Absolute stereochemistries and total synthesis of (+)-arisugacins A and B, potent, orally bioactive and selective inhibitors of acetylcholinesterase

In the current studies, we used the Kakisawa-Kashman modification of the Mosher NMR method to determine the complete absolute stereochemistry of arisugacins. We also report the convergent total synthesis of (+)-arisugacins A and B by a sequence including (i) ruthenium complex-catalyzed asymmetric reduction of the cyclohexenone derivative; (ii) stereoselective construction of the arisugacin skeleton by a Knoevenagel-type reaction of an α,β-unsaturated aldehyde derivative with production of a 4-hydroxy-2-pyrone derivative as a key reaction; and (iii) stereoselective dihydroxylation to give the diol derivative, followed by deoxygenation. Accordingly, we defined the absolute structures of arisugacins A and B as 4a-(R),6a-(R),12a-(R), and 12b-(S). Finally, we characterized the bioactivities of the synthetic intermediates to understand the structure-activity relationships of the arisugacins.     

Perturbation analysis for the rotational spectrum of the NiBr radical in the X2Pi3/2 and A2Delta5/2 states

The millimeter- and submillimeter-wave spectra of the NiBr radical in the X (2)Pi(3/2) and A (2)Delta(5/2) states were observed by a source-modulated microwave spectrometer. The NiBr radical was generated in a dc glow discharge through the mixture of Br(2) vapor and Ar gas by the sputtering reaction with a Ni cathode. Observed transition frequencies were independently analyzed for both electronic states using a standard polynomial expression of a Hund's case (c) approximation. Anomalous behavior of the effective molecular constants in the X (2)Pi(3/2) state was interpreted as the result of the perturbation between the X (2)Pi(3/2) and A (2)Delta(5/2) states. The deperturbed molecular constants were derived using a simplified supermultiplet Hamiltonian including the interaction terms between the two electronic states.     

Chiral self-dimerization of vanadium complexes on a SiO2 surface: the first heterogeneous catalyst for asymmetric 2-naphthol coupling

The self-dimerized chiral assembly of vanadium-Schiff-base complexes was found to occur on a SiO2 surface and to be the first heterogeneous catalyst for the asymmetric oxidative coupling of 2-naphthol with 100% selectivity and 90% enantioselectivity.     

An approach to analysis of pigment release from microcapsules with size distribution

We have studied the release curve for microcapsules with size distribution. On the basis of an analogy to the relaxation phenomena with multiple characteristic times, we propose a stretched exponential release curve for the system with size distribution and relate the release curve to the size distribution function of the microcapsule. This method was successfully applied to the transfer of azo-pigments from inner medium of dioctyl phthalate to dispersing medium of methanol through poly(ureaurethane) microcapsule membrane.     

Deuterium substitution effect on proton relaxation times as a direct means for elucidating molecular interaction in solution. An application to 2′,3′-isopropylideneadenosine

Proton T₁ measurement with the Fourier transform method combined with quenching of dipolar coupling through selective deuterium substitution is shown to be a useful method for elucidating intra- and intermolecular interactions in solution, with 2′,3′-isopropylideneadenosine as an example. Average distances between H-8 and ribose protons are determine in combination with carbon-13 T₁ measurement. The method is compared with the nuclear Overhauser effect.     

Diastereoselective allylations of allyl-propargyl hybrid cations: synthesis of conjugated 1,5-dien-7-yne frameworks bearing C(4)-stereogenic centers

[reaction: see text] Chiral C(4)-substituted (E)- or (Z)-1-alkynyl-1-trimethylsilyloxy-2-butene systems provide anti-(Z) or syn-(Z) conjugated dienyne, with a very high level of stereocontrol, on treatment with BF(3).OEt(2) in CH(2)Cl(2) at -50 degrees C in the presence of allyltrimethylsilane. The Cieplak conformation for (E)-substrates and neighboring-group participation for (Z)-substrates are considered to be responsible for the stereochemical consequences.     

Rotational correlation times of adenosine 5′-monophosphate in solution as deduced from 1H and 13C spin-lattice relaxation times

Rotational correlation times (τ_T) of the 5′-AMP molecule deduced from spin-lattice relaxation times (T₁) of different protons in the molecule agree fairly well with each other in the temperature range of 3.5–74°C. The same is true with τ_T values deduced from ¹³CT₁ values. These results indicate that the internal motions are slow as compared to the overall rotation of the 5′-AMP molecule.     

Super acid-induced Pummerer-type cyclization reaction: improvement in the synthesis of chiral 1,3-dimethyl-1,2,3,4-tetrahydroisoquinolines

Improved synthesis of four stereoisomeric chiral 1,3-dimethyl-1,2,3,4-tetrahydroisoquinolines (1a, b, ent-1a, b) was achieved via the super acid-induced cyclization of chiral N-[1-methyl-2-(phenylsulfinyl)ethyl]-N-(1-phenylethyl)formamides (4a, b, ent-4a, b) using the Pummerer-type cyclization reaction as a key step. The cyclization leading to the isoquinoline ring proceeded in a quantitative manner when trifluoromethane sulfonic acid (TFSA) was used as the super acid, although Friedel-Crafts-type alkylation of 4-phenylsulfanyl TIQ derivatives (5) with benzene used as the solvent accompanied cyclization to yield the 4-phenyl-TIQs (7). The byproduct (7) was exclusively formed when a large excess amount of TFSA was used.     

Carbon dioxide fixation by microalgae photosynthesis using actual flue gas discharged from a boiler

To mitigate CO₂ discharged from thermal power plants, studies on CO₂ fixation by the photosynthesis of microalgae using actual exhaust gas have been carried out. The results are as follows.

Chemistry of organosilicon compounds 118. Novel ring contraction reaction of (η4-1,2-disilacyclohexadiene)iron tricarbonyls

1,1,2,2-Dimethyl-3,6-diphenyl-1,2-disilacyclohexadiene reacts with iron pentacarbonyl or diiron nonacarbonyl to give the corresponding (diene)iron tricarbonyl complex which undergoes novel ring contraction reaction to (η⁴-1,1-dimethyl-2,5-diphenyl-1-silacyclopentadiene)iron tricarbonyl on thermolysis at 160°C. Similar results were observed with 1,1,2,2-tetramethyl-3,4,5,6-tetraphenyl-1,2-disilacyclohexadiene.