Siderophore models and cryptands

As a rule, the macrobicyclic catechoylamide compounds have been obtained by high-dilution techniques [135-138, 140]. However, the yield of these products is low. In particular, methyl-protected bicapped L1018 can be prepared via two high-dilution routes ( heme 4-16) in 3.5% and 27% yields. The product HeLlOlO is obtained by treatment of L1018 with boron tribromide in CH2CI2 [140]. 

It should be emphasised that the template method is extremely effective for the assembly of HeLlOlO [140], and quite promising for other similar products. 

4 Template synthesis of three-dimensional macrocyclic systems 

Synthesis of macrobicyclic H6L1022 possessing six convergent hydroxy groups, and which is thus a potential siderophore, has been achieved (Eq. 4.38) [142], 

The synthesis of H6L1022 was carried out by the high dilution technique (yield 18%), as well as in nearly quantitative yield through a template reaction using a published [140] procedure. Iron(III) is bound even more strongly in [Fe(L1022)J than to EDTA or natural siderophores, as shown by competition experiments in water at pH 11.5 [142]. The effectiveness of these applications of the coordination template effect is attributed to a number of favourable factors  

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