Stereocontrolled synthesis of bicyclic lactone derivatives via tungsten-mediated [3 + 2] cycloaddition of epoxides with a tethered alkynyl group

In the presence of BF3*Et2O, alkynyltungsten complexes underwent [3 + 2] cycloaddition with tethered epoxides to give bicyclic -lactones efficiently. Only one diastereomeric product was formed despite the presence of three stereogenic centers. A mechanism is proposed that involves formation of a tungsten-vinylidenium species via an SN2 attack of the epoxide carbon by an alkynyltungsten group to give a tungsten-enol ether species via counterattack at the central tungsten-vinylidenium carbon by the OBF3- terminus. Most of the tungsten enol ether species were too unstable for isolation and underwent hydrolysis to give only cis-fused -bicyclic lactones. This cyclization works for both cis- and trans-epoxides and tolerates various functional groups. In the case of trans-phenyl epoxide, the reaction led to an addition product via a 6-endo attack of epoxide by the tungsten fragment. This method provides a simple enantiospecific synthesis of complex bicyclic lactones if a chiral epoxide is used in the cyclization. It is also applicable to the one-pot synthesis of bicyclic unsaturated gamma-lactones if a suitable alkynyltungsten functionality is used.     

High speed cine observations of cavitating flow in a duct

The dynamics of cavities produced in cavitating flow confined in a duct was studied. The ultimate purpose of the work is to develop models of the flow to assist in predicting cavitation erosion and noise. Observations of the cavitating flow using high speed cine photography allowed confirmation to be made of the shedding mechanism originally described by Knapp, and measurements of the cavity dimensions to be determined as a function of time. It was found that the time for a cavity to collapse was found three times greater than expected from Rayleigh's classical theory.     

Regioselective haloaromatization of 1,2-bis(ethynyl)benzene via halogen acids and PtCl2. Platinum-catalyzed 6-pi electrocyclization of 1,2-bis(1'-haloethenyl)benzene intermediates

[reaction: see text] Treatment of 1,2-bis(ethynyl)benzene (1) with aqueous HX (X = Br, I) in hot 3-pentanone (100-105 degrees C, 2 h) afforded 1,2-bis(1'-haloethenyl)benzene species 2-Br and 2-I in 98% and 95% yields, respectively. The hydrochlorination of endiyne 1 failed to proceed at elevated temperature but was implemented efficiently by PtCl2 (5 mol %) in hot 3-pentanone (100 degrees C, 2 h) to give 1,2-bis(1'-chloroethenyl)benzene 2-Cl in 80% yield. In the presence of PtCl2 (5 mol %), these halides 2-Cl,2-Br, and 2-I were subsequently converted to 1-halonaphthalenes 3-Cl, 3-Br, and 3-I in the mother solution via sequential 6-pi electrocyclization and dehalogenation reactions. PtCl2 (5 mol %) also effected direct haloaromatization of endiyne 1 with HX (X = Cl, Br, I) and gave 1-halonaphthalenes 3-Cl, 3-Br, and 3-I in 64-71% yields. This investigation reports the scope and the regioselectivity of haloaromatization of various enediynes catalyzed by PtCl2.     

Complementary control by additives of the kinetics of amorphous CaCO3 mineralization at an organic interface: in-situ synchrotron x-ray observations

The kinetics of biomimetic mineralization at a fatty acid monolayer interface have been measured in situ by synchrotron x-ray reflectivity. The formation of biologically relevant amorphous calcium carbonate films is affected by soluble macromolecules, supersaturation rate of change, and Mg cations. We find that these solution conditions influence mineral film formation in a complementary fashion. Poly(sodium acrylate) extends the lifetime of metastable amorphous calcium carbonate, solution saturation controls the mineral film growth rate, and Mg cations create a longer induction time. This is the first quantification of potentially competitive biomineralization mechanisms that addresses nucleation and growth of the amorphous mineral phases, which are important in biomineralization.     

Crystal Structure of Lanthanide‐oxalate‐pyridine‐2,4‐dicarboxylate Coordination Polymers Suggesting the Reductive Coupling of Carbon Dioxide to Oxalate

Under the hydrothermal conditions, Nd(NO₃)₃·6H₂O reacted with pyridine‐2,4‐dicarboxylic acid (2,4‐pydcH₂) to give a 2D co‐ordination polymer with the empirical formula of C₁₆H₁₈N₂Nd₂O₁₈×H₂O ( 1 ). Pr(NO₃)₃·6H₂O also reacted with 2,4‐pydcH₂ to give another 2D coordination polymer (C₈H₉NO₉Pr)₂·H₂O ( 2 ). The structure of both polymers have been determined by X‐ray diffraction. X‐ray structural analyses show that both polymers contain bridging oxalate (C₂O₄^2?) ligands, which might have been formed by the coupling of two CO₂^?× radicals, released from pydc^2? ligands.     

A high-performance liquid chromatography method using ultraviolet and fluorescence detection for the quantitation of UCN-01, 7-hydroxystaurosporine, from human plasma and saliva

UCN-01, 7-hydroxystaurosporine, is an antagonist of protein kinase C, as well as causing cell cycle arrest. We developed and validated an HPLC assay method for the quantitation of UCN-01. Plasma and saliva standard curves were prepared at concentrations ranging from 0.2 to 20.0 microgram/mL and 4.0 to 200.0 ng/mL, respectively. The sample preparation consisted of acetonitrile precipitation. Separation was accomplished on a phenyl column and a C-18 precolumn insert utilizing a gradient-profile consisting of ammonium acetate and acetonitrile. UV detection was set at 295 nm for UCN-01 and 323 nm for umbelliferone, the internal standard. For fluorescence detection, excitation occurred at 290 nm, while emission was at 400 nm. The retention times were around 4 min for umbelliferone and 9.1 for UCN-01. Inter- and intra-assay errors of accuracy were less than 7. 0% and 10.7%, respectively, for the plasma standard curve and less than 7.1% and 6.7%, respectively, for the saliva standard curve. The recoveries of UCN-01 and umbelliferone from saliva were 81.4 +/- 0. 9% and 106.3 +/- 10.2%, respectively. The recovery of UCN-01 from plasma was 97.9 +/- 7.1% and for umbelliferone was 103.3 +/- 2.3%. This method is suitable for quantifying UCN-01 in patient samples and further characterizing the clinical pharmacology of this compound. Published in 2000 by John Wiley & Sons, Ltd.