Imine linkage, amine

Curtis and coworkers first reported the amine-imine linkage formation of the type shown in Figure 1 by condensation of two molecules of acetone with ethylenediamines in the presence of nickel(II) or copper(II) ions ( 1, 2 3). It was also shown that this type of reaction generally occurs with several carbonyl compounds (4, 5). Later, the mechanism of the linkage formation and the stereoisomerism and some reactions of the metal complexes with macrocycles were investigated in detail (5, 6, 7 ). 

Table II also includes the results of the reactions of Ni(S-ampr) + with some other ketones i.e., MNPK, HPO, MOX, and DAA. It is interesting that with these ketones the amine-imine linkage connects selectively the primary amino groups of two diamines. Linkage formation between a primary and a secondary amino group no longer occurs. It should be noted that these...

As far as S-apip and S-ahaz are concerned, products with less crowded ketones such as MVK, HBO, MNPK, or HPO have, without exception, the amine-imine linkage formed between primary and secondary amines. Hence, the products are either A or B, or sometimes both of them, as in the case of S-apip-MNPK and S-ahaz-MVK. Further, the yields are not so bad. Therefore it is very probable that linkage formation takes place, almost exclusively, on the five-coordinated structure of copper(II), as expected above. Such selectivity due to the coordination mode about copper(II) ion will not work well in the case of the S-ampr complex, because of its structure, so that a small amount of type C is obtained. 

As mentioned previously, Schiff-base condensations between amines and aldehydes or ketones have played a prominent role in metal-ion template chemistry. A generalized Schiff-base condensation (to produce an imine linkage) is given by [2.15],... 

The reverse reaction, namely hydrogenation, has also frequently been used to decrease the degree of unsaturation present in macrocyclic systems - typically converting imine linkages to amine groups. Such hydrogenations have usually been performed catalytically (for example, using H2 in the presence of Raney nickel or a precious metal catalyst) or by means of chemical reductants such as sodium borohydride. 

The functional groups creating the imine linkage were selected to have comparable activity, that is, aromatic aldehydes plus amines of similar nucleophilicity. This approach seeks to avoid large differences in reactivity that might excessively bias the hbrary composition. 

PLP does not exist as the free aldehyde when it is bound to the enzyme, but actually uses the aldehyde group in its binding. An imine linkage is formed between the aldehyde and the primary amine group of a lysine residue in the enzyme active site. When the substrate RNH2 binds to the enzyme to produce the intermediates shown above, it achieves this by a transimination reaction. 

The chemical and structural flexibility surrounding the amine/imine nitrogen linkages in PANI creates enormous diversity. Unlike the rigid-rod examples of the preceding section, PANI has limited solubility in a number of solvents and may be cast to yield free-standing films or precipitated into powders [46]. The chemical formula that most broadly describes this polymer is represented by... 

The most obvious disconnection is the imine linkage, which could arise from the corresponding amine and carbonyl component. The latte-... 

An imine moiety can, interestingly, be interposed in the ether linkage used to connect the two halogenated aromatic rings. The requisite oxime (55-1) is obtained in a straightforward fashion by reaction of imidazo acetophenone (54-2) with hydroxyl-amine alkylation with a,2,3-trichlorotoluene leads to oxiconazole (55-2) [60]. 

The free carbonyl function of this ligand may undergo further condensation reactions. With amines RNH2, products [PdLL l are obtained where both L and L may be N,N -bonded chelates (42 R = Me, Et, Pr, Bu)264,265 or L may be bonded through N(imine) and 0(oxime) (43 R = H).266 Similar linkage isomerism is seen for other oximato ligands of this type.267... 

A cursory glance at the structure of DNA shows that it is composed of hydrogen-bonded units, the purine and pyrimidine bases, attached to sugars that are linked by phosphate groups. There is no chemical reason why the perfectly symmetric phosphates should bind in the orientation that they do. The same problem arises in when a synthetic analogue of a DNA-type replicator is considered. The most useful linkages are imine and peptide bonds. Both require a terminal amine the former results from a reaction with an aldehyde and the latter with an activated carboxylic acid. The problem that occurs is that if these functional groups are present within the same molecule self-polymerization may occur unless a substantial effort is made to avoid this. 

In 1992, Goodwin and Lynn reported the first example of template-directed synthesis of DNA analogs via formation of a reversible imino linkage [21]. Five years later, Hue and Lehn described the first use of the reaction of imine condensation for the selection, by DCC, of carbonic anhydrase inhibitors from a library of amines and aldehydes [8], Upon addition of the enzyme, the formation of one library component was strongly amplified when compared to a similar reaction carried out in the absence of template. Since then, imine exchange reaction has been applied... 

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