Louis A. Silks

The hydrodeoxygenation of bioderived furans into alkanes

The conversion of biomass into fuels and chemical feedstocks is one part of a drive to reduce the worlds dependence on crude oil. For transportation fuels in particular, wholesale replacement of a fuel is logistically problematic, not least because of the infrastructure that is already in place. Here, we describe the catalytic defunctionalization of a series of biomass-derived molecules to provide linear alkanes suitable for use as transportation fuels. These biomass-derived molecules contain a variety of functional groups, including olefins, furan rings and carbonyl groups. We describe the removal of these in either a stepwise process or a one-pot process using common reagents and catalysts under mild reaction conditions to provide n-alkanes in good yields and with high selectivities. Our general synthetic approach is applicable to a range of precursors with different carbon content (chain length). This allows the selective generation of linear alkanes with carbon chain lengths between eight and sixteen carbons.

CC or CO Bond Cleavage in a Phenolic Lignin Model Compound: Selectivity Depends on Vanadium Catalyst†

The aerobic oxidation of a phenolic lignin model compound with a vanadium catalyst results in the oxidative cleavage of the C-C bond between the aryl ring and the adjacent hydroxy-substituted carbon atom. Labeling experiments indicate key mechanistic differences to a previously reported related C-O bond cleavage reaction. The selectivity in C-C versus C-O bond cleavage depends on the choice of the vanadium catalyst.

Mild and selective vanadium-catalyzed oxidation of benzylic, allylic, and propargylic alcohols using air.

Transition metal-catalyzed aerobic alcohol oxidation is an attractive method for the synthesis of carbonyl compounds, but most catalytic systems feature precious metals and require pure oxygen. The vanadium complex (HQ)(2)V(V)(O)(O(i)Pr) (2 mol %, HQ = 8-quinolinate) and NEt(3) (10 mol %) catalyze the oxidation of benzylic, allylic, and propargylic alcohols with air. The catalyst can be easily prepared under air using commercially available reagents and is effective for a wide range of primary and secondary alcohols.

Do enzymes recognise remotely located stereocentres? Highly enantioselective Candida rugosa lipase-catalysed esterification of the 2- to 8-methyldecanoic acids

Several racemic methyl decanoic acids have been synthesised and successfully resolved in esterification with 1-hexadecanol at aw=0.8 in cyclohexane using immobilised Candida rugosa lipase (CRL) as ...

Solution Structures of the Huntington's Disease DNA Triplets, (CAG)n

Highly polymorphic DNA triplet repeats, (CAG)n, are located inside the first exon of the Huntingtons disease gene. Inordinate expansion of this repeat is correlated with the onset and progression of the disease. NMR spectroscopy, gel electrophoresis, digestion by single-strand specific P1 enzyme, and in vitro replication assay have been used to investigate the structural basis of (CAG)n expansion. Nondenaturing gel electrophoresis and 1D 1H NMR studies of (CAG)5 and (CAG)6 reveal the presence of hairpins and mismatched duplexes as the major and minor populations respectively. However, at high DNA concentrations (i.e., 1.0-2.0 mM that is typically required for 2D NMR experiments) both (CAG)5 and (CAG)6 exist predominantly in mismatched duplex forms. Mismatched duplex structures of (CAG)5 and (CAG)6 are useful, because they adequately model the stem of the biologically relevant hairpins formed by (CAG)n. We, therefore, performed detailed NMR spectroscopic studies on the duplexes of (CAG)5 and (CAG)6. We also studied a model duplex, (CGCAGCG)2 that contains the underlined building block of the duplex. This duplex shows the following structural characteristics: (i) all the nucleotides are in (C2-endo, anti) conformations, (ii) mismatched A x A base pairs are flanked by two Watson-Crick G x C base pairs and (iii) A x A base pairs are stably stacked (and intra-helical) and are formed by a single N6-H--N1 hydrogen bond. The nature of A x A pairing is confirmed by temperature-dependent HMQC and HMQC-NOESY experiments on the [(CA*G)5]2 duplex where the adenines are 15N-labeled at N6. Temperature- and pH-dependent imino proton spectra, nondenaturing electrophoresis, and P1 digestion data demonstrate that under a wide range of solution conditions longer (CAG)n repeats (n> or =10) exist exclusively in hairpin conformation with two single-stranded loops. Finally, an in vitro replication assay with (CAG)8,21 inserts in the M13 single-stranded DNA templates shows a replication bypass for the (CAG)21 insert but not for the (CAG)8 insert in the template. This demonstrates that for a sufficiently long insert (n=21 in this case), a hairpin is formed by the (CAG)n even in presence of its complementary strand. This observation implies that the formation of hairpin by the (CAG)n may cause slippage during replication and thus may explain the observed length polymorphism.

