Schiff base approaches

Schiff base approaches have beenusedto synthesize mono-, di-, andtri-nuclear lanthanide complexes (73-78). Complexes of the macrobicyclic... 

Two other notable examples of expanded porphyrins pr ared via the [1 + 1] Schiff base approach are systems 9.97 and 9,99 22,29,39,5 cases the... 

An interesting variation of this Schiff base approach was reported by Okawa and co-workers... 

Synthesis of PYML-1 was based on the Schiff base approach originally developed by the total synthesis of BLM (Fig. 16) [53]. Thus, condensation of aldehyde (28) and amine (7) gave Schiff base (29) which was reduced by catalytic hydrogenation. The resulting secondary amine derivative (30) was hydrolyzed and coupled with the histidine component. PYML-1 was obtained by deprotection of dipeptide (31). 

Woodward s ingenious synthesis of chlorophyll a is based, in the first part of the synthetic approach, on a classical porphyrin synthesis using two dipyrrylmethanes for the formation of the macrotetracycle. The problem of regioselectivity in the connection of the two unsymmetric pyrrylmethane halves 1 and 2 was solved by the formation of SchifF base 3 between the two halves prior to the condensation so that the macrotetracycle formation occurred by an intramolecular reaction. 

Rhenium(IV) complexes with only one bidentate ligand have been described for chelating phosphines, Schiff bases, and A-heterocycles. The synthetic approaches are different and involve simple ligand exchange procedures as well as reduction of rhenium(V) or oxidation of rhe-nium(III) compounds. 

The highest flexibility for a variation of the functional group and the chains X and Y (i.e. the size of the rim of the lamp shade) will be realiad when the synthesis of 3 is convergent and modular (Scheme 1). Amide bonds can easily be formed in macrocyclizations [13], therefore macrocyclic diamines 7 and diacyl dichlorides 8 had to be prepared. For the synthesis of macrocyclic diamines 7, also a large number of reactions are known. However, in this case a reduction of a macrocyclic diamide could not be achieved [11]. Therefore, another route was used the formation of macrocyclic diimines 6 (bis-Schiff bases) followed by NaBH4 reduction to the macrocyclic diamines 7. This approach has the advantage that for the construction of macrocyclic diimines 6, the metal ion template effect [14] may be exploited. 

The EXAFS technique has been especially useful for metalloproteins. It has often provided the first clues as to the identity of atoms (O, N, S) surrounding a metal atom and either covalently bonded to it or coordinated with it (Chapter 16). Interpretations are often difficult, and a common approach is to try to simulate the observed spectrum by calculation from a proposed structure.118 Tautomerism in crystalline Schiff bases (see Eq. 23-24) has been studied by nearedge X-ray absorption fine structure (NEXAFS) employing soft X-rays.119... 

Pyridoxal phosphate forms a Schiff base (imine) with the glycine. A carbon-bound hydrogen is labile, and the resulting carbanion stabilized by resonance back into the pyridoxal phosphate. The carbanion approaches the carbonyl carbon of the succinyl-CoA. Following the elimination of the CoASH, the intermediate shown in figure 22.13 is formed. The intermediate then loses a C02, forming a carbanion that is resonance stabilized back into the pyridoxal phosphate. 

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