Chemistry of the podocarpaceae—III A new lignan, seco-isolariciresinol and further constituents of the heartwood of Podocarpus spicatus

A new lignan for which the name seco-isolariciresinol is proposed, has been isolated from the heartwood of Podocarpus spicatus. The structure has been shown to be 2:3-bis(4′-hydroxy-3′- methoxybenzyl)-butan-1:4-diol (II, R = H), and confirmed by an absolute synthesis from (−)-matairesinol (I, R = H). A further examination of the extractives of the heartwood has resulted in the isolation of the minor constituents, (+)-taxifolin, (+)-aromadendrin, kaempferol and sequoyitol, in addition to the previously reported compounds, matairesinol, -conidendrin, quercetin, genistein and podospicatin.     

Electrochemical studies of homocysteine and homocystine at mercury electrodes

The behaviour of homocysteine and cysteine at mercury electrodes is compared. The one-electron oxidation associated with thiols is shown to be the same for both compounds in acidic phosphate buffer, giving rise to an adsorbed thiol—mercury complex, (RS)₂Hg, at the electrode surface. Formation of this complex is utilized in the cathodic stripping voltammetric determination of homocysteine; the detection limit is 10^?9 M after a deposition time of 90 s at a hanging mercury drop electrode. The similar E_{$\text{1}\text{2}$} values for homocysteine and cysteine mean that prior separation is needed for their individual determination. Amperometric detection with a mercury-coated goal electrode after separation by cation-exchange liquid chromatography provides a method for the simultaneous determination of both compounds. Reduction of homocystine at the mercury electrode is also compared to that of cystine. The more negative reduction potential, and the maximum observed for homocystine on d.c. polarograms, which is not seen for cystine, is attributable to different reaction kinetics at the mercury electrode; the products of both the 2-electron reductions are the corresponding thiol-containing amino acids.     

Validation study to demonstrate the equivalence of a minor modification (TECRA ULTIMA protocol) to AOAC Method 998.09 (TECRA Salmonella Visual Immunoassay) with the cultural reference method

The TECRA Salmonella Visual Immunoassay (VIA) using Rappaport-Vassiliadis RV[R10] as a single selective enrichment broth has Final Action approval (AOAC Method 998.09). TECRA has recently developed a protocol (TECRA ULTIMA), which involves the addition of a new additive to a 1 mL aliquot of the RV[R10] broth, prior to the heat-killing step, thereby allowing the RV[R10] broth to be tested directly in the kit and thus eliminating the need for the 2 h post-enrichment in M broth. An in-house validation study was conducted to compare the modified AOAC Method 998.09 to the reference culture method. Three foods were used in the study: Naturally contaminated raw ground poultry at high (10-50 cells/25 g), and low (1-5 cells/25 g) levels; and milk powder and peanut butter, artificially inoculated at low and high levels with Salmonella bovismorbificans and S. enterica Mbandaka, respectively. Twenty test portions were analyzed for each level with 10 uninoculated control samples per food. Overall, no significant differences (p <0.05) were observed when the proportion of positive test portions for the modified VIA were compared with that for the reference method. This minor modification, which employs the additive (provided in the TECRA ULTIMA SALMONELLA Test Kit) to permit the direct analysis of RV[R10] broth has demonstrated the utility of the TECRA ULTIMA SALMONELLA protocol. It is recommended that the minor modification to Method 998.09 be approved First Action as an additional option within the method.     

BLUE LIGHT PERCEPTION BY ENDOGENOUS REDOX COMPONENTS OF THE PLANT PLASMA MEMBRANE

b-Type cytochromes of the higher plant plasma membrane may be reduced by irradiation with actinic blue light (light-induced absorbance change). Although this reaction has been reported to depend on the presence of an exogenous oxygen-scavenging system, significant cytochrome reduction was obtained in bean hook (Phaseolus vulgaris L. cv. “Limburgse Vroege”) plasma membranes without any addition. An endogenous oxygen-consuming reaction is apparently sufficient to achieve a proper redox balance. A blue light-mediated absorbance change with absorbance minima at 450 and 475 nm precedes cytochrome b reduction and indicates the presence of a flavoprotein in the plasma membrane fraction. Cytochrome b reduction by blue light in the absence of an oxygen scavenger is highly sensitive to flavin photosensitizers. Glucose oxidase, which has previously been used to lower the oxygen concentration in membrane samples, was demonstrated to have a photosensitizing effect. Inhibitors of flavin photochemical reactions (KI and phenylacetic acid) were highly effective in preventing cytochrome b reduction. These results indicate that the blue light-mediated reaction probably involves an endogenous plasma membrane flavoprotein as the photoreceptor. As plasma membrane NADH-dependent oxidoreductases potentially are flavoproteins these experiments raise the question whether a plasma membrane cytochrome b and a flavin-enzyme may cooperate in blue light reactions. Evidence is also discussed, suggesting the possible involvement of oxygen radicals in the blue light-induced cytochrome b reduction.     

Efficient 3D database screening for novel HIV-1 IN inhibitors

We describe the use of pharmacophore modeling as an efficient tool in the discovery of novel HIV-1 integrase (IN) inhibitors. A three-dimensional hypothetical model for the binding of diketo acid analogues to the enzyme was built by means of the Catalyst program. Using these models as a query for virtual screening, we found several compounds that contain the specified 3D patterns of chemical functions. Biological testing shows that our strategy was successful in searching for new structural leads as HIV-1 IN inhibitors.     

Dialyse

Ohne Zusammenfassung     

Anchoring of hydrophobically modified poly(sodium acrylate)s into DDP vesicle bilayers: hydrophobic match and mismatch

 Differential scanning microcalorimetric thermograms have been recorded for aqueous solutions containing vesicles formed by sodium di-n-dodecyl phosphate, in the presence of different concentrations of poly(sodium acrylate-co-n-alkyl methacrylate), where n-alkyl= C₉H₁₉, C₁₂H₂₅, C₁₈H₃₇. The mole fraction of hydrophobic moieties in the copolymer is 0.04. The main phase transition temperature (T _m) is hardly affected by the presence of poly(sodium acrylate)s bearing n-dodecyl chains, whereas the anchoring of polymers bearing n-nonyl or n-octadecyl groups reduces the main phase transition temperature significantly from ca. 34 °C to ca. 32 °C. In parallel, the enthalpy of transition per mole of DDP monomer (Δ_m H _int) is lowered upon adding polymer. Again, the polymer containing n-dodecyl moieties hardly affects Δ_m H _int. These patterns are explained by the notion that the extent of the disruptive effect of alkyl chains incorporated into the bilayer depends on the extent of the mismatch between the chain lengths of the intruding alkyl chains and the hydrophobic moieties composing the vesicle bilayer. Added hydrophobically modified polymers increase the cooperativity of the melting process, as shown by the increase of n _DDP. We suggest that the anchoring poly(sodium acrylate-co-n-alkyl methacrylate) relieves the strain in the curved outer monolayer of a pure DDP bilayer by allowing the presence of larger “patches” characterized by low curvature. Received: 12 May 1997 Accepted: 20 October 1997