Radical decarboxylative bromination of aromatic acids

Thiohydroxamic esters (mixed anhydrides) of aromatic and α,β-unsaturated carboxylic acids undergo clean decarboxylative bromination on treatment with bromotrichloromethane in the presence of a radical initiator.     

Identification of nuclear proteins of small cell lung cancer cell line H82: An improved procedure for the analysis of silver-stained proteins

An efficient method for digestion and extraction of proteolytic peptides from silver-stained proteins was applied to the characterization of nuclear proteins from the small cell lung cancer H82 (ATCC HTB 175) cell line previously separated by high-resolution large format two-dimensional gel electrophoresis. From 68 spots, evenly distributed on the gel area and representing a wide range of spot intensities, 63 (92%) were successfully identified by matrix-assisted laser desorption/ionization (MALDI) or electrospray ionozation-mass spectrometry (ESI-MS). In five cases where the identification was not possible, the presence of an intense background apparently due to the leakage of polymers from the microtubes or other plastics, was detected. Extensive analysis of peptide sequences by ESI MS/MS experiments allowed the identification of post-translational modifications, such as acetylation, phosphorylation, deamidation of asparagine residues and the presence of isoaspartic acid. A new protein variant not reported in sequence databases was also detected.     

Identification of<Emphasis Type="Italic"> N</Emphasis>-glycosylation sites of the murine neural cell adhesion molecule NCAM by MALDI-TOF and MALDI-FTICR mass spectrometry

Mass spectrometry has been shown in recent years to be a powerful tool to determine accurate molecular masses and sequences of peptides and proteins and post-translational modifications such as glycosylation, phosphorylation, and sulfation. For glycosylation, it has been increasingly recognized to be of pivotal importance to identify whether potential glycosylation sites are actually modified by glycans, because functions of proteins may be modulated or depend on the presence of glycans at specific sites. Several recent reports have established that mass spectrometric techniques such as matrix-assisted laser desorption/ionization or electrospray ionization mass spectrometry (MALDI-TOF or ESI-MS, respectively) with or without preceding HPLC and in combination with PNGase F treatment are suited to analyze whether consensus sequences for N-glycosylation are glycosylated or not. Here we report the mass spectrometric analysis of the six potential N-glycosylation sites of the neural cell adhesion molecule NCAM from adult mouse brain. Unmodified peptides and glycopeptides each carrying a single glycosylation site were generated from NCAM by AspN and trypsin treatment and submitted to reversed-phase HPLC with or without prior enzymatic release of N-glycans. The resulting peptides were analyzed by MALDI-TOF-MS. In addition, high-resolution Fourier transform–ion cyclotron resonance (MALDI-FTICR) mass spectrometry was performed after in-gel deglycosylation and subsequent trypsin digestion. By using these procedures all six consensus sequences were shown to be glycosylated; the observation of an unmodified peptide with the consensus sequence N-1 indicates only partial glycosylation at this site.Abbreviations amu atomic mass units - AspN endoproteinase AspN - CAM cell adhesion molecule - ESI electrospray ionization - FTICR Fourier transform–ion cyclotron resonance - IgSF immunoglobulin superfamily - MALDI-TOF matrix-assisted laser desorption ionization–time of flight - MS mass spectrometry - NCAM neural cell adhesion molecule - PNGase F peptide-N ⁴-(N-acetyl--glucosaminyl)asparagine amidase - PSA polysialic acid - TFA trifluoroacetic acid     

α-methyl amino acids by catalytic phase-transfer alkylations

The α-methyl amino acids, α-methyl p-chlorophenylalanine, α-methyl p-tyrosine, α-methyl m-tyrosine and α-methyl DOPA have been prepared in good yields from amino ester hydrochlorides. The key step in the method is the catalytic phase-transfer alkylation of Schiff base derivatives of mono alkyl amino acids.     

Ca5Sn2As6, das erste Inoarsenidostannat(IV)

Ca₅Sn₂As₆, The First Inoarsenidostannate(IV) The new compound Ca₅Sn₂As₆ crystallizes in the orthorhombic system (space group Pbam (No. 55)) with the lattice constants s. ?Inhaltsübersicht”?. In the structure SnAs₄-tetrahedra are connected by common corners to ?Einereinfach”? chains. The compound belongs to the “Zintlphases”.     

