N-(Diethoxyphosphoryl)-O-benzylhydroxylamine—a convenient substrate for the synthesis of N-substituted O-benzylhydroxylamines

Easily available N-(diethoxyphosphoryl)-O-benzylhydroxylamine was shown to be convenient, orthogonally protected substrate for regioselective N-alkylation by means of diverse halides under basic conditions (sodium hydride/tetrabutylammonium bromide). An efficient procedure for dephosphorylation of N-substituted N-(diethoxyphosphoryl)-O-benzylhydroxylamine to provide N-substituted O-benzylhydroxylamines was also established.     

Hydrolytic and transglycosylation reactions of N-acyl modified substrates catalysed by β-N-acetylhexosaminidases

The hydrolytic and transglycosylation capabilities of 35 fungal β-N-acetylhexosaminidases with p-nitrophenyl 2-amino-2-deoxy-β-d-glucopyranoside and its four N-acyl derivatives (CHO, COCH₂OH, COCH₂CH₃, COCF₃) as substrates were tested. The preparation of four novel p-nitrophenyl disaccharides from these unnatural substrates catalysed by enzymes from Aspergillus oryzae, Penicillium oxalicum and Talaromyces flavus represents a considerable extension of the synthetic potential of glycosidases.     

Poly(2-N-carbazolylethyl acrylate)-modified silica as a new polymeric stationary phase for reversed-phase high-performance liquid chromatography

Poly(2-N-carbazolylethyl acrylate) having terminal trimethoxysilyl groups was newly synthesized by radical polymerization and immobilized onto the silica surface (Sil-CEA). The chromatographic property of Sil-CEA was examined by applying polycyclic aromatic hydrocarbons as solutes. Poly(4-vinylpyridine)-modified silica (Sil-VP) and monomeric octadecylated silica (ODS) columns were used as the reference columns. Less sensitivity to molecular hydrophobicity and enhanced molecular planarity selectivity were obtained with Sil-CEA compared to ODS. On the other hand, high retention factors for the analyzed solutes and an opposite elution order for linear and disc-shaped solutes were obtained with Sil-CEA compared with Sil-VP. In this paper, the application for separation of tocopherols was also described.     

Design and synthesis of a novel water-soluble Aβ1-42 isopeptide: an efficient strategy for the preparation of Alzheimer's disease-related peptide, Aβ1-42, via O-N intramolecular acyl migration reaction

A novel water-soluble isopeptide of Alzheimer's disease-related peptide Aβ1-42, `26-O-acyl isoAβ1-42', which could efficiently convert to intact Aβ1-42 under physiological conditions via O-N intramolecular acyl migration, was synthesized providing a new system useful for investigation of biological function of Aβ1-42.     

Synthesis of novel 1-N-iminosugars from chiral nonracemic bicyclic lactams

This communication reported the synthesis of novel C-6 substituted isofagomine analogues from easily accessible chiral nonracemic bicyclic lactams. These azasugars have potentially very interesting structure and are difficult to obtain by other methods.     

A novel one-pot synthesis of hydroximoyl chlorides and 2-isoxazolines using N-tert-butyl-N-chlorocyanamide

Treatment of aldoximes with N-tert-butyl-N-chlorocyanamide gave hydroximoyl chlorides in quantitative yields in less than a minute, which on dehydrohalogenation in the presence of triethylamine gave the corresponding nitrile oxides. The nitrile oxides underwent 1,3-dipolar addition to dipolarophiles and gave 2-isoxazolines in excellent yields under mild conditions.     

Synthesis of undecaprenyl pyrophosphate-linked glycans as donor substrates for bacterial protein N-glycosylation

Synthesis of undecaprenyl pyrophosphate (Und-PP)-linked glycans is described. Bacterial ([E]₃,[Z]₇)-undecaprenol was synthesized from trans-geranylgeranyl sulfone and isoprenoid building blocks, which was converted to undecaprenyl phosphate (Und-P). It was coupled with glycosyl phosphates to afford Und-PP-linked glycans, including core trisaccharide of Campylobacter jejuni N-glycan. Our synthetic method for Und-PP-linked glycan would provide various substrates as a useful tool for systematic analysis of bacterial protein N-glycosylation.     

