Reactions of 9-alkyl-3-aminocarbazoles with ethyl-3-oxo-butanoate and identification of the products obtained

The reactions in benzene of 9-alkyl-3-aminocarbazoles with ethyl-3-oxobutanoate yielded ethyl-3-[(9-alkyl-9H-carbazol-3-yl)amino]but-2-enoate condensation products or N-(9-ethyl-9H-carbazol-3-yl)-3-oxobutanamide acylation products. The condensation products were cyclized to the corresponding 4,7-dihydro-pyrido[2,3-c]-carbazol-1-ones upon heating in mineral oil at 240-250 degrees C. The structures of the synthesized compounds were investigated by IR, mass spectrometry, (1)H- and (13)C-NMR spectroscopy and MM2 molecular mechanics and AM1 semi-empirical quantum mechanical methods.     

Supramolecular Subphthalocyanine Cage as Catalytic Container for the Functionalization of Fullerenes in Water

Herein we report the first example of a supramolecular cage that works as a catalytic molecular reactor to perform transformations over fullerenes in aqueous medium. Taking advantage of the ability of metallo–organic Pd(II)-subphthalocyanine (SubPc) capsules to form stable host:guest complexes with C₆₀, we have prepared a water-soluble cage that provides a hydrophobic environment for conducting cycloadditions over encapsulated C₆₀, namely, Diels–Alder reactions with anthracene. Indeed, the presence of catalytic amounts of SubPc cage dissolved in water promotes co-encapsulation of insoluble C₆₀ and anthracene substrates, allowing the reaction to occur inside the cavity under mild conditions. The lower stability of the host:guest complex with the resulting C₆₀ cycloadduct facilitates its displacement by pristine C₆₀, which grants catalytic turnover. Moreover, bis-addition compounds are regioselectively formed inside the cage when using excess anthracene.     

The role of fluorine in the stereoselective tandem aza-Michael addition to acrylamide acceptors: an experimental and theoretical mechanistic study

Aza-Michael additions of alpha-amino esters to fluorinated acceptors take place in a highly stereoselective manner, to give partially modified Psi[NHCH2]retropeptides incorporating a hydrolytically stable trifluoroalanine mimic. The reaction mechanism has been investigated experimentally and theoretically, in order to explain the effect of the trifluoromethyl group on the reactivity and the origins of the experimentally observed stereocontrol. The reaction is a two-step process, involving a tandem aza-Michael addition followed by a stereoselective hydrogen transfer. Both steps are base-catalyzed. The high level of stereocontrol is the result of a combination of electrostatic interactions and steric effects.     

Stereocontrolled access to orthogonally protected anti,anti-4-aminopiperidine-3,5-diols through chemoselective reduction of enantiopure beta-lactam cyanohydrins

The cyanosilylation of enantiopure 4-oxoazetidine-2-carbaldehydes with tert-butyldimethylsilyl cyanide was promoted by either molecular sieves or catalytic amount of sodium carbonate to give O-silylated beta-lactam cyanohydrins with good yield and diastereoselectivity. In contrast, Lewis acids did not effectively promote the cyanosilylation under different experimental conditions, and instead hydrocyanation took place affording the corresponding free cyanohydrins in variable yield and selectivity. Starting from beta-lactam cyanohydrin hybrids, two concise, complementary stereocontrolled routes to optically pure orthogonally protected anti,anti-4-amino-3,5-piperidine diols were achieved. Key features of the first approach include chemoselective reductive opening of the beta-lactam ring with LiBH4 to a 3-amino-5-hydroxy pentanenitrile followed by reductive cyclization of a conveniently functionalized cyanomesylate derivative with NaBH4/NiCl2. The second approach involves LiAlH4 reduction of protected anti,anti-4-amino-3,5-dihydroxypiperidin-2-ones, which were easily obtained by chemoselective reduction of the cyano group in the beta-lactam cyanohydrin hybrids with NaBH4/NiCl2 and subsequent intramolecular rearrangement of the resulting amino beta-lactams. Both routes make use of an oxidative N-dearylation with diacetoxyiodobenzene of a 4-methoxyphenylamino group as a common synthetic step. Specifically, the utility of this novel reaction sequence has been demonstrated by the synthesis of fully orthogonally protected sialidase inhibitors.     

I2-Catalyzed enantioselective ring expansion of beta-lactams to gamma-lactams through a novel C3-C4 bond cleavage. Direct entry to protected 3,4-dihydroxypyrrolidin-2-one derivatives

Molecular iodine (10 mol%) efficiently catalyzes the ring expansion of 4-oxoazetidine-2-carbaldehydes in the presence of tert-butyldimethyl cyanide to afford protected 5-cyano-3,4-dihydroxypyrrolidin-2-ones with good yield and high diastereoselectivity, through a novel C3-C4 bond cleavage of the beta-lactam nucleus.     

