Molecular design by cycloaddition reactions—36: Cycloaddition reactions of 7-azabenzonorbornadiene with troponoid compounds and photochemistry of the adducts

Reactions of 7-azabenzonorbornadiene 1 with tropone, tropolone and 2-aminotropone gave exclusively endo-exo adducts 3a–c in good yields. Similar reaction of other troponoid compounds like 2-acetylamino-, 2-acetoxy- and 2-methoxytropone afforded two isomeric cycloadducts in each case. Photolyses of tropone-adduct 3a in various solvents gave the corresponding cyclopropylcarboxylic acid derivatives 7–11 in high yields. Photochemical behaviors of these adducts 3c, e, f, 5e–f and 4d were also examined.     

The structures of novel antibiotics,saframycin B and C

The structure of saframycin C(3) has been established by an X-ray crystallographic analysis; this result allows the assignment of structure to the closely related saframycin B(2) by ¹³C NMR spectroscopy.     

Total synthesis of (+)-batzelladine A and (-)-batzelladine D, and identification of their target protein

Asymmetric total synthesis of batzelladine A (1) and batzelladine D (2) has been achieved. Our synthesis of batzelladines features 1) stereoselective construction of the cyclic guanidine system by means of successive 1,3-dipolar cycloaddition reaction and subsequent cyclization, 2) direct esterification of the bicyclic carboxylic acid 35 with the guanidine alcohol 8 or 59 to construct the whole carbon skeleton of batzelladines, and 3) one-step formation of the alpha,beta-unsaturated aldehyde 53 from the primary alcohol 47 with tetra-n-propylammoniumperruthenate (TPAP), providing an efficient route to the left-hand bicyclic guanidine alcohol of batzelladine A (1). With the synthetic compounds 1 and 2 in hand, their target protein was examined by using immobilized CD4 and gp120 affinity gels. The results indicated that batzelladines A (1) and D (2) bind specifically to CD4.     

Chiral organic radical cation and dication. A reversible chiroptical redox switch based on stepwise transformation of optically active tetrakis(p-alkoxyphenyl)ethylenes to radical cations and dications

Optically active tetrakis(p-alkoxyphenyl)ethylenes were found to function as reversible chiroptical switches upon redox transformations. Successive one-electron oxidations of chirally modified tetraarylethylene to the corresponding radical cation and then to the dication led to dramatic changes in the electronic absorption and circular dichroism (CD) spectra. The neutral species showed no color or CD in the visible region, while the radical ion was blue in color and exhibited a weak Cotton effect, with the dication green and giving an intense Cotton effect and a sign opposite that observed for the radical cation, at a longer wavelength. Molecular orbital calculations and X-ray crystallographic studies clearly indicate that the olefinic C=C bond is significantly twisted in the dication to minimize the electrostatic and steric repulsions. By lowering the temperature of the dication, the twist around the double bond is more firmly fixed in either P or M chirality to give a stronger Cotton effect and a larger anisotropy (g) factor. Since the spectral changes are completely reversible and reproducible for multiple redox cycles, this chiral redox system can be used in novel redox-driven chiroptical applications, such as molecular switches and memory devices, in which the information is written/read chiroptically in the ternary mode, giving zero CD signal in the neutral form, positive CD for the radical cation, and negative CD for the dication at a given wavelength.     

Glutamate production from CO2 by Marine CyanobacteriumSynechococcus sp.

