Mild and Efficient Chemoselective Synthesis of Acetals and Geminal Diacetates (Acylals) from Aldehydes using Lanthanum(III) Nitrate Hexahydrate

A mild and efficient chemoselective method has been developed for the preparation of acetals and gem‐diacetates in good to excellent yields through a reaction of aldehydes with ethlyleneglycol or acetic anhydride using catalytic amounts of lanthanum(III) nitrate hexahydrate as a catalyst under solvent‐free conditions.     

Novel Indole-Pyrazine Alkaloid: Synthesis,Characterization, and Crystal Structure

Crystallography Reports - A heterocyclic molecule of a novel class with a multiple ring system has been synthesized using a new and simple strategy and acetic acid as catalyst. The structure of the...     

A new piecewise exponential estimator of a survival function

In 1983, Kitchin, Langberg and Proschan introduced a piecewise exponential estimator (PEXE) of a survival function for censored data that is undefined beyond the last observation. We propose a new PEXE that provides an exponential tail with a hazard rate determined by a novel nonparametric consideration.     

Allosteric Inhibition of the SARS-CoV-2 Main Protease: Insights from Mass Spectrometry Based Assays**

The SARS-CoV-2 main protease (M^pro) cleaves along the two viral polypeptides to release non-structural proteins required for viral replication. M^Pro is an attractive target for antiviral therapies to combat the coronavirus-2019 disease. Here, we used native mass spectrometry to characterize the functional unit of M^pro. Analysis of the monomer/dimer equilibria reveals a dissociation constant of K_d=0.14±0.03 μM, indicating M^Pro has a strong preference to dimerize in solution. We characterized substrate turnover rates by following temporal changes in the enzyme-substrate complexes, and screened small molecules, that bind distant from the active site, for their ability to modulate activity. These compounds, including one proposed to disrupt the dimer, slow the rate of substrate processing by ≈35 %. This information, together with analysis of the x-ray crystal structures, provides a starting point for the development of more potent molecules that allosterically regulate M^Pro activity.     

Diels-alder reactions with 2-(Arylsulfinyl)-1,4-benzoquinones: effect of aryl substitution on reactivity, chemoselectivity, and pi-facial diastereoselectivity

Diels-Alder reactions of (SS)-2-(2'-methoxynaphthylsulfinyl)-1, 4-benzoquinone (1b), 2-(p-methoxyphenylsulfinyl)-1,4-benzoquinone (1c), and 2-(p-nitrophenylsulfinyl)-1,4-benzoquinone (1d) with cyclopentadiene are reported. These cycloadditions allowed the highly chemo- and stereoselective formation of both diastereoisomeric endo-adducts resulting from reaction on the unsubstituted double bond C(5)-C(6) of quinones working under thermal and Eu(fod)(3)- or BF(3).OEt(2)-catalyzed conditions. The synthesis of endo-adduct [4aS,5S,8R,8aR,SS]-9d resulting from cycloaddition on the substituted C(2)-C(3) double bond was achieved in a chemo- and diastereoselective way from quinone 1d in the presence of ZnBr(2). The reactivity and selectivity of the process proved to be dependent on the electron density of the arylsulfinyl group.     

Time domain investigation on vibrational dephasing and spectral diffusion in CO-doped solid N2

Infrared picosecond accumulated photon echo experiments have been performed for the first time, using the Orsay Free Electron Laser, on the v = 0-->v = 1 transition of CO in solid nitrogen. The vibrational dephasing time is found to be exceptionally long ( T2>/=120 ns) at low temperature. The analysis of the observed spectral diffusion leads one to assume different energy transfer mechanisms depending on the CO concentration.