Ultrasensitive and selective determination of trace amounts of nitrite ion with a novel fluorescence probe mono[6-N(2-carboxy-phenyl)]-β-cyclodextrin

A novel fluorescence probe, mono[6-N(2-carboxy-phenyl)]-β-cyclodextrin (OACCD), has been developed for the determination of trace nitrite, In dilute HCl medium, the fluorescence intensity of the newly synthesized fluorescence probe OACCD was quenched in presence of trace nitrite at room temperature. Based on this, a simple, sensitive, and selective method for rapid determination of nitrite was described. Furthermore, common ions do not interfere the determination of trace amounts of nitrite. The fluorescence quenching intensity was linear over a nitrite concentration of 0.02-1.7 μmol l⁻¹ with a detection limit of 0.2 nmol l⁻¹ (S/N = 3). The method was applied to the determination of nitrite in different water samples, soil samples, and food samples with satisfactory results.     

Synthesis and analytical application of a novel tetradentate N(2)O(2) Schiff base as a chromogenic reagent for determination of nickel in some natural food samples

A novel sensitive chromogenic reagent, N,N′-bis(3-methylsalicylidene)-ortho-phenylene diamine (MSOPD), has been synthesized and used in the spectrophotometric determination of nickel. At pH 8, MSOPD can react with nickel ion at room temperature to form a 1:1 complex. The apparent molar absorptivity is 9.5 × 10⁴ l mol⁻¹ cm⁻¹ at 430 nm. Beer's low is obeyed over the range 0-1.0 × 10⁻⁵ M of nickel with a detection limit of 1.36 × 10⁻⁸ M. The relative standard deviation for measurement of 3.41 × 10⁻⁶ M nickel is 1.3% (n = 10). The method has successfully been applied to determination of trace amounts of nickel in some natural food samples.     

First example of carbohydrate-based Prins cyclization: a novel class of sugar-annulated tetrahydropyrans

The secondary homoallylic alcohol derived from d-glucose undergoes smooth coupling with aldehydes in the presence of molecular iodine under mild reaction conditions to produce 7-iodofurano[3,2-b]pyrans in good yields. This method is highly stereoselective, affording cis-tetrahydropyrans exclusively.     

N-tert-Butyl-N-chlorocyanamide: a new reagent for the efficient preparation of gem-chloronitroso compounds

A new reagent for the efficient preparation of gem-chloronitroso compounds has been developed. The reaction of ketoximes with N-tert-butyl-N-chlorocyanamide takes place instantaneously in carbon tetrachloride at room temperature with excellent yields under mild conditions.     

Auxiliary strategies for the preparation of β-amino alcohols with reductive cross-coupling and a synthesis of (−)-cytoxazone

Imine auxiliaries including chiral N-tert-butanesulfinyl imines have been successfully utilized to provide stereochemical control to the reductive cross-coupling of imines with aldehydes or ketones. This methodology has been applied to the synthesis of (−)-cytoxazone.     

Novel reaction systems for the synthesis of O-glucosides by enzymatic reverse hydrolysis

Our studies are presented to replace alcohols as solvents in reverse hydrolytic reactions catalyzed by immobilized β-glucosidase to synthesize O-substituted β-d-glucopyranosides in preparative-scale. We found that 1,2-diacetoxyethane is a suitable solvent and O-alkyl or aryl β-d-glucosides were synthesized in moderate yields (after isolation 12-19%). In these reactions proportion of glucose and glucosyl acceptor hydroxy compounds was 1:20. We suggest that 1,2-diacetoxyethane can be useful not only for alcohols but for other glucosyl donor compounds unsuitable for the role of solvent (e.g., phenols) in the synthesis of O-β-d-glucosides by reverse hydrolysis.     

A novel method for the synthesis of dipyrromethanes by metal triflate catalysis

5-Substituted dipyrromethanes were synthesized by the reaction of N-tosyl imines with excess pyrrole in the presence of metal triflates. Tripyrromethane and other oligomeric side products were not observed. High yields of 5-substituted dipyrromethanes were obtained for electron donating and withdrawing substituents by performing the reaction at two different temperatures. The new reaction procedure is simple and anhydrous conditions are not required.     

Isolation and synthesis of N-acyladenine and adenosine alkaloids from a southern Australian marine sponge, Phoriospongia sp.

