Incorporation and translocation of 2-deoxy-2-[18F]fluoro-d-glucose in Sorghum bicolor (L.) Moench monitored using a planar positron imaging system

[¹⁸F]FDG (2-deoxy-2-[¹⁸F]fluoro-d-glucose) was fed to a sorghum plant [Sorghum bicolor (L.) Moench] from the tip of a leaf and its movement was monitored using a planar positron imaging system (PPIS). [¹⁸F]FDG was uptaken from the leaf tip and it was translocated to the basal part of the shoots from where it moved to the roots, the tillers and the sheaths. Autoradiographic analysis of the distribution of ¹⁸F, [¹⁸F]FDG and/or its metabolites showed translocation to the roots, tillers, and to the leaves that were younger than the supplied leaf. Strong labelling was observed in the basal part of the shoots, in the sheaths, the youngest leaf and the root tips. Our results indicate that [¹⁸F]FDG and/or its metabolites were absorbed from the leaf and translocated to the sites where nutrients are required. This strongly suggests that [¹⁸F]FDG can be utilised as a tracer to study photoassimilate translocation in the living plant. This is the first report on the use of [¹⁸F]FDG, which is routinely used as a probe for clinical diagnosis, to study source to sink translocation of metabolites in whole plants in real time.     

Age-related decline of dopamine synthesis in the living human brain measured by positron emission tomography with L-[beta-11C]DOPA

Loss of dopamine synthesis in the striatum with normal human aging has been observed in the postmortem brain. To investigate whether there is age-associated change in dopamine synthesis in the extrastriatal brain regions similar to that in the striatum, positron emission tomography studies with (11)C-labelled l-DOPA were performed on 21 normal healthy male subjects (age range 20-67 years). Decline in the tissue fraction of gray matter per region of interest was also investigated. The overall uptake rate constant for each region of interest was quantified by the Patlak plot method using the occipital cortex as reference region. Regions of interest were set on the dorsolateral prefrontal cortex, lateral temporal cortex, medial temporal cortex, occipital cortex, parietal cortex, anterior cingulate, thalamus, midbrain, caudate nucleus, and putamen. Test-retest analysis indicated good reproducibility of the overall uptake rate constant. Significant age-related declines of dopamine synthesis were observed in the striatum and extrastriatal regions except midbrain. The decline in the overall uptake rate constant was more prominent than in the tissue fraction of gray matter. These results indicate that the previously demonstrated age-related decline in striatal dopamine synthesis extends to several extrastriatal regions in normal human brain.     

Fast and efficient synthesis of a novel homologous series of L-fucosylated trisaccharides using the Helix pomatia alpha-(1-->2)-L-galactosyltransferase

The alpha-(1-->2)-L-galactosyltransferase from the albumen gland of the vineyard snail Helix pomatia exhibits high alpha-(1-->2)-L-fucosyltransferase activity and can be used to transfer L-fucose from GDP-L-fucose to terminal, non-reducing D-galactose residues of an oligosaccharide, thus providing facile access to a range of H-antigen-containing oligosaccharides. The enzymatic glycosylation was applied here on a milligram scale to a series of disaccharide acceptor substrates. Apparently the site of interglycosidic linkage between the terminal and subterminal acceptor sugar units is of little or no consequence. The homologous series of trisaccharides thus produced were fully characterised by NMR analysis of their peracetates.     

Major anthocyanins from purple asparagus (Asparagus officinalis)

Two major anthocyanins (A1 and A2) were isolated from peels of the spears of Asparagus officinalis cv. Purple Passion. They were purified by column, paper and high-performance liquid chromatographic separations, and their structures were elucidated by high-resolution Fourier transform ion cyclotron resonance mass spectrometry (HR-FT-ICR MS), 1H, 13C and two-dimensional NMR spectroscopic analyses and either acid or alkaline hydrolysis, respectively. A1 was identified as cyanidin 3-[3'-(O-beta-d-glucopyranosyl)-6'-(O-alpha-l-rhamnopyranosyl)-O-beta-d-glucopyranoside], whereas A2 was cyanidin 3-rutinoside, which is widely distributed in higher plants. Oxygen radical absorbance capacity (ORAC) assays proved their high antioxidant activities.     

