spherates, cavitates, or carcerates, respectively, when complexed. The combination of a macrocycle (crown ether or coro-nand) and a sidechain (podand) is typically called a lariat ether. 

The reaction of ferrocenecarbaldehyde (98) and resorcinol (99) under acidic conditions gave the phenolic macrocycle (100), which on addition of chlorobromomethane in the presence of a base produced the first redox-active cavitand (141,142) (101) (Scheme 31). An X-ray structural investigation on crystals of (101), obtained from a dichlorometh-ane-diethyl ether solvent mixture, revealed the inclusion of a dichloro-methane guest molecule within the cavitand host cavity (Fig. 23). Related redox-active cavitand host molecules ((102) and (103)) containing ferrocene moieties lining the wall of the cavitand cavity have also been prepared by our group (141, 142). 

Figure 3.16 Cavitands as examples of preorganized macrocycles (a substantial conformational flexibility remains in 32).

Metallosurfactants, where the cationic head group is a polyaza macrocycle or cavitand containing a strongly coordinated metal ion and the hydrophobic tail is a pendant arm attached to a nitrogen atom of the... 

A class of cavitand macrocycles with a formal structural core related to that of tetraoxa[24]porphyrin-(2.2.2.2) 4.154 vide supra) was reported by Cram and coworkers in 1983 (Scheme 4.6.6). The first of these was prepared from the dibromo-bis(benzofuran) species 4.205 by treatment with first 5-BuLi followed by Fe(acac)3. Evidence supporting the formation of macrocycle 4.208 was gleaned from a preliminary mass spectrometric analysis. However, 4.208 exhibited extremely low solubility and could, therefore, not be purified or characterized further. To overcome this solubility problem. Cram prepared the ethyl- and trimethylsilyl-substituted congeners 4.209 and 4.210. These macrocycles were prepared via the condensation of... 

A macrocycle containing a formal structural core related to that of the hex-aoxa- and hexathia[36]porphyrin-(2.2.2.2.2) macrocycles 7.80 and 7.82 has been reported by Cram and coworkers.This product, the so-called cavitand macrocycle 7.88, was prepared by treating the dimeric dibenzofuran species 7.87 with s-BuLi followed by Fe(acac)3 (Scheme 7.7.7). After fractional crystallization and chromatography, 7.88 was isolated in 1.6% yield. 

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