Boron binding

Tartrolon B and also previously isolated boromycin, aplasmomycin, and borophycin are polyketides and have the same boron-binding substructure C1-C7 in each half of the symmetric molecules (Fig. 4). 

Fig. 4.The boron binding substructures of different boron-containing antibiotics.

Tartrolons (tartrolon B, 86) are 42-membered ring macrodiolides produced by S. cellulosum [109]. Compound 86 contains a boron atom, and the substructure and configuration of the boron-binding site are identical to those of boromycin (63). 

Capped RNA chains are bound specifically by 3-aminophenylboronate-sub-stituted agarose, the binding being most effective above pH 8. The boronate binds specifically to the cw-diol of the 7-methylguanosine residue in the cap, and the positive charge on the residue is necessary for efficient binding. ... 

The starting material is symmetrical so it doesn t matter which face of which alkene you attack. The only important things are that boron binds to the more nucleophiUc end of the alkene and that R2B and H are added cis. AlkaUne H2O2 makes the hydroperoxide anion (HOO ) which attacks boron. 

N. V. C. Ralston, C. D. Hunt, Diadenosine phosphates and S-adenosylmethi-onine novel boron binding biomolecules detected by capillary electrophoresis, Biochimica Et Biophysica Acta - General Subjects 2001,1527, 20. 

A comparison of the data resulting from the labeling experiments with permeabilized cells with the data obtained by analysis of the boronate-binding fraction suggests the existence of several ADP-ribosylated nuclear matrix proteins. Beginning with a weak, but distinct electrophoretic band at approximately 300 kD, there are modified proteins at 300,220,140,116,73,69,64,60,51,46,43,41 kD. 

The first detailed investigation of Lewis acidic boron binding to fluoride ion was published in 1985 by Katz (compound 67 pictured in Scheme 8). The adduct 67 F was characterized successfully by and... 

Hydroboration is not only stereospeciflc (syn addition), it is also regioselective. LFnlike the electrophilic additions described previously, steric more than electronic factors primarily control the regioselectivity The boron binds to the less hindered (less substituted) carbon. The reactions of the trialkylboranes resulting from these hydroborations are of special interest to us, as the next section will explain. 

Amin, S.A., Kiipper, F.C., Green, D.H., Harris, W.R., and Carrano, C.J. (2007) Boron binding by a siderophore isolated from marine bacteria associated with the toxic dinoflagellate Gymnodinium catenatum. J. Am. Chem. Soc., 129, 478-479. 

The affinity method may be biospecific, for example as an antibody-antigen interaction, or chemical as in the chelation of boronate by ci5-diols, or of unknown origin as in the binding of certain dyes to albumin and other proteins. 

Alcohols can be selectively bound to the same host type if they are combined with an amine and vice versa, considering that a cation and an anion will be formed through a proton transfer. The so-formed alkoxide anion will bind to the boron atom, while the ammonium ion will be complexed by the crown ether (147, Fig. 39). Competition experiments involving benzyl-amine have shown enhanced selectivity for the complexation of alcohols with... 

Bidentate binding of two Lewis acidic boron centers to one methoxide anion was first reported in 1967 [241]. Further examples did not appear until 1985 [242]. Today, other bis(boronates) like 152 and 154-158 (Fig. 41) are known that can be applied to the selective complexation of amines and diamines [243-247]. 

Fig. 42. A series of boronic acids 159-166 with chromophoric groups has been evaluated with respect to its capacity to selectively bind d-glucose or other saccharides...

In 159 and 163-166 the tertiary amine function is coordinated to the boron atom and transmits the electronic change due to the ester formation to the chromophore. In 160-162 the boron atom is directly connected to the chromophore. After the complexation of the saccharide, the change of the charge transfer, e.g., for 159 [249-251], or the fluorescence bands, e.g., for 160-166 [252-255], can be measured and interpreted. The most selective binding of n-glucose has been achieved with host 164 that forms a 1 1 complex with a macrocyclic structure (Scheme 1). 

Crude chloroform-methanol-water (30 60 8, v/v) extracts of immunostainedTLC bands were analyzed without further purification by nanoelectrospray low-energy mass spectrometry. The authors showed that this effective PLC/MS-joined procedure offers a wide range of applications for any carbohydrate-binding agents such as bacterial toxins, plant lectins, and others. Phenyl-boronic acid (PBA) immobilized on stationary support phases can be put to similar applications. This technology, named boronate affinity chromatography (BAC), consists of a chemical reaction of 1,2- and 1,3-diols with the bonded-phase PBA to form a stable... 

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