CVD graphene electrochemistry: biologically relevant molecules

We investigate the electrochemical properties of CVD grown graphene towards the detection of various biologically prevalent analytes including l-ascorbic acid (AA), dopamine hydrochloride (DA), β-nicotinamide adenine dinucleotide (NADH), uric acid (UA) and epinephrine (EP). We find that the observed electrochemical response of the CVD-graphene towards these select analytes does not originate from the graphene, however, from various other contributions including the presence of 'graphitic islands' on the surface of the CVD-graphene which dominate its electrochemistry. In the systems studied within, it appears at best, CVD-graphene acts akin to that of an edge plane pyrolytic graphite (EPPG) electrode constructed from highly ordered pyrolytic graphite. However, in other cases, the response of the CVD-graphene is worse than that of an EPPG electrode, which is likely due to the low O/C ratio.     

Synthesis of some biologically relevant beta-C-glycoconjugates

[reaction: see text] An esterification-RCM approach to a variety of biologically relevant beta-C-glycoconjugates is reported herein. A range of carboxylic acids were coupled with several different olefin alcohols 1 to provide esters 3. The esters were then converted to the final ring-closed product 6 in three steps in 49-60% overall yield. The formed compounds are biologically relevant and serve as stable carbohydrate mimics of the corresponding O-glycosides.     

Enantioselective allyltitanations. Synthesis of optically active 1,2-diol units: useful intermediates for the preparation of biologically active compounds

1,2-Diol units were synthesized with excellent enantiomeric excess by using an enantioselective allyltitanation of α-alkoxy-substituted aldehydes.     

Synthesis and characterization of some coumarins with two hydroxy or methoxy substituents

The first synthesis of the 6‐hydroxy‐4‐methoxycoumarin ( 5 ) was carried out in 25 % overall yield from 6‐methoxy‐4‐hydroxycoumarin ( 1 ) by hydrolysis of the methoxy group and subsequent selective methylation of the hydroxyl group at position 4. The ¹H and ¹³C NMR data of compounds 1–6 are reported.     

Synthesis of substituted tetralones as intermediates of CNS agents via palladium-catalyzed cross-coupling reactions

A series of substituted tetralones as intermediates of CNS agents has been synthesized via Pd-catalyzed coupling reactions of 3-(methoxycarbonyl)-1,2,3,4-tetrahydro-1-oxonaphthalen-6-yl trifluoromethanesulfonate (5) with a variety of organometallic reagents.     

Synthesis of versatile intermediates of the ferrocene series: reductive amination of ferrocenecarbaldehyde

Reductive amination of ferrocenecarbaldehyde with several primary and secondary amines in the presence of sodium triacetoxyborohydride was studied. This method was used for the synthesis of new ferrocenylmethylamines, viz., N-(ferrocenylmethyl)isoleucine methyl ester, N,N-bis(ferrocenylmethyl)glycine ethyl ester, and N-(3,5-dibenzyloxybenzyl)-N-(ferrocenylmethyl)methylamine. The latter is a potential precursor of a dendrimer with the chiral ferrocenyl plane in the core.     

Next generation techniques in the high resolution spectroscopy of biologically relevant molecules

Recent advances in the technology of test and measurement equipment driven by the computer and telecommunications industries have made possible the development of a new broadband, Fourier-transform microwave spectrometer that operates on principles similar to FTNMR. This technique uses a high sample-rate arbitrary waveform generator to construct a phase-locked chirped microwave pulse that gives a linear frequency sweep over a wide frequency range in 1 μs. The chirped pulse efficiently polarizes the molecular sample at all frequencies lying within this band. The subsequent free induction decay of this polarization is measured with a high-speed digitizer and then fast Fourier-transformed to yield a broadband, frequency-resolved rotational spectrum, spanning up to 11.5 GHz and containing lines that are as narrow as 100 kHz. This new technique is called chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy. The technique offers the potential to determine the structural and dynamical properties of very large molecules solely from fully resolved pure rotational spectra. FTMW double resonance techniques employing a low-resolution UV laser facilitate an easy assignment of overlapping spectra produced by different conformers in the sample. Of particular interest are the energy landscapes of conformationally flexible molecules of biological importance, including studies of their interaction with solvent and/or other weakly bound molecules. An example is provided from the authors' work on p-methoxyphenethylamine, a neurotransmitter, and its complexes with water.     

