Direct electrochemistry of an [FeFe]-hydrogenase on a TiO2 electrode

[FeFe]-hydrogenases are efficient natural catalysts that can be exploited for hydrogen production. Immobilization of the recombinant [FeFe]-hydrogenase CaHydA was achieved for the first time on an anatase TiO(2) electrode. The enzyme is able to interact and exchange electrons with the electrode and to catalyze hydrogen production with an efficiency of 70%.     

Preparative access to medicinal chemistry related chiral alcohols using carbonyl reductase technology

Libraries of highly enantioenriched secondary alcohols in both enantiomeric forms were synthesised by enzymatic reduction of their parent ketones using selectAZyme? carbonyl reductase (CRED) technology. Commercially available CREDs were able to reduce a range of substrate classes efficiently and with very high enantioselectivity. Matching substrate classes to small subsets of CREDs enabled the fast development of preparative bioreductions and the rapid generation of 100–1500 mg samples of chiral alcohols in typically >95% ee and the majority in ?99.0% ee. The conditions for small scale synthesis were then scaled up to 0.5 kg to deliver one of the chiral alcohols, (S)-1-(4-bromophenyl)-2-chloroethanol, in 99.8% ee and 91% isolated yield.     

Covalently functionalized hexagonal boron nitride nanosheets by nitrene addition

The covalent functionalization of exfoliated hexagonal boron nitride (h-BN) nanosheets by nitrene addition is described. Integration of functionalized h-BN nanosheets within a polycarbonate matrix is demonstrated and was found to afford significant increases in mechanical properties. This integration methodology was further extended by the covalent modification of the h-BN nanosheets with polymer chains of a polycarbonate analogue, and the integration of the polymer modified h-BN within the polymer matrix.     

Antibody adsorption and orientation on hydrophobic surfaces

The orientation of a monoclonal, anti-streptavidin human IgG1 antibody on a model hydrophobic, CH(3)-terminated surface (1-dodecanethiol self-assembled monolayer on gold) was studied by monitoring the mechanical coupling between the adsorbed layer and the surface as well as the binding of molecular probes to the antibodies. In this study, the streptavidin antigen was used as a probe for the Fab portions of the antibody, while bacteria-derived Protein G' was used as a probe for the Fc region. Bovine serum albumin (BSA) acted as a blocking protein. Monolayer coverage occurred around 468 ng/cm(2). Below 100 ng/cm(2), antibodies were found to adsorb flat-on, tightly coupled to the surface and unable to capture their antigen, whereas the Fc region was able to bind Protein G'. At half-monolayer coverage, there was a transition in the mechanism of adsorption to allow for vertically oriented antibodies, as evidenced by the binding of both Protein G' and streptavidin as well as looser mechanical coupling with the surface. Monolayer coverage was characterized by a reduced level in probe binding per antibody and an even less rigid coupling to the surface.     

Polyketide double bond biosynthesis. Mechanistic analysis of the dehydratase-containing module 2 of the picromycin/methymycin polyketide synthase

Picromycin/methymycin synthase (PICS) is a modular polyketide synthase (PKS) that is responsible for the biosynthesis of both 10-deoxymethynolide (1) and narbonolide (2), the parent 12- and 14-membered aglycone precursors of the macrolide antibiotics methymycin and picromycin, respectively. PICS module 2 is a dehydratase (DH)-containing module that catalyzes the formation of the unsaturated triketide intermediate using malonyl-CoA as the chain extension substrate. Recombinant PICS module 2+TE, with the PICS thioesterase domain appended to the C-terminus to allow release of polyketide products, was expressed in Escherichia coli. Purified PICS module 2+TE converted malonyl-CoA and 4, the N-acetylcysteamine thioester of (2S,3R)-2-methyl-3-hydroxypentanoic acid, to a 1:2 mixture of the triketide acid (4S,5R)-4-methyl-5-hydroxy-2-heptenoic acid (5) and (3S,4S,5R)-3,5-dihydroxy-4-methyl-n-heptanoic acid-delta-lactone (10) with a combined kcat of 0.6 min(-1). The triketide lactone 10 is formed by thioesterase-catalyzed cyclization of the corresponding d-3-hydroxyacyl-SACP intermediate, a reaction which competes with dehydration catalyzed by the dehydratase domain. PICS module 2+TE showed a strong preference for the syn-diketide-SNAC 4, with a 20-fold greater kcat/K(m) than the anti-(2S,3S)-diketide-SNAC 14, and a 40-fold advantage over the syn-(2R,3S)-diketide-SNAC 13. PICS module 2(DH(0))+TE, with an inactivated DH domain, produced exclusively 10, while three PICS module 2(KR(0))+TE mutants, with inactivated KR domains, produced exclusively or predominantly the unreduced triketide ketolactone, (4S,5R)-3-oxo-4-methyl-5-hydroxy-n-heptanoic acid-delta-lactone (7). These studies establish for the first time the structure and stereochemistry of the intermediates of a polyketide chain elongation cycle catalyzed by a DH-containing module, while confirming the importance of key active site residues in both KR and DH domains.     

