Now showing 1 - 10 of 18
  • Publication
    A simple and efficient method for the synthesis of Erlenmeyer azlactones
    We have recently developed a novel and efficient method for synthesising Erlenmeyer azlactones under mild and rapid conditions. The reaction is performed by reacting 2-phenyl-5-oxazolone with an aldehyde in dichloromethane using alumina as a catalyst. The materials react instantly at room temperature, negating the need for high temperatures and long reaction times. We have successfully used this method for both aliphatic, aromatic and heteroaromatic aldehydes, synthesising previously unmade Erlenmeyer azlactones in moderate to high yields.
    Scopus© Citations 64  2829
  • Publication
    From amines to diketopiperazines: a one-pot approach
    An efficient one-pot synthesis is described for the preparation of 1,4-disubstituted piperazine-2,5-diones starting from a suitable amine and chloroacetyl chloride in the presence of an aqueous base. The resulting chloroacetamide is cyclised in situ by employing the phase-transfer (PT) catalyst, benzyltriethylammonium chloride (TEBA). The products are isolated in excellent yields of up to 90%.
      468Scopus© Citations 5
  • Publication
    Characterization of a novel amine transaminase from Halomonas elongata
    Chiral amines are indispensable building blocks in the production of biologically active compounds. They are fundamental for the pharmaceutical industry, both as active molecules themselves and as chiral auxiliaries in asymmetric synthesis; however, the available synthetic strategies often present disadvantages. ω-Transaminases (ω-TAs) appear as an attractive alternative by driving the stereoselective amination of prochiral ketones. HEWT is a novel amine transaminase from the moderate halophilic bacterium, Halomonas elongata DSM 2581, which is highly (S)-selective, being able to fully convert (S)-1-phenylethylamine to acetophenone and showing no activity with the corresponding (R)-1-phenylethylamine. HEWT has a broad substrate scope, active with a range of amino donors and acceptors, and naturally accepts isopropylamine (IPA) as amino donor in asymmetric synthesis providing a 41% conversion of pyruvate in 24 h at 37 °C starting with 1:1 molar ratio between the reagents. HEWT also accepts ortho-xylylenediamine as amino donor in for amine synthesis, in particular, with benzaldehyde yielding high conversions between 90 and 95%. The enzyme is also tolerant to the presence of cosolvents up to 20% making it a promising candidate for industrial applications.
    Scopus© Citations 72  413
  • Publication
    Production of lipopeptides in Bacillus sp. CS93 isolated from Pozol
    Bacillus sp. strain CS93, which was previously isolated from Pozol, was previously shown to produce iturin A, bacilysin and chlorotetaine. To investigate the biosynthetic mechanism of chlorotetaine production, the bac genes were amplified from genomic DNA of Bacillus sp. CS93 by PCR and sequenced. The genes bacABCDE were determined, but no gene that might code for a halogenating enzyme was detected either within the gene cluster or in the flanking sequences. Following further analysis of culture supernatants that were active against bacteria by liquid chromatography-MS, it was not possible to detect bacilysin/chlorotetaine. However, in methanolic fractions containing antibacterial activity, molecular ions characteristic of surfactins and fengycin were detectable by electrospray MS. Using primers complementary for conserved regions of nonribosomal peptide synthase, it was possible to amplify gene fragments that had a high degree of homology with known surfactin and fengycin biosynthetic genes. Thus, in addition to the known antimicrobial compounds, we have shown that this strain produces other bioactive lipopeptides, which might account for some of the medicinal properties of Pozol.
    Scopus© Citations 17  800
  • Publication
    A comparison of two novel alcohol dehydrogenase enzymes (ADH1 and ADH2) from the extreme halophile Haloferax volcanii
    Haloarchaeal alcohol dehydrogenases are exciting biocatalysts with potential industrial applications. In this study, two alcohol dehydrogenase enzymes from the extremely halophilic archaeon Haloferax volcanii (HvADH1 and HvADH2) were homologously expressed and subsequently purified by immobilized metal-affinity chromatography. The proteins appeared to copurify with endogenous alcohol dehydrogenases, and a double Δadh2 Δadh1 gene deletion strain was constructed to prevent this occurrence. Purified HvADH1 and HvADH2 were compared in terms of stability and enzymatic activity over a range of pH values, salt concentrations, and temperatures. Both enzymes were haloalkaliphilic and thermoactive for the oxidative reaction and catalyzed the reductive reaction at a slightly acidic pH. While the NAD+-dependent HvADH1 showed a preference for short-chain alcohols and was inherently unstable, HvADH2 exhibited dual cofactor specificity, accepted a broad range of substrates, and, with respect to HvADH1, was remarkably stable. Furthermore, HvADH2 exhibited tolerance to organic solvents. HvADH2 therefore displays much greater potential as an industrially useful biocatalyst than HvADH1.
