Comment on “the specific production of NO(B2IIr) from the recombination of no on a nickel surface” by Caubet,Dearden and Dorthe

This note calls attention to mathematical and conceptual errors that could lead to a broadened interpretation of the data reported.     

Ppt range iridium determination by RNAA and application of that method on a Permian/Triassic boundary section,Bálvány,Bükk Mts., Hungary

A modified fire assay type analytical sample preparation method has been developed in order to extend iridium analysis of geological samples to the ppt level by neutron activation analysis (NAA). This method development was essential to trace a potential Ir signal at the Permian/Triassic boundary, the largest mass extinction event in the Phanerozoic history of Earth. The new analytical procedure was calibrated by several synthetic and natural standards and then applied for measuring the Ir profile in the continuous marine Permian/Triassic sedimentary sequence Bálvány north, Bükk Mts., Hungary. The analytical problem of applying the method also on practically pure limestones has been overcome, adding extra SiO₂ sand, to avoid the crucible being attacked by the fire assay flux. The nugget after the nickel fire-assay pre-concentration was identified by X-ray diffractometry and energy dispersive spectrometry (EDS–SEM) as heazlewoodite (Ni₃S₂), hosting iridium in the form of pure metal inclusions, mainly of 2–5 μm size (EDS–SEM). Based on these observations, the filter size of the original preparation protocol was decreased to 0.2 μm, in order to get the highest yield for Ir in the analytical preparation process. By applying the new technique, we determined the iridium profile in the Bálvány north section. The whole profile studied, except for the lowest 10 cm of the “boundary shale”, can be characterized of a several hundred ppt—up to one ppb Ir concentration. At the lowest part of the “boundary shale” the Ir content drops below 100 ppt. These values show no sign of any meteorite impact at this border section. The detailed geological interpretation of the high Ir background and the negative course Ir peak at the lithological border needs further studies.     

Claoxylones A–I,prenylbisabolane diterpenoids with anti-Coxsackie B virus activity from the branches and leaves of Claoxylon polot

Nine new prenylbisabolane diterpenoids, claoxylones A–I (1–9), were isolated from the branches and leaves of Claoxylon polot. This is the first example of prenylbisabolane diterpenoids with furan and tetrahydrofuran rings. Their structures and relative configurations were established by spectroscopic and conformational analysis, and the absolute configurations were determined by single-crystal X-ray diffraction and electronic circular dichroism (ECD) analysis. Compounds 1–9 exhibited antiviral activity against Coxsackie B3 virus, with IC₅₀ values of 6.0–33.3 μM.     

Chemoenzymatic synthesis of (2S,3S,4S)-form, the physiologically active stereoisomer of dehydroxymethylepoxyquinomicin (DHMEQ), a potent inhibitor on NF-κB

A new route for (2S,3S,4S)-form, the physiologically active stereoisomer of dehydroxymethylepoxyquinomicin (DHMEQ), a potent NF-κB inhibitor, was established by chemoenzymatic approach. Elaboration on the asymmetric epoxidation of a p-benzoquinone monoketal with benzylcinchonidinium tert-butylhydroperoxide yielded an epoxyenone, in 79.8% ee and 57% yield in reproducible manner. By way of the transformation of this key intermediate to enantiomerically pure (2S,3S,4S)-DHMEQ, the contaminating undesired enantiomer could be effectively removed by applying Burkholderia cepacia lipase-catalyzed hydrolysis of diacylated precursor. The above integrated combination of chemical asymmetric synthesis and enzyme-catalyzed kinetic resolution enabled us to prepare active DHMEQ in a large-scale.