Organization and polysaccharides of sponge aggregation factor.

Aggregation factor, the macromolecular complex which mediates species-specific aggregation of dissociated sponge cells, was isolated from several species, partially characterized, and visualized by electron microscopy. All factors were large fibrous complexes with a backbone and side chains or arms. In some factors, the backbone is linear. In others it is circular and the complex appears as a sunburst with arms extending like rays from the circle. The size and location of the polysaccharide chains have been studied using purified preparations of Microciona prolifera. "Sunbursts" treated with ethylenediaminetraacetate (EDTA) for 4 weeks at 0 degrees C dissociate into 3 protein- and polysaccharide-containing components. Sodium dodecyl sulfate does not cause the sunburst to dissociate nor does it inhibit dissociation in the presence of EDTA suggesting that dissociation is not due to hydrolytic enzymes. The dissociation products were fractionated on a 977-A pore size micropore glass column. Fifteen percent of the material is excluded and appears in the electron microscope as the central circle of the sunburst. Digestion of the circles with 10(-3) M dithiothreitol (DTT) and 0.5 mg/ml proteinase K for 72 h at 37 degrees C produces 2 polysaccharide chains of 65,000 and 6,000 daltons as fractionated and sized on a 233-A pore size micropore glass column using Pharmacia dextrans as standards. The included fractions of the EDTA-treated material are subunits of the arms which contain 70% of the polysaccharide. A single polysaccharide of 6,000 daltons as measured on 233-A size glass beads and Sephadex G-75 is released from these subunits by proteinase digestion. Pharmacia dextrans are used as standard on both columns. We calculate that there would be four 65,000-dalton chains and one hundred 6,000-dalton chains per circle and fifty 6,000-dalton chains per arm. The third component of the EDTA-treated preparation is partially included on the column. It appears as linear fibrils in the electron microscope and contains polydisperse polysaccharides of several-hundred-thousand daltons. It may be an impurity since there is apparently less than 1 of the large polysaccharide chains per sunburst.     

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.     

Effect of Organic Ligands Used in Sol-Gel Process on the Formation of Mullite

The preparation of mullite by the sol-gel method using organic polydentate ligands and the effect of the raw materials and organic polydentate ligands on the formation of mullite were investigated. Two series of samples were prepared using tetraethoxyorthosilicate (TEOS) and aluminum nitrate nonahydrate, or dibutoxyethylacetoacetatoaluminum (Al(OBu)₂(AcAcEt)) as the silica and alumina sources, respectively, and using ethylene glycol (EG), 1,3-propanediol (PD), 1,3-butanediol (BD), 2-methyl-2, 4-pentanediol (MPD), diethlene glycol monoethyl ether (DEME) and ethoxyethanol as the ligands. When the alumina source was aluminum nitrate nonahydrate, mullite was apt to appear in the order of EG>PD>MPD. When Al(OBu)₂(AcAcEt) was the alumina source, the tendency toward the appearance of mullite crystalline phase was EG>BD>DEME>MPD. Between the two alumina sources, aluminum nitrate nonahydrate gave mullite much easier than Al(OBu)₂(AcAcEt). These relationships were discussed from the viewpoints of the coordination ability of the ligands and the miscibility between the silica and alumina.     

Mechanism of the molecular hysteresis

The redox behavior in acetone solution of (1,5-dithiacyclooctane 1-oxide)bis(pentaammineruthenium(II)) has been characterized, where the concept of “molecular hysteresis” is presented. Detailed thermodynamics for the complex are studied, in which intramolecular electron transfer rates for Ru³⁺OS/Ru²⁺→Ru²⁺SO/Ru³⁺ were determined as 0.12 sec^?1 and 0.055 sec^?1. The molecular hysteresis consists of two important factors: isomerizations for the sulfoxideruthenium complexes and the slow intramolecular electron transfer in the complex; both are examined. Isomerization rates for Ru³⁺S→O and Ru²⁺O→S determined range from 0.4 to 5000 sec^?1 and from 0.7 to 16 sec^?1, respectively, for [Ru(NH₃)₅(sulfoxide)]^2+/3+. A mechanism for the slow electron transfer in the complex is also presented. Features of molecular hysteresis are discussed.     

