Conformational analysis of Amphotericin B.

Within a theoretical approach to the problem of antifungal action of Amphotericin B (AmB), a conformational analysis of the neutral and zwitterionic form of this antibiotic in vacuo was performed by the MM2P and AM1 methods. The analysis was carried out with regard to the mutual orientation of the macrolidic and glycosidic fragments of the molecule, which is defined by the phi and psi steric angles. This orientation defines the overall shape of the molecule and is postulated to be important for the antifungal action of the drug.

Cycloartane triterpene glycosides from Astragalus trigonus.

Three new cycloartane glycosides, trigonoside I, II and III, and the known astragalosides I and II were isolated from the roots of Astragalus trigonus. The structures of the new glycosides were totally elucidated by high field (600 MHz) NMR analyses as cycloastragenol-6-O-beta-xylopyranoside, cycloastragenol-3-O-[alpha-L-arabinopyranosyl(1-->2)-beta-D- xylopyranosyl]- 6-O-beta-D-xylopyranoside and cycloastragenol-3-O-[alpha-L-arabinopyranosyl (1-->2)-beta-D-(3-O-acetyl)-xylopyranosyl]-6-O-beta-D-xylopyranoside.

Stereostructure of Rimocidin.

NMR studies of rimocidin, consisting of DQF-COSY, ROESY, HSQC, HMBC and 1D-TOCSY experiments, resulted in the assignment of the absolute configuration of the rimocidin chiral centers as 2S, 3R, 9S, 11R, 13S, 14R, 15S, 17R, and 27R. The geometry of tetraene chromophore was found to be all-trans.

Stereostructure of perimycin A.

The gross structure of perimycin A was revised: the position of the keto group was changed from C-13 to C-5. The stereostructure of perimycin A was established based upon NMR studies.

Minor taxoids from Taxus wallichiana.

The needles of Taxus wallichiana afforded a new analogue of taxinine M [1a] and two derivatives of brevifoliol [2a, 3a]. The conformation of 3a was investigated by nmr spectroscopy with the aid of variable-temperature experiments and in situ reactions.

Immunorecognition of ring skeleton of taxanes by chicken egg yolk antibodies.

Anti-10 deacetylbaccatin III (DAB) antibodies (IgY) were elicited in hens immunized with a succinyl-DAB/BSA conjugate and extracted from egg yolk. As shown by indirect competitive inhibition enzyme immunoassay (CIEIA), the addition of free-DAB competitively inhibited the binding of affinity purified anti-DAB IgY to DAB/BSA solid phase conjugated antigen. The assay enabled the detection of DAB in concentrations as low as 7.

The role of amphotericin B amino group basicity in its antifungal action. A theoretical approach.

The role of basicity of the amine group of amphotericin B in the molecular mechanism of antifungal activity of this antibiotic has been investigated by AM1 and MNDO quantum chemistry methods. Calculations of proton affinity of the amine group, as a measure of its basicity, for appropriate models of free amphotericin B and its N-alkyl derivatives were carried out. These studies were preceded by a critical examination of the usefulness and reliability of both methods to predict the proton affinities of several aliphatic amines.

Stereostructure and NMR characterization of the antibiotic candidin.

The stereostructure of the heptaene macrolide antibiotic candidin was established on the basis of NMR studies: 13C, DQF-COSY, ROESY and C,H-COSY experiments. The absolute configuration of the candidin chiral centers were assigned as 3R, 5S, 10R, 11R, 13R, 15S, 16R, 17S, 19S, 34S, 35R, 36R and 37S.

Elucidation of the structure and conformation of a methylated tetrasaccharide-alditol acetate by n.m.r. spectroscopy.

The structure of the methylated derivative (1) of the tetrasaccharide-alditol-O-beta-L-rhamnopyranosyl-(1----3)-O-beta-D- xylopyranosyl-(1----4)-O-beta-L-rhamnopyranosyl-(1----2)-1,5-di-O-acetyl -L- arabinitol has been determined solely on the basis of n.m.r.

Determination of O6-butylguanine in DNA by immunoaffinity extraction/gas chromatography-mass spectrometry.

