Recent Advances in the Total Synthesis of Piperidine Azasugars

A combination of 11B and 13C NMR spectroscopy with several model compounds has been used to elucidate the nature of the ester formation between borate and D-mannitol, D-glucitol, D-fructose and D-glucose in aqueous solution at pH 6-12 and at 25 °C. At high carbohydrate/borate ratios, D-mannitol shows the selective formation of bis(D-mannitol) 3,4:3′4′ -borate, whereas D-glucitol forms a mixture of six different bis(D-glucitol) borate esters involving both 2,3- and 3,4-dihydroxyl moieties. Bis(D-fructose) and bis(D-glucose) borate esters consist of pairs of diastereomers of the 2,3-β-and 1,2-α-furanose moieties, respectively. At low carbohydrate/borate ratios, mono-, di- and, sometimes, tri-borate esters are formed, e.g. mixture of α-D-glucofuranose 1,2:3,5-diborate and α-D-glucofuranose 1,2:5,6-diborate for D-glucose and a mixture of β-D-fructopyranose 1,2:4,5-diborate and β-D-fructopyranose 2,3:4,5-diborate for D-fructose. The overall stability constant for the borate di-esters of D-mannitol, D-glucitol and D-fructose is about two orders of magnitude higher than that of D-glucose.

Studies on borate esters III. Borate esters of D-mannitol, D-glucitol, D-fructose and D-glucose in water†

A new facile method for monoacylation of diols has been developed. A variety of cyclic and acyclic diols, in particular 1,2-diols, were selectively monobenzoylated in good yields by the reaction with benzoyl chloride in the presence of a catalytic amount of dimethyltin dichloride and inorganic bases such as potassium carbonate. Furthermore, the method was successfully applied to a kinetic resolution of racemic 1-phenyl-1,2-ethanediol using a chiral organotin catalyst. The ee was dependent on the kind of base, water as an additive, and the reaction temperature.

Chemo- and stereoselective monobenzoylation of 1,2-diols catalyzed by organotin compounds

Complex formation between p-tolylboronic acid and D-fructose was investigated by 13C NMR spectroscopy both in neutral nonaqueous and alkaline aqueous solutions to evaluate the possibilities of boronic acid based fructose sensors. Under both conditions a mixture of complexes was observed. The structures of the complexes in solution were assigned on the basis of 1JCC coupling constants which provided the information of the binding sites for the formed cyclic boronic esters. In alkaline aqueous solution seven different complexes were observed. At a 1:1 boronic acid: fructose ratio the major complex (82%) was β-D-fructofuranose 2,3,6-tri-O-(p-tolylorthoboronate)1. The minor complex was β-D-fructofuranose 2,3-(p-tolylhydroxyboronate) present in two diastereomeric forms 2a and 2b. At higher boronic acid:fructose ratios four additional complexes were observed namely the four possible diastereomeric forms of β-D-fructopyranose 2,3:4,5-bis(p-tolylhydroxyboronate) 3a–d. Under nonaqueous conditions signals arising from 13 different compounds were observed. Five of these complexes were structurally assigned. At a 1:1 boronic acid : fructose ratio the major complex was β-D-fructofuranose 2,3(p-tolylboronate) 5 present in 46%. At a ratio of 4:1 the major species was β-D-fructopyranose 2,3:4,5-bis(p-tolylboronate) 7 present in 67%. Two additional monoesterified pyranoses and one furanose were observed. They were assigned to the β-D-fructopyranose 1,2-(p-tolylboronate) 8, the α-D-fructopyranose 1,3-(ptolylboronate) 9 and the β-D-fructofuranose 1,3-(p-tolylboronate) 6. It is concluded that results of earlier studies on binding constants bear no relation to the actual formed complexes.

Boronic acids as fructose sensors. Structure determination of the complexes involved using 1JCC coupling constants

Synthetic studies on (+)-hydantocidin (3): a new synthetic method for construction of the spiro-hydantoin ring at the anomeric position of D-ribofuranose

Halo sugar nucleosides. V. Synthesis of angustmycin A and some base analogues

Tardigrades are microscopic ecdysozoans that can withstand extreme environmental conditions. Several tardigrade species undergo reversible morphological transformations and enter into cryptobiosis, which helps them to survive periods of unfavorable environmental conditions. However, the underlying molecular mechanisms of cryptobiosis are mostly unknown. Tubulins are evolutionarily conserved components of the microtubule cytoskeleton that are crucial in many cellular processes. We hypothesize that microtubules are necessary for the morphological changes associated with successful cryptobiosis. The molecular composition of the microtubule cytoskeleton in tardigrades is unknown. Therefore, we analyzed and characterized tardigrade tubulins and identified 79 tardigrade tubulin sequences in eight taxa. We found three α-, seven β-, one γ-, and one ε-tubulin isoform. To verify in silico identified tardigrade tubulins, we also isolated and sequenced nine out of ten predicted Hypsibius exemplaris tubulins. All tardigrade tubulins were localized as expected when overexpressed in mammalian cultured cells: to the microtubules or to the centrosomes. The presence of a functional ε-tubulin, clearly localized to centrioles, is attractive from a phylogenetic point of view. Although the phylogenetically close Nematoda lost their δ- and ε-tubulins, some groups of Arthropoda still possess them. Thus, our data support the current placement of tardigrades into the Panarthropoda clade. 

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Jiri. Smejkal

Papers

Halo sugar nucleosides. V. Synthesis of angustmycin A and some base analogues

Phylogenetic and functional characterization of water bears (Tardigrada) tubulins

Immunocapturing rare cells from blood: A simple and robust microsystem approach.