An efficient enantioselective synthesis of (2R)-hydroxymethyl glutamic acid and an approach to the (2R)-hydroxymethyl-substituted sphingofungins

We have developed a short enantioselective synthesis of (2R)-hydroxymethyl glutamic acid (HMG) starting from Garner's aldehyde using an alkylidene carbene 1,5-CH insertion as a method to construct the quaternary stereocenter. A variety of conditions were examined for the oxidative cleavage of the key cyclopentene intermediate and we found that RuCl3/NaIO4 led directly to the desired amino bis-acid product. We were also able to show that oxidative cleavage of the cyclopentene 1,5-CH insertion product could be used to produce the amino acid-containing skeleton of the sphingofungin family of natural products.     

Are branched chain fatty acids the natural substrates for P450(BM3)?

Branched chain fatty acids are substrates for cytochrome P450(BM3) (CYP102) from Bacillus megaterium; oxidation of C15 and C17 iso and anteiso fatty acids by P450(BM3) leads to the formation of hydroxylated products that possess high levels of regiochemical and stereochemical purity.     

Development of a novel high-throughput assay for the investigation of GlyT-1b neurotransmitter transporter function

The glycine transporter (GlyT-1b) is a Na(+)/Cl(-)-dependent electrogenic transporter which mediates the rapid re-uptake of glycine from the synaptic cleft. Based on its tissue distribution, GlyT-1 has been suggested to co-localise with the NMDA receptor where it may modulate the concentration of glycine at its co-agonist binding site. This data has led to GlyT-1 inhibitors being proposed as targets for disorders such as schizophrenia and cognitive dysfunction. Radiolabelled uptake assays (e.g. [(3)H]glycine) have been traditionally used in compound screening to identify glycine transporter inhibitors. While such an assay format is useful for testing limited numbers of compounds, the identification of novel glycine uptake inhibitors requires a functional assay compatible with high-throughput screening (HTS) of large compound libraries. Here, the authors present the development of a novel homogenous cell-based assay using the FLIPR membrane potential blue dye (Molecular Devices) and FLEXstation. Pharmacological data for the GlyT-1 inhibitors Org 24598 and ALX 5407 obtained using this novel electrogenic assay correlated well with the conventional [(3)H]-glycine uptake assay format. Furthermore, the assay has been successfully miniaturised using FLIPR(3) and therefore has the potential to be used for high-throughput screening.     

Designing 129Xe NMR biosensors for matrix metalloproteinase detection

Xenon-129 biosensors offer an attractive alternative to conventional MRI contrast agents due to the chemical shift sensitivity and large nuclear magnetic signal of hyperpolarized (129)Xe. Here, we report the first enzyme-responsive (129)Xe NMR biosensor. This compound was synthesized in 13 steps by attaching the consensus peptide substrate for matrix metalloproteinase-7 (MMP-7), an enzyme that is upregulated in many cancers, to the xenon-binding organic cage, cryptophane-A. The final coupling step was achieved on solid support in 80-92% yield via a copper (I)-catalyzed [3+2] cycloaddition. In vitro enzymatic cleavage assays were monitored by HPLC and fluorescence spectroscopy. The biosensor was determined to be an excellent substrate for MMP-7 (K(M) = 43 microM, V(max) = 1.3 x 10(-)(8) M s(-1), k(cat)/K(M) = 7,200 M(-1) s(-1)). Enzymatic cleavage of the tryptophan-containing peptide led to a dramatic decrease in Trp fluorescence, lambda(max) = 358 nm. Stern-Volmer analysis gave an association constant of 9000 +/- 1,000 M(-1) at 298 K between the cage and Trp-containing hexapeptide under enzymatic assay conditions. Most promisingly, (129)Xe NMR spectroscopy distinguished between the intact and cleaved biosensors with a 0.5 ppm difference in chemical shift. This difference most likely reflected a change in the electrostatic environment of (129)Xe, caused by the cleavage of three positively charged residues from the C-terminus. This work provides guidelines for the design and application of new enzyme-responsive (129)Xe NMR biosensors.     

