Sulfur ylides. 10. Modified method for the synthesis of pyrrolizine- and indolizinediones

A modified method for the synthesis of derivatives of pyrrolizinedione and indolizinedione was proposed. The method is based on the intramolecular cyclization of keto-stabilized sulfur ylides generated in situ from diazo ketones and Me₂S in the presence of Rh₂(OAc)₄.     

Density functional calculations for modeling the active site of nickel-iron hydrogenases. 2. Predictions for the unready and ready States and the corresponding activation processes

ZORA relativistic DFT calculations are presented which aim to model the geometric and electronic structure of the active site of NiFe hydrogenases in its EPR-active oxidized states Ni-A (unready state) and Ni-B (ready state). Starting coordinates are taken from the X-ray structure of a mutant of Desulfovibrio fructosovorans hydrogenase refined at 1.81 A resolution. Nine possible candidates for Ni-A and Ni-B are analyzed in terms of their geometric and electronic structure. Comparison of calculated geometric and magnetic resonance parameters with available experimental data indicates that both oxidized states have a micro-hydroxo bridge between the two metal centers. The different electronic structures of both forms can be explained by a modification of a terminal cysteine in Ni-B, best modeled by protonation of the sulfur atom. A possible mechanism for the activation of both oxidized forms is presented.     

Simple method for the isolation and purification of hemoglobin components.

A simple method for the isolation and purification of hemoglobin components from starch gel by electrophoresis is described. An inverted bottle with a cut off bottom is used. Pieces of gel containing the hemoglobin are embedded in potato starch, wetted with buffer, and placed in the neck of the inverted bottle, the mouth of which has been closed with filter paper and tape. Connection with the negative tank buffer is achieved by inserting a layer of starch gel between the potato starch and the negative tank buffer. By electrophoresis, the hemoglobin migrates and accumulates in a dialysing tube tied around the mouth of the bottle and hanging into the positive tank buffer.     

Agents for the treatment of overactive detrusor. I. Synthesis and structure-activity relationships of 1,1'-biphenyl derivatives.

A series of 1,1'-biphenyl-2,6-dicarboxylic acid diesters were synthesized and examined for their inhibitory activity on guinea-pig detrusor muscle contraction at electrical field stimulation in vitro. Among them, 6-isopropyl 2-methyl 3-hydroxy-5-methyl-2'-nitro-(1,1'-biphenyl)-2,6-dicarboxylate, FR75513 (8a) was one of the potent compounds (IC50 = 3.3 x 10(-6) g/ml). This compound (8a) exhibited a strong inhibitory activity on detrusor contraction after intravenous administration in anesthetized rats (ID50 = 0.04 mg/kg).     

Miniemulsion copolymerization of vinyl acetate and butyl acrylate. III. Experimental evidence for the role of the cosurfactant

The role of the cosurfactant (hexadecane) in the miniemulsion copolymerization of 50 : 50 molar ratio vinyl acetate–butyl acrylate monomer mixture is analyzed from an experimental point of view. The main factor responsible for the different kinetic behavior between the miniemulsion and conventional emulsion copolymerization processes was found to be the different particle nucleation mechanism operating in each process. Experimental evidence is presented indicating that in the miniemulsion copolymerization particle nucleation takes place in the preformed stable submicron monomer droplets.     

Zeolites. Efficient and Eco-friendly Catalysts for the Synthesis of Benzimidazoles

Summary. A superior method of synthesis of 2-substituted benzimidazoles by means of the heterogeneous catalysis of synthetic and natural zeolites in the reaction of 1,2-diaminobenzene with acid chlorides is described.     

Analysis of the equations for the temperature dependence of the retention index. I. Relation between equations.

The relation between the parameters of several equations for the retention index temperature dependence was established, taking the hyperbola deduced from the retention theory as starting point. The transformation factors depend only on methylene contributions to the thermodynamic functions of solution and temperature. Their evolution with the mean temperature of the range was illustrated for SE-30 and Carbowax-20M glass capillary columns. On this basis the post-run standardisation of dI/dT values at a reference mean temperature is possible. Examples and statistical correlation between series of parameters from different equations for perfumery solutes were shown.     

Nitroazines. 5. Use of the japp-klingemann reaction for the synthesis of nitrotriazines

Condensation of diazoles with -dicarbonyl nitro compounds (nitromalondialdehyde and nitromalondiester) gives derivatives of azolo[5,1-c] [1,2,4]triazine with a nitro group in the triazine ring.For 4, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 662–665, May, 1986.     

Alternating copolymer of butadiene and propylene. IV. Studies on the catalysts for alternating copolymerization

The catalysts for alternating copolymerization of butadiene and propylene were investigated by means of ESR technique and potentiometric titration. It was found that several kinds of active species for the production of alternating copolymer, 1,2-polybutadiene, and trans-1,4-polybutadiene are formed, depending upon the catalyst composition of VO(acac)₂? Et₃Al? Et₂AlCl. ESR and potential titration studies suggest that the active species for alternating copolymerization is a divalent vanadium compound existing in an associated form.     

Synthetic studies of rifamycins. VI. Preparation and elaboration of the aromatic segment for the synthesis of rifamycin W

A convenient preparation of the aromatic segment 3 starting from 3,5-dibromo-2,6-dimethoxytoluene 5 and furan was described along with the elaboration of 3 by the aldol coupling with the aliphatic segment 2 to the synthetic precursor 4 of rifamycin W.     

Reagents and synthetic methods 55. New methods for the preparation of t-butyldimethylsilyl triflate and trimethylsilyl triflate.

An expeditious synthesis of t-butyldimethylsilyl triflate is described from triflic acid and t-butyldimethylsilane. Reaction between trichloromethyltrimethylsilane and triflic acid is also reported.