Nanocomposite materials of clay nanoparticles and polystyrene were prepared using living anionic surface-initiated polymerization (LASIP). The montmorillonite clay surface and intergallery interfaces were intercalated with 1,1-diphenylethylene (DPE), an organic cation and initiator derivative for anionic polymerization. Its intercalation was confirmed by a series of characterization methods including X-ray diffraction (XRD), FT-IR spectroscopy, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The results showed a complete replacement of the Na counterions by the charged initiators. LASIP was performed in a high-vacuum reaction setup for anionic polymerization using different styrene monomer/initiator ratios. A living anionic polymerization mechanism was determined from molecular weight (MW) data and the molecular weight distribution. A comparison of FT-IR, TGA, XPS, XRD, and atomic force microscopy (AFM) data confirmed that polystyrene was indeed “grafted from” clay surfaces for these composite materials. The initiation efficiency was distinguished between surface- and intergallery interface-bound initiators.

The first total asymmetric synthesis of (+)-xestoquinone (1) has been accomplished in 68% ee by a palladium(0)-catalyzed polyene cyclization of naphthyl triflate 44 using (S)-(+)-BINAP as the chiral ligand. Attempts at an asymmetric polyene cyclization using the corresponding naphthyl bromide 41 gave poor enantioselectivities even in the presence of silver salts, thus exemplifying the effect of the coordination state of palladium on the enantioselectivity. A new method for the preparation of 6,7-dihydroisobenzofurans is also described using a [1,2]-Wittig rearrangement on a seven-membered cyclic ether precursor.

The solution-phase parallel synthesis of tethered dimers was employed to identify lead inhibitors of bacterial NAD synthetase. Active dimers contained two aromatic end groups joined by a polymethylene linker, with one end group containing a permanent positive charge. Effective inhibitors of NAD synthetase also inhibited the growth of Gram-positive (but not Gram-negative) bacteria, including antibiotic-resistant strains. The desmethyl precursors of active inhibitors lacked a permanent positive charge and were inactive as either enzyme inhibitors or antibacterial agents. Similarly, a close structural analogue of the most active inhibitors contained two additional ether oxygens in the tether and was inactive in both assays. These results are consistent with the premise that NAD synthetase inhibition is responsible for the antibacterial actions and support further studies on NAD synthetase as a new target for antibacterial agents.

No abstract