Synthesis of glycophostones: cyclic phosphonate analogues of biologically relevant sugars

Analogues of L-fucose, N-acetyl-D-glucosamine, N-acetyl-D-mannosamine, and N-acetyl neuraminic acid in which the anomeric carbon atom was replaced by a phosphonyl group (phostones or cyclic phosphonates) were synthesized by stereocontrolled methods relying on the Abramov reaction.     

Hormone-receptor interations. Synthesis of a biologically active cysteinyl-angiotensin derivative and its use for the preparation of spin-labelled and polymer-supported molecules

(N-t-Butoxycarbonyl-S-acetamido-methyl-L -cysteinyl)-[1- asparagine, 5-valine]-angiotensin II ( 2 ) was prepared from [1-asparagine, 5-valine]‥angiotensin II ( 1 ). With respect to enhancement of rat blood pressure, it is a full agonist displaying about 20–25% of the potency of 1 . The sulfur atom of the cysteine group represents a specific nucleophile by which the hormone can easily be attached to other molecules in a well-defined manner. Thus, 2 has been added to N-substituted maleimides through its (deprotected) thiol group to produce the spin-labelled derivative 3 :{N-t-butoxy-carbonyl-S-[N-(1-oxy-2,2,5,5-tetramethyl- pyrrolidin-3-yl-methyl)-imidosuccin-3-yl]-L -cysteinyl}-[1-asparagine,5-valine]-angiotensin II, and the polymer-supported derivative 6 : S-(N-{5-[7-(sepharosyl-oxy-carbonimidoyl-amino)-4-azaheptylcarbamoyl]-pentyl}-imidosuccin-3-yl)-L -cysteinyl-[1-asparagine, 5-valine]-angiotensin II. The ESR. spectra of 3 in different solvents, and its principal NMR. characteristics, are reported. We are using the compound for studying its interaction with receptor molecules and for purification of target cells and membrane vesicles by affinity aggregation.     

Synthesis of advanced intermediates for the preparation of aza-analogues of podophyllotoxin

Some central intermediates useful for the synthesis of aza-analogues of the anti-cancer drug podophyllotoxin have been prepared starting from l-DOPA and (R)-Garner aldehyde.     

Selones as intermediates in the preparation of extremely sterically hindered molecules

The preparation and reactions of selones, selenium analogues of ketones, are described with particular emphasis on their utility in the preparation of extremely sterically hindered molecules. Mechanistic questions related to these reactions are discussed and evidence for “active selenium” is presented. Selenophilic additions of organometallic compounds to selones are also reported.     

Synthesis of novel methoxy and hydroxy derivatives of 2-phenyl-1H-benz[g]indoles

The synthesis of novel methoxy-derivatives of 2-phenyl-1H-benz[g]indole 3 by condensation of α-naphthyl-amines 1 with N-phenacyl-pyridinium salts 2 is described, as well as their conversion into the corresponding hydroxy-derivatives 5 . Unexpected quinoxaline derivatives 4 were obtained when in the condensation reaction the N-nitrophenacylpyridinium salts 2d,e have been used.     

Aminohydroxyacetone synthons: versatile intermediates for the organocatalytic asymmetric aldol reaction

A practical method for the synthesis of 1,3-aminohydroxyacetone synthons was developed, and their utility in the organocatalytic asymmetric aldol reaction was demonstrated in a short synthesis of aza-sugars.     

Simplified cytochalasins. 1. Synthesis of versatile perhydroisoindolone intermediates.

The chiral synthesis of key intermediates in the preparation of simplified cytochalasin based biological probes is described.     

