Photoinduced selective hydrophosphinylation of allylic compounds with diphenylphosphine oxide leading to γ-functionalized P-ligand precursors

A series of bifunctional phosphine compounds promising as γ-functionalized phosphine ligand precursors are conveniently synthesized by the radical addition of diphenylphosphine oxide (Ph₂P(O)H) to allylic compounds under photoirradiation. The photoinduced addition proceeds regioselectively in an anti-Markovnikov manner, and phosphines having hydroxy, alkoxy, aryloxy, acyloxy, and thio groups at the γ-position can be prepared by simple operation. Interestingly, novel continuous addition of Ph₂P(O)H to two molecules of allylic ethers and related compounds is also observed, although their yields are moderate. The substituent and steric effects of the allylic substituents on the radical addition are discussed in detail.

     

Small Figure-Eight Luminophores: Double-Twisted Tethered Cyclic Binaphthyls Boost Circularly Polarized Luminescence

Double-twisted cyclic binaphthyls, in which two naphthalenes are tethered by -O(CH₂)_nO- linkage (n=1–3), have been synthesized. X-ray analyses and DFT calculations revealed a tightly constrained stereogenic figure-eight geometry. Tethering of two naphthalenes by short linkage forces a small dihedral angle, and the cyclic binaphthyls with short tether (n=1, 2) exhibit remarkable boosting of the g_lum value (1.0–1.6×10⁻²) in circularly polarized luminescence (CPL) and unusual g_lum/g_abs ratios (0.93–1.3). These experimental high |g_lum| values are in accord with the results of excited state TD-DFT calculations, which show transannular interactions and that consequent extensive delocalization occurs throughout the figure-eight π-core. As a result, the present figure-eight luminophore promote the elongation of the magnetic transition dipole moment that results in significant increases in g_lum values.     

Synthesis of the Core Oligosaccharides of Lipooligosaccharides from Campylobacter jejuni: A Putative Cause of Guillain–Barré Syndrome

The chemical synthesis of the highly branched core oligosaccharides of lipooligosaccharides (LOSs) found in Campylobacter jejuni, which causes Guillain–Barré syndrome by a preceding infection, is described. The target LOS mimics, consisting of eight or nine monosaccharides, were classified into three groups as key building blocks: ganglioside-core tetra-/pentasaccharides (GM1-/GD1a-like), l -glycero-d -manno-heptose-containing trisaccharides, and 3-deoxy-d -manno-2-octulosonic acid (KDO) residues. These synthetic fragments were obtained from commercially available monosaccharides. Less obtainable l -glycero-d -manno-heptose and KDO residues, as key components of the LOSs, were synthesized from p-methoxyphenyl d -mannoside and di-O-isopropylidene-protected d -mannose, respectively. The synthesis of α-KDO glycoside, as one of the most difficult stereocontrolled glycosidic constructions, was achieved by treating a 2,3-ene derivative of KDO with phenylselenyl trifluoromethanesulfonate as a suitable α-directing reagent. All synthetic blocks were constructed through a convergent synthetic route, which resulted in the first synthesis of structurally challenging LOS core glycans containing ganglioside GM1 and GD1a-core sequences.     

Photoalignmentability of silsesquioxane-containing citraconimide and its solvent-induced surface enrichment in PMMA matrix

Photo-reactive polymer of silsesquioxane-containing citraconimide (SQ-CI) was synthesised and evaluated as a photoalignment layer for polymerisable liquid crystals (PLC). A generation mechanism of the anisotropy by the linearly polarised ultraviolet light was discussed by comparing optical retardation of SQ-CI with theoretical calculations using density functional theory. In addition, the SQ-CI and poly(methyl methacrylate) were blended for a model of unification of photoalignment layer and protection layer in liquid crystal display. The orientation of PLC on the blend film was dominated by the solvent used for the sample preparation of PMMA/SQ-CI blend. We found that the SQ-CI was enriched at surface of the blend film prepared from the ?-butyrolactone solution, while not in the case of the film prepared from cyclopentanone solution. The surface enrichment in the film prepared from ?-butyrolactone solution does not follow the conventional mechanism which is that the lower surface free energy component segregates to the blend surface, because the surface free energy of SQ-CI is higher than that of PMMA. Based on the result of solvent-annealing effect and photoalignmentability, we concluded that the mechanism of surface enrichment was explained due to the difference of affinity between the polymer and the solvent.     