MUC1 Aptamer-Capped Mesoporous Silica Nanoparticles for Navitoclax Resistance Overcoming in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype. In the last years, navitoclax has emerged as a possible treatment for TNBC. Nevertheless, rapid navitoclax resistance onset has been observed thorough Mcl-1 overexpression. As a strategy to overcome Mcl-1-mediated resistance, herein we present a controlled drug co-delivery system based on mesoporous silica nanoparticles (MSNs) targeted to TNBC cells. The nanocarrier is loaded with navitoclax and the Mcl-1 inhibitor S63845 and capped with a MUC1-targeting aptamer ( apMUC1-MSNs(Nav/S63845) ). The apMUC1-capped nanoparticles effectively target TNBC cell lines and successfully induce apoptosis, overcoming navitoclax resistance. Moreover, navitoclax encapsulation protects platelets against apoptosis. These results point apMUC1-gated MSNs as suitable BH3 mimetics nanocarriers in the targeted treatment of MUC1-expressing TNBC.     

GC-MS Study of Mono- and Bishaloethylphosphonates Related to Schedule 2.B.04 of the Chemical Weapons Convention: The Discovery of a New Intramolecular Halogen Transfer

A new class of compounds, mono- and bis-haloethylphosphonates (HAPs and bisHAPs, respectively), listed in Schedule 2.B.04 of the Chemical Weapons Convention (CWC), has been synthesized and studied by GC-MS with two aims. First, to improve the identification of this type of chemicals by the Organization for the Prohibition of Chemical Weapons, (OPCW). Second, to study the synergistic effect of halogen and silicon atoms in molecules undergoing mass spectrometry. Fragmentation patterns of trimethylsilyl derivatives of HAPs were found to depend on the nature of the halogen atom; this was in agreement with DFT-calculations. The data suggest that a novel intramolecular halogen transfer takes place during the fragmentation process.

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Graphical Abstract ?

     

Topological effects of a rigid chiral spacer on the electronic interactions in donor-acceptor ensembles

Two triads (donor-spacer-acceptor), exTTF-BN-C60 (6) and ZnP-BN-C60 (7), in which electron donors (i.e., exTTF or ZnP) are covalently linked to C60 through a chiral binaphthyl bridge (BN), have been prepared in a multistep synthetic procedure starting from a highly soluble enantiomerically pure binaphthyl building block (1). Unlike other oligomeric bridges, with binaphthyl bridges, the conjugation between the donor and the acceptor units is broken and geometric conformational changes are facilitated. Consequently, distances and electronic interactions between the donor and C60 are drastically changed. Both donor-spacer-acceptor (D-s-A) systems (i.e., 6 and 7) exhibit redox processes that correspond to all three constituent electroactive units, namely, donor, BN, and C60. Appreciable differences were, however, observed when comparing triad 6, in which no significant exTTF-C60 interactions were noted, with D-s-A 7, whose geometry favors donor-acceptor and pi-pi interactions that result in ZnP-C60 electronic communication. This through-space interaction is, for example, reflected in the redox potentials. Excited-state studies, carried out by fluorescence and transient absorption spectroscopy, also support through-space rather than through-bond interactions. Although both triads form the corresponding radical-ion pair, that is, exTTF*+-BN-C60*- and ZnP*+-BN-C60*-, dramatic differences were found in their lifetimes: 165 micros and 730 ns, respectively.     

In situ powder diffraction study of belite sulfoaluminate clinkering

Belite sulfoaluminate (BSA) cements have been proposed as environmentally friendly building materials, as their production may release up to 35% less CO₂ into the atmosphere when compared with ordinary Portland cement fabrication. However, their formation mechanism has not been studied in detail so far. Here, an in situ high‐temperature high‐resolution synchrotron X‐ray powder diffraction study is reported. Two types of BSA clinkers have been characterized, both containing 50–60 wt% C₂S and 20–30 wt% C₄A₃ as main phases. One type is iron‐rich and a second type (with different phase assemblage) is aluminium‐rich. Furthermore, the C₂S phase reacts slowly with water, thus activation of this compound is desirable in order to enhance the mechanical strength development of the resulting cements. To do so, iron‐rich BSA clinkers have been doped with minor amounts of B₂O₃ and Na₂O to promote stabilization of α‐forms of C₂S, which are more reactive with water. The decarbonated raw materials were loaded into Pt tubes and heated to between 973 K and 1673 K, and patterns were collected using a high‐energy synchrotron beam of wavelength λ = 0.30 Å. The thermal stability of Klein's salt in these clinkers has been clarified. Several reactions have been followed: formation and decomposition of Klein's salt, melting of aluminates and ferrite, and polymorphic transformations of dicalcium silicate: ‐C₂S →α‐C₂S. Changes in mineralogical phase assemblages at a given temperature owing to the addition of minor amounts of selected elements have also been determined.