Construction of Trinervitane and Kempane Skeletons Based on Biogenetical Routes

Based on the putative biogenesis of trinervitane‐ and kempane‐type diterpenes (Scheme 1), a biogenetic‐type transformation was simulated by cyclization of 7,16‐secotrinervita‐7,11,15‐triene‐2α,3α,17‐triol ( 23 ) and of its 17‐chloro derivative 30 . The requisite substrates were prepared from geranylgeranoic acid chloride 6 (Schemes 2, 4, and 5). Treatment of 30 with AgClO₄ at −20° provided the trinervitantrienediols 32 and 33 in 68 and 5% yields, while kempadienediol 35 was obtained in 50% yield by the same reagent at +20° (Scheme 7). The structures of the cyclization products were elaborated from detailed inspection of NMR spectra including H,H COSY, C,H COSY, and NOESY (Tables 1 and 2). The conformation of 30 and its plausible cyclization intermediate was discussed with the help of physical evidence, including X‐ray crystallographic analysis.     

Low-coherence interferometer with 10 MHz repetition rate and compensation of nonlinear chromatic dispersion

Optical Review - We developed a low-coherence interference measurement system using the time-stretch dispersive Fourier transformation technique and demonstrated 10 MHz measurements of the...     

Lewis Acid Catalyzed Ring‐Opening Reactions of Sugar‐Derived Semicyclic N,O‐Acetals

N‐(Alkoxycarbonyl)‐N‐glycosides (polyoxygenated semicyclic N,O‐acetals) were efficiently synthesized from regular acetyl or methyl glycosides (glucopyranoside, ribofuranoside, arabinofuranoside, and 2‐deoxyribofuranoside) and a carbamate by treatment of trimethylsilyl trifluoromethanesulfonate and 4 Å molecular sieves. It was found that these N‐glycosides underwent Lewis acid catalyzed ring‐opening reactions with silylated nucleophiles to give ring‐opened amino alcohols with good‐to‐high diastereoselectivity. The reactivity order, 2‐deoxyribofuranoside > arabinofuranoside > ribofuranoside > glucopyranoside, was revealed. Ring‐opening reductions were also investigated with silanes or diisobutylaluminium hydride. An appropriate reducing agent was found to be dependent on the N‐glycosides used. A glycosidase inhibitor, (2S,3R,4R)‐2‐hydroxymethylpyrrolidine‐3,4‐diol ( 7 ) was synthesized by means of the reactions.     

Signal Formation of Image-Edge Motion Based on Biological Retinal Networks and Implementation into an Analog Metal-Oxide-Silicon Circuit

A simplified model was proposed for the formation of edge signals and generation of motion signals of a target based on the information processing mechanisms of outer and inner retinas of a vertebrate. Analog metal-oxide-silicon (MOS) integrated circuits were designed based on the model. Simulation program with integrated circuit emphasis (SPICE) simulation results showed the performance of local adaptation over a wide dynamic range in the outer retinal circuit and generation of the velocity signal of a moving edge in the inner retinal circuit. Preliminary experimental results showed local adaptation in a given input range in the outer retinal circuit and the generation of motion pulsed signals in the inner retinal circuit.     

Thermo- and pH-responsive gels for application in colon delivery systems

Swelling-controlled drug delivery copolymer gels were synthesized by introducing thermo- and pH-responsive methacryloyl-glycine (MA-Gly) of pH-responsive methacrylic acid (MA-Ac) into thermo-responsive acryloyl- -proline ethyl ester (A-ProOEt). The threshold of swelling for copolymer gels consisting of A-ProOEt/MA-Gly and A-ProOEt/MA-Ac with a composition of 40/60 mol% was found to be pH 3.0 and pH 5.5, respectively, in buffer solutions at 37°C. The diffusion characteristics of 2-(3-benzoylphenyl)propionic acid (ketoprofen) from such copolymer gels were evaluated in buffer solutions at pHs more than 5.5, and it was found that A-ProOEt/MA-Gly gel possessed a Case II transport, while the A-ProOEt/MA-Ac gel exhibited a non-Fickian (or anomalous) diffusion behavior under the same conditions.     

On the D-affinity of the flag variety in type B2

The flag varieties in characteristic 0 are well-known to be D-affine. In positive characteristic, however, only those in type A ₁ and A ₂ have been proved to be so. In this paper we will show in type B ₂ the cohomology vanishing of the first term in the p-filtration of the sheaf of differential operators on the flag variety. This is a necessary condition for the variety to be D-affine. Received: 7 February 2000 / Revised version: 30 June 2000     

Generation of coherent terahertz radiation by photomixing of dual-mode lasers

We have reviewed and discussed the generation of continuous-wave terahertz radiation by the photomixing of dual-mode lasers, which includes a multi-mode laser diode (LD), a dual-mode microchip laser, a monolithic dual-mode DBR LD, and a widely tunable dual-mode external cavity LD. It is demonstrated by several experiments that the beat frequency of a dual-mode laser is more stable than the original laser modes because of the common-mode rejection effect. We also suggest a novel scheme by which the optical beat is stabilized to less than 1 kHz and its frequency can be precisely determined as well.