Synthesis of 1,2-dihydroxyindolizidines from 1-(2-pyridyl)-2-propen-1-ol

1-(2-Pyridyl)-2-propen-1-ol, obtained by vinylation of commercially available picolinaldehyde, resulted a good starting material for the synthesis of the indolizidine skeleton. In particular, a simple process involving bromination, reduction, and nucleophilic substitution (via elimination and addition) allowed an easy conversion of the starting material into (±)-lentiginosine in ~27% overall yield.     

Rapid quantification of total genomic DNA methylation degree by short-end injection capillary zone electrophoresis

We propose a new capillary zone electrophoresis method applying short-end injection technique for the fast evaluation of methylcystosine/total cytosine ratio after acidic DNA hydrolysis. By short-end injection and by using a 100 mmol/l Tris solution titrated with 1 mol/l phosphoric acid to pH 3.75 as background electrolyte, cytosine and methylcytosine were separated with a good resolution in less than 1.5 min. Stepwise multiple linear regression with DNA methylation degree as the dependent variable and age, cysteine, homocysteine and methionine as independent variables, showed a negative association with age and that total cysteine is the most important determinant of DNA methylation.     

New reactivity of 1-(2-pyridyl)-2-propen-1-ol with nitro derivatives

1-(2-Pyridyl)-2-propen-1-ol showed an unprecedented reactivity behaving as Hantzsch ester 1,4-dihydropyridine mimic for the metal-free reduction of the nitro group of electron-deficient aromatic and heteroaromatic nitro compounds to the corresponding amino function. The redox mechanism is part of a domino process involving a direct trapping of the amino derivatives through aza-Michael addition to the vinyl ketone intermediate leading to the one-pot formation of new functionalised aminoacylpyridines.     

Forging C−S Bonds on the Azetidine Ring by Continuous Flow Photochemical Addition of Thiols and Disulfides to Azetines

A strategy for anti-Markovnikov hydroalkyl/aryl thiolation and disulfidation of 2-azetines under continuous flow conditions has been developed. Thiyl radicals are generated from thiols or disulfides and subsequently propagate into the azetine unsaturation to forge the C−S bond and shape a secondary radical intermediate. This carbon-centered radical chain transfers to another thiol via hydrogen atom transfer (HAT) or another disulfide to regenerate the key thiyl radical intermediates. The use of flow technology ensures efficient irradiation of the reaction mixture leading to extremely fast, robust, and scalable protocols. Furthermore, ethyl acetate was adopted as an environmentally responsible solvent.     

Stereochemistry of cyclopentane derivatives from (2,3)J(CH) dependence on dihedral angle (theta H--C--C--X)

The (2,3)J(CH) dependence on dihedral angle (theta H--C--C--X) for cyclopentane derivatives was investigated. We observed that the combined use of experimentally obtained (2,3)J(CH) values and the theoretically determined dihedral angles between the corresponding nuclei can be used to infer the relative stereochemistry of the ring substituents in cyclopentane derivatives. There is a good correlation between the magnitude of (3)J(CH) and the dihedral angle between the hydrogen and the coupled carbon (R2 = 0.88).     

Nanostructure of calcium alginate aerogels obtained from multistep solvent exchange route

Ca-alginate materials were studied by small-angle X-ray scattering (SAXS) at different steps of conversion from gel to aerogel in order to determine the relation between the polymer organization at the nanoscale in the gels and the final dry aerogel. In all cases, i.e. before and after the different exchanges of solvents and after the formation of the aerogel, the SAXS patterns exhibit an asymptotic behavior at low q values (in the experimental q range 7x10(-3) up to 2.10(-2) A(-1)) close to I(q) approximately q(-1), indicative of randomly oriented rod-like scattering objects. The evolution of the diameter of such rod-like objects was thus deduced from the maxima observed on Kratky plots, i.e. I(q) q2 vs q. The results are in perfect agreement qualitatively (rod-like anisometry type of the scattering objects) and quantitatively (diameter of the rods) with direct SEM observations of the morphology of aerogels and with the results of N2 adsorption on the aerogel. This is evidence that in the chosen experimental processing conditions, the morphology of the aerogel depends on the morphology of pre-existing objects within the gel, i.e. that the structure of the aerogel provides a correct image of the structure of the parent gel.     

Molecular simulation of adsorption and intrusion in nanopores

This paper reports Monte Carlo simulations of the adsorption or intrusion in cylindrical silica nanopores. All the pores are opened at both ends towards an external bulk reservoir, so that they mimic real materials for which the confined fluid is always in contact with the external phase. This realistic model allows us to discuss the nature of the filling and emptying mechanisms. The adsorption corresponds to the metastable nucleation of the liquid phase, starting from a partially filled pore (a molecular thick film adsorbed at the pore surface). On the other hand, the desorption occurs through the displacement at equilibrium of a gas/liquid hemispherical interface (concave meniscus) along the pore axis. The intrusion of the non-wetting fluid proceeds through the invasion in the pore of the liquid/gas interface (convex meniscus), while the extrusion consists of the nucleation of the gas phase within the pore. In the case of adsorption, our simulation data are used to discuss the validity of the modified Kelvin equation (which is corrected for both the film adsorbed at the pore surface and the curvature effect on the gas/liquid surface tension).     

Rotational barriers of biphenyls having heavy heteroatoms as ortho-substituents: experimental and theoretical determination of steric effects

The free energies of activation for the aryl-aryl rotation of 17 biphenyl derivatives, bearing a heavy heteroatom (S, Se, Te, P, Si, Sn) as ortho substituent, have been measured by variable temperature NMR. These numbers, so called B values, represent a meaningful measure of the steric hindrance exerted by the selected substituents. DFT computations match quite satisfactorily the experimental barriers and the ground state geometries as well (determined, in two cases, by X-ray diffraction). The present values extend the available list of B values and thus provide an enlarged basis for the compilation of the space requirements of standard substituents, based solely on experimental determinations.