Physicochemical properties and stability in the acidic solution of a new macrolide antibiotic, clarithromycin, in comparison with erythromycin.

Clarithromycin (6-O-methylerythromycin), a new 14-membered macrolide antibiotic, has been studied to clarify its physicochemical properties and stability in acidic solution, as compared with erythromycin (EM). The solubility of clarithromycin (CAM) in distilled water was lower than that of EM and decreased with increasing temperature. The solubilities of CAM and EM in the phosphate buffer solution at 37 degrees C decreased with an increasing pH and kept constant above pH 9. From pH-solubility profiles, the dissociation constants of CAM and EM were determined to be 8.76 and 8.36, respectively. The partition coefficient of CAM took a higher value than that of EM and increased with an increasing pH. In the acidic solution, the decomposition of CAM and EM obeyed the pseudo-first order kinetics. From the decomposition rate constants, the half life (T1/2) of CAM and EM were determined. In pH 1.39, CAM degraded with a T1/2 of 17 min while EM kinetics corresponded to a T1/2 of 3 s. Therefore, CAM was 340-fold more stable in pH 1.39 and markedly more stable in the acidic solution than EM.     

Macrocycles in the construction of acyclic stereochemistry

The conformations of macrocyclic intermediates provide a useful medium through which distant chiral centers may control chemical reactions. In this paper, we show that macrocycles made by cyclization of simple acyclic starting materials with an auxiliary spacer may be used to prepare stereochemically complex acyclic products.     

Some pyridylazo compounds as sensitive reagents for the spectrophotometric determination of nickel

Six 2-(2-pyridylazo)-5-alkoxyphenol derivatives were synthesized, and their application to the spectrophotometric determination of nickel was studied; 2-(2-pyridylazo)-5-methoxyphenol and the corresponding ethoxyphenol are very sensitive and selective. The molar absorptivity of the nickel chelate of the former is 11.3 × 10⁴ l mol^-1 cm^-1. A solvent extraction procedure for the selective determination of 1–8 μg of nickel is described.     

Tensammetric determination of microgram amounts of vanadium by catalytic oxidation of o-aminophenol

A tensammetric method is proposed for the determination of microgram amounts of vanadium, based on catalysis of the oxidation of o-aminophenol with sodium chlorate in acidic solution (pH 2.0). The oxidation product gives a very sensitive tensammetric wave; under optimum conditions, the wave-height is proportional to the concentration of va vanadium. From 0.2 to 3.0 mug of vanadium can be determined in a final volume of 50 ml. Mo(VI), W(VI), Mn(VII), Ce(IV) and large amounts of Al(III) and Fe(III) cause positive errors, and Hg(II) and thiosulphate negative errors. Interference from Fe(III), Al(III) and Cu(II) can be eliminated by solvent with oxine at about pH 8.0.     

Synthesis of a novel bridged nucleoside bearing a fused-azetidine ring, 3′-amino-3′,4′-BNA monomer

A novel bridged nucleic acid monomer, 3′-amino-3′-deoxy-5-methyl-3′-N,4′-C-methyleneuridine, was successfully synthesized via a useful and convenient azetidine ring formation under Staudinger's conditions. A ¹H NMR experiment and a PM3 calculation revealed that the sugar moiety of the novel bridged nucleic acid monomer, 3′-amino-3′,4′-BNA, was restricted to S-type conformation.     

Catalytic asymmetric syntheses and biological activities of singly dehydroxylated 19-nor-1alpha,25-dihydroxyvitamin D(3) A-ring analogs in cancer cell differentiation and apoptosis

BACKGROUND: 1alpha,25-Dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) has been shown to modulate not only proliferation and differentiation, but also apoptosis in malignant cells, indicating that it could be useful for treating cancer. Little information is available concerning the structural motifs of the 1alpha, 25(OH)(2)D(3) molecule responsible for modulation of differentiation and apoptosis, however. We set out to synthesize singly dehydroxylated A-ring analogs of 19-nor-1alpha,25(OH)(2)D(3) in a catalytic asymmetric fashion, and to investigate their biological activities in leukemia HL-60 cells. RESULTS: A series of singly dehydroxylated 19-nor-1alpha,25-dihydroxyvitamin D(3) A-ring analogs were synthesized using a combinatiorial sequence of regioselective propiolate-ene reaction and catalytic asymmetric carbonyl-ene cyclization. Surprisingly, the analogs could be clearly divided into two categories; one group, bearing 1alpha-hydroxy or 3beta-hydroxy groups in the A-ring, were potent differentiators and the second group, bearing 1beta-hydroxy or 3alpha-hydroxy groups, were potent stimulators of apoptosis. CONCLUSIONS: We have clearly identified the structural motifs of 19-nor-1alpha,25(OH)(2)D(3) analogs responsible for differentiation and apoptosis in HL-60 cells. These findings will provide useful information not only for development of therapeutic agents for treatment of leukemia and other cancers, but also for structure-function studies of 1alpha,25(OH)(2)D(3).     

