Catechol template

Scheme 10-125 A catechol template makes possible the synthesis of a cysteine-dimer analog using RCM.

Macrocyclization of esters of allylglycine with diols has been successfully used to prepare derivatives of 2,7-diaminosuberic acid [861,864]. The latter are surrogates of cystine, and therefore of interest for the preparation of peptide mimetics. For unknown reasons protected allylglycine derivatives can not be directly dimerized by self metathesis [864]. However, catechol [864], ethylene glycol [861], and 1,2- or 1,3-di(hydroxymethyl)benzene derivatives [860] of allylglycine are suitable templates for the formal self metathesis of this amino acid via RCM. 

May JJ, Wendrich TM, Mahariel MA (2001) The dhb Operon of Bacillus subtilis Encodes the Biosynthetic Template for the Catecholic Siderophore 2,3-Dihydroxybenzoate-glycine-threonine Trimeric Ester Bacillibactin. J Biol Chem 276 7209... 

Fig. 23 Formation of a series of M4L6 tetrahedra 6, 35 and 36 from the fris-catecholate ligands 5, 33 and 34. Tetrahedron 6 forms with or without the presence of suitable guest molecules [68], whereas 35 and 36 require thermodynamic guest templates [76,146], Without the presence of NMe4+ guest molecules, ligand 33 forms the dinuclear, triple helicate 37 [76]...

The chosen catalytic test reaction was the oxidation of phenol, which yields a mixture of catechol, hydro-quinonc, and 1,4-benzoquinone (Scheme I). The reaction was conducted at atmospheric pressure by continuously adding aqueous H2O2 to a mixture of catalyst, phenol, water, and a solvent (either methanol or acetone) at the reaction temperature (usually 373 K) reaction times were l-4h. Conversions and product sclectivities depended on the composition of this mixture under the best conditions, H2O2 conversion was 100%, phenol conversion 27%, and phenol hydrox-ylation selectivity 91%. The ratio of o />-substituted products (Scheme 1) was usually about unity. It was concluded that catalytic performance depended critically on calcination conditions, i.e. on the completeness of removal of the template. Many facets of the reaction remain to be investigated. 

An extension of the scaffold concept introduced with compound 66 is given in the following examples (Figure 9.20). Typically, up to three substituents are orientated by using a heterobicylic template like benzoxazole 85, benzimidazole 86, or adenines 87, 88 [79-81], Since one of these substituents is always a catechol... 

Reactions such as the one that gave Pedersen the first crown can produce additional products. Thus, catechol (1,2-dihydroxybenzene) reacts with 0(CH2CH2)2C1 in the presence of base to give dibenzo-18-crown-6. Tribenzo-27-crown-9 and benzo-9-crown-3 have also been identified as resulting from this process. For this reason, such crown preparations are sometimes referred to as shotgun reactions. Attempts have been made to direct the cyclization to the correct receptor size by including a K+ template ion to direct formation of 18-membered ring. 

Based on ion-exchange and self-assembly techniques, in this paper we try to synthesize porous silica-montmorillonite heterostructured materials, starting with natural sodium montmorillonite which are ubiquitous so their cost effectiveness will continue to be lower than any synthetic competitive materials. The silica will be orderly assembled within gallery of layers, using the template-directing action. Through the catalytic alkylation reaction of catechol to produce polymerization inhibitor 4-tertbutylcatechol, the catalytic properties of porous silica-montmorillonite heterostructure were evaluated. 

Spin-casting techniques have also been used to prepare imprinted thin films. Makote and Collinson recently prepared metal oxide thin films imprinted with recognition sites for dopamine [18], The dopamine template was loaded at 4 mole % in a sol with a 10 1 ratio of tetramethoxysilane and phenyltrimethoxysilane. The prepared film had a thickness of ca. 450 nm. CV analysis found that 90% of the templates could be removed by washing the films with pH 7 phosphate buffer. The opened receptor sites offered selective binding for related molecules containing catechol amines, such as dopamine, epinephrine and norepinephrine, as determined by CV. The use of phenyltrimethoxysilane turns out to be an essential ingredient for the gel matrix and is believed to provide some complementary affinity for the catechol amines via hydrophobic and/or 7i-stacking interactions. 

A completely different approach to the total synthesis of enterobaetin has been reported by Shanzer and Libman 100>. This is based on a single-step conversion of the tritylated serine-lactone to the cyclic triester enterobaetin backbone via the use of a cyclic organotin compound as template. This is followed by subsequent replacement of the trityl protecting groups by catechol residues to yield enterobaetin. 

However, perhaps the most spectacular example of kinetic locking was reported by Raymond et al. Using highly labile gallium(III) metal ion (M) to template the self-assembly of inflexible C2 symmetric bis-catecholate... 

Saito, Y., Kawano, T., Shimomura, M., Yabu, H. Fabrication of mussel-inspired highly adhesive honeycomb films containing catechol groups and their applications for substrate-independent porous templates. Macromol. Rapid Comm 34, 630-634 (2013)... 

Inorganic ions, drugs, nucleic acids, proteins, and even cells are successful examples of imprinting. In this way, affinity sensors, receptor sensors, and catalytic sensors based on MIPs have been explored. For affinity sensors, immunosensor-like devices were prepared by a 2D MIP technique with molecular imprinting on chemisorbed alkanethiol SAMs then after necessary procedures, vitamins Ki, K2, E, cholesterol, and adamantine could be detected by the strong electrochemical signals yielded. The sensors for nucleic acids, cholesterol, and catechol derivatives can be fabricated first by their adsorption as a template on the ITO surface and then by the treatment of the electrode with adsorbed template using trimethyl chlorosilane from the gas phase. 

When an aromatic group is required in a crown ether, it is usually incorporated through the reaction of catechol because it gives an ideal coordination environment for a deprotonating metal to remain bonnd to the ligand. The same metal then forms a template that preorganizes the difunctionaUzed polyether, introdnced to form the remainder of the macrocycle, snch that it can react with the phenolic nncleophile. 

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