Bioanalysis of bevacizumab and infliximab by high-temperature reversed-phase liquid chromatography with fluorescence detection after immunoaffinity magnetic purification

This study presents two simple and rapid methods for the quantification of therapeutic mAbs based on LC. Two mAbs (bevacizumab and infliximab) in plasma samples were purified using magnetic beads immobilized with a commercially-available idiotype antibody for each mAb. Purified mAbs were separated with HT-RPLC and detected with their native fluorescence. Using immunoaffinity beads, each mAb was selectively purified and detected as a single peak in the chromatogram. The HT-RPLC achieved good separation for the mAbs with sharp peaks within 20 min. The calibration curves of the two mAbs ranged from 1 to 20 μg mL⁻¹ (bevacizumab) and 1–10 μg mL⁻¹ (infliximab), and they had strong correlation coefficients (r² > 0.998). The LOD of bevacizumab and infliximab was 0.07 and 0.15 μg mL⁻¹, and the LLOQ of bevacizumab and infliximab was 0.12 and 0.25 μg mL⁻¹, respectively. Thus, the sensitivities were sufficient for clinical analysis. Immunoaffinity purification with HT-RPLC produced a selective and accurate bioanalysis without an LC-MS/MS instrument. Both methods could become general-purpose analytical methods and complement the results obtained with conventional LBA.     

Characterization of the CYP3A4 active site by homology modeling

Human microsomal cytochrome P450s participate in drug metabolism and detoxification. Among them, CYP3A4 is the most important isoform for drug-drug interactions. To gain a better understanding of the active site, a homology model of CYP3A4 was constructed based on the crystallographic coordinates of mammalian CYP2C5. The putative active site is much larger than that of CYP2C5 and is divided into three parts (i.e. a proximal and two distal sites from the heme). Most residues reported to be important for ligand-binding are located in the active site of the model. Moreover, some inhibitors (paclitaxel etc.) docked into the model have complementary shapes to the pocket. Pharmacophore docking of 14 substrates was also performed using Ph4Dock of MOE. Calculated interaction energies showed a moderate correlation with the logarithm of apparent K(m) values. These results suggest that this model is reliable enough to be used in the design of compounds for removing undesirable CYP3A4 inhibition.     

Separation of amino acid and peptide stereoisomers by nonionic micelle-mediated capillary electrophoresis after chiral derivatization

Enantiomers of amino acids and peptides were derivatized with a fluorescent chiral reagent, 4-(3-isothiocyanatopyrrolidin-1-yl)-7-nitro-2,1,3-benzoxadiazole [R-(−)- or S-(+)-NBD-PyNCS] and the resulting diastereomeric derivatives separated by capillary electrophoresis (CE). The CE running buffer consisted of 25 mM acetate buffer (pH 4) and 10 mM of the nonionic surfactant Triton X-100. The excitation maximum of NBD-PyNCS at 480 nm matches the major Ar-ion emission line at 488 nm allowing sensitive laser-induced fluorescence detection with limits of detection around 50 nM.

Full-size image

-Proline and

Full-size image

-aspartate spiked (at 10⁻⁴ M and 10⁻⁵ M concentrations, respectively) into complex biological matrices (rabbit serum and homogenate of Aplysia californica buccal ganglion) are detected without matrix interferences. This method has also been applied to the determination of

Full-size image

- and

Full-size image

-amino acid residues in peptides after acid hydrolysis. Results from the chiral analysis of the naturally-occurring peptide, gramicidin D, are shown.     

Furopyridines. XIX. Reaction of furo[2,3-b]-, -[3,2-b]-, -[2,3-c]- and -[3,2-c]pyridine with acetic anhydride

Acetoxylation of N-oxide of furo[2,3-b]- 2a , -[3,2-b]- 2b , -[2,3-c]- 2c and -[3,2-c]pyridine 2d with acetic anhydride afforded compounds substituted normally at the α- or γ-position to the ring nitrogen, 3a, 4a, 4b, 3d, 4d, 8 and 9 , and in addition compounds substituted on the furan ring, 5a, 6a, 5b, 6b, 7b, 5c and 7c which were unexpected compounds. The structures of these compounds were established from the ir, nmr and mass spectra, and x-ray crystal analysis of 5b .     