Engineered biosynthesis of plant polyketides: chain length control in an octaketide-producing plant type III polyketide synthase

The chalcone synthase (CHS) superfamily of type III polyketide synthases (PKSs) produces a variety of plant secondary metabolites with remarkable structural diversity and biological activities (e.g., chalcones, stilbenes, benzophenones, acrydones, phloroglucinols, resorcinols, pyrones, and chromones). Here we describe an octaketide-producing novel plant-specific type III PKS from aloe (Aloe arborescens) sharing 50-60% amino acid sequence identity with other plant CHS-superfamily enzymes. A recombinant enzyme expressed in Escherichia coli catalyzed seven successive decarboxylative condensations of malonyl-CoA to yield aromatic octaketides SEK4 and SEK4b, the longest polyketides known to be synthesized by the structurally simple type III PKS. Surprisingly, site-directed mutagenesis revealed that a single residue Gly207 (corresponding to the CHS's active site Thr197) determines the polyketide chain length and product specificity. Small-to-large substitutions (G207A, G207T, G207M, G207L, G207F, and G207W) resulted in loss of the octaketide-forming activity and concomitant formation of shorter chain length polyketides (from triketide to heptaketide) including a pentaketide chromone, 2,7-dihydroxy-5-methylchromone, and a hexaketide pyrone, 6-(2,4-dihydroxy-6-methylphenyl)-4-hydroxy-2-pyrone, depending on the size of the side chain. Notably, the functional diversity of the type III PKS was shown to evolve from simple steric modulation of the chemically inert single residue lining the active-site cavity accompanied by conservation of the Cys-His-Asn catalytic triad. This provided novel strategies for the engineered biosynthesis of pharmaceutically important plant polyketides.     

Synthesis and pharmacology of 3,4-dihydro-3-oxo-1,4-benzoxazine-8-carboxamide derivatives, a new class of potent serotonin-3 (5-HT3) receptor antagonists.

A series of 3,4-dihydro-3-oxo-1,4-benzoxazine-8-carboxamide derivatives was synthesized and evaluated for serotonin-3 (5-HT3) receptor antagonistic activity assessed by their ability to antagonize the von Bezold-Jarish (BJ) effect in rats. Derivatives bearing 1-azabicyclo[2.2.2]oct-3-yl moiety as a basic function attached to the carboxamide at position 8 showed more potent antagonistic activity than those bearing the other three basic moieties. Structure-activity relationships of this series showed that methyl and chloro groups were more effective as substituents at positions 4 and 6, respectively. The representative compound 15 (Y-25130) in this series showed potent antagonistic activity on the BJ effect (ED50 = 1.3 micrograms/kg i.v.), high affinity for 5-HT3 receptor (Ki = 2.9 nM) and complete protection against cisplatin-induced emesis in dogs at a dose of 0.1 mg/kg i.v.     

X-ray gated Mössbauer spectroscopic studies on57Co-labelled cobalt/II/ fluoride

KX-ray-gated emission Mössbauer spectra of⁵⁷Co-labelled CoF₂ and CoF₂.2H₂O were measured at room temperature, using the coincidence technique. A difference was found in the relative intensity of⁵⁷Fe(II)/⁵⁷Fe(III) between the X-ray-gated and non-gated emission spectra. The results are explained in terms of local radiolytic effects of water of crystallization and the chemical effects associated with the de-excitation processes caused by EC-decay.     

Effect of the mobility of ligands in polyrotaxanes on order structure of water clusters

The effect of the mobility of ligands (maltose groups) in the polyrotaxanes (pRXs) on the structure of the surrounding water molecules was investigated. Raman spectra of collective OH stretching vibration of water molecules in aqueous solutions of maltose-pRX conjugates with different alpha-cyclodextrin (alpha-CD) threading on a poly(ethylene glycol) (PEG) chain was measured. The mobility of maltose groups was estimated by measuring the relaxation time T2 of the C1 protons in maltose groups bound on alpha-CD by NMR experiment. A positive correlation between the Raman intensity of the collective band and the relaxation time T2 was obtained. This result indicates that the degree of order of the water clusters is higher as the mobility of maltose groups increases in these conjugate solutions. It is suggested that rapid motion of maltose groups in the pRX conjugate can contribute to preserving ordered structure of the bulk water clusters.     

Thalidomide as a nitric oxide synthase inhibitor and its structural development

Thalidomide has been found to exhibit weak nitric oxide synthase (NOS)-inhibitory activity. Structural development studies of thalidomide showed that some N-2,6-dimethylphenylhomophthalimide analogs possess NOS-inhibiting activity.     

Marginal electron density and density-difference functions

Summary For visual analysis of the density reorganization and distortion, the one-dimensional cut (x, y ₀,z ₀) and the two-dimensional cut (x, y, z ₀) of the three-dimensional electron density difference function (x, y, z) are frequently employed. However, these cut functions do not satisfy any sum rules in contrast to the original difference function (x, y, z). To avoid this difficulty, the use of the marginal electron density functions _x (x) and _xy (x, y) and their difference functions _x (x) and _xy (x, y) is proposed. The marginal densities are condensation of the three-dimensional density onto a particular plane or line of our interest, and they satisfy the sum rule (i.e., the conservation of the number of electrons) exactly. Some basic properties of the marginal electron density are clarified for typical diatomic molecular orbitals. An illustrative application is given for the bonding and antibonding processes in the H₂ system.