Analogues of Sialic Acids as Potential Sialidase Inhibitors. Synthesis of C6 and C7 Analogues of N-Acetyl-6-amino-2,6-dideoxyneuraminic Acid

The piperidines 12 – 18 , piperidmose analogues of Neu5Ac ( 1 ) with a shortened side chain, were synthesized from N-acetyl-D -glucosamine via the azidoalkene 32 and tested as inhibitors of Vibrio cholerae sialidase. Deoxygenation at C(4) of the uronate 22 , obtained from the known D -GlcNAc derivative 20 , was effected by β-elimination (→ 23 ), exchange of the AcO at C(3) with a (t-Bu)Me₂SiO group and hydrogenation (→ 26 ; Scheme 1). Chain extension of 26 by reaction with Me₃SiCH₂MgCl gave the D -ido-dihydroxysilane 28 , which was transformed into the unsaturated L -xylo-mesylate 29 and further into the L -lyxo-alcohol 30 , the mesylate 31 , and the L -xylo-azide 32 . The derivatives 29 – 31 prefer a sickle zig-zag and 32 mainly an extended zig-zag conformation (Fig. 2). The piperidinecarboxylate 15 was obtained from 32 by ozonolysis (→ 33 ), intramolecular reductive animation (→ 34 ), and deprotection, while reductive animation of 34 with glycolaldehyde (→ 35 ) and deprotection gave 16 (Scheme 2). An intramolecular azide-olefin cycloaddition of 32 yielded exclusively the fused dihydrotriazole 36 , while the lactone 39 did not cyclize (Scheme 3). Treatment of 36 with AcOH (→ 37 ) followed by hydrolysis (→ 38 ) and deprotection led to the amino acid 18 . To prepare the (hydroxymethyl)piperidinecarboxylates 12 and 17 , 32 was first dihydroxylated (Scheme 4). The L -gluco-diol 40 was obtained as the major product, in agreement with Kishi's rule. Silylation of 40 (→ 42 ), oxidation with periodinane (→ 44 ), and reductive animation gave the L -gluco-piperidine 45 . It was, on the one hand, deprotected to the amino acid 12 and, on the other hand, N-phenylated (→ 46 ) and deprotected to 17 . While 45 and 12 adopt a ²C₅ conformation, the analogous N-Ph derivatives 46 and 17 adopt a ₅C² and a B_3,6 conformation, respectively, on account of the allylic 1,3-strain. The conformational effects of this 1,3-strain are also evident in the carbamate 47 , obtained from 45 (Scheme 5), and in the C(2)-epimerized bicyclic ether 48 , which was formed upon treatment of 47 with (diethylamino)sulfur trifluoride (DAST). Fluorination of 40 with DAST (→ 49 ) followed by treatment with AcOH led to the D -ido-fluorohydrin 50 . Oxidation of 50 (→ 51 ) followed by a Staudinger reaction and reduction with NaBH₃CN afforded the (fluoromethyl)piperidine 52 , while reductive amination of 51 with H₂/Pd led to the methylpiperidine 55 , which was similarly obtained from the keto tosylate 54 and from the dihydrotriazole 36 . Deprotection of 52 and 55 gave the amino acids 13 and 14 , respectively. The aniline 17 does not inhibit V. cholerae sialidase; the piperidines 12 – 16 and 18 are weak inhibitors, evidencing the importance of an intact 1,2,3-trihydroxypropyl side chain.     

Synthesis, photophysical, photochemical and biological properties of caged GABA, 4-[[(2H-1-benzopyran-2-one-7-amino-4-methoxy) carbonyl] amino] butanoic acid

The photorelease of a caged neurotransmitter can be used to investigate the function of neuronal circuits in tissues. We have designed and synthesized a stable, caged gamma-aminobutyric acid (GABA) derivative, 4-[[(2H-1-benzopyran-2-one-7-amino-4-methoxy)carbonyl]amino] butanoic acid (BC204), that releases the neurotransmitter in physiological medium when irradiated with UV light at 300-400 nm in PBS at pH 7.4. The release of GABA occurs with the formation of the major photoproduct, 7-amino-4-(hydroxymethyl)-2H-1-benzopyran-2-one, via a solvolytic photodegradation mechanism of the coumarin moiety and was confirmed by electrospray mass spectrometry/mass spectrometry (ESI MS/MS). BC204 is chemically stable and shows no intrinsic activity after many hours under physiological dark conditions. These properties suggest that BC204 is an excellent form of caged GABA that is well suited for long-term biological studies.     

PHYTOCHROME DESTRUCTION IN DARK - AND LIGHT-GROWN AMARANTHUS CAUDATUS SEEDLINGS

Abstract— Slow destruction of the far-red-absorbing form of phytochrome (P_fr), which has been observed in light-grown oat and maize, occurs in light- and dark-grown Amaranthus, Pharbitis , and Brassica seedlings as well. Destruction of P_fr in these seedlings shows two phases: if a high level of P_fr is produced in dark-grown seedlings, the destruction is fast in the beginning and then slows after a low P_fr level has been reached. Slow P_fr destruction is predominant in light-grown tissue.     

New strategy for the synthesis of phosphatase inhibitors TMC-69-6H and analogs

An efficient method for the synthesis of antitumor TMC-69-6H and related analogs which have been demonstrated to be phosphatase (PTP1B, VHR, and PP1) inhibitors, is reported. This strategy involves two key steps: a diastereoselective aldol reaction and a one-pot tandem ring-closing and cross metathesis for the construction of the pyran moiety.