Ascertainment of boric acid esters in wine by11B NMR

Recent developments with boron as a platform for novel drug design

INTRODUCTION

After decades of development, the medicinal chemistry of compounds that contain a single boron atom has matured to the present status of having equal rights with other branches of drug discovery, although it remains a relative newcomer. In contrast, the medicinal chemistry of boron clusters is less advanced, but it is expanding and may soon become a productive area of drug discovery.

AREAS COVERED

The author reviews the current developments of medicinal chemistry of boron and its applications in drug design. First generation boron drugs that bear a single boron atom and second generation boron drugs that utilize boron clusters as pharmacophores or modulators of bioactive molecules are discussed. The advantages and gaps in our current understanding of boron medicinal chemistry, with a special focus on boron clusters, are highlighted.

EXPERT OPINION

Boron is not a panacea for every drug discovery problem, but there is a good chance that it will become a useful addition to the medicinal chemistry tool box. The present status of boron resembles the medicinal chemistry status of fluorine three decades ago; indeed, currently, approximately 20% of pharmaceuticals on the market contain fluorine. The fact that novel boron compounds, especially those based on abiotic polyhedral boron hydrides, are currently unfamiliar could be advantageous because organisms may be less prone to developing resistance against boron cluster-based drugs.

The Arabidopsis-related halophyte Thellungiella halophila: boron tolerance via boron complexation with metabolites?

Tolerance to boron (B) is still not completely understood. We tested here the hypothesis that Thellungiella halophila, an Arabidopsis thaliana-related 'extremophile' plant, with abundance of B in its natural environment, is tolerant to B, and examined the potential mechanisms of this tolerance. With 1-10 mm B applied ([B](ext)) to Thellungiella and Arabidopsis grown in hydroponics, the steady-state accumulated B concentration ([B](int)) in the root was below [B](ext), and was similar in both, suggesting both extrude B actively. Whether grown in soil or hydroponically, the shoot [B](int) was higher in Arabidopsis than in Thellungiella, suggesting more effective net B exclusion by Thellungiella root. Arabidopsis exhibited toxicity symptoms including reduced shoot fresh weight (FW), but Thellungiella was not affected, even at similar levels of shoot-accumulated [B](int) (about 10 to 40 mm B in 'shoot water'), suggesting additional B tolerance mechanism in Thellungiella shoot. At [B](ext) = 5 mm, the summed shoot concentration of the potentially B-binding polyhydroxyl metabolites (malic acid, fructose, glucose, sucrose and citric acid) in Arabidopsis was below [B](int) , but in Thellungiella it was over twofold higher than [B](int) , and therefore likely to allow appreciable 1:2 boron-metabolite complexation in the shoot. This, we suggest, is an important component of Thellungiella B tolerance mechanism.

Application of bivariate statistics to full wine bottle diamagnetic screening data

A bivariate correlated Student distribution is applied to full wine bottle diamagnetic screening measurements. Previous work involving a limited number of rare wines indicated that like wines cluster in a plot of the first two principal component scores derived from a covariance matrix of the diamagnetic screening measurements. This study extends the approach to a much larger, statistically meaningful sixty bottle wine library where bivariate statistics are used to comment on the measured data. The full bottle diamagnetic screening of thirty-six identically labeled, sealed bottles of wine obtained from four different sources combined with principal component analysis data reduction followed by treatment with a bivariate distribution permit the effect of wine transport and storage to be observed. The usefulness and future success of the method towards the identification of counterfeit wines is mentioned.

Using low frequency full bottle diamagnetic screening to study collectible wine

A low frequency ν < 30 MHz spectrometer capable of noninvasively and nondestructively screening the diamagnetic properties of full intact bottles of wine is described, and along with principal component analysis, used to compare and contrast sealed bottles of wine. The sensitivity of this approach to various ionic and molecular wine solutes is established by analyzing standard solutions. The successful application of this full bottle method to a library of collectible wine is discussed and suggests that the method can be used to identify counterfeit wine without violating the bottle.

Using low frequency dielectric absorption to screen full intact wine bottles

A ν<25 MHz low frequency spectrometer capable of noninvasively and nondestructively screening the dielectric properties of full intact bottles of wine is described, and along with principal component analysis, used to screen rare wine. The sensitivity of this full bottle method to various ionic and molecular wine solutes was established by analyzing standard solutions. Application of the approach to a library of collectible wine and the identification of counterfeit wine are discussed.

Towards rapid throughput NMR studies of full wine bottles

A rapid throughput method for the quantitation of the oxidation level of intact full bottles of wine based on the 1331 water suppression pulse sequence is described. The ideal pulse sequence suppresses water in the (1)H nuclear magnetic resonance spectrum while uniformly and phase coherently exciting the resonances pertaining to ethyl alcohol at 1.1 ppm and oxidation products at 2.1 ppm. The anticipated results of the pulse sequence based on simulations are tested in small sample and full bottle standards and an application to the detection of wine spoilage in more than century old wine is provided.

Structural characterization of red wine rhamnogalacturonan II

The pectic polysaccharide rhamnogalacturonan II (RG-II), which accounts for approximately 20% of the ethanol-precipitable polysaccharides in red wine, has been isolated from wine polysaccharides by anion-exchange chromatography. Four fractions enriched with RG-II were obtained and the RG-II then purified to homogeneity by Concanavalin A affinity and size-exclusion chromatographies. The glycosyl-residue compositions of the four RG-IIs are similar; all the RG-IIs contain the monosaccharides (apiose, 2-O-methyl-L-fucose, 2-O-methyl-D-xylose, Kdo, Dha, and aceric acid) that are diagnostic of RG-II. The glycosyl-linkages of the neutral and acidic sugars, including aceric acid, were determined simultaneously by GC-EIMS analysis of the methylated alditol acetates generated from per-O-methylated and carboxyl-reduced RG-II. Two of the RG-IIs contain boron, most likely as a borate di-ester that cross-links two molecules of RG-II together to form a dimer. The dimer contains 3'- and 2,3,3'-linked apiosyl residues whereas the monomer contains only 3'-linked apiosyl residues which suggests that the borate di-ester is located on at least one of the apiosyl residues of RG-II. Although the wine RG-IIs all have similar structures they are not identical since they differ in the length and degree of methyl-esterification of the RG-II backbone and in the presence or absence of borate di-esters. Nevertheless, these studies show that the major structural features of wine and primary cell wall RG-II are conserved.