Two-step regio- and stereoselective syntheses of [19F]- and [18F]-2-deoxy-2-(R)-fluoro-beta-D-allose

Replacement of specific hydroxyl groups by fluorine in carbohydrates is an ongoing challenge from chemical, biological, and pharmaceutical points of view. A rapid and efficient two-step, regio- and stereoselective synthesis of 2-deoxy-2-(R)-fluoro-beta-d-allose (2-(R)-fluoro-2-deoxy-beta-d-allose; 2-FDbetaA), a fluorinated analogue of the rare sugar, d-allose, is described. TAG (3,4,6-tri-O-acetyl-1,5-anhydro-2-deoxy-d-arabino-hex-1-enitol or 3,4,6-tri-O-acetyl-d-glucal), was fluorinated in anhydrous HF with dilute F(2) in a Ne/He mixture or with CH(3)COOF at -60 degrees C. The fluorinated intermediate was hydrolyzed in 1N HCl and the hydrolysis product was purified by liquid chromatography and characterized by 1D (1)H, (13)C, and (19)F NMR spectroscopy as well as 2D NMR spectroscopy and mass spectrometry. In addition, (18)F-labeled 2-deoxy-2-(R)-fluoro-beta-d-allose (2-[(18)F]FDbetaA) was synthesized for the first time, with an overall decay-corrected radiochemical yield of 33+/-3% with respect to [(18)F]F(2), the highest radiochemical yield achieved to date for electrophilic fluorination of TAG. The rapid and high radiochemical yield synthesis of 2-[(18)F]FDbetaA has potential as a probe for the bioactivity of d-allose.     

Structure of the O-specific polysaccharide of Proteus vulgaris O15 containing a novel regioisomer of N-acetylmuramic acid, 2-acetamido-4-O-[(R)-1-carboxyethyl]-2-deoxy-D-glucose

An acidic O-specific polysaccharide was obtained by mild acid degradation of the lipopolysaccharide of Proteus vulgaris O15 and studied by sugar and methylation analyses along with 1H and 13C NMR spectroscopy, including 2D COSY, TOCSY, ROESY, and H-detected 1H,(13)C HMQC experiments. The polysaccharide was found to contain an ether of GlcNAc with lactic acid, and the following structure of the repeating unit was established:-->3)-alpha-D-GlcpNAc4(R-Lac)6Ac-(1-->2)-beta-D-GlcpA-(1-->3)-alpha-L-6dTalp2Ac-(1-->3)-beta-D-GlcpNAc-(1-->where L-6dTal and D-GlcNAc4(R-Lac) are 6-deoxy-L-talose and 2-acetamido-4-O-[(R)-1-carboxyethyl]-2-deoxy-D-glucose, respectively. The latter sugar, which to our knowledge has not been hitherto found in nature, was isolated from the polysaccharide by solvolysis with anhydrous triflic acid and identified by comparison with the authentic synthetic compound. Serological studies with the Smith-degraded polysaccharide showed an importance of 2-substituted GlcA for manifesting of the immunospecificity of P. vulgaris O15.     

Regioselective [3+2] cycloaddition of chalcones with a sugar azide: easy access to 1-(5-deoxy-d-xylofuranos-5-yl)-4,5-disubstituted-1H-1,2,3-triazoles

[3+2] Cycloaddition of 5-azido-5-deoxy-1,2-O-isopropylidene-α-d-xylofuranose with 1,3-diphenyl-prop-3-enones, followed by oxidation of the intermediate triazolines in a tandem manner, led to the regioselective formation of 4-benzoyl-1-(5-deoxy-1,2-O-isopropylidene-α-d-xylofuranos-5-yl)-5-phenyl-1H-1,2,3-triazoles in moderate to good yields.     

Stabilization of the human beta2-adrenergic receptor TM4-TM3-TM5 helix interface by mutagenesis of Glu122(3.41), a critical residue in GPCR structure

G protein-coupled receptor (GPCR) instability represents one of the most profound obstacles in the structural study of GPCRs that bind diffusible ligands. The introduction of targeted mutations at nonconserved residues that lie proximal to helix interfaces has the potential to enhance the fold stability of the receptor helix bundle while maintaining wild-type receptor function. To test this hypothesis, we studied the effect of amino acid substitutions at Glu122^3.41 in the well-studied β₂-adrenergic receptor (β₂AR), which was predicted from sequence conservation to lie at a position equivalent to a tryptophan residue in rhodopsin at the 3,4,5 helix interface among transmembrane (TM) domains 3, 4, and 5. Replacement of Glu122^3.41 with bulky hydrophobic residues, such as tryptophan, tyrosine, and phenylalanine, increases the yield of functionally folded β₂AR by as much as 5-fold. Receptor stability in detergent solution was studied by isothermal denaturation, and it was found that the E122W and E122Y mutations enhanced the β₂AR thermal half-life by 9.3- and 6.7-fold, respectively, at 37 °C. The β₁AR was also stabilized by the introduction of tryptophan at Glu147^3.41, and the effect on protein behavior was similar to the rescue of the unstable wild-type receptor by the antagonist propranolol. Molecular modeling of the E122W and E122Y mutants revealed that the tryptophan ring edge and tyrosine hydroxyl are positioned proximal to the helical break in TM5 introduced by the conserved Pro211^5.50 and may stabilize the helix by interacting favorably with the unpaired carbonyl oxygen of Val206^5.45. Conformational flexibility of TM5 is likely to be a general property of class A GPCRs; therefore, engineering of the TM4-TM3-TM5 interface at the 3.41 position may provide a general strategy for the stabilization of other receptors.