Synthesis and antibacterial activity of new <Emphasis Type="Italic">N</Emphasis>-substituted 7-amino-4-methyl-2<Emphasis Type="Italic">H</Emphasis>-chromen-2-ones

N-Substituted 7-amino-4-methyl-2H-chromen-2-ones containing one or two functionalized azole or azine moieties were synthesized. The structures of all synthesized compounds were confirmed by IR, ¹H NMR, and ¹³C NMR spectroscopy. Some of the synthesized compounds exhibited weak antibacterial activity against Rhizobium radiobacter, Escherichia coli, and Xanthomonas campestris.     

Intracellular Delivery and Triggered Release of DNA Using Biodegradable Poly(2‐hydroxypropylene imine)s Containing Cystamine Units

Poly(2‐hydroxypropylene imine)s containing segments of cystamine (PHPI‐CA) are synthesized by polycondensation of 1,3‐dibromo‐2‐propanol with a mixture of 1,3‐diamino‐2‐propanol and cystamine. High molecular weight fractions of these polymers are collected by ultrafiltration and characterized by chemical analysis, ¹H and ¹³C‐NMR spectroscopy, size‐exclusion chromatography with triple detection, and potentiometric titration, and are tested for DNA delivery in vitro. It is shown that PHPI‐CA are highly branched polymers containing disulfide linkages. Transfection efficiency of PHPI‐CA for DNA gives similar results to that of PHPI with GFP⁺ cell percent reaching 80–90%. Cytotoxicity levels for PHPI‐CA are lower than that of PHPI. Novel polymers containing different amounts of disulfide linkages are able to disintegrate and release DNA following the treatment with reducing agent 1,4‐dithiothreitol. Downstream application of PHPI‐CA transfected cells for RNA purification shows that RNA yield is not affected even after the double transfection suggesting that these polymers could be great candidates for in vitro and in vivo transfection.

     

Spider silk and amyloid fibrils: a structural comparison

Although spider silks have been studied for decades, the assembly properties of the underlying silk proteins have still not been unravelled. Previously, the detection of amyloid-like nanofibrils in the spider's silk gland suggested their involvement in the assembly process.Recombinantly produced spider silk also self-assembles into nanofibrils. In order to investigate the structural properties of such silk nanofibrils in more detail, they have been compared to amyloid-like fibrils to highlight structural similarities.     

Taking control of P1, P1' and double bond stereochemistry in the synthesis of Phe-Phe (E)-alkene amide isostere dipeptidomimetics

A protocol for the stereocontrolled independent preparation of both C-2 epimers of Phe-Phe trans-vinyl amide isostere dipeptidomimetics has been devised based on a Wittig-type reaction, in which two chiral building blocks were joined with excellent E-selectivity to give compounds of the type PhePsi[(E)-CH[double bond, length as m-dash]CH]-PheOH.     

Redox characteristics of a de novo quinone protein

The electrochemistry of 2,6-dimethylbenzoquinone (DMBQ) has been characterized for three different systems: DMBQ freely solvated in aqueous buffer; DMBQ bound to a neutral, blocked cysteine (N-acetyl-L-cysteine methyl ester) and the resulting DMBQ-bCys compound solvated in aqueous buffer; and DMBQ bound to a small model protein denoted alpha(3)C. The goal of this study is to detect and characterize differences in the redox properties of the protein-ligated DMBQ relative to the solvated quinones. The alpha(3)C protein used here is a tryptophan-32 to cysteine-32 variant of the structurally defined alpha(3)W de novo protein (Dai et al. J. Am. Chem. Soc. 2002, 124, 10952-10953). The properties of alpha(3)C were recently described (Hay et al. Biochemistry 2005, 44, 11891-11902). DMBQ was covalently bound to bCys and alpha(3)C through a sulfur substitution reaction with the cysteine thiol. In contrast to the solvated DMBQ and DMBQ-bCys compounds, diffusion controlled electrochemistry of DMBQ-alpha(3)C showed well-behaved and fully reversible n = 2 oxidation/reduction with a peak separation of approximately 30 mV between pH 5 and 9. DMBQ-alpha(3)C could also be immobilized on a gold electrode modified with a self-assembled monolayer of 3-mercaptopropionoic acid, allowing the measurement, by cyclic voltammetry, of an apparent rate of electron transfer of 22 s(-1). The (cysteine) sulfur substitution significantly lowers one of the hydroquinone pKA's from 10.4 in DMBQ to 6.8 in DMBQ-bCys. This pKA is slightly elevated in DMBQ-alpha(3)C to 7.0 and the E1/2 at pH 7.0 is raised by 110 mV from +190 mV in DMBQ-bCys to +297 mV in DMBQ-alpha(3)C.     

Calculation of measurement uncertainty in quantitative analysis of genetically modified organisms using intermediate precision--a practical approach

Quantitative characterization of nucleic acids is becoming a frequently used method in routine analysis of biological samples, one use being the detection of genetically modified organisms (GMOs). Measurement uncertainty is an important factor to be considered in these analyses, especially where precise thresholds are set in regulations. Intermediate precision, defined as a measure between repeatability and reproducibility, is a parameter describing the real situation in laboratories dealing with quantitative aspects of molecular biology methods. In this paper, we describe the top-down approach to calculating measurement uncertainty, using intermediate precision, in routine GMO testing of food and feed samples. We illustrate its practicability in defining compliance of results with regulations. The method described is also applicable to other molecular methods for a variety of laboratory diagnostics where quantitative characterization of nucleic acids is needed.     

Synthesis of functionalized, unsymmetrical 1,3,4,6-tetrasubstituted 2,5-diketopiperazines

A general and efficient method for the synthesis of unsymmetrical 1,3,4,6-tetrasubstituted 2,5-diketo- piperazines (DKPs) is described. Cyclization of N-amide alkylated dipeptide methyl esters, followed by alkylation, furnished the corresponding tetrasubstituted DKPs in good overall yields. The influence of steric hindrance in the alkylation reactions appeared to be of lesser importance as long as reactive alkylating agents were used. Furthermore, we have demonstrated the use of tetrasubstituted DKPs as a scaffold for further chemical manipulations to produce novel DKPs with desired properties.     

Trapping of peroxidic intermediates with sulfur and phosphorus centered electrophiles

The trapping ability of a new peroxidic trapping agent relative to several well-established trapping agents was measured. Two different methods for this measurement were utilized. It was shown that adamantylidene adamantane reacts under the trapping conditions to give adamantylidene adamantane epoxide via a more complicated process than previously recognized and is consequently an inappropriate system to make this measurement. In contrast, the use of diethyl sulfide is straightforward and gives reliable values. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:51–56, 1998