Structural features of aliphatic N-nitrosamines of 7-azabicyclo[2.2.1]heptanes that facilitate N-NO bond cleavage

N-Nitrosamines can be considered as potential nitric oxide (NO)/nitrosonium ion (NO(+)) donors. However, the relation of the structures of N-nitrosamines, in particular of aliphatic N-nitrosamines, to the characteristics of release of NO or NO(+) remains unclear. Here we show that aliphatic N-nitrosoamines of 7-azabicyclo[2.2.1]heptanes can undergo heterolytic N-NO bond cleavage. On the basis of the observation of reduced rotational barriers of the N-NO bonds in solution and nitrogen-pyramidal structures of the N-nitroso group in the solid state, we postulate that N-NO bond cleavage of N-nitrosamines is enhanced by a reduction of the resonance in the N-NO group. Computational studies suggest that these structural features of the N-nitrosamines of 7-azabicyclo[2.2.1]heptane are derived from angle strain imposed on the CNC angles.     

Rhodium-catalyzed cyclization of 1,6-enynes triggered by addition of arylboronic acids

1,6-Enynes reacted with arylboronic acids in the presence of a catalytic amount of a rhodium(I) complex under mild conditions to give (Z)-1-(1-arylethylidene)-2-vinylcyclopentanes. The regioselective addition of an arylrhodium(I) species across the carbon-carbon triple bond triggered the cyclization process. Intramolecular carborhodation onto the pendent alkene in a 5-exo mode furnished a five-membered ring. Finally, the rhodium(I) methoxide generated by beta-methoxy elimination reacted with the arylboronic acid to promote the next catalytic cycle.     

Fluorescence modification of Gb3 oligosaccharide and rapid synthesis of oligosaccharide moieties using fluorous protective group

The use of the bisfluorous chain-type propanoyl (Bfp) group as a fluorous protective group made it possible to rapidly synthesize the Gb2 and Gb3 oligosaccharide derivatives by a simple fluorous-organic extraction purification. Furthermore, the fluorescence-labeled Gb2 and Gb3 oligosaccharides were prepared as a potential Vero Toxins detecting reagent.     

Synthesis of 3-substituted 4H-1-benzothiopyran-4-ones

3-Substituted 2-phenyl-4H-1-benzothiopyran-4-ones (thioflavones) were prepared to test antimicrobial activity. It was found that 3-(phenyl)thiochromone derivatives (isothioflavones) were prepared by the Meerwein reaction of thiochromone with p-nitrobenzenediazonium ion. 3-(Formyl)thioflavone exhibits weak antimicrobial activity against Trichophytons and Candida.     

A rigorous control of logarithmic corrections in four-dimensional ϕ4 spin systems

Using Gawedzki and Kupiainen's rigorous block spin transformation method, we study critical phenomena in ⁴ spin systems in four dimensions. In Part I of this work we investigate in detail the renormalization group trajectory of the system not exactly at the critical point.     

Aurilide, a cytotoxic depsipeptide from the sea hare Dolabella auricularia: isolation, structure determination, synthesis, and biological activity

The bioassay-guided fractionation of the cytotoxic constituents of the Japanese sea hare Dollabella auricularia led to the isolation of aurilide (1), a 26-membered cyclodepsipeptide. The gross structure of 1 was established by spectroscopic analysis including 2D NMR techniques. The absolute stereostructure was determined by chiral HPLC analysis of acid hydrolysates of 1 and by the enantioselective synthesis of a degradation product arising from a dihydroxylated fatty acid portion. The enantioselective synthesis of 1 was achieved in 12% overall yield (16 steps) and confirmed the absolute stereostructure of 1. The cytotoxicity of 1 was evaluated using a synthetic sample, which was found to exhibit potent cytotoxicity against HeLa S₃ cells with an IC₅₀ of 0.011 μg/mL. Further biological and pharmacological studies of 1 have been carried out by using synthetic 1.     

Heteroatom-guided torquoselective olefination of alpha-oxy and alpha-amino ketones via ynolates

Ynolates were found to react with alpha-alkoxy-, alpha-siloxy-, and alpha-aryloxyketones at room temperature to afford tetrasubstituted olefins with high Z selectivity. Since the geometrical selectivity was determined in the ring opening of the beta-lactone enolate intermediates, the torquoselectivity was controlled by the ethereal oxygen atoms. From experimental and theoretical studies, the high Z selectivity is induced by orbital and steric interactions rather than by chelation. In a similar manner, alpha-dialkylamino ketones provided olefins with excellent Z selectivity. These products can be easily converted into multisubstituted butenolides and gamma-butyrolactams in good yield.     

Combinatorial synthesis of MUC1 glycopeptides: polymer blotting facilitates chemical and enzymatic synthesis of highly complicated mucin glycopeptides

The chemoselective polymer blotting method allows for rapid and efficient synthesis of glycopeptides based on a "catch and release" strategy between solid-phase and water-soluble polymer supports. We have developed a heterobifunctional linker sensitive to glutamic acid specific protease (BLase). The general procedure consists of five steps, namely (i) the solid-phase synthesis of glycopeptide containing BLase sensitive linker, (ii) subsequent deprotections and the release of the glycopeptide from the resin, (iii) chemoselective blotting of the glycopeptide intermediates in the presence of water-soluble polymers with oxylamino functional groups, (iv) sugar elongations using glycosyltransferases, and (v) the release of target glycopeptides from the polymer platform by selective BLase promoted hydrolysis. The combined use of the solid-phase chemical syntheses of peptides and the enzymatic syntheses of carbohydrates on water-soluble polymers would greatly contribute to the production of complicated glycopeptide libraries, thereby enhancing applicative research. We report here a high-throughput synthetic system for the various types of MUC1 glycopeptides exhibiting a variety of sugar moieties. It is our belief that this concept will become part of the entrenched repertoire for the synthesis of biologically important glycopeptides on the basis of glycosyltransferase reactions in automated and combinatorial syntheses.