Synthetic macrocycle

Pedersen, Cram and Lehn received the Nobel Prize in Chemistry in 1987 for their work on synthetic macrocyclic compounds. In their Nobel lectures, Pedersen (1988) described the discovery of crown ethers, Cram (1988) and Lehn (1988) the further development of work on new synthetic macrocycles and their host-guest properties. 

Since 1960, a very large number of other synthetic macrocycles has been prepared and this has resulted in a great increase in interest in all aspects of the chemistry of macrocyclic systems. From about this time there has also been enhanced interest in the role of metal ions in biological systems and many such bioinorganic studies have involved complexes of both natural and synthetic macrocycles. Thus there has been an element of cross-fertilization between these two developing areas, viz ... 

Synthetic macrocycles - Natural macrocycles Bioinorganic chemistry ... 

As mentioned already, a considerable amount of the research involving synthetic macrocycles has been directed towards the preparation of... 

Resulting from the widespread interest in macrocyclic ligand chemistry, an impressive array of synthetic procedures for macrocyclic systems has been developed. In spite of this, the synthesis of a new ring system frequently turns out to be far from trivial. Indeed, synthetic macrocyclic chemistry is often very challenging and, as well as a thorough knowledge of any metal-ion chemistry involved, skill in the subtle art of organic synthesis is also a valuable asset for those involved in the preparation of new cyclic systems. 

Synthetic lubricating oils, higher olefin polymers in, 20 432 Synthetic macrocyclic compounds chelating agents, 5 713t Synthetic manganese carbonate, 15 573 Synthetic manganese dioxides, 15 586-588 Synthetic marble, 16 283... 

The properties of natural macrocycles, the cyclodextrins, has stimulated interest in the preparation of synthetic macrocycles. Three basic types have been made macrocyclic amines, cyclophanes, and cyclic peptides. Hersh-field and Bender (33) prepared a bicyclic amine with hydroxamate sub-... 

The synthesis of a small library of very large (up to 60-membered) steroid/ peptide hybrid macrocycles has been achieved using double and fourfold Ugi reactions. This type of compound has not previously been described in literature. Neither have multicomponent reactions been used so far to form directly macrocycles of this size. In fact, synthetic macrocycles of this size with this structural complexity are very rare. 

Recently reported synthetic macrocyclic molecules with hydrophilic cavities containing multiple binding atoms and with hydrophobic exteriors make possible controlled studies of selective cation complexa-tion. Certain of these cation-ligand systems appear to mimic biological systems which have remarkable element specificities. Such cation-ligand systems may be considered as models for the study of this unusual property of living systems. 

Contrary to most other synthetic macrocycles, Calixarenes are easy available since one can synthesize them using inexpensive chemicals in a one-pot ... 

Avermectin Bi a Synthetic Macrocyclic lactone C48H72O14 872 237, 245, MeOH, EtOH, H2O, BuOH, ... 

Ivermectin Bia Synthetic Macrocyclic lactone C48H74O14 874 238, 245 Methyl ethyl... 

Newkome et al.294 have reviewed the preparation of synthetic macrocyclic compounds possessing heterocyclic subunits, more specifically, pyridine, furan, and thiophene. 

A comprehensive review of synthetic macrocycles gave detailed tabulations of preparations, effects of binding sites and thermodynamic data known up to 1973.456 Table 60 gives thermodynamic data for the formation of silver(I) crown ethers in aqueous solution and includes several more recent figures.457,458... 

The field, as we now know it, started with the selective binding of alkali metal cations by natural [1.21-1.23] as well as by synthetic macrocyclic and macropoly-cyclic ligands, the crown ethers [1.24,1.25] and the cryptands [1.26,1.27]. The out-... 

Although some scattered examples of binding of alkali cations (AC) were known (see [2.13,2.14]) and earlier observations had suggested that polyethers interact with them [2.15], the coordination chemistry of alkali cations developed only in the last 30 years with the discovery of several types of more or less powerful and selective cyclic or acyclic ligands. Three main classes may be distinguished 1) natural macrocycles displaying antibiotic properties such as valinomycin or the enniatins [1.21-1.23] 2) synthetic macrocyclic polyethers, the crown ethers, and their numerous derivatives [1.24,1.25, 2.16, A.l, A.13, A.21], followed by the spherands [2.9, 2.10] 3) synthetic macropolycyclic ligands, the cryptands [1.26, 1.27, 2.17, A.l, A.13], followed by other types such as the cryptospherands [2.9, 2.10]. 

Indeed, macrobicyclic ligands such as 7-9 form cryptates [Mn+ c cryptand], 10, by inclusion of a metal cation inside the molecule [1.26, 1.27, 2.17, 2.24-2.26]. The optimal cryptates of AC and AEC have stabilities several orders of magnitude higher than those of either the natural or synthetic macrocyclic ligands. They show pronounced selectivity as a function of the size complementarity between the cation... 

Cryptands of type 7-9 and derivatives thereof carry alkali cations [6.4], even under conditions where natural or synthetic macrocycles are inefficient. The selec-tivities observed depend on the structure of the ligand, the nature of the cation and the type of cotransported counteranion. Designed structural changes allow the transformation of a cation receptor into a cation carrier [6.1, 6.4]. The results obtained with cryptands indicated that there was an optimal complex stability and phase-transfer equilibrium for highest transport rates. Combined with data for various other carriers and cations, they give a bell-shaped dependence of transport rates on extraction equilibrium (Fig. 11), with low rates for too small or too large... 

In Section 2.2.1-2.2.3, a brief discussion on the chemistry, properties and structure of contracted, isomeric, and inverted porphyrins has been presented. Here, a brief sketch of the structural diversity in expanded porphyrins is given. Expanded porphyrins represent those synthetic macrocycles in which pyrrole or heterocyclic rings possess connectivity through mcso-carbon bridges. The conjugation of the porphyrin has been... 

Cations are known to be transported through membranes by synthetic macrocyclic polyethers as well as by antibiotics. When the rate-determining step is the ion extraction from the IN aqueous phase to the membrane phase, the transport rate increases with the increasing stability constant. On the other hand, when the rate-determining step is the ion-release from the membrane phase to the OUT aqueous phase, the carrier must reduce the stability constant in order to attain efficient decomplexation. Some polyether antibiotics feature... 

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