Synthesis of biologically active dicarba analogues of the peptide hormone oxytocin using ring-closing metathesis

Facile synthesis of cis and trans olefinic analogues of oxytocin 1 that have carbon in place of sulfur is achieved via ring-closing metathesis (RCM) on a resin-bound linear precursor peptide. Hydrogenation of the cis olefin, 3, proceeds selectively to generate the previously reported saturated derivative 5. Biological testing on rat uterus strips shows that cis compound 3 has an EC50 value of 38 ng/mL (EC50 for oxytocin is 2.7 ng/mL) whereas 5 and trans olefin 4 are less active. [reaction--see text]     

Treatment of radioactive wastes: an X-ray absorption spectroscopy study of the reaction of technetium with green rust

Technetium is a long-lived product of nuclear fission that readily forms the soluble pertechnetate anion [TcO(4)](-). Green rusts (layered hydrous oxides containing both Fe(II) and Fe(III) and with interlayer sulfate or carbonate anions) concentrate >99.8% of 99Tc, present as [TcO(4)](-), from aqueous solution, even in the presence of high concentrations of NaNO(3), a common constituent of radioactive waste streams. The mechanism of removal from solution is apparently reduction and formation of strong Tc(IV) surface complexes. X-ray absorption spectroscopy shows that [TcO(4)](-) is indeed reduced by reaction with both sulfate- and carbonate-form green rusts and is found in a TcO(2)-like environment. On contact with air, the green rusts oxidize to poorly crystalline goethite but the Tc environment is unchanged. There is no increase in Tc solubility associated with oxidation of the host green rust. This behavior suggests that green rusts may be useful in the treatment of Tc-containing waste streams, in groundwater cleanup, and in restricting Tc migration from repositories.     

The enumerative geometry of surfaces and modular forms

Let be a surface, and let be a holomorphic curve in representing a primitive homology class. We count the number of curves of geometric genus with nodes passing through generic points in in the linear system for any and satisfying .

When , this coincides with the enumerative problem studied by Yau and Zaslow who obtained a conjectural generating function for the numbers. Recently, Göttsche has generalized their conjecture to arbitrary in terms of quasi-modular forms. We prove these formulas using Gromov-Witten invariants for families, a degeneration argument, and an obstruction bundle computation. Our methods also apply to blown up at 9 points where we show that the ordinary Gromov-Witten invariants of genus constrained to points are also given in terms of quasi-modular forms.     

Modification of Glycosylation as A Therapeutic Strategy

1. INTRODUCTION

Glycoconjugates play important roles in many cellular and physiological processes, including development, differentiation, cell to cell contact, formation of the intracellular matrix, recognition of microorganisms, macromolecules and small molecules and intracellular transport of proteins.^2,3     

Synthesis of photocleavable poly(methyl methacrylate‐block‐d‐lactide) via atom‐transfer radical polymerization and ring‐opening polymerization

The synthesis and characterization of a photocleavable block copolymer containing an ortho‐nitrobenzyl (ONB) linker between poly(methyl methacrylate) and poly(d ‐lactide) blocks is presented here. The block copolymers were synthesized via atom transfer radical polymerization (ATRP) of MMA followed by ring‐opening polymerization (ROP) of d ‐Lactide and ROP of d ‐lactide followed by ATRP of MMA from a difunctional photoresponsive ONB initiator, respectively. The challenges and limitations during synthesis of the photocleavable block copolymers using the difunctional photoresponsive ONB initiator are discussed. The photocleavage of the copolymers occurs under mild conditions by simple irradiation with 302 nm wavelength UV light (Relative intensity at 7.6 cm: 1500 μW/cm²) for several hours. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4309–4316     

Ring‐opening metathesis copolymerization of cyclooctene and a carborane‐containing oxanorbornene

The incorporation of a silyl‐protected oxanorbornene imide carborane (SONIC) in polyethylene‐like materials is reported. These copolymers were obtained via ring‐opening metathesis copolymerization of (SONIC) and cyclooctene followed by hydrogenation with p‐toluenesulfonylhydrazide. The composition of the copolymer was varied by altering the feed ratio. Structural and thermal properties were investigated and compared with that of a model polymer so as to gauge the impact on the inclusion of the silyl‐functionalized carborane. An initial observation of the modification of the chain sequence upon changing solvent polarity is also discussed. Finally, the potential utilization of these materials as radiation shielding materials is mentioned. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2557–2563, 2010     

Iminosugars: from botanical curiosities to licensed drugs

George Fleet was a pioneer in establishing the structures of naturally occurring iminosugars and in developing novel methods for the chemical synthesis of iminosugars and related compounds. Iminosugars can inhibit or moderate the activity of a wide range of enzymes that act on carbohydrates and can probably affect the function of other carbohydrate-recognising proteins. These effects can be exploited for therapeutic purposes by using iminosugars to modify the glycosylation of eukaryotic cells, the metabolism of carbohydrates and glycoconjugates, the carbohydrate-dependent properties of glycoproteins such as folding and transport and the carbohydrate-mediated interaction of host cells with infective agents. The synthetic derivative of DNJ, N-hydroxyethyl DNJ, which inhibits intestinal disaccharidases and delays postprandial hyperglycemia, was approved for use in type 2 diabetes in 1996. Initially iminosugars were found to disrupt the lysosomal catabolism of glycoconjugates by inhibition of lysosomal glycosidases thereby causing chemically induced phenocopies of genetic lysosomal storage diseases. Paradoxically iminosugars are now being tested as potential therapeutic agents for human lysosomal storage diseases by exploiting some of their other properties. N-Butyl-DNJ, which inhibits the first step in the biosynthesis of many glycosphingolipids, is licensed for substrate reduction therapy for non-neuronopathic Gaucher’s and Niemann-Pick C diseases. 1-Deoxygalactonojirimycin can act as a molecular chaperone for mutant alpha-galactosidases in patients with Fabry disease. Several other compounds are being evaluated in pre-clinical studies or early clinical trials for lysosomal storage and other diseases.