Easily grafted polyurethanes with reactive main chain functional groups. Synthesis,characterization, and antithrombogenicity of poly(ethylene glycol)-grafted poly(urethanes)

A novel synthesis of poly(ethylene glycol) (PEG)-grafted poly(urethanes) (PURs) is described based on a precursor PUR containing free amino groups in the main chain. Three different poly(urethane) backbones were prepared: a homopoly(urethane) comprised of N-Bocdiethanolamine (BDA) and 4,4′-methylenebis(phenyl isocyanate) (MDI), a copoly(urethane) (COPUR) consisting of BDA, N-benzyldiethanolamine and MDI, and a poly(urethane urea) (PUU) that was prepared from BDA, MDI, and ethylenediamine as the chain extender. The M_n of these poly(urethanes) ranged from 32,000 to 72,000 g/mol. PEG (750, 1,900, and 5,000 g/mol) was grafted onto the boc-deprotected poly(urethanes) via the chloroformate. Films of the polymers were spin cast from dilute solutions, annealed, and the surfaces analyzed by goniometry. Water contact angle data indicates increasing PEG surface coverage of the poly(urethanes) with increasing PEG molecular weight. Reorientation of the polymer films is evidenced by contact angle hysteresis. Polymer thrombogenicity, which was studied using blood perfusion experiments, shows that COPUR-g-PEG5000 and PUU-g-PEG5000 exhibit very little platelet adhesion. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3441–3448, 1999     

The products of the reaction of the hydroxyl radical with 2-ethoxyethyl acetate

The gas-phase reaction products of the OH radical with 2-ethoxyethyl acetate (EEA, CH₃C(O)OCH₂CH₂OCH₂CH₃) have been investigated. 1,2-Ethanediol acetate formate (EAF, CH₃C(O)OCH₂CH₂OC(O)H) and ethyl formate (EF, HC(O)OCH₂CH₃) were identified as the two main products. A third product, ethylene glycol diacetate (EGD, CH₃C(O)OCH₂CH₂OC(O)CH₃), was also observed. EAF, EF, and EGD formation yields were determined to be 0.37 ± 0.03 and 0.328 ± 0.018 and 0.040 ± 0.005, respectively. Proposed reaction mechanisms are discussed and compared with these data. © 1996 John Wiley & Sons, Inc.     

Dual aromatase-sulfatase inhibitors based on the anastrozole template: synthesis, in vitro SAR, molecular modelling and in vivo activity

The synthesis and biological evaluation of a series of novel Dual Aromatase-Sulfatase Inhibitors (DASIs) are described. It is postulated that dual inhibition of the aromatase and steroid sulfatase enzymes, both responsible for the biosynthesis of oestrogens, will be beneficial in the treatment of hormone-dependent breast cancer. The compounds are based upon the Anastrozole aromatase inhibitor template which, while maintaining the haem ligating triazole moiety crucial for enzyme inhibition, was modified to include a phenol sulfamate ester motif, the pharmacophore for potent irreversible steroid sulfatase inhibition. Adaption of a synthetic route to Anastrozole was accomplished via selective radical bromination and substitution reactions to furnish a series of inhibitory aromatase pharmacophores. Linking these fragments to the phenol sulfamate ester moiety employed S(N)2, Heck and Mitsunobu reactions with phenolic precursors, from where the completed DASIs were achieved via sulfamoylation. In vitro, the lead compound, 11, had a high degree of potency against aromatase (IC(50) 3.5 nM), comparable with that of Anastrozole (IC(50) 1.5 nM) whereas, only moderate activity against steroid sulfatase was found. However, in vivo, 11 surprisingly exhibited potent dual inhibition. Compound 11 was modelled into the active site of a homology model of human aromatase and the X-ray crystal structure of steroid sulfatase.     

Dual aromatase-sulfatase inhibitors based on the anastrozole template: synthesis, in vitro SAR, molecular modelling and in vivo activity

The synthesis and biological evaluation of a series of novel Dual Aromatase-Sulfatase Inhibitors (DASIs) are described. It is postulated that dual inhibition of the aromatase and steroid sulfatase enzymes, both responsible for the biosynthesis of oestrogens, will be beneficial in the treatment of hormone-dependent breast cancer. The compounds are based upon the Anastrozole aromatase inhibitor template which, while maintaining the haem ligating triazole moiety crucial for enzyme inhibition, was modified to include a phenol sulfamate ester motif, the pharmacophore for potent irreversible steroid sulfatase inhibition. Adaption of a synthetic route to Anastrozole was accomplished via selective radical bromination and substitution reactions to furnish a series of aromatase inhibitory pharmacophores. Linking these fragments to the phenol sulfamate ester moiety employed SN2, Heck and Mitsunobu reactions with phenolic precursors, from where the completed DASIs were achieved via sulfamoylation. In vitro, the lead compound, 11, had a high degree of potency against aromatase (IC50 3.5 nM), comparable with that of Anastrozole (IC50 1.5 nM) whereas, only moderate activity against steroid sulfatase was found. However, in vivo, 11 surprisingly exhibited potent dual inhibition.Compound 11 was modelled into the active site of a homology model of human aromatase and the X-ray crystal structure of steroid sulfatase.