X-ray scattering by water molecules studied by using synchrotron radiation

The energy spectra of free water molecules were measured at scattering angles 2θ ranging from 10.5° to 75.7°, using an angle-dispersive-type diffractometer and synchrotron radiation as an X-ray source. A silicon (111) monochrometer was used to obtain incident X-rays with the wavelengths of (1.543/n) Å (n = 1,3,4,5). Observed inelastic scattering peaks are clearly separated from eleastic ones at s values [s = (4π/λ) sin Å] larger than 8 Å^?1. The increase of the separation with an increasing s value was consistent with the classical theory of the Compton shift. The total (elastic plus inelastic) intensities were obtained over a range of s = 0.74–5.0 Å^?1. Experimental difference intensities Δσ_ee and Δσ_ne were obtained separately by combining the X-ray and high-energy electron scattering data. The experimental results are in reasonable agreement with the theoretical intensities calculated from SCF and CI molecular wave functions with a basis set of double-zeta plus polarization functions. © 1994 John Wiley & Sons, Inc.     

Practical enantioselective synthesis of endothelin antagonist S-1255 by dynamic resolution of 4-methoxychromene-3-carboxylic acid intermediate

A practical multikilogram-scale synthesis of enantiomerically pure S-1255 (1), a potent and orally active ET(A) receptor antagonist, is described. Utilizing readily available starting materials and reagents, the entire sequence of reactions starting from 2,5-dihydroxyacetophenone 8 proceeded under mild conditions to give 1 in an excellent chemical yield (8 steps, 41% overall yield) and in a high enantiopurity (98% ee). The crucial step of the synthesis is a dynamic resolution of key intermediate 16. (R)-Methoxy acid (R)-16 having 97-99% ee was obtained in 83-84% yield from racemic 16 as a crystalline (1S,2R)-(+)-norephedrine or (+)-cinchonine salt by the dynamic resolution comprising concurrent crystallization and in situ racemization. A mechanism of the dynamic resolution through a ring-opened zwitterionic intermediate is discussed. In the final synthetic step, an effective carbon-carbon bond formation between the C4 carbon and the p-anisyl group was accomplished by a conjugate addition-elimination reaction of Grignard reagent 3 to (R)-16 to give 1 having 98% ee. Owing to high efficiencies of functional group transformations, carbon-carbon bond formations, and the dynamic resolution, the synthesis required no chromatographic purification and was amenable to a multikilogram-scale preparation. Several kilograms of 1 for clinical trials were successfully prepared by this process.     

Structural assignment of isomeric 2-aminopyridine-derivatized oligosaccharides using negative-ion MSn spectral matching

To investigate the possibility of structural assignment based on negative-ion MS2 spectral matching, three isomeric pairs of 2-aminopyridine (PA)-derivatized non-fucosylated, fucosylated, and sialylated oligosaccharides (complex type N-glycans) were analyzed using high-performance liquid chromatography/ion trap mass spectrometry (HPLC/ITMS) with a sonic-spray ionization (SSI) source. In the SSI negative-ion mode the deprotonated molecule [M-2H]2- becomes prominent. Negative-ion MS2 spectra derived from such ions contain many fragment types (B and Y, C and Z, A, and D) and therefore are more informative than the positive-ion MS2 spectra derived from [M+H+Na]2+ ions, which usually consist mainly of B and Y fragment ions. In particular the internal ions (D- and E-type ions) provided useful information about the alpha1-6 branching patterns and the bisecting GlcNAc residue. Spectral matching based on the correlation coefficients between negative-ion MS2 spectra was performed in a manner similar to the positive-ion MS2 spectral matching previously reported. It was demonstrated that negative-ion MS2 spectral matching is as useful and applicable to the structural assignment of relatively large non-fucosylated, fucosylated, and sialylated PA-oligosaccharide isomers as its positive-ion counterpart.