A binary hydrogen bonding motif based on homochiral recognition: crystal structures and hydrogen bonding networks of meso-(R,S)-bis(trifluorolactate)s

A series of meso-compounds incorporating both enantiomers of a trifluorolactate constructed two-dimensional supramolecular sheets via homochiral hydrogen bonding chains as a binary hydrogen bonding motif.     

Aggregation feature of fluorine-substituted benzene rings and intermolecular C-H.F interaction: crystal structure analyses of mono- and trifluoro-L-phenylalanines

X-Ray crystal structures of four different fluorine-substituted phenylalanines (two mono- and two tri-substitutions) were analyzed to investigate the effect of fluorine atom on the association pattern of benzene rings. Although respective structures showed similar molecular packing in such a way that the layers of hydrophobic benzene rings and hydrophilic amino/carboxyl groups were alternately running along a crystallographic axis, the association patterns of benzene rings were different depending on the substitution position and number of fluorine atoms. The general features could be that the partially displaced face-to-face interactions are increased with increase in the number of fluorine atoms, whereas the edge-to-face interactions are decreased. The C-H bond next to a fluorine-substituted carbon atom could serve as a donor of an intermolecular C-H.F hydrogen bond.     

Thermal diffusivity measurement of low-k dielectric thin film by temperature wave analysis

Thermal diffusivity of thin film with low dielectric constant (k), what is called low-k dielectric thin film, 0.31-1.14 μm, including hydrogen-silsesquioxane (HSQ), methyl-silsesquioxane (MSQ), and poly(arylen ether) was examined by temperature wave analysis. The phase shift of temperature wave was observable up to 100 kHz. Thermal diffusivity of HSQ was 4.7 × 10⁻⁷ m² s⁻¹, on the other hand it was not higher than 1.1 × 10⁻⁷ m² s⁻¹ for MSQ or poly(arylen ether) at room temperature. Temperature dependence of thermal diffusivity/thermal conductivity of MSQ was obtained, thermal diffusivity decreased but thermal conductivity increased in a heating scan at 30-150 °C. It was shown that the thermal diffusivity of low-k thin film was correlated with the chemical and the physical structures, the latter was formed in the spin-coating and the curing process.     

Conformational Requirements for Sweet-Tasting Peptides and Peptidomimetics

The molecular basis o taste has been extensively studied over many years. The research carried out in our laboratories is focused on the elucidation of detailed structure–taste relationships of peptides and peptidomimetics using an “integrated” approach employing synthesis, analysis of NMR spectra, computer simulations, and X-ray crystallography. Various peptidomimetic residues have been incorporated to introduce predictable structural constraints into taste ligands. These constraints eliminate some of the molecular flexibility and allow us to develop structure–activity relationships. We describe here the topochemical requirements of the sweet and bitter taste receptor(s) and develop detailed structure-taste relationships with considerable predictive power for peptides and related molecules.     

Trifluoromethyl-stabilized optically active oxiranyl and aziridinyl anions for stereospecific syntheses of trifluoromethylated compounds

Optically active 2,3-epoxy-1,1,1-trifluoropropane was converted into the corresponding oxiranyl anion and reacted with electrophiles such as aldehydes, ketones and halides to give the corresponding adducts in moderate to good yields. The whole reaction occurred with retention of configuration at the stereogenic carbon center. In a similar manner, trifluoromethyl stabilizing aziridinyl anions were generated from the optically active N-tosyl and N-anisyl-2-trifluoromethylaziridines. They also reacted well with various electrophiles. The products of these reactions are versatile synthetic intermediates useful for the synthesis of a variety of trifluoromethylated compounds with quaternary chiral carbon centers.     

High-performance liquid chromatography with photochemical fluorimetric detection of tryptophan based on 4-fluoro-7-nitrobenzo-2-oxa- 1,3-diazole : Total protein amino acid analysis

The simultaneous determination of amino acids including trytophan is described. The NBD- F forms a single adduct with tryptophan as with other amino acids, but the adduct lacks intrinsic fluorescence. After ultraviolet irradiation, the adduct fluoresces (pale-green); the fluorescence intensity increases with increasing irradiation time at pH 2-10, Under the same conditions, the other amino acid adducts are slowly decomposed. When the tryptophan adduct, separated on a Nucleosil ODS column (150×4.6 mm, 6 μm), is irradiated in an on-line photochemical reactor (310 nm), its fluorescence peak appears between those of the phenylalanine and lysine adducts. The detection limit for tryptophan by the proposed method is 3 pmol; the limits for other amino acids are 10–100 fmol.