Multilayered polymer microspheres by thermal imprinting during microsphere growth

Modulation of the polymerization temperature in precipitation polymerizations was used to form onion-type polymer microspheres consisting of multiple nested layers. Specifically, the copolymerization of chloromethylstyrene and divinylbenzene-55 in acetonitrile, at temperatures ramping between 65 and 75 degrees C, led to monodisperse, cross-linked microspheres of about 10 mum diameter that have radial density profiles closely reflecting the thermal profiles used. This thermal imprinting is attributed to the copolymer formed being close to its theta point during the polymerization. As the microspheres grow by continuously capturing oligomers from solution, the resulting transient surface gel layer expands and contracts with temperature, and thus records the reaction temperature profile in the form of a corresponding density profile, even as it cross-links.     

An alpha-helical peptidomimetic inhibitor of the HIV-1 Rev-RRE interaction

The interaction between the HIV-1 Rev protein and the Rev-Responsive Element (RRE) RNA is an attractive target for anti-viral therapy. We have designed alpha-helical peptidomimetics of Rev-like peptides using side chain-side chain macrolactam formation between positions i and i+4. One peptidomimetic having an appropriate location, orientation, and length of the macrolactam exhibited both significant helical character and specific RRE binding. This molecule displays 2-fold greater RNA specificity than the wild-type Rev peptide and more than 20-fold greater specificity than an uncyclized control peptide. Thus, specific, high affinity recognition of the RRE is feasible utilizing a small, relatively rigid peptidomimetic scaffold.     

Chemically selective sensing through layer-by-layer incorporation of biorecognition into thin film substrates for surface-enhanced resonance Raman scattering

In this work, the fabrication, characterization, and application of avidin/Ag nanoparticle layer-by-layer (LbL) films as chemically selective substrates for surface-enhanced resonance Raman scattering (SERRS) is demonstrated. The biospecific interaction between avidin and the small molecule biotin, one of the strongest known to exist in nature, is exploited to preferentially capture biotinylated species from solution. This highly favored adsorption is shown to yield SERRS concentration enhancements and improved detection sensitivities of ca. 102 for commercially available and in situ prepared biotinylated species over their nontagged counterparts.     

Ethidium and proflavine binding to a 2',5'-linked RNA duplex

Despite over 40 years of physical investigations, fundamental questions persist regarding the energetics of RNA and DNA intercalation. The dramatic unwinding of a nucleic acid duplex upon intercalation immediately suggests that the nucleic acid backbone should play a significant role in dictating the free energy of intercalation. However, the contribution of the backbone to intercalation free energy is difficult to appreciate given the intertwined energetics associated with intercalation (e.g., pi-pi stacking and solvent effects). Fluorescence titrations were used to determine the association constants of two known intercalators, proflavine and ethidium, for duplex 2',5'-linked RNA. Proflavine was found to bind 2',5' RNA with an association constant 25-fold greater than that measured for standard, 3',5'-linked RNA. In contrast, ethidium binds 2',5' RNA less favorably than standard RNA.     

New stepwise approach to inert heterometallic triple-stranded helicates

The new tripodal fac-functionalized building block, fac-ruthenium(II) tris-(5-hydroxymethyl-2,2'-bipyridine), has been synthesized as a single geometric isomer and used as starting point in the isolation of a kinetically inert heterometallic helicate by the stepwise inclusion of additional 2,2'-bipyridine chelating groups followed by a second metal ion. This stepwise synthetic methodology gives access to a new range of chiral nanoscale structures inaccessible by traditional self-assembly procedures.     

Subnanosecond isomerization in an osmium-dimethyl sulfoxide complex

We report the structure, spectroscopy, and electrochemistry of cis-[Os(bpy)(2)(DMSO)(2)](OTf)(2), where bpy is 2,2'-bipyridine, DMSO is dimethyl sulfoxide, and OTf is trifluoromethanesulfonate. Electrochemical measurements are consistent with S-to-O isomerization following the oxidation of Os(2+) (1.8 V vs Ag/AgCl). Visible irradiation of the metal-to-ligand charge-transfer transition (355 nm) of [Os(bpy)(2)(DMSO)(2)](2+) in the solid state and solution yields an emissive S-bonded excited state and S-to-O excited-state isomerization on a subnanosecond time scale. These results and a comparison to the nonphotoactive [Os(bpy)(2)Cl(DMSO)](+) are discussed.