PubMed Health⌕ Search

Biomedical subjects

M Adamczyk

Publications and source records attributed to M Adamczyk.

At least 19 recordsLinked to original sources
PubMed2001

Enantioselective synthesis of (2-pyridyl)alanines via catalytic hydrogenation and application to the synthesis of L-azatyrosine.

[reaction: see text] A novel method for the synthesis of (2-pyridyl)alanines 2a-b was developed by converting (2-pyridyl)dehydroamino acid derivatives 1a-b to the corresponding N-oxides 3a-b followed by asymmetric hydrogenation using (R,R)-[Rh(Et-DUPHOS)(COD)]BF(4) [(R,R)-6] catalyst and subsequent N-oxide reduction in 80-83% ee. This methodology was applied to the total synthesis of L-azatyrosine [(+)-12], an antitumor antibiotic, starting from (5-benzyloxy)-2-pyridylmethanol (7), in >96% enantiomeric purity.

Alanine↗
PubMed2001

Quenching of biotinylated aequorin bioluminescence by dye-labeled avidin conjugates: application to homogeneous bioluminescence resonance energy transfer assays.

[see reaction]. Avidin conjugates containing the covalently attached dyes QSY-7 and dabcyl were prepared and shown to quench the bioluminescence of biotinylated aequorin. Quenching efficiency was shown to be dependent on both the label-to-avidin ratio and the concentration of the avidin conjugate. These properties were exploited to develop a homogeneous bioluminescence resonance energy transfer (BRET) assay for biotin.

Aequorin↗
PubMed2001

Bone collagen cross-links: a convergent synthesis of (+)-deoxypyrrololine.

A convergent total synthesis of (+)-deoxypyrrololine (Dpl, 4), a putative cross-link of bone collagen, is described starting from a commercially available L-glutamic acid derivative, (4S)-5-(tert-butoxy)-4-[(tert-butoxycarbonyl)amino]-5- oxopentanoic acid (16). Condensation of aldehyde (S)-(-)-17 with nitro compound (S)-(-)-27, both of which were prepared from a common precursor (S)-16, gave the alpha-hydroxynitro compound 28, which upon acetylation afforded alpha-acetoxynitro compound 14 in good yield. Subsequent condensation and cyclization of alpha-acetoxynitro compound 14 with benzyl isocyanoacetate (15) in the presence of DBU in THF gave the key pyrrole intermediate (S,S)-(-)-12 in 57% yield. N-Alkylation of pyrrole (S,S)-(-)-12 with iodide (S)-(-)-13 using t-BuOK in THF afforded the 2-benzyloxycarbonyl-1,3,4-substituted pyrrole derivative (-)-29 in 42% yield. Removal of the protective groups in (-)-29 followed by hydrogenolysis and decarboxylation afforded the cross-link (+)-Dpl (4) in good overall yield. The synthesis of an analogue (S)-(+)-24 and formation of a novel tetrahydroindole derivative (-)-31 are also described.

Amino Acids↗
PubMed2001

Quantitative determination of noncovalently bound acridinium in protein conjugates by liquid chromatography/electrospray ion trap mass spectrometry.

A sensitive and robust liquid chromatography/electrospray ion trap mass spectrometry (LC/MS/MS) method has been developed for the quantitative determination of noncovalently bound acridinium free acid in protein-acridinium conjugates. The lower level of quantitation (LOQ) for acridinium free acid was determined to be 0.6 ng. The assay was validated with a linear concentration range of 0.6-60 ng. The method requires minimum sample handling and is specific, reproducible, and provides a new aspect for protein-acridinium conjugate characterization.

Acridines↗
PubMed2001

Selective analysis of phosphopeptides within a protein mixture by chemical modification, reversible biotinylation and mass spectrometry.

A new method combining chemical modification and affinity purification is described for the characterization of serine and threonine phosphopeptides in proteins. The method is based on the conversion of phosphoserine and phosphothreonine residues to S-(2-mercaptoethyl)cysteinyl or beta-methyl-S-(2-mercaptoethyl)cysteinyl residues by beta-elimination/1,2-ethanedithiol addition, followed by reversible biotinylation of the modified proteins. After trypsin digestion, the biotinylated peptides were affinity-isolated and enriched, and subsequently subjected to structural characterization by liquid chromatography/tandem mass spectrometry (LC/MS/MS). Database searching allowed for automated identification of modified residues that were originally phosphorylated. The applicability of the method is demonstrated by the identification of all known phosphorylation sites in a mixture of alpha-casein, beta-casein, and ovalbumin. The technique has potential for adaptations to proteome-wide analysis of protein phosphorylation.

Amino Acid Sequence↗
PubMed2001

[Cochlear implantation: relationship between speech development and insertion depth in children].

