Synthesis of 2-aryl-4-hydroxy-5-thio substituted 1,3-thiazin-6-ones via sulfenylation of 2-aryl-4-hydroxy-[1,3]thiazin-6-ones with sulfenyl chlorides

A series of 2-aryl-4-hydroxy-5-thio substituted 1,3-thiazin-6-ones were synthesized for human immunodeficiency virus-1 protease inhibition. These compounds were synthesized by the treatment of 4-hydroxy-5-thio substituted-1,3-thiazin-6-ones with the corresponding sulfenyl chlorides. The products were obtained in good isolated yields, inspite of the presence of bulkyl substitutents at the ortho position of phenyl sulfenyl chloride portion.     

Synthèse de céphalosporine-lactones

Condensation of azetidinones 2a and 2b with mercaptan 3 gave respectively compound 10 or a 1:1 mixture of 17 and 17 ′. Bromination of 10 , afforded cis and trans-bromohydrins 13a and of 17 and 17 ′ cis and trans-bromohydrins 18a . Acetylation and reduction with zinc and acetic acid of these bromohydrins gave cephems 4a or 4b and 4b ′ respectively.     

Electrolytic destruction of organic matter in urine

A novel electrolytic method has been developed for destroying organic matter in urine. A combination of potassium permanganate, sulfuric acid and nitric acid has yielded about 99% destruction in initial organic content of urine within two hours when electrolysis is carried out with an applied voltage of about 2.5 V, while maintaining a current density of 8.23 mA/cm² at 373 K.     

Determination of enterostatin in human cerebrospinal fluid by capillary electrophoresis with laser induced fluorescence detection

A capillary electrophoresis (CE) method with laser induced fluorescence (LIF) detection is described for quantification of enterostatin (Val-Pro-Asp-Pro-Arg), a pentapeptide involved in appetite regulation and insulin secretion. Enterostatin and two other pentapeptides belonging to the enterostatin family (i.e. Ala-Pro-Gly-Pro-Arg and Val-Pro-Gly-Pro-Arg) were well separated from each other. The peptides were fluorescently tagged with naphthalene-2,3- dicarboxaldehyde (NDA) and separated by micellar electrokinetic chromatography (MEKC) in the presence of methanol as an organic modifier. Coupled with LIF detection, the method had a detection limit of 4.8 x 10(-6) M for enterostatin. The relative standard deviation was to be 4.0% from five determinations of enterostatin at 37.2 microM in a human cerebrospinal fluid (CSF) sample. Twenty-three human CSF samples were analyzed. The level of enterostatin ranged from 24 microM to 51 microM with a mean (+/- SEM) value of 41.7 +/- 2.0 microM.     

Theoretical and experimental studies of asymmetric organozinc additions to benzaldehyde catalyzed by flexible and constrained gamma-amino alcohols

The cis-decalin based gamma-amino alcohols, 1-5, were synthesized, resolved, and employed as catalysts in the addition of organozincs to benzaldehyde. Despite large facial differentiation in the RZn adducts of the ligands, the enantioselectivities were found to be moderate. Transition structure calculations were done using several quantum chemical methods to examine the underlying causes of the selectivity for three gamma-amino alcohols, 1, 2, and 3. The tricyclic mu-oxo (6/4/4), rather than the bicyclic six-membered (6/6), transition structures were found to explain the observed enantioselectivity for 2 and 3. MP2 calculations gave the best correlation to the experimental results compared to B3LYP and HF calculations. The conformational flexibility of the chiral ligands was found to be an important factor in the selectivity.     

The application of "click chemistry" for the decoration of 2(1H)-pyrazinone scaffold: generation of templates

The "click chemistry" approach has been explored on the 2-(1H)-pyrazinone scaffold for the generation of pharmacologically interesting heterocyclic moieties. Huisgen 1,3-dipolar cycloaddition has been evaluated as the key step for the construction of the 1,2,3-triazole ring at the C-3 position of 2-(1H)-pyrazinones. Two different pathways have been successfully evaluated: (1) via C-C or C-O linkage of the acetylenic part to the C-3 position of the 2-(1H)-pyrazinone scaffold or (2) via azide introduction in the C-3 position. The subsequent application of "click chemistry" resulted in the formation of hitherto unknown skeletons. Microwave irradiation has successfully been applied in different steps of the sequence.     

A samarium cyclooctatetraene complex as catalyst for hydroamination/cyclisation catalysis

The cyclooctatetraene-bis(phosphinimino)methanide complex [[CH(PPh2NSiMe3)2]Sm(eta8-C8H8)] has been prepared; although this compound has no alkyl or amide ligand it shows moderate activity as a catalyst for the hydroamination/cyclisation reaction.     

Stability of lyophobic sols

The coagulation of positively charged sol of hydrous ferric oxide of different average sizes for potassium sulphate has been studied in the presence of glucose and urea which stabilise the sol. The degree of stabilisation increases with the fineness of dispersed particles. It has been concluded that the adhesive tendency of the surface of dispersed particles decreases in the presence of said non-electrolytes leading to a decrease in the frequency of collisions resulting in stabilisation. The stability ratioW increases in the presence of glucose and urea for the same amount of the coagulant.

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Zusammenfassung Die Koagulation positiv geladener Sole von wäßrigem Ferrioxid verschiedener mittlerer Partikelgrößen mit Kaliumsulfat wird in Gegenwart von Glykose und Harnstoff, die beide das Sol stabilisieren, untersucht. Der Grad der Stabilisierung hängt von der Teilchengröße ab. Es wird geschlossen, daß die Adhäsionstendenz der Oberflächen der dispergierten Partikel in Gegenwart besagter Nichtelektrolyte abnimmt und so zur Abnahme der Kollisionshäufigkeit und damit zur Stabilisierung führt. Das StabilisierungsverhältnisW wächst in Anwesenheit von Glykose und Harnstoff für gleiche Beträge des Koagulators.

     

Hydrophobicity dependence of oxidation of tetrapeptides of elastin sequences with Mn(III): Synthesis,characterization, kinetics,and mechanistic study

The analogues of elastin sequences, glycyl‐glycyl‐alanyl‐proline (GGAP), glycyl‐glycyl‐phenylalanyl‐proline (GGFP), and glycyl‐glycyl‐isoleucyl‐proline (GGIP) were synthesized by classical solution phase method and characterized. The kinetics of oxidation of these tetrapeptides (TETP) by Mn(III) has been studied in the presence of sulphate ions in acidic solution at 25°C. The reaction was followed spectrophotometrically at λ_max = 500 nm. A first‐order dependence of rate on both [Mn(III)] and [TETP] was observed. The rate is independent of the concentration of the reduction product, Mn(II), and hydrogen ions. The effects of varying the dielectric constant of the medium and addition of anions such as sulphate, chloride, or perchlorate were studied. Activation parameters have been evaluated using Arrhenius and Erying plots. The oxidation products were isolated and characterized. A mechanism involving the reaction of TETP with Mn(III) in the rate‐limiting step is suggested. An apparent correlation was noted between the rate of oxidation and the hydrophobicity of these sequences, where increased hydrophobicity results in increased rate of oxidation. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 39–48, 2002     

Synthesis of C60-diphenylaminofluorene dyad with large 2PA cross-sections and efficient intramolecular two-photon energy transfer

The first, highly two-photon active C60 derivative comprised of a A-sp3-D conjugate structure was synthesized showing effective two-photon absorption cross-sections (sigma 2' = 196 x 10(-48) cm4 sec-1 molecule-1) in the nanosecond regime among the best values for diphenylaminofluorene-based AFX chromophores.