Pendant-Type Helicene Oligomers with p-Phenylene Ethynylene Main Chains: Synthesis, Reversible Formation of Ladderlike Bimolecular Aggregates, and Control of Intramolecular and Intermolecular Aggregation

Pendant-type (P)-helicene oligomers with p-phenylene ethynylene main chains up to a tetramer were synthesized by a building block method. The (P)-tetramer reversibly formed a ladderlike bimolecular aggregate upon cooling and disaggregated upon heating in (trifluoromethyl)benzene. Two bis(tetramer)s, in which two (P)-tetramers were connected by hexadecamethylene linkers, were also synthesized. The head-to-tail bis(tetramer) formed an intramolecular aggregate, and the head-to-head bis(tetramer) formed an intermolecular aggregate in toluene. The results suggest the antiparallel aggregation structure of the pendant-type (P)-tetramers. The structure of the linker was proven to be effective in controlling intramolecular and intermolecular aggregations.

The RING finger- and PDZ domain-containing protein PDZRN3 controls localization of the Mg2+ regulator claudin-16 in renal tube epithelial cells

Ion exchange in the renal tubules is fundamental to the maintenance of physiological ion levels. Claudin-16 (CLDN16) regulates the paracellular reabsorption of Mg²⁺ in the thick ascending limb of Henle's loop in the kidney, with dephosphorylation of CLDN16 increasing its intracellular distribution and decreasing paracellular Mg²⁺ permeability. CLDN16 is located in the tight junctions, but the mechanism regulating its localization is unclear. Using yeast two-hybrid systems, we found that CLDN16 binds to PDZRN3, a protein containing both RING-finger and PDZ domains. We also observed that the carboxyl terminus of the cytoplasmic CLDN16 region was required for PDZRN3 binding. PZDRN3 was mainly distributed in the cytosol of rat kidney cells and upon cell treatment with the protein kinase A inhibitor H-89, colocalized with CLDN16. H-89 also increased mono-ubiquitination and the association of CLDN16 with PDZRN3. Mono-ubiquitination levels of a K275A mutant were lower, and its association with PDZRN3 was reduced compared with wild-type (WT) CLDN16 and a K261A mutant, indicating that Lys-275 is the major ubiquitination site. An S217A mutant, a dephosphorylated form of CLDN16, localized to the cytosol along with PDZRN3 and the endosomal marker Rab7. PDZRN3 siRNA increased cell-surface localization of WT CLDN16 in H-89-treated cells or containing the S217A mutant and also suppressed CLDN16 endocytosis. Of note, H-89 decreased paracellular Mg²⁺ flux in WT CLDN16 cells, and PDZRN3 siRNA increased Mg²⁺ flux in the H-89-treated WT CLDN16 and S217A mutant cells. These results suggest that PDZRN3 mediates endocytosis of dephosphorylated CLDN16 and represents an important component of the CLDN16-trafficking machinery in the kidney.

Thieme Chemistry Journals Awardees – Where Are They Now? Rhodium-Catalyzed Synthesis of Unsymmetric Di(heteroaryl) Ethers Using Heteroaryl Exchange Reaction

Unsymmetric di(heteroaryl) ethers were synthesized by the rhodium-catalyzed heteroaryl exchange reaction of heteroaryl aryl ethers and heteroaryl esters at equilibrium. Diverse unsymmetric di(heteroaryl) ethers containing five- and six-membered heteroarenes were obtained. Di(heteroaryl) ethers can be synthesized starting from diaryl ethers, because heteroaryl aryl ethers are obtained by the heteroaryl exchange reaction of diaryl ethers.

Multiple competing pathways for chemical reaction: drastic reaction shortcut for the self-catalytic double-helix formation of helicene oligomers

Competition among multiple pathways in a chemical reaction exhibits notable kinetic phenomena, particularly when amplification by self-catalysis is involved. A pseudoenantiomeric 1 : 1 mixture of an aminomethylene helicene (P)-tetramer and an (M)-pentamer formed enantiomeric hetero-double helices B and C in solution when random coil A was cooled. When a solution of A at 70 °C was directly cooled to 25 °C, the A-to-B reaction was predominant, then B was slowly converted to C over 60 h. The slow conversion in the A-to-B-to-C reaction was due to the formation of the hetero-double helix B, which was an off-pathway intermediate, and the slow B-to-C conversion. In contrast, when a solution of A at 70 °C was snap-cooled to -25 °C before then maintaining the solution at 25 °C, the A-to-C reaction predominated, and the formation of C was complete within 4 h. The reactions involve competition between the self-catalytic A-to-B and A-to-C pathways, where B and C catalyze the A-to-B and A-to-C reactions, respectively. Subtle differences in the initial states generated by thermal pretreatment were amplified by the self-catalytic process, which resulted in a drastic reaction shortcut.