Carbohydrates boronates

To date, the most extensively studied polyboron hydride compounds in BNCT research have been the icosahedral mercaptoborane derivatives Na2[B22H22SH] and Na [(B22H22S)2], which have been used in human trials with some, albeit limited, success. New generations of tumor-localizing boronated compounds are being developed. The dose-selectivity problem of BNCT has been approached using boron hydride compounds in combination with a variety of deUvery vehicles including boronated polyclonal and monoclonal antibodies, porphyrins, amino acids, nucleotides, carbohydrates, and hposomes. Boron neutron capture therapy has been the subject of recent reviews (254). 

Although boronates are quite susceptible to hydrolysis, they have been found useful for the protection of carbohydrates. It should be noted that as the steric demands of the diol increase, the rate of hydrolysis decreases. For example, pin-acol boronates are rather difficult to hydrolyze in fact, they can be isolated from aqueous systems with no hydrolysis. 

An interesting example from carbohydrate chemistry is the boron trifluoride-diethyl ether complex catalyzed nucleophilic addition of silyl enol ethers to chiral imines (from n-glyceralde-hyde or D-serinal)22. This reaction yields unsaturated y-butyrolactones with predominantly the D-arabino configuration (and almost complete Cram-type erythro selectivity). 

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... 

The value of methylation studies in structural determination of carbohydrates is well known. Methylation of sucrose has generally been achieved by the use of dimethyl sulfate-sodium hydroxide,34,35 methyl iodide-silver oxide-acetone,20 sodium hydride-methyl io-dide-N,N-dimethylformamide,35 or diazomethane-boron trifluoride etherate.36,37 The last method (already applied to monosaccharides38,39) has been found particularly useful for sucrose, because it proceeds without concomitant migration of acyl groups. The reaction of 2,3,6,T,3, 4, 6 -hepta-0-acetylsucrose (21) and 2,3,4,6,1, 3, 4 -hepta-O-acetylsucrose (22) with diazomethane in dichloromethane in the presence of a catalytic proportion of boron trifluoride etherate for 0.5 h at —5° gave the corresponding 4-methyl (23) and 6 -methyl (24)... 

Applying the coupling conditions established by Guillaumet et al.,n9 Leconte et al. have developed the coupling reaction of carbohydrate-connected benzylsulfanyl OZTs with boronic acids and stannanes in good yields (Scheme 63).122... 

Rollin et al 5 have applied those direct coupling conditions in a Suzuki-type process-using p-methoxyphenyl boronic acid and CuTc-to three carbohydrate-based OZTs but the coupling reaction only resulted in moderate yields (42%-47%). Using the same thionocarbamates, a direct Stille... 

Suppliers of visible spectrophotometers are reviewed in Table 1.1. Spectroscopic methods are applicable to the determination of phenols, chlorophenols, amines, mixtures of organics, boron, halogens, total nitrogen and total phosphorus in soils, cationic surfactants, carbohydrates, total nitrogen, phosphorus and sulphur in non-saline sediments, boron, total organic carbon, total sulphur and arsenic in saline sediments, cationic surfactants, adenosine triphosphate and total organic carbon in sludges. 

Qy-boronate derivatives have the ability to form covalent bonds with d,v-diol sugars at alkaline pH. Unlike lectins, which typically bind only the terminal sugar in a complex carbohydrate, boronates can bind any physically accessible CM-diol on a glycoprotein.23-25 When hydrophobic boronate derivatives are used, the hydrophobicity of each complexation site is enhanced. To the extent that the protein components of a sample are differentially glycosylated, this can provide a tool for exploiting those differences. 

Carbohydrate detection is important for applications such as glucose monitors these are arguably one of the most successful and relevant biosensors. An interesting fluorescence recovery-type saccharide sensor based on the reactivity of carbohydrates with boronic acids was reported in 2002 [36]. Specifically, modification of the cationic viologen-linked boronic acid derivative 40 to a zwitterionic species 41 upon covalent and reversible reaction of boronic acid with monosaccharides (Scheme 1) can cause the dissociation of the ion-pair in-... 

Scheme 1 Interaction between 4,4 -i r,i T-bis(benzyl-4-boronic acid)-bipyridinium dibromide with a carbohydrate at near-neutral pH...

Glad, M., Ohlson, S., Hansson, L., Mansson, M.-O., and Mosbach, K., High-performance liquid affinity chromatography of nucleosides, nucleotides and carbohydrates with boronic acid-substituted microparticulate silica, J. Chromatogr., 200, 254-260, 1980. 

OH Boronic ester Diols, carbohydrates Wulff and Sarhan (1972), Wuhf, Vesper et al. (1977)... 

Scheme 15.2 Covalent imprinting of a-phenyl-o-mannopyranoside in a divinyl benzene/4-vinylphenylboronic acid matrix, via the formation of covalent boronic ester linkages between the 4-vmylphenylboronic acid and the carbohydrate. Adapted from Wulff, Vesper, et al. (1977). Copyright 1977 Wiley InterScience.

Boron derivatives of carbohydrates, particularly borinates (32) and cyclic boronates (33), find considerable use as partially protected, syn-... 

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