Chemical fractionation of the southern Australian marine sponge Phoriospongia sp. (CMB-03107) yielded phorioadenine A (1) as a nematocidal agent and the first reported example of a 6-N-acyladenine natural product. The structure of 1 was confirmed by spectroscopic analysis and the chemical synthesis of racemic (1a) and enantiomeric (1b) analogues. HPLC–ESIMS analysis of the crude sponge extract with comparisons to the synthetic 6-N-acyladenosine 2a provided evidence that the biosynthetically related adenosine, phorioadenosine A (2), was present as a trace co-metabolite. The rare starfish metabolite asterubine (3) was also isolated as a co-metabolite, and its structure confirmed by spectroscopic analysis and chemical synthesis. Biological investigations confirmed that natural products 1–3 and synthetic analogues 1a–e and 2a were not cytotoxic to multiple mammalian cancer cell lines, or Gram-positive or -negative bacteria. Nematocidal activity (inhibition of larval development of Haemonchus contortus) detected in the Phoriospongia sp. extract was attributed to 1 (LD₉₉ 31 μg/mL), with preliminary structure–activity relationship investigations confirming the importance of the N-acyl side chain.     

A novel three-component reaction of N-fluoropyridinium salts: a facile approach to imidazo[1,2-a]pyridines

The reaction of N-fluoropyridinium triflate with isonitriles in acetonitrile and propionitrile in the presence of NaBH(OAc)₃ led to the formation of the corresponding imidazo[1,2-a]pyridines in 44-73% yields. The proposed reaction mechanism involves the intermediate formation of a highly reactive carbene species and apparent reduction of the pyridinium intermediate with NaBH(OAc)₃ to yield the targeted heterocycles.     

A novel synthetic route for the total synthesis of (±)-uleine

In this study, a new synthetic route for the total synthesis of (±)-uleine is described. The important step in the synthesis of this alkaloid consists of an intramolecular cyclization of the D ring of the azocino[4,3-b]indole skeleton. Reduction of (N-methyl){3-β-ethyl-4-oxo-2,3,4,9-tetrahydrospiro[1H-carbazole-1,2′(1,3)dithiolane]-2-yl}-2-acetamide with borane yielded the corresponding (N-methyl){3-β-ethyl-4-hydroxy-2,3,4,9-tetrahydrospiro[1H-carbazole-1,2′(1,3)dithiolane]-2-yl}-2-acetamide, which underwent acid-catalyzed ring closure to produce azocino[4,3-b]indole core. Finally, the synthesis of (±)-uleine was completed through several steps from the azocino[4,3-b]indole core.     

N-Hydroxy indoles as flexible substrates in rearrangements—a novel reaction with activated triple bonds

A novel rearrangement of N-hydroxy indole derivatives obtained from addition of N-hydroxy indoles to the activated triple bonds of alkynes was found to coexist with 3,3-sigmatropic rearrangements to the indolic ring. A mechanism involving an intermediate oxaziridinium ring rationalizes the transformation.     

Highly enantioselective (OC)Ru(salen)-catalyzed sulfimidation using N-alkoxycarbonyl azide as nitrene precursor

Enantioselective imidation of alkyl aryl sulfides with N-alkoxycarbonyl azide as a nitrene precursor was effected by using (OC)Ru(salen) complex 1 as catalyst. The steric and electronic nature of the N-alkoxycarbonyl group was found to strongly affect the enantioselectivity and the reaction rate, and high enantioselectivity (up to 99% ee) and good chemical yields were achieved by using 2,2,2-trichloro-1,1-dimethylethoxycarbonyl azide as the nitrene precursor at room temperature.     

Efficient palladium-mediated or base-induced 5-endo-dig cyclisation of C5-alkynylated pyrimidine derivatives: conventional and microwave-assisted synthesis of novel furo[2,3-d]pyrimidines

A series of the novel 5-alkynyl- and furo[2,3-d]pyrimidine derivatives in which the sugar moiety is replaced by a methoxymethyl (MOM) group is synthesised using the Sonogashira cross-coupling reaction under both conventional and microwave conditions, in good to excellent yields. The 5-endo-dig cyclisation of 5-alkynylpyrimidine derivatives promoted by a Pd-catalyst or base gives the corresponding furo[2,3-d]pyrimidines in good yields.