Synthesis of 4′-substituted 2′-deoxy-4′-thiocytidines and its evaluation for antineoplastic and antiviral activities

4′-Azido- (7), 4′-C-fluoromethyl- (8) 4′-C-ethynyl- (9) and 4′-C-cyano- (10) 2′-deoxy-4′-thiocytidines have been synthesized. In this study, it was found that the isolated yield of 4′-thiouracil nucleoside 13 in a Lewis acid-promoted Vorbrüggen-type glycosidation utilizing 12 was better than that of the electrophilic glycosidation reaction between silylated uracil and 11. This improved result prompted us to perform the glycosidation utilizing 36 and 43 for the synthesis of 37 and 44. Introduction of the azido group was carried out by nucleophilic substitution in the 4′-benzoyloxy derivative 22a. On the other hand, 9 and 10 were synthesized by way of the chemical manipulation of the hydroxymethyl group at the 4′-position of 46.Evaluation of the antineoplastic activity of 2 and 7–10 against human B-cell (CCRF-SB) and T-cell leukemia (Molt-4) cell lines revealed that 4′-azido- (7) and 4′-C-fluoromethyl- (8) derivatives exhibited cytotoxic activity whereas no cytotoxicity was observed in the 4′-C-ethynyl- (9) and 4′-C-cyano- (10) derivatives as well as the parent compound 2. Compound 7 was also found to possess promising antiviral activity against VZV and HSV-1 without any cytotoxity against HEL host cells. It is noteworthy that 7 exhibited potent inhibitory activities against the thymidine kinase-deficient (TK^?) mutant of VZV and HSV-1.     

Unprecedented Sequence Control and Sequence-Driven Properties in a Series of AB-Alternating Copolymers Consisting Solely of Acrylamide Units

Herein, we report a method to synthesize a series of alternating copolymers that consist exclusively of acrylamide units. Crucial to realizing this polymer synthesis is the design of a divinyl monomer that contains acrylate and acrylamide moieties connected by two activated ester bonds. This design, which is based on the reactivity ratio of the embedded vinyl groups, allows a “selective” cyclopolymerization, wherein the intramolecular and intermolecular propagation are repeated alternately under dilute conditions. The addition of an amine to the resulting cyclopolymers afforded two different acryl amide units, i.e., an amine-substituted acryl amide and a 2-hydroxy-ethyl-substituted acryl amide in alternating sequence. Using this method, we could furnish ten types of alternating copolymers; some of these exhibit unique properties in solution and in the bulk, which are different from those of the corresponding random copolymers, and we attributed the differences to the alternating sequence.     

Novel protection of 1,2-diol for trans-dihydroxycyclopentene ring construction by the CH insertion of alkylidene carbene: Formal total synthesis of (+)-trehazolin

The chiral vicinal diol was protected as 6-methylene-1,4-dioxepane to construct a cyclopentene ring by the CH insertion of alkylidene carbene. The removal of the protecting group was achieved in a few steps, affording the corresponding diol in a reasonable yield. Using these reactions, the known synthetic intermediate for (+)-trehazolin was synthesized from d-diethyl tartrate. In addition, a short route to the intermediate from a d-mannitol derivative was described.     

Enantioselective total synthesis of heliespirone B

The first enantiocontrolled total synthesis of heliespirone B has been accomplished employing a biomimetic intramolecular oxy-Michael reaction followed by the regio- and diastereoselective reduction of the carbonyl function as key steps.