Chemistry of the Heterotriquinanes and Heterotriquinacenes

Triquinanes are tricyclic hydrocarbons that have fused cyclopentane rings. Although there are linear and angular triquinanes that are doubly fused, this Account focuses exclusively on the ‘triquinacane’, or triply fused structure with a heteroatom (nitrogen or oxygen) on the C 3v symmetry axis. Azatriquinane- and oxatriquinane-based species tend to show remarkable and often unexpected chemistry, and have variously comprised the most basic trialkyl amine, a superbasic proton chelate, trigonal pyramidal ligand platforms, novel calixiform hosts, aromatic hemispheres of hetero-C20 fullerenes, cocrystallizing agents for eliminating rotational disorder in fullerene crystals, the first water-stable, chromatographable trialkyloxonium species, the first isolable allylic oxonium species, world-record C–O bond lengths, rapid SN2 reaction at a tertiary center, and R4O2+ (oxadionium) species.1 Introduction2 Azatriquinane3 Azatriquinacene4 Aromatic Azatriquinacene-Based Systems5 Oxatriquinane6 Tetravalent Oxygen7 Oxatriquinacene8 The Future

Esterification of Alginate with Alkyl Bromides of Different Carbon Chain Lengths via the Bimolecular Nucleophilic Substitution Reaction: Synthesis, Characterization, and Controlled Release Performance

To extend the alginate applicability for the sustained release of hydrophobic medicine in drug delivery systems, the alkyl alginate ester derivative (AAD), including hexyl alginate ester derivative (HAD), octyl alginate ester derivative (OAD), decyl alginate ester derivative (DAD), and lauryl alginate ester derivative (LAD), were synthesized using the alkyl bromides with different lengths of carbon chain as the hydrophobic modifiers under homogeneous conditions via the bimolecular nucleophilic substitution (SN2) reaction. Experimental results revealed that the successful grafting of the hydrophobic alkyl groups onto the alginate molecular backbone via the SN2 reaction had weakened and destroyed the intramolecular hydrogen bonds, thus enhancing the molecular flexibility of the alginate, which endowed the AAD with a good amphiphilic property and a critical aggregation concentration (CAC) of 0.48~0.0068 g/L. Therefore, the resultant AAD could form stable spherical self-aggregated micelles with the average hydrodynamic diameter of 285.3~180.5 nm and zeta potential at approximately −44.8~−34.4 mV due to the intra or intermolecular hydrophobic associations. With the increase of the carbon chain length of the hydrophobic side groups, the AAD was more prone to self-aggregation, and therefore was able to achieve the loading and sustained release of hydrophobic ibuprofen. Additionally, the swelling and degradation of AAD microcapsules and the diffusion of the loaded drug jointly controlled the release rate of ibuprofen. Meanwhile, the AAD also displayed low cytotoxicity to the murine macrophage RAW264.7 cells. Thanks to the good amphiphilic property, colloidal interface activity, hydrophobic drug-loading performance, and cytocompatibility, the synthesized AAD exhibited a great potential for the development of hydrophobic pharmaceutical formulations.

A water-soluble naphthalenediimide-containing hexacationic cage

A water-soluble cage containing three naphthalenediimide (NDI) units was synthesized in a one-pot manner without chromatographic purification, during which six irreversible C−N bonds formed simultaneously via SN2 reaction. The cage...

Facilitated inversion complicates the stereodynamics of an SN2 reaction at nitrogen center

Multiple-inversion, the analogue of the double-inversion pathway recently revealed for SN2@C, is the key mechanism in SN2 at N center undermining stereospecificity.

Diastereopure Synthesis of Novel Cyclohexane-Ring-Based Constrained Lanthionine and α-Methyllanthionine through an SN2 Reaction with a β-Bromoalanine as a Key Step

Here we report the diastereopure synthesis of a novel protected lanthionine derivative substituted with a cyclohexane ring as well as the diastereopure synthesis of an α-methyllanthionine derivative. By starting from enantiopure α,β-cyclohexane-substituted cystine, or α-methylcysteine, we designed a straightforward route that permits the preparation of orthogonally protected modified lanthionines in diastereopure form. The key step of the methodology is the formation of a thioether bond through the use of an β-bromoalanine derivative. The strategy developed should be valuable in the preparation of a wide range of modified constrained lanthionines that might be finally attached to a peptide sequence, which would be especially useful in the syntheses of novel lantibiotics.