Pyrrolidine-5,5-trans-lactams. 2. The use of X-ray crystal structure data in the optimization of P3 and P4 substituents

[reaction: see text] In this, the second of two letters, we describe the elaboration of the pyrrolidine-5,5-trans-lactam template to delineate the requirements for optimal substitution of the pyrrolidine and lactam nitrogen atoms. Central to the strategy is the use of rapid iterative synthesis in conjunction with X-ray crystal structure determination of ligand-protein complexes.     

The formation of polycyclic aromatic hydrocarbons from the supercritical pyrolysis of 1-methylnaphthalene

In order to better understand the pyrolytic reactions leading to the formation of polycyclic aromatic hydrocarbons (PAH) and carbonaceous solids under supercritical conditions, we have pyrolyzed the model fuel 1-methylnaphthalene (critical temperature, 499 °C; critical pressure, 36 atm) in an isothermal silica-lined stainless-steel reactor coil at 585 °C, 110 atm, and 140 s. Analysis of the reaction products by high-pressure liquid chromatography with diode-array ultraviolet-visible absorbance detection and mass spectrometric detection has led to the identification of 37 individual 2- to 7-ring PAH—fifteen of which have never before been reported as products of 1-methylnaphthalene pyrolysis. The absence, among the reaction products, of single-ring aromatics and acetylene indicates that there is no aromatic ring rupture in this reaction environment, and the structures of each of the 5- to 7-ring PAH products reveal the intactness of the two 2-ring naphthalene units required in their construction. Proposed reaction pathways involving species plentiful in the reaction environment—1-naphthylmethyl radical, methyl radical, 1-methylnaphthalene, naphthalene, and 2-methylnaphthalene—account for the formation of the observed 5- to 7-ring PAH products. These reaction pathways, along with consideration of bond dissociation energies and relative abundances of reactant species, account for the extremely high product selectivity exhibited by the observed product PAH. The detection of seven 8- and 9-ring PAH, each requiring construction from three naphthalene or methylnaphthalene units, provides evidence that the types of reaction mechanisms outlined here—for the combination of two naphthalene entities to form 5- to 7-ring PAH—are also likely to apply to the combination of three and more such entities in the formation of larger-ring-number PAH and eventually carbonaceous solids.     

Pyrrolidine-5,5-trans-lactams. 4. Incorporation of a P3/P4 urea leads to potent intracellular inhibitors of hepatitis C virus NS3/4A protease

[reaction: see text] In this, the first of two Letters, we describe how a P3/P4 urea linking unit was used to greatly enhance the biochemical and replicon potency of inhibitors based upon the pyrrolidine-5,5-trans-lactam template. Compound 7b demonstrated a 100 nM IC(50) in the replicon cell-based surrogate HCV assay.     

Reactive scattering of H2 from Cu(100): six-dimensional quantum dynamics results for reaction and scattering obtained with a new, accurately fitted potential-energy surface

Six-dimensional quantum dynamical calculations are reported for the dissociative chemisorption of (v=0, 1, j=0) H(2) on Cu(100), and for rovibrationally inelastic scattering of (v=1, j=1) H(2) from Cu(100). The dynamics results were obtained using a new potential-energy surface (PES5), which was based on density-functional calculations using a slab representation of the adsorbate-substrate system and a generalized gradient approximation to the exchange-correlation energy. A very accurate method (the corrugation reducing procedure) was used to represent the density-functional theory data in a global potential-energy surface. With the new, more accurately fitted PES5, the agreement between the dynamics results and experimental results for reaction and rovibrationally elastic scattering is not as good as was obtained with a previous potential-energy surface (PES4), which was based on a subset of the density-functional theory data not yet including the results for the low-symmetry Cu sites. Preliminary density-functional theory results suggest that the agreement between theory and experiment will improve over that obtained with PES5 if the density-functional calculations are repeated using a larger basis set and using more copper layers than employed in PES4 and PES5.     

Pyrrolo-dC and pyrrolo-C: fluorescent analogs of cytidine and 2-deoxycytidine for the study of oligonucleotides

Pyrrolo-dC (1a, 6-methyl-3-(2-deoxy-β-d-ribofuranosyl)-3H-pyrrolo[2,3-d]pyrimidin-2-one) and its cyanoethyl phosphoramidite 2a were synthesized. The latter was incorporated into oligodeoxyribonucleotides by standard automated synthesis techniques, where pyrrolo-dC was found to serve as a fluorescent analog of deoxycytidine. The cyanoethylphosphoramidite (2b) of pyrrolo-C (2a, 6-methyl-3-(β-d-ribofuranosyl)-3H-pyrrolo[2,3-d]pyrimidin-2-one) was also synthesized and may find use for the site-specific incorporation of a fluorescent cytidine analog into oligoribonucleotides.     

The electrochemistry of organotransition-metal complexes : II. Formation and reactivity of the radical cations [trans-Fe(CO3(PR3)2]+ and [Fe(CO)3 (Ph2 PCH2 CH2 PPh2)]+

[Fe(CO)₃ L₂] (L = PPh₃, PPh₂Me, P(OPh)₃ or P(NMe₂)₃; L₂ = Ph₂ PCH₂ CH₂ PPh₂⁺) undergo reversible one-electron oxidations to give the radical cations [Fe(CO)₃L₂]⁺ which have been studied by IR and ESR spectroscopy.     

Structural Influence of Lone Pairs in GeP2N4, a Germanium(II) Nitridophosphate

Owing to their widespread properties, nitridophosphates are of high interest in current research. Explorative high-pressure high-temperature investigations yielded various compounds with stoichiometry MP₂N₄ (M=Be, Ca, Sr, Ba, Mn, Cd), which are discussed as ultra-hard or luminescent materials, when doped with Eu²⁺. Herein, we report the first germanium nitridophosphate, GeP₂N₄, synthesized from Ge₃N₄ and P₃N₅ at 6 GPa and 800 °C. The structure was determined by single-crystal X-ray diffraction and further characterized by energy-dispersive X-ray spectroscopy, density functional theory calculations, IR and NMR spectroscopy. The highly condensed network of PN₄-tetrahedra shows a strong structural divergence to other MP₂N₄ compounds, which is attributed to the stereochemical influence of the lone pair of Ge²⁺. Thus, the formal exchange of alkaline earth cations with Ge²⁺ may open access to various compounds with literature-known stoichiometry, however, new structures and properties.     

Determination of phytase activity in feed by a colorimetric enzymatic method: collaborative interlaboratory study.

Fourteen laboratories participated in a collaborative study (coded fyt9404) and 13 laboratories participated in a study (coded fyt9410) to validate a colorimetric assay for determination of microbial phytase activity in feed. For each study, all laboratories received 6 laboratory samples provided by one commercial supplier (phytase activity levels within the range of 200-400 per kg) to be analyzed in duplicate. Method performance was calculated and statistical calculations were executed according to AOAC guidelines. Results from 3 laboratories for study fyt9404 and from one laboratory for study fyt9410 were excluded from statistical analysis because of invalid data determined during initial review by Youden pair, value versus laboratory. For study fyt9404, repeatability relative standard deviation (RSDr) values ranged from 6.2 to 8.6%, and reproducibility relative standard deviation (RSDR) values ranged from 14.1 to 27.6%. No outliers were identified. For study fyt9410, RSDr values ranged from 3.9 to 7.9%, and RSDR values ranged from 14.0 to 20.5%. With outliers excluded, RSDr values ranged from 2.5 to 7.9%, and RSDR values ranged from 14.0 to 20.5%.