Reductive cleavage of N-O bonds using Samarium(II) iodide in a traceless release strategy for solid-phase synthesis

A strategy for making amides and ureas using a polymer-supported hydroxylamine resin as a traceless linker is described. The cleavage of the linker by samarium(II) iodide is reported for the first time.     

Preparation of 3-methyl-4-vinyl-1,2,5-oxadiazole and 3-methyl-4-vinyl-1,2,5-thiadiazole

Short and high yielding preparations of 3-Methyl-4-vinyl-1,2,5-oxadiazole ( 6a ) and 3-Methyl-4-vinyl-1,2,5-thiadiazole ( 6b ) are described.     

Evaluation of PTMSP membranes in achieving enhanced ethanol removal from fermentations by pervaporation

The use of membrane processes for the recovery of fermentation products has been gaining increased acceptance in recent years. Pervaporation has been studied in the past as a process for simultaneous fermentation and recovery of volatile products such as ethanol and butanol. However, membrane fouling and low permeate fluxes have imposed limitations on the effectiveness of the process. In this study, we characterize the performance of a substituted polyacetylene membrane, poly[(l-trimethylsilyl)-l-propyne] (PTMSP), in the recovery of ethanol from aqueous mixtures and fermentation broths. Pervaporation using PTMSP membranes shows a distinct advantage over conventional poly(dimethyl siloxane) (PDMS) membranes in ethanol removal. The flux with PTMSP is about threefold higher and the concentration factor is about twofold higher than the corresponding performance achieved with PDMS under similar conditions. The performance of PTMSP with fermentation broths shows a reduction in both flux and concentration factor relative to ethanol-water mixtures. However, the PTMSP membranes indicate initial promise of increased fouling resistance in operation with cell-containing fermentation broths.     

Second‐Generation Inhibitors for the Metalloprotease Neprilysin Based on Bicyclic Heteroaromatic Scaffolds: Synthesis,Biological Activity,and X‐Ray Crystal‐Structure Analysis

A new class of nonpeptidic inhibitors of the Zn^II‐dependent metalloprotease neprilysin with IC₅₀ values in the nanomolar activity range (0.034–0.30 μM ) were developed based on structure‐based de novo design (Figs. 1 and 2). The inhibitors feature benzimidazole and imidazo[4,5‐c]pyridine moieties as central scaffolds to undergo H‐bonding to Asn542 and Arg717 and to engage in favorable π‐π stacking interactions with the imidazole ring of His711. The platform is decorated with a thiol vector to coordinate to the Zn^II ion and an aryl residue to occupy the hydrophobic S1′ pocket, but lack a substituent for binding in the S2′ pocket, which remains closed by the side chains of Phe106 and Arg110 when not occupied. The enantioselective syntheses of the active compounds (+)‐ 1 , (+)‐ 2 , (+)‐ 25 , and (+)‐ 26 were accomplished using Evans auxiliaries (Schemes 2, 4, and 5). The inhibitors (+)‐ 2 and (+)‐ 26 with an imidazo[4,5‐c]pyridine core are ca. 8 times more active than those with a benzimidazole core ((+)‐ 1 and (+)‐ 25 ) (Table 1). The predicted binding mode was established by X‐ray analysis of the complex of neprilysin with (+)‐ 2 at 2.25‐Å resolution (Fig. 4 and Table 2). The ligand coordinates with its sulfanyl residue to the Zn^II ion, and the benzyl residue occupies the S1′ pocket. The 1H‐imidazole moiety of the central scaffold forms the required H‐bonds to the side chains of Asn542 and Arg717. The heterobicyclic platform additionally undergoes π‐π stacking with the side chain of His711 as well as edge‐to‐face‐type interactions with the side chain of Trp693. According to the X‐ray analysis, the substantial advantage in biological activity of the imidazo‐pyridine inhibitors over the benzimidazole ligands arises from favorable interactions of the pyridine N‐atom in the former with the side chain of Arg102. Unexpectedly, replacement of the phenyl group pointing into the deep S1′ pocket by a biphenyl group does not enhance the binding affinity for this class of inhibitors.     

SIMULTANEOUS MEASUREMENT OF ACTION SPECTRA FOR PHOTOREACTIONS I AND II OF PHOTOSYNTHESIS

Abstract— We have devised a method of obtaining simultaneous action spectra for photoreactions I and II by analysis of direct and indirect effects involved in enhancement. The method requires previous determination of the neutral wavelength which gives maximum quantum yield by virtue of equal fractions of open reaction centers ( p and q ) for each photoreaction. A sufficient intensity of the neutral wavelength is used as a constant background. Upon addition of a weak modulated measuring light of intensity I_m and wavelength λ _m two amperometric signals are obtained for rate of oxygen evolution. A modulated signal (AC¯) isolates the direct effect of I_m and gives action of photoreaction II as AC/ I_m . An increment in total rate (ΔDC) also includes an indirect effect of I_m in perturbing reaction center conditions ( p and q ). From analysis of interaction of the two photoreactions, action for photoreaction I can be estimated as (2 ΔDC-AC)/ I_m . The method is applicable to whole cells, properly scales the two action spectra to each other, and removes contribution of the State 1-State 2 phenomena. Action spectra were obtained for Chlorella.     

Trifluoroethylene Sultone: Structure and Chemistry

The gas phase structure of trifluoroethylene sultone, ( 1 ) (3,4,4-trifluoro-1,2-oxathietane-2,2-dioxide) was determined by gas electron diffraction, and the four-membered ring was found to be planar. The following ring parameters (r_a distances and ∠_α angles with 3σ uncertainties) were derived in the electron diffraction analysis: C? O = 1.41 Å (ass.), C? C = 1.541(18) Å, S? O = 1.652(5) Å, S? C = 1.822(8) Å, S? C? C = 86.2(15)°, C? C? O = 97.1(28)°, C? O? S = 97.5(21)°, and O? S? C = 79.1(8)°. New spectral data (IR, NMR) of 1 , its acyclic isomer FSO₂CFHC(O)F ( 2 ), and the related anhydride, FSO₂OSO₂CFHC(O)F ( 3 ), are reported. New esters containing the fluorosulfonyl function, FSO₂CFHC(O)OCH₂CF₃ ( 4 ), FSO₂CFHC(O)OCH₂CH = CH₂ ( 5 ), and (FSO₂CFHC(O)OCH₂CH? CH₂? )_n ( 6 ) have been prepared and characterized.