Synthesis of 3,6-diaminophthalimides for ureidophthalimide-based foldamers

[reaction: see text]. Herein, we report an improved methodology for the synthesis of a variety of 3,6-diaminophthalimides in high yields. This enables decoration of the periphery of foldamers with a wide range of functionalities.     

Metal-catalyzed regioselective oxy-functionalization of internal alkynes: an entry into ketones, acetals, and spiroketals

[reaction: see text] Platinum(II) and an unusual cationic gold(I) complex were identified as mild catalysts for the room temperature cycloisomerization or tandem hydroalkoxylation/acetal formation of unactivated internal alkynols. Under the appropriate conditions, 5-endo, 5-exo, 6-endo, and 6-exo cycloisomerization modes are all available.     

Numerical accuracy of real inversion formulas for the Laplace transform

In this article, we investigate and compare a number of real inversion formulas for the Laplace transform. The focus is on the accuracy and applicability of the formulas for numerical inversion. In this contribution, we study the performance of the formulas for measures concentrated on a positive half-line to continue with measures on an arbitrary half-line. As our trial measure concentrated on a positive half-line, we take the broad Gamma probability distribution family.     

Comparing frontier methods for economic–environmental trade-off analysis

This paper uses a mechanistic frontier approach as a reference to evaluate the ability of conventional parametric (SFA) and non-parametric (DEA) frontier approaches for analyzing economic–environmental trade-offs. Conventional frontier approaches are environmentally adjusted through incorporating the materials balance principle. The analysis is worked out for the Flemish pig finishing case, which is both representative and didactic. Results show that, on average, SFA and DEA yield adequate economic–environmental trade-offs. Both methods are good estimators for technical efficiency. Cost allocative and environmental allocative efficiency scores are less robust, due to the well-known methodological advantages and disadvantages of SFA and DEA. For particular firms, SFA, DEA and the mechanistic approach may yield different economic–environmental trade-offs. One has therefore to be careful when using conventional frontier approaches for firm-specific decision support. The mechanistic approach allows for optimizing performances per average present finisher, which is the production unit in pig finishing. Conventional frontier methods do not allow for this optimization since the number of average present finishers varies along the production functions. Since the mechanistic production function is based on underlying growth, feed uptake and mortality functions, additional firm-specific indicators can also be calculated at each point of the production function.     

Characterization and sequence confirmation of unnatural amino acid containing peptide libraries using electrospray ionization mass spectrometry

The content of 24 12-membered heptapeptide libraries was investigated using capillary liquid chromatography coupled with an electrospray ionization quadrupole orthogonal acceleration time-of-flight mass spectrometer. Adjustment of the chromatographic parameters led to the separation of most of the components. Extraction of the [M + 2H]2+ ions allowed us to demonstrate the presence of all expected species in the library and to evaluate their relative abundance in the mixture. Rapid sequence confirmation was achieved by subtraction of product ion spectra, a way to eliminate common ions and to simplify the spectra for interpretation. This technique can also easily be applied to other libraries consisting of components with a common core.     

Synthesis and Conformational Analysis of 2′-Deoxy-2′-(3-methoxybenzamido)adenosine,a rational-designed inhibitor of trypanosomal glyceraldehyde phosphate dehydrogenase (GAPDH)

A series of 2′-benzamido-2′-deoxyadenosine analogues were synthesized in an effort to find new lead structures for the treatment of sleeping sickness. The 2′-deoxy-2′-(3-methoxybenzamido)adenosine ( 1h ) was proved to be a selective inhibitor of the parasite glyceraldehyde 3-phosphate dehydrogenase which confirms the modeling studies. The solution-state conformation of 2′-(thiophene-2-carboxamido) analogue 1d demonstrates a 2′-endo conformation, an orientation of the thiophene ring under the ribose moiety, and the base part occupying a ‘syn’/‘anti’ equilibrium.     

Radiation damage in Si1−x Ge x heteroepitaxial devices

Results are presented of an extended study on the induced lattice defects and their effects on the degradation of Si_1−x Ge _x devices, subjected to a 20 MeV alpha-ray, 1 MeV electron, 1 MeV fast neutron, and 20 and 86 MeV proton irradiations. The degradation of the electrical device performance increase with increasing fluence, while it decreases with increasing germanium content. In the Si_1−x Ge _x epitaxial layers, electron capture levels associated with an interstitial-substitutional boron complex are induced. The radiation source dependence of performance degradation is attributed to the difference of mass and the probability of nuclear collision for the formation of lattice defects.     

Amplification of Chirality in Helical Supramolecular Columns

Strong amplification of chirality occurs in dynamic, but highly ordered, helical columns in n-butanol, for which one chiral seed molecule suffices to render a column of 400 molecules to become homochiral. The chiral columns are formed in a thermally dependent stepwise process. The transition from achiral stacks to helical columns is highly cooperative owing to well-defined intermolecular interactions. `Sergeant and Soldiers' measurements allow for the calculation of the association constant and cooperativity length of the homochiral segments. The `Sergeant and Soldiers' data on the number of molecules within a column show a strikingly good match with data obtained from a theoretical model describing the self-assembly of the discotic molecules as a function of temperature and concentration.     

Characterization of modification sites during peptide synthesis using liquid secondary ion/collision-induced dissociation mass spectrometry and a computer program

Side-reactions often occur during peptide synthesis resulting in modified amino acid moieties. To identify these residues, liquid secondary ion/collision-induced dissociation mass spectra were recorded. The main fragments are generated by cleavage of the peptide bond. To facilitate interpretation of the spectra and assignment of the structure, a simple, but flexible and efficient, computer program is presented. The program allows the verification of the correct structure of the synthesized peptides and the deduction of the type of side-products formed, such as alkylation of tryptophan residues.     

Iterative tandem catalysis of racemic AB monomers

Racemic AB monomers encompassing a secondary hydroxy group and a methyl ester moiety were synthesized and converted to chiral polyesters by iterative tandem catalysis (ITC). The concurrent action of an enantioselective acylation catalyst (Novozym 435) and a racemization catalyst (Ru(Shvo)) results in the high conversion of the racemic monomers to enantio‐enriched polymers. Several factors are important for attaining high ee's and high molecular weights. The enantioselectivities observed for the novel AB monomers by Novozym 435 are high enough at 70 °C (E ratio ≥ 200) for the monomers to be useful for ITC. ITC of methyl 6‐hydroxyheptanoate showed that a catalyst loading of ～1.4 mol % Ru(Shvo), 25 mg Novozym 435/mmol AB monomer, and 0.5 mmol DMP/mmol monomer employing a monomer concentration of 1 mol/L gave a monomer conversion of 94%, an ee of 91%, and an M_p of 6.0 kg/mol. Application of these conditions to the other AB monomers revealed the sensitivity of the system. Reduced enantioselectivities were observed when longer reaction times were required for attaining high conversions. These long reaction times were necessary due to the slow (or absent) racemization activity of the Ru(Shvo) catalyst as a result of catalyst deactivation. Since quantitative conversions are crucial to attain high molecular weight polymers in polycondensation reactions, we could significantly improve the system by switching to isopropyl esters of the AB monomers and/or by strict exclusion of oxygen during the ITC. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2721–2733, 2008