A simple route to metalla-2-indane-1,3-diones

A simple and high yielding synthesis of metalla-2-indane-1,3-diones (phthaloyl metal complexes) by the insertion of low-valent transition metal complexes (ClRh(PPh₃)₃, ClCo(PPh₃)₃, Fe(CO)₅) into benzocyclobutenedione is reported. The structure of the rhodium complex was established by an X-ray analysis.     

Steric interference modification of the hammerhead ribozyme

Although the structure of the hammerhead ribozyme is well characterized, many questions remain about its catalytic mechanism. Extensive evidence suggests the necessity of a conformational change en route to the transition state. We report a steric interference modification approach for investigating this change. By placing large 2' modifications at residues insensitive to structurally conservative 2'-deoxy modifications, we hoped to discover structural effects distal to the site of modification. Of twenty residues tested, six were identified where the addition of 2' bulk inhibits cleavage, even though these bulky modifications could be accommodated in the crystal structure without steric clash. It is proposed that these 2'-modifications inhibit cleavage by preventing formation of the alternate, active conformation. Since these 2' effects are present in both domain I and domain II of the hammerhead, the entire catalytic core must undergo conformational changes during catalysis.     

The Synthesis of 3,5-Diamino-1,2,4-oxadiazoles. 2nd Communication

The 5-amino-3-arylamino-1,2,4-oxadiazoles 2 are conveniently prepared by oxidative cyclization of the arylamidinoureas 10 . The process is also capable of producing a variety of the 5-substituted-amino analogs 32 when the appropriately substituted guanidine 31 is employed as the substrate. Two different types of rearrangement leading to triazol-3-ones accompany cyclization depending on the choice of starting material. The structures of the rearranged products were established by X-ray crystallographic analysis and the reaction mechanisms leading to these unexpected products are discussed.     

Challenges in determining perchlorate in biological tissues and fluids: implications for characterizing perchlorate exposure

The ability to measure environmental contaminants in biological tissues and fluids is important in the characterization of exposure. However, the analysis of certain contaminants in these matrices presents significant challenges. Perchlorate (ClO₄⁻) has emerged as a potential contaminant of concern primarily in drinking water and also in contaminated food. Significant advances have been made in the analysis of perchlorate in environmental matrices (water, soil) by ion chromatography (IC). In contrast, the analysis of perchlorate in extracts of biological tissues and fluids (vegetation, organs, milk, blood, urine, etc.) presents several challenges including small sample sizes, extracts with high matrix conductivity, and co-elution of other ions during IC analysis. To be able to detect low concentrations of perchlorate in biological samples, interferences must be removed or minimized, such as through the use of preparative chromatography cleanup techniques and/or alternative analytical methods less susceptible to common interferences (preconcentration or mass spectrometric detection). We present discussion and examples of the challenges encountered in the analysis of tissue extracts and fluids for perchlorate by IC and how some of those analytical challenges have been overcome.     

Umwandlung von Phthalidisochinolinalkaloiden in Benzazepinalkaloide, 1. Mitt.

Zusammenfassung Als Modell für die geplante Umformung von Phthalidisochinolinalkaloiden in natürliche Benzazepinalkaloide (Rhoeadinalkaloide) wird das aus (–)-Narcotin zugängliche Nornarcein2a oder dessen Äthylester2b ² in das Rheadan8b ¹ übergeführt. Ein Rheadan mit dem aromatischen Substitutionsmuster von8b wurde bisher in der Natur noch nicht aufgefunden.

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Conversion of Phthalideisoquinolines into Benzazepine Alkaloids

As a model for the planned conversion of phthalideisoquinoline alkaloids into natural benzazepine alkaloids (rhoeadine type), nornarceine2a or its ethyl ester2b [obtained from (–)-narcotine,1]² have been transformed into the rheadane8b ¹. The aromatic substitution pattern of8b has not yet been observed in nature.

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Herrn Prof. Dr.O. Kratky zum 70. Geburtstag gewidmet.