Macrocycle binding studies

In a study of chiral dipeptide [2]rotaxanes it was found that the presence of an intrinsically achiral benzylic amide macrocycle near to the chiral center could induce an asymmetric response in the aromatic ring absorption bands [62], This induced circular dichroism (ICD) effect was stronger in apolar solvents (Fig. 9), where intercomponent interactions are maximized, showing a direct relationship to the tightness with which the macrocycle binds the chiral thread. Computer simulations showed that chirality is transmitted from the amino acid asymmetric center on the thread via the achiral macrocycle to the aromatic rings of the achiral C-terminal stopper. 

Diaz P, Tovilla JA, Ballester P et al (2007) Synthesis, structural characterization and anion binding studies of palladium macrocycles with hydrogen-bonding ligands. Dalton Trans 3516-3525... 

The synthesis of the two bile-acid-derived macrocycles shown in Figure 39 were recently reported by us [56]. Even though Corey-Pauling-Koltun (CPK) models showed that the cavities in these two compounds would be able to encapsulate monocyclic aromatic compounds, detailed binding studies carried out in organic solvents with a variety of aromatic compounds did not show any evidence for appreciable binding. There is clearly scope for design improvement to overcome this problem since the construction of this type of macrocycle is synthetically rather flexible. 

A new synthesis of oxacalix[3]arene macrocycles and alkali-metal-binding studies, R D. Hampton, Z. Bencze, W. D. Tong and C. E. Daitch, J. Org. Chem., 1994,59,4838. 

As detailed in earlier sections. Beer and co-workers (1469,1470) prepared a range of complexes in which two zinc bis(dithiocarbamate) centers are incorporated into macrocycles (Fig. 255). The terphenyl-based macrocycles 477 bind bidentate Lewis bases in their cavities (as discussed in Section IV.H.l.a), while 478 containing the well-known [Ru(bpy)3] " subunit has been utilized in anion-binding studies. The same group have also prepared a number of ferrocenyl-containing macrocycles 479-481, containing up to six iron(II) centers, probing their electrochemical properties (see later) (1468). 

Jurczak and co-workers reported cyclic and acyclic amide-based receptors 9a-e, 10 and 11 [33, 34]. The crystal stmctures of 9a F and 9a-Cl indicated that the anion was coordinated by four H-bonds with N F distance ranging from 2.742 to 2.881 A and N C1 from 3.211 to 3.520 A, respectively (Figs. 5.6a and 5.7a). However, the fluoride ion was almost in the plane of the macrocycle (Fig. 5.6b), while the larger chloride hovered above the plane of the macrocycle (Fig. 5.7b). Solution-phase binding studies also proved that the smaller fluoride ion fit better to the macrocycle K = 830 M ) than chloride K = 65 M ). Base on these results, Kanbara et al. transformed amide 9a to thioamide 9f which was found to exhibit strong affinity toward anions [35]. Although acyclic receptors 10 and 11 have... 

Other, closely related, nicotinic acid derivatives and the unsubstituted system itself have also been studied and undergo similar reactions. Moreover, the approach may be extended to 2,2 -bipyridyls. Newkome and his collaborators have used the 2,2 -bipyridyl unit 19) as an electrophile in which ortho-hr ommes served as leaving groups. They have also used halomethyl systems and formed the macrocycles from these systems . A compound derived from the latter starting material 20) is reported to form a cobalt complex, in which both nitrogens and only one of the oxygen atoms participate in the binding . The two precursor units are shown below as 79 and 20, respectively. 

Although the first all-sulfur macrocycles were prepared many years ago " the first systematic study of such compounds was initiated by Busch and his coworkers , who were interested in the cation binding properties of such ligands. A sequential synthesis was utilized to produce 1,4,8,11-tetrathiacyclotetradecane [tetrathia-14-crown-4 (70)] . In the first step, 1,3-propanedithiol is metallated using sodium and alkylated with 2-chloroethanol. The diol was then treated with thiourea to form the dimercapto-dithioether compound 9. The latter was once again metallated with sodium and allowed to react with 1,3-dibromopropane. The yield of 70 in the ring closure step, conducted at high dilution in absolute ethanol, was 7.5% after recrystallization. The entire sequence is illustrated in Eq. (6.8) . ... 

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