A sensitive, specific, and rapid method for quantitating the minor adduct O6-butylguanine (O6BuG) in hydrolyzed DNA has been developed by combining immunoaffinity chromatography and high resolution gas chromatography-negative ion chemical ionization-mass spectrometry. Polyclonal antibodies raised against O6BuG were coupled to CNBr-activated Sepharose 4B and used for sample clean-up and extraction of the specific O6-alkylguanine. After addition of O6BuG and its deuterium labeled analogue (O6BuG-D7), used as internal standard, hydrolyzed DNA was applied on the immunoaffinity column and washed with water, and the immunoadsorbed butylated guanines were eluted with acetone/water cetome/water (95/5) before gas chromatographic derivatization.

The structure of vacidin A, an aromatic heptaene macrolide antibiotic. II. Stereochemistry of the antibiotic.

On the basis of coupling constants and rotating frame nuclear Overhauser effect spectroscopy of vacidin A methoxycarbonylmethylamide, the stereochemistry of the antibiotic was established. The configuration of the aglycone was determined as (3R,7R,9R,11S,13S,15R,17S,18R,19S,21R, 36S,37R,38S). The aminosugar constituent of the antibiotic was identified as beta-(D)-mycosamine.

The structure of vacidin A, an aromatic heptaene macrolide antibiotic. I. Complete assignment of the 1H NMR spectrum and geometry of the polyene chromophore.

The constitution of vacidin A, a representative of the aromatic heptaene macrolide antibiotics was established on the basis of 13C and 1H-1H double quantum filtered correlated spectroscopy, rotating frame nuclear Overhauser effect spectroscopy, J-resolved 1H as well as 1H-13C correlation NMR spectra. Geometry of the polyene chromophore was determined as 22E,24E,26E,28Z,30Z,32E,34E.

Constituents of Shashen (Adenophora axilliflora).

From the ethyl acetate extract of the Chinese drug "Shashen", the root of Adenophora axilliflora Borb., three triterpenoids, cycloartenol acetate ( 1), lupenone ( 2) and beta-sitosterol ( 3), two triterpenoid derivatives, beta- D-glucopyranosyl-(1-->3)-beta-sitosterol ( 7) and its 6- O-palmitoyl ester ( 6), along with two coumarins, (+)-praeruptorin A ( 4) and 3'-angeloyl-4'-isovaleryl-(3' S, 4' S) CIS-khellactone ( 5) have been isolated. A detailed (1)H-NMR analysis of compounds 6, 7 and their acetates is reported.

Horseradish peroxidase/hydrogen peroxide-catalyzed oxidation of VP16-213. Identification of a new metabolite.

VP16 was submitted to oxidation catalyzed by horseradish peroxidase (HRP) and H2O2 in phosphate buffer (pH 7.0). The product of the reaction, which has a high performance liquid chromatographic (HPLC) retention time different from the previously known metabolites of VP16, was identified as 1,2,3,4-tetradehydro-VP16 by 1H-NMR and mass spectrometry (MS) analysis.

Identification of a nitrosamino aldehyde and a nitrosamino acid resulting from beta-oxidation of N-nitrosodiethanolamine.

N-nitrosodiethanolamine is converted to N-(2-hydroxyethyl)-N-(formylmethyl)nitrosamine (EFMN) and N-(2-hydroxyethyl)-N-carboxymethyl) nitrosamine (ECMN) by rat S9 liver preparation as a result of beta-oxidation. The beta-oxidized metabolites were isolated and identified by gas chromatography-mass spectrometry (GC-MS) by comparison with authentic standards. An original gas chromatographic method with thermal energy detection was set up to measure both metabolites quantitatively.

Isolation and structure determination of enzymatically formed styrene oxide glutathione conjugates.

When styrene oxide was incubated with glutathione in the presence of rat liver cytosolic fraction, two conjugates were formed. Structural investigation by mass spectrometry (MS), proton magnetic resonance (PMR) analysis and chemical fragmentation showed the presence of two positional isomers, namely S-(1-phenyl-2-hydroxyethyl)glutathione and S-(2-phenyl-2-hydroxyethyl)glutathione in a ratio of approx. 60 : 40.