A photobioreactor was constructed in the form of a Perspex column 900 mm tall with an internal diameter of 70 mm. The reactor volume was 1.8 L and the light source consisted of a metal-halide lamp to reproduce sunlight. Light was distributed through the culture using a new type of optical fiber that diffuses light out through its surface, perpendicular to the fiber axis. A cluster of 661 light-diffusing optical fibers (LDOFs) pass from the light source through the reactor column (60-cm culture depth) and are connected to a mirror at the top of the reactor. This biosolar reactor has been used for the production of glutamate from CO₂ by the marine cyanobacterium Synechococcus sp. NKBG040607. We present here details of the construction of the biosolar reactor and characterization of its properties. The effect of light intensity on glutamate production was measured. Carbon dioxide-to-glutamate conversion ratios were determined at different cell densities: the maximum conversion ratio (28%) was achieved at a cell density of 3x10⁸ cells/mL. A comparison of glutamate production using the LDOF biosolar reactor described here with production by batch culture using free or immobilized cells showed that use of an optical-fiber biosolar reactor increased glutamate-production efficiency 6.75-fold. We conclude that as a result of its high surface-to-volume ratio (692/m) increased photoproduction of useful compounds may be achieved. Such a system is generally applicable to all aspects of photobiotechnology.     

On Σ -Π separability in the electronic transitions of conjugated molecules

The π → π¹ transitions to triplets are shown to be independent of the σ → σ¹ transitions if the zero differential overlaps are assumed between the pi- and sigma-orbitals. For the singlet transitions, however, Σ—Π coupling does not vanish, and its inclusion is explicitly depicted.     

Dihydrosilaanthracenylidene and dihydroanthracenylidene

Carbenes generated from 10-diazo-9,9-dimethyl-9,10-dihydro-9-silaanthracene and 10-diazo-9,9-dimethyl-9,10-dihydroanthracene gave hydrogen abstraction products by the triplet nature of these carbenes. The triplet dihydrosilaanthracenylidene was shown by the electron spin resonance study.     

Suppression of the bitterness of enteral nutrients using increased particle sizes of branched-chain amino acids (BCAAs) and various flavours: a taste sensor study

An improved formulation of the enteral nutrient Aminoleban EN (Otsuka Pharmaceutical Co., Ltd., Tokyo, Japan), has been commercially available since Spring 2004. Like the previous formulation, the improved product contains branched-chain amino acids (BCAAs) L-isoleucine (L-Ile), L-leucine (L-Leu), and L-valine (L-Val), but the average particle size of these amino acids has been increased to 180 to 250 microm in the improved formulation, compared with 40 to 90 microm in the old product. The improved formulation has a significantly lower bitterness intensity score than the older formulation, as evaluated both in human gustatory tests and using the artificial taste sensor. We propose that this improved taste masking is due to the larger particle size of the BCAA crystals, due to which their release rates are reduced. The addition of improved flavours has also helped to reduce the bitterness of the improved Aminoleban EN formulation significantly. Analysis of the taste sensor data suggests that the sourness and sweetness of the added flavours were critical in diminishing the bitterness of Aminoleban EN.     

Optical resolution by preferential crystallization of (RS)-2-benzoylamino-2-benzyl-3-hydroxypropanoic acid and its use in synthesizing optically active 2-amino-2-methyl-3-phenylpropanoic acid

To synthesize optically active 2-amino-2-methyl-3-phenylpropanoic acid (1), (RS)-2-benzoylamino-2-benzyl-3-hydroxypropanoic acid [(RS)-2] was first optically resolved using cinchonidine as a resolving agent to yield optically pure (S)- and (R)-2 in yields of about 70%, based on half of the starting amount of (RS)-2. Next, the racemic structure of (RS)-2 was examined based on melting point, solubility, IR spectrum, and binary and ternary phase diagrams, with the aim of optical resolution by preferential crystallization of (RS)-2. Results indicated that the (RS)-2 exists as a conglomerate at room temperature, although it forms a racemic compound at the melting point. The optical resolution by preferential crystallization yielded (S)- and (R)-2 with optical purities of about 90%, which were fully purified by recrystallization. After O-tosylation of (S)- and (R)-2, reduction by zinc powder and sodium iodide gave (R)- and (S)-1, respectively.     

Partial synthesis of 23-hydroxyursolic acid isolated from medicinal plants of the Rubiaceae family

23-Hydroxyursolic acid (2), previously isolated from medicinal plants of the Rubiaceae family, was synthesized in ten steps via methyl 23-hydroxy-3-oxours-12-en-28-oate (5) from commercially available ursolic acid (6).