Macrocyclic systems

Coronand Any medium sized or macrocyclic system having only one ring and containing any heteroatom(s). 

The structural variations reported by Cram and coworkers relate to an appreciable extent to the various ancillary functions which have been appended to the binaphthyl units or elsewhere in the macrocyclic system. Enhancements of the chiral barrier or functionalization through arms has generally been effected at the 3-or 6-positions. These positions are adjacent to the hydroxyl group or directly across the second ring from it, respectively. 

The corphins 2 and 3 formed can be tautomerized back to pyrrocorphins,6 but less complicated model compounds bearing methyl groups can also be similarly tautomerized.yab When magnesium nonamethylpyrrocorphin is first methylated and then tautomerized, the D pyrrole ring is regioselectively attacked by iodomethane followed by tautomerization to establish a pyrrole ring in the C position of the macrocyclic system 4. 

The concept of expansion of the porphyrin macrocycle by formally inserting additional carbon atoms between the pyrrole rings was first considered and synthetically realized by LeGoff/ He also suggested a nomenclature for these macrocyclic systems using the word platyrin which... 

Understanding the acidity and/or basicity of acids and bases in macrocyclic systems has an important connection to biological problems. It should help us to understand enzymes. In many proteins, drastically varying pKa values have been found for functional groups in the active site for example, the... 

A series of zinc(II) phthalocyanines with other sorts of solubilizing groups in exo or endo positions (carboxyalkyl, carboxyalkoxy, amino acid) has been synthesized and subjected to preliminary in vitro assays.257 Interestingly, the seryl derivative zinc(II) 2,9,16,23-tetrakis(l-car-boxy-2-hydroxyethylaminocarbonyl)phthalocyanine proved to be cytotoxic (i.e., toxic in the dark) which is not so commonly observed with macrocyclic systems. 

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 ... 

Factors influencing the macrocyclic hole size. The hole size of a macrocyclic ligand is a fundamental structural parameter which will usually influence, to a large degree, the properties of resultant metal complexes relative to those of the corresponding non-cyclic ligands. The large number of X-ray diffraction studies now complete for macrocyclic systems makes it possible to define many of the parameters which affect hole size... 

Apart from this one-reaction type, the routine use of metal template procedures for obtaining a wide range of macrocyclic systems stems from 1960 when Curtis discovered a template reaction for obtaining an isomeric pair of Ni(n) macrocyclic complexes (Curtis, 1960). Details of this reaction are discussed later in this chapter. The template synthesis of these complexes marked the beginning of renewed interest in macrocyclic ligand chemistry which continues to the present day. 

As mentioned already, Curtis reported the first (Curtis, 1960) of a number of pioneering template reactions for macrocyclic systems which were published in the period 1960 to 1965. In the Curtis synthesis, a yellow crystalline product was observed to result from the reaction of [Ni(l,2-diaminoethane)3]2+ and dry acetone. This product was initially thought to be a bis-ligand complex of the diimine species (58). However, the stability of the product in the presence of boiling acid or alkali was... 

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. 

Co-facial dimers consist of two simple macrocyclic systems connected by linkages such that the respective cyclic portions are constrained to stack one above the other. Such molecules define three cavities two within the macrocyclic subunits and a third between these subunits. 

The metal-ion chemistry of polyether and related macrocyclic systems... 

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