Exploring the solid-phase synthesis of 3,4-disubstituted beta-lactams: scope and limitations

This work describes a comprehensive study on the solid-phase synthesis of 3,4-disubstituted beta-lactams. In situ generated ketenes react with immobilized aldimines under mild conditions to generate libraries of beta-lactams in good to very good overall isolated yields. Different commercially available solid supports were studied, with the cost-effective Wang resin proving to be the most effective. The utility of the protocol was also demonstrated by the highly efficient asymmetric versions when homochiral ketenes or homochiral aldimines were used. A practical technique for the preparation of manual solid-phase parallel libraries of biologically interesting beta-lactam compounds, using Mukaiyama's salt as dehydrating agent, is also presented. Reactions were easily monitored by FT-IR and gel-phase 13C NMR using conventional equipment.     

Bioactivity and chemical composition of the leaf essential oils of Zanthoxylum rhoifolium and Zanthoxylum setulosum from Monteverde, Costa Rica

The leaf essential oils of Zanthoxylum rhoifolium and Zanthoxylum setulosum (Rutaceae) from Monteverde, Costa Rica have been obtained by hydrodistillation and analyzed by gas chromatography-mass spectrometry. The principal constituents of Z. rhoifolium leaf oil were germacrene D (14.6%), limonene (12.5%), trans-2-hexenal (11.3%), beta-elemene (9.2%), 2-undecanone (9.2%), myrcene (7.9%), bicyclogermacrene (7.5%), and germacrene A (5.2%). The leaf oil of Z. setulosum was composed largely of beta-phellandrene (37.5%), beta-caryophyllene (13.7%), alpha-pinene (11.9%), germacrene D (10.9%), myrcene (5.9%), and nerolidol (5.4%). The essential oils were screened for in-vitro cytotoxic activity against Hep G2, MCF-7, and PC-3 human tumor cell lines; antibacterial activity against Bacillus cereus, Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli; and for Artemia salina (brine shrimp) lethality. Neither Z. rhoifolium nor Z. setulosum leaf oils exhibited cytotoxicity or antibacterial activity. Both oils showed activity against A. salina.     

Oxazolinethiones and oxazolidinethiones for the first copper-catalyzed desulfurative cross-coupling reaction and first sonogashira applications

Cyclic thionocarbamates, namely chiral oxazolidinethiones (OZT) and aromatic oxazolinethiones (OXT), were involved, for the first time, in Sonogashira cross-coupling. A cooperative effect of two different copper (I) species-CuI and CuTC-accounts for this new copper-catalyzed desulfurative carbon-carbon cross-coupling reaction. This cooperative reactivity could also be extended to other copper (I) catalysts.     

Homogeneous Hilbert scheme

Let be a locally noetherian scheme and an -graded -algebra of finite type. We say that is a homogeneous variety over . In this paper we prove that the functor

is representable by an -scheme that is a disjoint union of locally projective schemes over . The proof is very simple, and it only makes use of the theory of graded modules and standard flatness criteria. From this, one obtains an elementary construction (which does not make use of cohomology) of the ordinary Hilbert scheme of a locally projective -scheme.

     

First synthesis of 5-fluoro-(+)-MK7607, its 1-epimer and 6-deoxy derivative

(+)-MK7607 is a patented naturally occurring unsaturated pseudo-carbasugar possessing herbicidal activity. We present herein the first synthesis of the 5-fluorinated analogue (1S, 2S, 3R, 4R)-5-fluoro-6-(hydroxymethyl)cyclohex-5-ene-1,2,3,4-tetrol as well as that of two related compounds, namely its 1-epimer and its 6-deoxy derivative.     

Diamine bis(phenolate) and pendant amine bis(phenolate) ligands: catalytic activity for the room temperature palladium‐catalyzed Suzuki–Miyaura coupling reaction

A series of amine bis(phenolate) ligands bearing aryl substituents of varying steric bulk are reported and characterized using single‐crystal X‐ray diffraction, NMR spectroscopy and high‐resolution mass spectrometry experiments. Palladium complexes derived in situ from these ligands are evaluated as catalysts for the Suzuki–Miyaura coupling of phenylboronic acid and aryl bromides. High conversions are observed for these reactions in methanol solvent at low catalyst loadings (0.01 mol%), short reaction times (30 min) and mild temperatures (30°C). Conversion is observed for a range of substrates, and is found to depend on the nature of the external base and solvent employed. These findings demonstrate the utility of catalysts derived from late transition metal complexes of amine bis(phenolate) ligands, particularly those bearing bulky cumyl substituents. Copyright © 2015 John Wiley & Sons, Ltd.     

Water-trapping of unstable carbocations taking place into the inverted region of the Marcus equation. First experimental and computational evidence

The reaction rates of the water-trapping of unstable 1-norbornyl cations in relation to the rates of their rearrangement (ring contraction) have been experimentally determined. The activation barrier of the rearrangement reactions was calculated with the QST2 method, whereas the Marcus theory was applied to predict the activation barrier of the trapping reaction. All computations in gas phase were performed with the DFT B3LYP/6-31G(d) method, while the PCM model was used for the computation of unspecific solvent effects. The established methodology was able to predict the major product formed in the solvolysis of the corresponding triflate precursors of the studied carbocations. The agreement between experiment and theory supports, for the first time, the interesting conclusion that the very exergonic trapping-reaction of unstable 1-norbornyl cations takes place with relatively high barriers of activation and, hence, into the Marcus inverted region. Additionally, a noteworthy relationship between the free energy of activation for the carbocation rearrangement in gas phase and the length of the rearranging bond in the ground state is reported.     

Signal processing with multicomponent systems based on metal complexes

Molecular-level systems that respond to external stimulation by changing some physical or chemical properties can be viewed as input–output devices and therefore may be useful for processing information. In recent years, several investigations on species capable of mimicking the function of macroscopic wires, switches, connectors, memories, logic gates, and circuits have been reported. The rational basis for this research stems from the fact that in living organisms information is transported, elaborated and stored by molecular or ionic substrates operating in a solution-based environment. Because of their diverse and valuable physico-chemical properties, metal complexes have been extensively used as functional components for the construction of artificial molecular devices capable of processing information. Here we illustrate recent progress, and discuss limitations and perspectives of this research area.