Synthesis of a 1α-C-methyl analogue of 25-hydroxyvitamin D3: interaction with a mutant vitamin D receptor Arg274Leu

Vitamin D₃ analogues have been developed for a mutant vitamin D receptor (VDR), Arg274Leu. The mutant VDR has a mutation at Arg274, which forms an important hydrogen bond with 1α-OH of 1α,25-dihydroxyvitamin D₃ to anchor the ligand tightly in the VDR ligand binding pocket. Stereoselective synthesis of the A-ring part of the novel vitamin D analogue, 2α-(3-hydroxypropyl)-1α-methyl-25-hydroxyvitamin D₃ (4), from d-galactose was accomplished with the key steps of the introduction of the methyl and allyl groups to the chiral building blocks. The new analogue 4 is ca. 7.3-fold more active than the natural hormone 1α,25-dihydroxyvitamin D₃ (1).     

Synthesis of GaN crystal by the reaction of Ga with Li3N in NH3 atmosphere

A novel method to synthesize GaN crystals was studied by the reaction of Ga with Li₃N under NH₃ atmosphere. We have already reported the synthesis technique of GaN by the reaction of Ga₂O₃ with Li₃N. However, the size of GaN crystals obtained by this method was limited to be smaller than several micrometers because of the solid phase reaction. In order to increase the size of GaN crystals, the method using liquid Ga as gallium source was studied for solid–liquid phase reaction. We found that the GaN crystals with the size of more than 100 μm were synthesized at 750 °C for 24 h under NH₃ atmosphere. We propose the possible reaction mechanism as follows. Lithium amide (LiNH₂) is synthesized by the reaction of Li₃N with NH₃ gas and then the crystal growth of GaN occurs by the reaction of Ga with LiNH₂. We found that LiNH₂ is a useful nitrogen source for the GaN synthesis method.     

Sequential Intramolecular Diels–Alder Reaction of 3‐Heteroaryl‐2‐propenylamides of Ethenetricarboxylate

The reaction of 1,1,2‐ethenetricarboxylic acid 1,1‐diethyl ester with E‐3‐(2‐furyl)‐2‐propenylamines under the amide condensation conditions (EDCI/HOBt/Et₃N) on heating at 80–110°C afforded cis‐fused tricyclic compounds, furo[2,3‐f]isoindoles as major product. On the other hand, the reaction with E‐3‐(3‐furyl)‐2‐propenylamines afforded trans‐fused tricyclic compounds predominantly. The formation of amide/[4 + 2] cycloaddition/hydrogen‐shift reactions proceed sequentially. The observed stereoselectivity of the fused rings has been investigated by the density functional theory calculations. The reaction of 1,1,2‐ethenetricarboxylic acid 1,1‐diethyl ester with 3‐(3‐pyridinyl)‐2‐propen‐1‐amine under the amide condensation conditions afforded HOBt‐incorporated 3,4‐trans‐pyrrolidine selectively. The chemoselectivity and stereoselectivity of the reactions with (3‐heteroaryl)‐2‐propen‐1‐amines depend on the nature of heteroarenes.     

Molecular structure of 9,10-bis[bis(4-tert-butylphenyl)methylene)-9,10-dihydroanthracene: A butterfly-shaped Thiele's hydrocarbon derivative

The molecular structure of 9,10-bis[bis(4-tert-butylphenyl)methylene)-9,10-dihydroanthracene, an anthraquinodimethane derivative having four aryl groups on exocyclic methylene positions, was experimentally and theoretically characterized. Single-crystal diffraction study revealed that the title molecule takes a butterfly shape, i.e., two exocyclic carbons rise from the molecular plane, defined by four carbons of central quinoidal ring, by 1.257(3) Å (average). The dihedral angle of the butterfly wing, i.e., the angle between the two annulated benzenes is 137.71(5)°. Characteristic bond alternation was observed for the central quinoidal moiety and the exocyclic double bond. Theoretical study indicated that this butterfly shape is the stable structure. The two optimized structures nearly reproduced the experimentally observed molecular structures, bond distances, and angles.     

Limited slowdown of endocrine-disruptor diffusion in confined fluid lipid membranes

Self-diffusion rates of lipids and trapped bisphenol A (BPA) are determined in various sizes of confined but fluid membranes by high-field-gradient NMR at 600 MHz. Micelles and vesicles of 3- to 400-nm diameters are used as model membranes to get an insight into the molecular diffusion in such soft environments. The slowdown of BPA and lipid motions is leveled off in 100- and 400-nm vesicles, although the hydrodynamic continuum model gives the aggregate motion slowed inversely to the aggregate size. Instead, the limited motion is related to the intra-membrane fluidity.     

Anisotropy of the Raman spectra of nanographite ribbons

A polarized Raman study of nanographite ribbons on a highly oriented pyrolytic graphite substrate is reported. The Raman peak of the nanographite ribbons exhibits an intensity dependence on the light polarization direction relative to the nanographite ribbon axis. This result is due to the quantum confinement of the electrons in the 1D band structure of the nanographite ribbons, combined with the anisotropy of the light absorption in 2D graphite, in agreement with theoretical predictions.