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The article explains a new approach for the synthesis of the bicyclic octosyl nucleoside derivative of the enzomycins, the antifungal natural products that belong to the complex peptidyl nucleoside family of antibiotics. The methodology is shown to be much more flexible and accurate, as compared to the conventional approaches.

Efficient generation of hydrogen from renewable resources requires development of catalysts that avoid deep wells and high barriers. Information about the energy landscape for H2 production can be obtained by chemical characterization of catalytic intermediates, but few have been observed to date. We have isolated and characterized a key intermediate in 2e- + 2H+ → H2 catalysis. This intermediate, obtained by treatment of Cp*Rh(bpy) (Cp*, η5-pentamethylcyclopentadienyl; bpy, κ2-2,2'-bipyridyl) with acid, is not a hydride species but rather, bears [η4-Cp*H] as a ligand. Delivery of a second proton to this species leads to evolution of H2 and reformation of η5-Cp* bound to rhodium(III). With suitable choices of acids and bases, the Cp*Rh(bpy) complex catalyzes facile and reversible interconversion of H+ and H2. [ABSTRACT FROM AUTHOR]

Derivatives of the fully twisted bicyclic amide 7-hypoquinuclidone are synthesized using a Schmidt--Aubé reaction. Their structures were unambiguously confirmed by X-ray diffraction analysis and extensive spectroscopic characterization. Furthermore, the stability and chemical reactivity of these anti-Bredt amides are investigated. 7-Hypoquinuclidonium tetrafluoroborate is shown to decompose to a unique nitrogen bound amide--BF3 complex of 7-hypoquinuclidone under anhydrous conditions and to react instantaneously with water making it one of the most reactive amides known to date. [ABSTRACT FROM AUTHOR]

A precursor to a new tridentate LX2type ligand,bis(thiophenol)pyridine((SNS)H2= (2-C6H4SH)2-2,6-C5H3N), was prepared. Bis(thiophenolate)pyridinecomplexes of Ti, Zr, and Ta having dialkylamido coligands were synthesizedand structurally characterized. The zirconium complex (SNS)Zr(NMe2)2(4) displays C2symmetry in the solid state, unlike a related bis(phenolate)pyridinecompound, Cs-symmetric(ONO)Ti(NMe2)2. This change is likely the resultof strain about the sulfur atom in the six-membered chelate with longermetal–sulfur and carbon–sulfur bonds. Solid-state structuresof tantalum complexes (SNS)Ta(NMe2)3(5) and (SNS)TaCl(NEt2)2(6) also display pronounced C2twistingof the SNS ligand. 1D and 2D NMR experiments show that 5is fluxional, with rotation about the Ta–N(amide) bonds occurringon the NMR time scale that interchange the equatorial amide methylgroups (ΔG⧧393= 25.0(3) kcal/mol). The fluxional behavior of 6in solution was also studied by variable-temperature 1H NMR. Observation of separate signals for the diastereotopicprotons of the methylene unit of the diethylamide indicates that thecomplex remains locked on the NMR time scale in one diastereomericconformation at temperatures below −50 °C, fast rotationabout the equatorial amide Ta–N bonds occurs at higher temperature(ΔG⧧393= 13.4(3) kcal/mol), and exchange of diastereomeric methyleneprotons occurs via inversion at Ta that interconverts antipodes (ΔG⧧393≈14(1) kcal/mol). [ABSTRACT FROM AUTHOR]

Though Lewis acids (LAs) have been shown to have profound effects on carbon dioxide (CO 2 ) reduction catalysis, the underlying cause of the improved reactivity remains unclear. Herein, we report a well-defined molecular system for probing the role of LA additives in the reduction of CO 2 to carbon monoxide (CO) and water. Mo(0) CO 2 complex (2) forms adducts with a series of LAs, demonstrating CO 2 activation that correlates linearly with the strength of the LA. Protons induce C-O cleavage of these LA adducts, in contrast to the CO 2 displacement primarily observed in the absence of LA. CO 2 cleavage shows dependence on both bond activation and the residence time of the bound small molecule, demonstrating the influence of both kinetic and thermodynamic factors on promoting productive CO 2 reduction chemistry.

[reaction: see text] We have previously described a model of paclitaxel-microtubule binding that led to the prediction that analogues of paclitaxel lacking any D ring could stabilize microtubules as well as paclitaxel if the substituent present at C4 did not have unfavorable steric interactions with the binding pocket. We report the synthesis of a 4-methyl paclitaxel analogue, compound 1, which bears this prediction out. Compound 1 is as potent as paclitaxel at microtubule stabilization in vitro; however, it has only about one-four-hundredth the cytotoxicity of paclitaxel.