Simple enantiomeric excess determination of amines using chiral selones: unusual N–H⋯Se bonding detected by HMQC 1H/77Se NMR spectroscopy

One-pot coupling of a chiral selone derivatizing agent to a series of chiral and racemic amines mediated with triphosgene gives adducts in yields ranging from 80–99%; 77Se NMR spectroscopy evaluation of the diastereoisomeric adduct conveniently allows the determination of the enantiomeric excesses of the parent chiral amines.

SYNTHESIS AND 125TE NMR SPECTROSCOPY OF ALPHA -TELLUROCARBONYL COMPOUNDS AND DERIVATIVES

Abstract The reaction of lithium alkyl-, alkenyl-, alkynyl-, and aryl tellurolates with α-bromocarobonlyl compounds in anhydrous tetrahydrofuan gives the title compounds in yields ranging from 55–92%. The 125Te NMR chemical shift range for these compounds is 405–1024 ppm.

Synthesis of L-selenocystine,L-[77Se]selenocystine andL-tellurocystine

Synthetic routes for the synthesis of stable isotope nlabelled amino nacids which contain either a selenium or a tellurium atom have been nexplored. L-Selenocystine, nL-[77Se]selenocystine and nL-tellurocystine have been constructed in four steps from ncommercially available methyl n(2S)-2-[(tert-butoxycarbonyl)amino]-3- nhydroxypropionate. The sequence of reactions has been successfully nscaled up giving significant quantities of the chalcogen based amino nacids in fair to good overall yield.

Reaction of alcohols (via the Mitsunobu reaction) and alkyl halides with chiral selone derivatizing agents

Abstract Coupling of a selone chiral derivatizing agent (CDA) to d , l -alkyl halides gives Se-alkylated adducts in yields ranging from 76–97%. Reaction of d , l -alcohols with the selone CDAs via the Mitsunobu reaction has given rise to Se-alkylated adducts in yields ranging from 82–92%. Examination of the 77 Se NMR spectra of the resulting diastereomeric adducts indicates that discrimination of remotely disposed chiral centers is possible using this technique.

Synthesis and incorporation of [6,7]-selenatryptophan into dihydrofolate reductase.

Until recently, the only selenium containing amino acid which could be used to completely substitute for a wild type amino acid was selenomethionine (SeMet). In the last decade the preparation of SeMet containing proteins has proved to be valuable tools in the determination of three-dimensional structure by multiwavelength anomalous diffraction (MAD) techniques. The potential utility of a selenium containing tryptophan analog, beta-seleno[3,2-b]pyrrolyl-L-alanine ([4,5]selenatryptophan), has recently been demonstrated in the literature. This finding shows promise for the bioincorporation of its positional isomer, beta-selenolo[2,3-b]pyrrolyl-L-alanine ([6,7]selenatryptophan), thereby adding to the essential arsenal of selenium-containing amino acids for use in the characterization of proteins. The synthesis of [6,7]selenatryptophan by enzymatic biotransformation with tryptophan synthase from selenolo[2,3-b]pyrrole was carried out as well as its characterization by NMR spectroscopy and thin layer chromatography. Selenatryptophyl dihydrofolate reductase ([6,7]SeTrp-DHFR) was then synthesized in vivo, purified, and found to exhibit no perturbations to enzymatic activity.