      627Scopus© Citations 38
  • Publication
    Alternative mild route to the synthesis of 4-methylenecyclohex-2-enone, a key moiety of the anticancer compounds ottelione A and B
    Rare 4-methylenecyclohex-2-enone is prepared from a Diels-Alder methanesulfonate adduct and sodium iodide in acetone in up to 70% yield under mild conditions. This procedure is envisaged to be relevant to the synthesis of 4-methylenecyclo hex-2-enone analogues, structurally similar to the key functionality of cytotoxic otteliones and with potentially significant bioactivity.
      541Scopus© Citations 3
  • Publication
    Novel approach to the synthesis of aliphatic and aromatic alpha-keto acids
    A new practical and efficient synthesis of alpha-keto acids was accomplished starting from the synthon 1,4-diacetylpiperazine-2,5-dione. The synthesis encompasses both aromatic and aliphatic substrates proving to be versatile and innovative with excellent carbon economy and recycling of the glycine by-product.
    Scopus© Citations 14  468
  • Publication
    Characterization of alcohol dehydrogenase (ADH12) from Haloarcula marismortui, an extreme halophile from the Dead Sea
    Haloarchaeal alcohol dehydrogenases are of increasing interest as biocatalysts in the field of white biotechnology. In this study, the gene adh12 from the extreme halophile Haloarcula marismortui (HmADH12), encoding a 384 residue protein, was cloned into two vectors: pRV1 and pTA963. The resulting constructs were used to transform host strains Haloferax volcanii (DS70) and (H1209), respectively. Overexpressed His-tagged recombinant HmADH12 was purified by immobilized metal-affinity chromatography (IMAC). The His-tagged protein was visualized by SDS-PAGE, with a subunit molecular mass of 41.6 kDa, and its identity was confirmed by mass spectrometry. Purified HmADH12 catalyzed the interconversion between alcohols and aldehydes and ketones, being optimally active in the presence of 2 M KCl. It was thermoactive, with maximum activity registered at 60°C. The NADP(H) dependent enzyme was haloalkaliphilic for the oxidative reaction with optimum activity at pH 10.0. It favored a slightly acidic pH of 6.0 for catalysis of the reductive reaction. HmADH12 was significantly more tolerant than mesophilic ADHs to selected organic solvents, making it a much more suitable biocatalyst for industrial application.
    Scopus© Citations 26  886
  • Publication
    A stereoselective synthesis of α-deuterium labelled (S)-α-amino acids
    An atom-efficient and stereoselective synthesis has been developed for the preparation of a-2H-labelled(S)-a-amino acids, starting from a novel chiral diketopiperazine scaffold. Efficient mono-alkylation of the chiral template afforded the (S)-substituted adducts with the nature of the electrophile significantly effecting the stereochemical outcome. Subsequent alkylation was totally selective producing the 1,4-cis adduct as the sole diastereoisomer. The deprotection was carried out using cerium ammonium nitrate followed by acid hydrolysis affording the enantipure a-amino acids.
      413Scopus© Citations 3
  • Publication
    The synthesis and biological testing of bacilysin analogues
    A series of compounds based on the structure of bacilysin were synthesised and tested for antibacterial activity. The key steps in the syntheses are the coupling of an iodide to a diketopiperazine (DKP) and mono-lactim ether scaffold, respectively. The diastereoselectivity of the coupling reactions was dependant on the scaffold, with selectivity for DKP of about 4:1 and mono-lactim ether exceeding 98:2. Subsequent elaboration of the compounds to give open chain dipeptides and DKPs that mimic the structure of bacilysin but substitute the epoxy ketone for a saturated or unsaturated ketone is described. Overall yield from coupling to final product was between 5 and 21 %, with the yield of the saturated products notably higher. The open chain dipeptides demonstrated moderate antibacterial and antifungal activity.
      302Scopus© Citations 3