Diastereoselective Electrophilic Amination of Chiral 1‐Benzoyl‐2,3,5,6‐tetrahydro‐3‐methyl‐2‐(1‐methylethyl)pyrimidin‐4(1H)‐one for the Asymmetric Syntheses of α‐Substituted α,β‐Diaminopropanoic Acids

The chiral compounds (R)‐ and (S)‐1‐benzoyl‐2,3,5,6‐tetrahydro‐3‐methyl‐2‐(1‐methylethyl)pyrimidin‐4(1H)‐one ((R)‐ and (S)‐ 1 ), derived from (R)‐ and (S)‐asparagine, respectively, were used as convenient starting materials for the preparation of the enantiomerically pure α‐alkylated (alkyl=Me, Et, Bn) α,β‐diamino acids (R)‐ and (S)‐ 11 – 13 . The chiral lithium enolates of (R)‐ and (S)‐ 1 were first alkylated, and the resulting diasteroisomeric products 5 – 7 were aminated with ‘di(tert‐butyl) azodicarboxylate’ (DBAD), giving rise to the diastereoisomerically pure (≥98%) compounds 8 – 10 . The target compounds (R)‐ and (S)‐ 11 – 13 could then be obtained in good yields and high purities by a hydrolysis/hydrogenolysis/hydrolysis sequence.     

Metabolic probes for imaging endosymbiotic bacteria within toxic dinoflagellates

Fluorescence microscopy offers an important tool for the study of complex biological phenomena such as symbiosis. Here we identify a strategy that adapts the unique differences between the secondary metabolism in host and guest symbiotic species to selectively image endosymbiotic organisms. The method is demonstrated by application to the complex symbiotic relationships in toxic marine dinoflagellates.     

Fourier transform Raman and DFT study of three annulated oligothiophenes with different molecular shapes.

Herein, we study the conjugation properties of three different thienoacenes, each of which has three or four fused thiophene rings, by means of Fourier transform Raman spectroscopy. The B3LYP/6-31G** vibrational analysis of all of the collected spectroscopic data evidences that the selective enhancement of a limited number of Raman scatterings is related to the occurrence in the three thienoacenes of a vibronic coupling between the lowest unoccupied frontier molecular orbital (LUMO) and some Raman-active skeletal nu(C==C) stretching modes of 1600-1300 cm(-1).     

Homogeneous,unimolecular gas‐phase elimination kinetics of ethyl esters of glyoxylic, 2‐oxo‐propanoic,and 3‐methyl‐2‐oxo‐butanoic acids

The rates of elimination of several ethyl esters of 2‐oxo‐carboxylic acid were determined in a seasoned static reaction vessel over the temperature range 350–430°C and pressure range 33–240 Torr. The reactions, in the presence of a free‐radical inhibitor, are homogeneous, unimolecular, and follow a first‐order rate law. The overall and partial rate coefficients are expressed by the Arrhenius equation. Ethyl glyoxalate Ethyl 2‐oxo‐propionate Ethyl 3‐methyl‐2‐oxo‐butyrate The mechanisms of these elimination reactions are described in terms of concerted cyclic transition state structures. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 268–275, 2007     

Synthesis and characterization of three novel perfluoro-oligothiophenes ranging in length from the trimer to the pentamer

In this Article, we report on the synthesis and full characterization of three perfluorinated oligothiophenes, ranging in length from the trimer to the pentamer (PF-nT, with n = 3, 4, or 5). The differential pulse voltammetry (DPV) analysis of the compounds showed that they can be both oxidized and reduced (i.e., they display a dual or amphoteric electrochemical behavior), with the reduction peaks positively shifted relative to those of the corresponding unsubstituted oligothiophenes. The electrochemically determined energy gaps are in agreement with those measured from the UV-vis-NIR absorption spectra in solution. The conjugational properties have been investigated by means of FT-Raman spectroscopy, both as pure solids and as dilute solutes in CH(2)Cl(2), revealing that: (i) pi-conjugation does not still reach saturation with chain length for the longest oligomer, and (ii) conformational distortions from a nearly coplanar arrangement of the successive thiophene units upon solution are not too large. DFT and TDDFT quantum chemical calculations have been performed, at the B3LYP/6-31G level, to assess information about the optimized molecular structure, equilibrium atomic charges distribution, energies and topologies of the frontier molecular orbitals (MO) around the gap, vibrational normal modes associated with the most outstanding Raman scatterings, and vertical one-electron excitations that give rise to the main optical absorptions.