Synthesis of chiral amino epoxyaziridines: useful intermediates for the preparation of chiral trisubstituted piperidines

Chiral aminoalkyl epoxyaziridine 1 is synthesized in high yield and diastereoselectivity from L-serine. Ring opening of epoxyaziridine 1 with primary amines is carried out with total chemo- and regioselectivity, affording chiral polyfunctionalized piperidines 8. The structure of these trisubstituted piperidines is established by NMR studies.     

Synthesis of hydroxy and methoxy perylene quinones, their spectroscopic and computational characterization, and their antiviral activity

Hydroxy and methoxy perylene quinones are synthesized in an attempt to isolate the essential spectroscopic and biological features of light-induced antiviral agents such as hypericin and hypocrellin. Unlike their naturally occurring counterparts, these synthetic quinones bear the carbonyl, hydroxyl, and methoxy groups in the "bay region." The hydroxy and methoxy compounds have rich absorption spectra with broad features in the visible (approximately 450-800 nm) and relatively more intense and narrow features at wavelengths < or = 350 nm. High-level ab initio quantum mechanical calculations assign the features in the absorption spectra to electronic transitions from S0 to S2 and to higher-lying electronic states. The calculations indicate that in the ground state the trans dihydroxy isomer is 12.5 kcal/mol lower in energy than the cis dihydroxy isomer and is thus the only species present. The lowest-energy trans methoxy ground state isomer and the lowest-energy cis methoxy ground state isomer are found to be degenerate. An additional cis methoxy isomer 6.3 kcal/mol higher in energy than the global minimum is assumed to contribute to the spectrum and is also considered. Finally, the synthetic compounds exhibit similar light-induced antiviral activity to each other, but significantly less than that of hypericin.     

Kinetics and mechanism of the reactions of Au(III) complexes with some biologically relevant molecules

The kinetics of the substitution reactions between the mono-functional Au(III) complexes, [Au(dien)Cl](2+) and [Au(terpy)Cl](2+) (dien = 3-azapentane-1,5-diamine, terpy = 2,2';6',2'-terpyridine) and bi-functional Au(III) complexes, [Au(bipy)Cl(2)](+) and [Au(dach)Cl(2)](+) (bipy = 2.2'-bipyridine, dach = (1R,2R)-1,2-diaminocyclohexane) and biologically relevant ligands such as l-histidine (l-His), inosine (Ino), inosine-5'-monophosphate (5'-IMP) and guanosine-5'-monophosphate (5'-GMP), were studied in detail. All kinetic studies were performed in 25 mM Hepes buffer (pH = 7.2) in the presence of NaCl to prevent the spontaneous hydrolysis of the chloride complexes. The reactions were followed under pseudo-first order conditions as a function of ligand concentration and temperature using stopped-flow UV-vis spectrophotometry. The results showed that the mono-functional complexes react faster than the bi-functional complexes in all studied reactions. The [Au(terpy)Cl](2+) complex is more reactive than the [Au(dien)Cl](2+) complex, which was confirmed by quantum chemical (DFT) calculations. A more than 50% lower activation energy for the terpy than for the dien based complex was found. The bi-functional [Au(bipy)Cl(2)](+) complex is more reactive than the [Au(dach)Cl(2)](+) complex. The reactivity of the studied nucleophiles follows the same order for all studied systems, viz. l-His > 5'-GMP > 5'-IMP > Ino. According to the measured activation parameters, all studied reactions follow an associative substitution mechanism. Quantum chemical calculations (B3LYP/LANL2DZp) suggest that ligand substitution in [Au(terpy)Cl](2+) and [Au(dien)Cl](2+) by imidazole follows an interchange mechanism with a significant degree of associative character. The results demonstrate the strong connection between the reactivity of the complexes toward biologically relevant ligands and their structural and electronic characteristics. Therefore, the binding of gold(III) complexes to 5'-GMP, constituent of DNA, is of particular interest since this interaction is thought to be responsible for their anti-tumour activity.