BACKGROUND: The goal in pediatric cochlear implantation is improved hearing leading to better speech development, which may allow their integration into mainstream schools. Whether the intracochlear position of the electrode array has an influence on speech development or not is controversially discussed. PATIENTS: Between 1996 and 1998 29 children ranging from 1.5 to 11.8 years (median 4 years) were provided with a Nucleus 22M or 24M cochlear implant system. Speech and language skills were assessed by a closed-set test (Mainzer test) and by the Schmid-Giovannini score for hearing development pre-implantation and at 6, 12, 18 and 24 months post-implantation. The position of the electrode array was determined by the surgical record and by a postoperative transorbital x-ray. Since the promontory has a thickness of one to two electrode bands, we defined deep insertion as more than 24 bands intracochlear. RESULTS: The patients were divided into 2 groups according to the insertion depth: Group 1 (n = 8) 24 bands (22 electrodes and 2 stiffening rings correspond to < or = 18 mm) or less and group 2 (n = 21) more than 24 bands intracochlear correspond to > 18 mm). The mean closed-set test scores 12 months post-implantation were 51.4% and 68.5% for group 1 and group 2, respectively. Schmid-Giovannini test scores were 8.7 for group 1 and 10.1 for group 2. There was no significant statistical difference in the closed-set and Schmid-Giovannini test scores. We observed incomplete insertion (i.e. less than 22 active bands are intracochlear) because of electrode extrusion in only one child. CONCLUSION: Speech development in children does not improve with deeper insertion of the cochlear implant electrode array.

Age Factors↗
PubMed2001

Selective vestibular ablation by KTP laser in endolymphatic hydrops.

OBJECTIVES AND HYPOTHESIS: Vertigo, the cause of disability in many patients with Ménière's disease, may be the result of the effects of endolymphatic hydrops on the semicircular canals. We hypothesize that intractable vertigo may be controlled by destruction of the semicircular canal neuroepithelium using visible light lasers without the need for extensive fenestration of the bony labyrinth. This study was designed to assess the cochlear effects of potassium titanyl phosphate (KTP) laser-assisted triple semicircular canal ablation (TSCA) in endolymphatic hydrops. STUDY DESIGN: Randomized, prospective, and controlled. METHODS: Forty-one adult guinea pigs underwent either a unilateral endolymphatic duct occlusion to induce hydrops or a sham procedure. Ten weeks after induction of the hydrops, a KTP laser-assisted TSCA or a sham surgery was performed. RESULTS: Electrocochleographic thresholds to clicks and tone-bursts (2-20 kHz) did not change significantly up to 4 weeks after TSCA in hydropic ears. Cross-sectional histology confirmed the presence of hydrops and the ablation of the semicircular canals. Cochlear whole-mounts for hair cell counts showed no significant loss of outer or inner hair cells in hydropic ears treated with TSCA. CONCLUSION: KTP laser-assisted TSCA can be performed in the guinea pig model of endolymphatic hydrops without significant loss of hearing. Evaluation of this technique may be warranted in patients with intractable Ménière's disease.

Animals↗
PubMed2000

An efficient enantioselective synthesis of (S)-(-)-acromelobic acid.

[reaction: see text] A highly efficient enantioselective synthesis of (S)-(-)-acromelobic acid (1) was achieved via asymmetric hydrogenation of dehydroamino acid derivative (3) using (R,R)-[Rh(DIPAMP)(COD)]BF(4) catalyst followed by removal of protective groups in >98% ee and good over all yield. The key intermediate (3) was prepared from the commercially available citrazinic acid (4) in six steps.

Alanine↗
PubMed2000

7beta-hydroxysterol is cytotoxic to neonatal rat astrocytes in primary culture when cAMP levels are increased.

We have shown previously that 7beta-hydroxycholesterol (7betaOHCH) and 7beta-hydroxycholesteryl-3-oleate (7betaOHCH- 3-OL) are potent inhibitors of lesion-induced astrogliosis in the rat cortex or spinal cord; these substances reduce reactive astrocyte proliferation and hypertrophy. In this study, we employed cultured newborn rat astrocytes with increased cAMP levels as an in vitro model of reactive astrocytes. Treatment with either dibutyryl-cAMP (dbcAMP) or isoproterenol resulted in morphologic differentiation of astrocytes which became fibrous. Concomitant incubation with 30 microM 7betaOHCH and dbcAMP (or isoproterenol) provoked the cells to retract and was cytotoxic. When the beta-adrenergic receptor-mediated cAMP increase was abolished by propranolol, the 7betaOHCH cytotoxicity was inhibited. Immunocytochemical labelling for glial fibrillary acidic protein (GFAP) and beta-tubulin and electron microscopy suggested that intermediate filament and microtubular organizations were modified by 7betaOHCH. Analysis of the activity of cAMP-dependent protein kinase (PKA) in astrocytes treated with dbcAMP and 7betaOHCH showed a rapid and marked inhibition of the phosphotransferase activity which lasted for 24 hr. We suggest that this culture system provides an experimental system to study the molecular mechanisms involved in the effect of oxysterols on astrocytic hypertrophy. The cytotoxicity of 7betaOHCH seems to be mediated by inhibition of PKA, which phosphorylates intermediate filaments and the transcription factor cyclic AMP responsive element binding.

