4-Hydroxydibenzyl: a novel metabolite from the human gut microbiota after consuming resveratrol.

Resveratrol (RSV) was known to be metabolised by the gut microbiota to dihydroresveratrol, lunularin (LUNU), and (or) 3,4'-dihydroxy-trans-stilbene (DHST). We describe here for the first time that LUNU can be further dehydroxylated, but only at the 3-position, to yield 4-hydroxydibenzyl, a novel metabolite found in human urine after RSV intake in 41 out of 59 healthy participants. In contrast, DHST was not further dehydroxylated, and thus, 4-hydroxy-trans-stilbene was not detected as a gut microbial metabolite of RSV. Faecal in vitro incubations confirmed the in vivo results.

Homo and heteroassembly of amide-based [2]rotaxanes using α,α'-dimethyl-p-xylylenediamines.

The formation of [2]rotaxanes via a fumaramide-templated clipping reaction using α,α'-dimethyl-p-xylylenediamines is described. This process selectively affords two out of seven possible interlocked isomers due to a noticeable effect of the methyl groups on the in/out disposition of the amide CO groups.

Light-responsive peptide [2]rotaxanes as gatekeepers of mechanised nanocontainers.

Novel mechanized silica nanoparticles incorporating a peptide-based molecular shuttle as a photo-responsive interlocked gatekeeper of nanocontainers are described including the uptake and delivery studies of a model cargo.

On the mechanism of conversion of N-acyl-4-acyloxy-beta-lactams into 2-substituted 1,3-oxazin-6-ones. Can a low-barrier transition state be antiaromatic?

The mechanism of the conversion of N-acyl-4-acyloxy-beta-lactams into 1,3-oxazin-6-ones has been investigated using ab initio and density functional theories. It has been found that two pseudopericyclic reactions are involved in the whole process. The first key reaction is a retro-[4-exo-dig] cyclization instead of a thermal conrotatory electrocyclic ring opening. Magnetic characterization of the corresponding transition structure shows antiaromatic character, despite the low activation energy associated with this process. The second step is very exothermic and has no activation barrier. It corresponds to another pseudopericyclic reaction instead of a six-electron disrotatory electrocyclization. These results confirm that there is no correlation between aromaticity and pseudopericyclic reactions. In contrast, thermal-symmetry-allowed pericyclic reactions are always aromatic. Therefore, magnetic analysis of the corresponding transition structures constitutes a useful tool to distinguish between both kinds of processes.

New stereoselective intramolecular

Efficient 1,4-asymmetric induction has been achieved in the highly stereocontrolled intramolecular [2 + 2] cycloadditions between ketenimines and imines, leading to 1,2-dihydroazeto[2, 1-b]quinazolines. The chiral methine carbon adjacent to the iminic nitrogen controls the exclusive formation of the cycloadducts with relative trans configuration at C2 and C8. The stepwise mechanistic model, based on theoretical calculations, fully supports the stereochemical outcome of these cycloadditions.

Highly efficient induction of chirality in intramolecular

Highly stereocontrolled, intramolecular [2 + 2] cycloadditions between ketenimines and imines leading to 1,2-dihydroazeto[2, 1-b]quinazolines have been achieved. The source of stereocontrol is a chiral carbon atom adjacent either to the iminic carbon or nitrogen atom. In the first case, the stereocontrol stems from the preference for the axial conformer in the first transition structure. In the second case, the origin of the stereocontrol lies on the two-electron stabilizing interaction between the C-C bond being formed and the sigma orbital corresponding to the polar C-X bond, X being an electronegative atom. These models can be extended to other related systems for predicting the stereochemical outcome in this intramolecular reaction.

Conversion of N-acyl-4-acyloxy-beta-lactams into 1,3-oxazin-6-ones: two consecutive pseudopericyclic processes

N-Acyl-4-acyloxy-beta-lactams are converted into 1,3-oxazin-6-ones under basic conditions. This transformation is believed to proceed via N-acylazetones, which rearrange to the final products by a sequence of two electrocyclic processes. The calculated (RHF and B3LYP) transition structures of both concerted reactions are shown to present characteristic pseudopericyclic orbital topologies.

Guanidinium-based potentiometric SO2 gas sensor.

An SO2 gas sensor was developed by using a hydrogen sulfite-selective electrode positioned behind a gas-permeable membrane (GPM). The hydrogen sulfite-selective electrode was prepared by incorporating a multicyclic guanidinium ionophore in a plasticized poly(vinyl chloride) membrane. This gas sensor presents important advantages over the conventional Severinghaus-type SO2 gas sensor that contains a pH electrode immersed in an internal solution behind the GPM. The Severinghaus gas sensor suffers interferences from weak acids that can cross the GPM as gases and change the pH of the internal solution. In contrast, in the proposed sensor, the excellent selectivity of the HSO3- electrode and the ability of the GPM to discriminate gaseous from nongaseous species combine to generate the most selective potentiometric SO2 gas sensor reported to date.

Salicylate-selective electrode based on a biomimetic guanidinium ionophore.

A biomimetic strategy was employed in the development of oxoanion-selective ionophores containing the guanidinium functional group. These ionophores mimic the selective interaction observed between arginine residues of proteins and oxoanions. In previous work, it was demonstrated that a structurally rigid guanidinium ionophore exhibited excellent hydrogen sulfite selectivity (Anal. Chem. 1994, 66, 3188-3192). Herein, we describe guanidinium-containing ionophores that are selective for the oxoanion salicylate. The ability to rationally design anion-selective electrodes through this biomimetic strategy, and to both alter selectivity and improve response characteristics through structural changes to the ionophore, has been demonstrated. (1)H-NMR complexation and modeling studies were used to examine and correlate the selectivity observed with the structure of the guanidinium compounds.