Synthetic Approaches to Taxodione. Synthesis of Methyl 12-Oxopodocarpa-5,9(11)-diene-8β-Carboxylate

In connection with studies leading to the total synthesis of taxodione¹ (1), we required the tricyclic enone 3. We have previously described² an AB→ABC approach to this intermediate which was flawed by a low yield in the penultimate closure of the C ring (2→3). We now wish to report an alternate synthesis of 3 which involves a BC→ABC approach for the construction of this tricyclic system.     

Synthesis of Substituted Trans-1,6-Dimethylbicyclo[4.3.0]-non-2-enes Using A Claisen Rearrangement of α-(Thioalkoxy) Esters

The Claisen rearrangement of α-(thioalkoxy)-esters provided access to substituted trans-1, 6-dimethylbicyclo[4.3.0]non-2-enes characteristic of the CD rings of the cucurbitanes.     

A new approach to the synthesis of conjugated polymer-nanocrystal composites for heterojunction optoelectronics

We report a simple one pot process for the preparation of lead sulfide (PbS) nanocrystals in the conjugated polymer poly (2-methoxy-5-(2'ethyl-hexyloxy)-p-phenylene vinylene)(MEH-PPV), and we demonstrate electronic coupling between the two components.     

Kinetic and thermodynamic characterization of the cobalt and manganese oxyhydroxide cores formed in horse spleen ferritin

Horse spleen ferritin (HoSF) containing 800-1500 cobalt or 250-1200 manganese atoms as Co(O)OH and Mn(O)OH mineral cores within the HoSF interior (Co-HoSF and Mn-HoSF) was synthesized, and the chemical reactivity, kinetics of reduction, and the reduction potentials were measured. Microcoulometric and chemical reduction of HoSF containing the M(O)OH mineral core (M = Co or Mn) was rapid and quantitative with a reduction stoichiometry of 1.05 +/- 0.10 e/M forming a stable M(OH)(2) mineral core. At pH 9.0, ascorbic acid (AH(2)), a two-electron reductant, effectively reduced the mineral cores; however, the reaction was incomplete and rapidly reached equilibrium. The addition of excess AH(2) shifted the reaction to completion with a M(3+)/AH(2) stoichiometry of 1.9-2.1, consistent with a single electron per metal atom reduction. The rate of reaction between M(O)OH and excess AH(2) was measured by monitoring the decrease in mineral core absorbance with time. The reaction was first order in each reactant with second-order rate constants of 0.53 and 4.74 M(-1) min(-1), respectively, for Co- and Mn-HoSF at pH 9.0. From the variation of absorbance with increasing AH(2) concentration, equilibrium constants at pH 9.0 of 5.0 +/- 1.9 for Co-HoSF and 2.9 +/- 0.9 for Mn-HoSF were calculated for 2M(O)OH + AH(2) = 2M(OH)(2) + D, where AH(2) and D are ascorbic acid and dehydroascorbic acid, respectively. Consistent with these equilibrium constants, the standard potential for the reduction of Co(III)-HoSF is 42 mV more positive than that of the ascorbic acid reaction, while the standard potential of Mn(III)-HoSF is 27 mV positive relative to AH(2). Fe(2+) in solution with Co- and Mn-HoSF under anaerobic conditions was oxidized to form Fe(O)OH within the HoSF interior, resulting in partial displacement of the Co or Mn by iron.     

Determination of the in vitro metabolism of (+)- and (-)-epibatidine

The oxidative in vitro metabolism of epibatidine was investigated using liver microsomes from rat, dog, rhesus monkey and human. Analysis was performed using liquid chromatography-mass spectrometry (LC-MS) using both achiral and chiral stationary phases. Comparison of the metabolism of the (+)- and (-)-enantiomers revealed species differences in the extent of metabolism, with rhesus monkey>dog>rat=human. Furthermore, differences in the routes of metabolism for epibatidine enantiomers were also observed, with mass spectra consistent with hydroxylation of the azabicycle for (-)-epibatidine and with the formation of diastereomeric N-oxides for (+)-epibatidine being obtained. For chiral LC-MS, a volatile ion-pair reagent of heptafluorobutyric acid was used in place of pentanesulphonic acid with no deterioration in chiral selectivity. Analysis of the same samples by chiral LC-MS revealed no evidence for metabolic chiral interconversion and chiral analysis from a metabolic time course of racemic material revealed enantiomers to be metabolised to approximately the same extent. Such findings may be important particularly should epibatidine be investigated in non-rodent species.     

The crystal structure of bicyclo [3.3.3]undecane-1,5-diol and the conformation of bicyclo[3.3.3]undecane (manxane)

The crystal structure of bicyclo [3.3.3]undecane-1,5-diol has been determined. It is monoclinic, P2₁/c, a = 12.99(2), b = 14.16(2), c = 12.50(1)A,β = 112.42(2)°, with two independent molecules in the asymmetric unit. One of these is disordered, but the other has almost exact C_3h symmetry and its conformation and precise molecular geometry agree well with previous calculations by molecular mechanics. The molecule shows considerable angle strain, having bridge angles in the range 118–121°     

Nucleation of persistent slip bands

The slip-unslip phenomenon has been used to examine the depth of penetration of persistent slip bands in a low-strain amplitude fatigue specimen. The conclusion is that the concentration of strain may well be nucleated in the bulk of the specimen.I would like to thank the Czechoslovak Academy of Sciences for their hospitality. The research described in this paper was done at McMaster University under the direction of I. D. Embury and R. K. Ham and was supported by the National Research Council of Canada.     

Exact shell-model and projected Hartree-Fock calculations for Mg

The results of a projected Hartree-Fock calculation are compared with those of an exact shell-model calculation for states of J ? 6 in the nucleus ²⁴Mg. The realistic Kuo interaction is used, and gives reasonable agreement with experiment.