An Unusual Terpene Cyclization Mechanism Involving a Carbon–Carbon Bond Rearrangement

Terpene cyclization reactions are fascinating owing to the precise control of connectivity and stereochemistry during the catalytic process. Cyclooctat‐9‐en‐7‐ol synthase (CotB2) synthesizes an unusual 5‐8‐5 fused‐ring structure with six chiral centers from the universal diterpene precursor, the achiral C₂₀ geranylgeranyl diphosphate substrate. An unusual new mechanism for the exquisite CotB2‐catalyzed cyclization that involves a carbon–carbon backbone rearrangement and three long‐range hydride shifts is proposed, based on a powerful combination of in vivo studies using uniformly ¹³C‐labeled glucose and in vitro reactions of regiospecifically deuterium‐substituted geranylgeranyl diphosphate substrates. This study shows that CotB2 elegantly demonstrates the synthetic virtuosity and stereochemical control that evolution has conferred on terpene synthases.     

Total Synthesis of Ellagitannins through Regioselective Sequential Functionalization of Unprotected Glucose

Short total syntheses of natural glycosides (ellagitannins) were performed through sequential and regioselective functionalization of the hydroxy groups of unprotected glucose. The key reactions are β‐selective glycosidation of a gallic acid derivative by using unprotected glucose as a glycosyl donor and catalyst‐controlled regioselective introduction of a galloyl group into the inherently less reactive hydroxy group of the glucoside.     

Final‐Stage Site‐Selective Acylation for the Total Syntheses of Multifidosides A–C

The first total syntheses of multifidosides A–C have been achieved. The synthetic strategy is characterized by catalytic site‐selective acylation of unprotected glycoside precursors in the final stage of the synthesis. High functional‐group tolerance of the site‐selective acylation, promoted by an organocatalyst, enabled the conventionally difficult molecular transformation in a predictable and reliable manner. An advantage of this strategy is to avoid the risks of undesired side reactions during the removal of the protecting groups at the final stage of the total synthesis.     

Identification of a Conformational Equilibrium That Determines the Efficacy and Functional Selectivity of the μ‐Opioid Receptor

G‐protein‐coupled receptor (GPCR) ligands impart differing degrees of signaling in the G‐protein and arrestin pathways, in phenomena called “biased signaling”. However, the mechanism underlying the biased signaling of GPCRs is still unclear, although crystal structures of GPCRs bound to the G protein or arrestin are available. In this study, we observed the NMR signals from methionine residues of the μ‐opioid receptor (μOR) in the balanced‐ and biased‐ligand‐bound states. We found that the intracellular cavity of μOR exists in an equilibrium between closed and multiple open conformations with coupled conformational changes on the transmembrane helices 3, 5, 6, and 7, and that the population of each open conformation determines the G‐protein‐ and arrestin‐mediated signaling levels in each ligand‐bound state. These findings provide insight into the biased signaling of GPCRs and will be helpful for development of analgesics that stimulate μOR with reduced tolerance and dependence.     

Oxygen induced surface structure of Mo(1 1 0) studied by scanning tunneling microscopy

The oxygen induced surface structures formed on Mo(1 1 0) by oxygen exposure at 1300 K in UHV has been studied by scanning tunneling microscopy (STM). Two kinds of oxygen-adsorbed surface structures are observed. One consists of one-dimensional rows running along or directions at substrate molybdenum lattices, and another shows more complex structure including discrete arrangement of large protrusions and zig-zag alignments of small protrusions. This complex structure is probably a further oxygen-adsorbed structure than the well-known p(2 × 2) structure of 0.3 ML coverage. On the basis of STM image, an atomic model is proposed, where adsorbed oxygen atoms occupy both long-bridge and the quasi-threefold sites of molybdenum lattice (0.4 ML coverage). This structure is presumed to be a transient state during site-conversion with increase of oxygen exposure.     

Ion-pair chromatographic separation of glycoprotein derived oligosaccharides as their 8-aminopyrene-1,3,6-trisulfonic acid derivatives

A reversed-phase ion-pair gradient liquid chromatographic method has been developed for separation of 8-aminopyrene-1,3,6-trisulfonic acid (APTS) labeled oligosaccharides derived from some glycoproteins. This separation mode has high capability for structural recognition of oligosaccharide isomers, which are usually difficult to separate using commonly used partition chromatography. In addition, some glycoprotein-derived complex-type oligosaccharides that have linkage isomers in one lactosamine arm and neuraminic acids existing in fetuin, as well as differences in the numbers of lactosamine branches, are separable using this mode. The ion-pair mode is promising for simple analyses of glycoprotein-derived oligosaccharides that are labeled with APTS.     

Synthesis and fluorescence of 2h‐pyrone derivatives for organic light‐emitting diodes (OLED)

2H‐Pyrone derivatives were synthesized through the reaction of aryl acetyl compounds with ketene dithioacetals in the presence of sodium hydroxide, and they showed very strong fluorescence in the solid state. The light‐emitting region of these 2H‐pyrones is 447‐630 nm in the solid states.     

Lewis acid-catalyzed conjugate addition-cyclization reactions of ethenetricarboxylates with substituted propargyl alcohols: stereoselectivity in the efficient one-pot synthesis of methylenetetrahydrofurans

Oxygen-containing heterocyclic systems are important structures in organic chemistry because of their presence in many biologically active compounds. In this work, a Lewis acid-catalyzed cyclization of ethenetricarboxylate derivatives 1 with substituted propargyl alcohols to give methylenetetrahydrofurans was investigated. Reaction of 1 and gamma-silicon-substituted propargyl alcohols 4 with ZnBr2 at 80-110 degrees C led to (Z)-silicon-substituted products stereoselectively. Reaction of 1 and gamma-ester-substituted propargyl alcohol 7 in the presence of various Lewis acids gave ester-substituted methylenetetrahydrofurans stereoselectively. Interesting Lewis acid dependency on stereoselectivity for the reaction of 7 was found. Reaction of alpha-substituted propargyl alcohols also gave cyclized products.     

Rearrangement of indene skeletons under mild conditions

Isomerization between two isomers of 1,2-disubstituted 3-aminoindenes occurs via the rearrangement of indene frameworks. In contrast to previous rearrangements of indene derivatives, which occur under high-temperature conditions or the irradiation of light, this rearrangement proceeds at room temperature without UV light irradiation. An amino group at the 3-position plays an important role to accelerate the rearrangement under mild conditions.     

Facile synthesis of amine-terminated aromatic polyamide dendrimers via a divergent method

[structure: see text]. A novel, rapid, inexpensive, and highly efficient divergent approach for the synthesis of a 32-amine-terminated G4 polyamide dendrimer has been developed. Each generation dendrimer was successfully obtained by the condensation of the preceding generation dendrimer with the building block and the deprotection with hydrazine in one pot. All the dendrimers were easily purified by precipitation in alkaline water, and the purity was confirmed by NMR, MALDI-TOF mass spectra, and elemental analysis.