Adrenergic beta-Agonists↗
PubMed2000

Efficient synthesis of rhodamine conjugates through the 2'-position.

Reaction of substrates containing primary amines with rhodamine 2'-esters cleanly produces fluorescent rhodamine 2'-amide conjugates at ambient temperature. Only primary amines react with the esters under these conditions. Chemoselectivity can thus be achieved in substrates containing different types of amines.

Amides↗
PubMed2000

Binding interactions of vancomycin tracers with a bacterial cell wall peptidoglycan analogue.

Binding interactions between several vancomycin tracers and (N,N'-diacetyl)KDADA in solution were evaluated in a competition format using a surface plasmon resonance instrument. Tracers derivatized from the carboxy terminus or the N-vancosaminyl sugar moiety of vancomycin bind the peptide with an affinity similar to that of underivatized vancomycin. In contrast, N-methylleucyl derivatized vancomycin tracers bind the peptide with a reduced affinity relative to vancomycin.

Anti-Bacterial Agents↗
PubMed2000

Papain digestion of different mouse IgG subclasses as studied by electrospray mass spectrometry.

On-line liquid chromatography-electrospray ionization mass spectrometry (LC/ESI-MS) has been utilized to monitor the papain digestion of mouse monoclonal antibodies (mAb) of different subclasses (IgG1, IgG2a, IgG2b, and IgG3). The method is simple, rapid, sensitive, and allows for simultaneous determination of digestion products and the identification of microheterogenous fragments. The results provide important insight into the mechanism of papain digestion of mouse IgGs of different subclasses.

Animals↗
PubMed2000

Sequencing of anti-thyroxine monoclonal antibody fab fragment by ion trap mass spectrometry.

A comprehensive mass spectrometric strategy is described for the sequencing of anti-thyroxine monoclonal antibody Fab region (48 000 Da). After reduction and S-carboxymethylation of the Fab, the modified light chain and Fd fragment were separated and subjected to multiple proteolytic digestions. The resulting digests were characterized by on-line microbore liquid chromatography/electrospray ionization ion trap mass spectrometry. Database search against published immunoglobulins (IgGs) allowed identification of all the peptides in constant domains. The homologous framework residues in the IgGs were utilized as 'sequence maps' for the sequence determination of variable domains. S-Carboxymethylation with an isotopic-enriched moiety greatly facilitated the recognition and data elucidation of cysteinyl peptides through the unique isotopic distribution patterns specific to the modified peptides. Methylation of peptide mixtures provided additional information for the interpretation of MS/MS spectra, allowing easy differentiation of Asp/Asn and Gln/Glu pairs. This study clearly demonstrates the power of mass spectrometry for the sequencing of antibodies without knowing the corresponding DNA sequences.

Amino Acid Sequence↗
PubMed2000

Evidence of nucleophilic addition to chemiluminescent N-sulfonylacridinium-9-carboxamides from electrospray ionization mass spectrometry.

Addition of nucleophiles to the chemiluminescent acridinium-9-carboxamide 1 resulted in the formation of the acridan adduct 7. The relative ratio of 1/7 present in solution could be determined by electrospray ionization mass spectrometry (ESI-MS) for a number of nucleophiles that are commonly employed during the use of 1 as a label in medical diagnostic assays.

Acridines↗
PubMed2000

Application of surface plasmon resonance toward studies of low-molecular-weight antigen-antibody binding interactions.

Methods for studying low-molecular-weight antigen-antibody binding interactions using surface plasmon resonance detection are presented. The experimental parameters most relevant to studies of low-molecular-weight antigen-antibody binding interactions are discussed. Direct kinetic analysis of the binding interactions is most informative, providing both apparent association and dissociation rate constants from which equilibrium constants can be calculated. Equilibrium analysis, including steady-state and solution affinity studies, offers an alternative approach to direct kinetic analysis when knowledge of the individual kinetic rate constants is not required or difficult to determine. The various methods are illustrated by studies of an anti-T(4) Fab fragment binding interaction with several thyroxine analogs. The methods utilized were dependent on the affinity of the interaction. The high-affinity anti-T(4) Fab fragment/l-T(4) binding interaction was evaluated using direct kinetic analysis. An intermediate affinity anti-T(4) Fab fragment/l-T(3) binding interaction was evaluated using a combination of direct kinetic analysis, steady-state analysis, and solution affinity analysis. The relatively weak anti-T(4) Fab fragment/l-T(2) binding interaction was evaluated using steady-state and solution affinity analysis protocols. Several thyroxine tracers that could not be immobilized to a biosensor surface were also evaluated via the solution affinity format. In cases where a given binding interaction was examined using multiple methods the results were comparable.

Animals↗