1,721,239 research outputs found
Recent results in the chemistry of echinoderms: steroidal glycosides and polyhydroxysteroids
No full textCircular dichroic method for determining the position of glycosidic linkages of deoxy sugar moieties. Antitumor antibiotic chromomycin A3
No full textA 3-step method shows the glycosidic linkages and abs. configuration of oligosaccharide moieties attached to a complex labile aglycon by measuring the split CD curves resulting from interacting benzoate chromophores on the hexopyranose ring. Thus, the chromosome units of chromomycin A3 in the oligosaccharide moiety are all 2,6-deoxy sugars and hence lack sufficient OH groups which can be benzoylated to give coupled benzoate groups. Accordingly, the anomeric position were benzoylated as well; chromomycin A3 was directly permethylated in DMF/NaH with MeI, hydrolyzed with 50% AcOH, and per-p-bromobenzoylated. The coupled CD spectra resulting from chiral interaction between the 1-benzoate groups attached to other carbons were used to det. the position of glycosidic linkages and abs. configurations
Constituents of the digestive gland of the molluscs of the genus - I. Novel diterpenes from
No full textDictyol A (I) and B (II; R = OH) and pachydictyol A (II; R = H) were isolated from the digestive glands of A. depilans. The structures of I and II (R = OH) were detd. from chem. and spectral data. I and II (R = OH) arose from feeding by A. depilans on the brown algae Dictyota dichotoma
Starfish saponins. Part 39. Steroidal oligoglycoside sulfates and polyhydroxysteroids from the starfish Asterina pectinifera
No full textA reinvestigation of the exts. of the starfish A. pectinifera has led to the isolation of a novel asterosaponin pectinioside G (I) along with the already reported pectiniosides A, D, and acanthaglycoside C. The exts. contained asterosaponin P-1, previously isolated as sodium salt from Patiria pectinifera and Oreaster reticulatus, and now isolated also as tyramonium salt, and 5 highly hydroxylated steroids, among which I is new
Effects of Petrosapongiolide R on the Surface Topology of bee venom PLA2: a Limited Proteolysis and Mass Spectrometry Analysis
No full textPolyoxygenated steroids of marine origin
No full textA review, with 386 refs., on polyoxygenated steroids of marine origin, e.g. marine algae, Porifera, Coelenterata, Bryozoa, Mollusca, Echinodermata, Arthropoda, tunicates, and vertebrates (fish)
DFT/NMR integrated approach: a valid support to the total synthesis of chiral molecules.
No full textSTARFISH SAPONINS .38. STEROIDAL GLYCOSIDES FROM THE STARFISH PYCNOPODIA-HELIANTHOIDES
No full textThree novel steroidal monoglycosides, pycnopodiosides A, B, and C (I, II, and III, resp.), together with 1 novel polyhydroxysteroid (IV) were isolated from the starfish P. helianthoides collected off the Gulf of California. These compds. co-occur with the common asterosaponin thornasteroside A, the known steroidal monoglycoside, coscinasteroside B, and 2 known polyhydroxysteroids. The structures of the new metabolites were detd. from spectral data and comparison with those of related steroids
Effect of Electronegative Substituents and Angular Dependence on the Heteronuclear Spin-Spin Coupling Constant 3JC-H: An Empirical Prediction Equation Derived by Density Functional Theory Calculations
No full textA general carbon-proton vicinal coupling constant (3JC-H) prediction equation has been empirically
derived by a coupling constant database of 2157 3JC-H calculations (at the hybridDFTMPW1PW91/
6-31G(d,p) level). The equation includes the electronegativity effect of the substituents attached to the
13C-C-C-1Hfragment and the dihedral (Φ) dependence of the heteronuclear spin-coupling.Aset of
butane and pentane models were built, systematically varying both theΦtorsion angle in 30 steps and
the substitution pattern with several electronegative substituents (Br, NH2, F, Cl, SH, OH) in order to
obtain the coupling constant database. The here reported 3JC-H equation is a quantitative prediction
tool, particularly useful as a support in the analysis of NMR data for the structural elucidation of
organic compounds characterized by specific substitution patterns. To confirm the accuracy of our
equation in the prediction of the experimental 3JC-H couplings, we tested the equation, comparing 114
experimental 3JC-H values obtained from29 polysubstituded benchmark organic compounds with the
predicted data. In addition, a set of 3JC-H coupling bidimensional Karplus-type curves correlating the
calculated 3JC-H values to the specific dihedral angle for every substitution pattern considered were
built in order to evaluate the magnitude of the electronegativity effect
Starfish saponins, part 43. Structures of two new sulfated steroidal fucofuranosides (imbricatosides A and B) and six new polyhydroxysteroids from the starfish Dermasterias imbricata
No full textTwo new sulfated steroidal glycosides, imbricatoside A (I) and imbricatoside B (II), which inhibited cell division of fertilized sea urchin eggs, were isolated from the aq. exts. of whole bodies of the starfish D. imbricata. They contain the same disaccharide chain, i.e., 2,4-di-O-methyl-β-D-quinovopyranosyl-(1→2)-5-O-sulfate-β-D-fucopyranosyl, which is linked to C-24 of 5α-cholestane-3β,4β,6α,7α,8,15β,24-heptaol and 5α-cholestane-3β,6α,7α,8,15β,24-hexaol aglycons. The exts. also contained 6 new polyhydroxysteroids, to which structures were assigned. (22E,24R)-5α-Cholest-22-ene-3β,6α,8,15β,24-pentaol showed strong antifungal activity and also inhibited cell division of fertilized sea urchin eggs
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