Asymmetric total syntheses of (+)-mycoepoxydiene and related natural product (-)-1893A: application of one-pot ring-opening/cross/ring-closing metathesis to construct their 9-oxabicyclo[4.2.1]nona-2,4-diene skeleton

The total syntheses of (+)-mycoepoxydiene and (-)-1893A have been completed. The present synthetic strategy features the use of one-pot ring-opening/cross metathesis (ROM/CM) followed by a ring-closing metathesis (RCM) reaction, allowing for the concise construction of the 9-oxabicyclo[4.2.1]nona-2,4-diene framework from a 7-oxabicyclo[2.2.1]hept-2-ene derivative and 1,3-butadiene. The sequential metathesis product was converted into (+)-mycoepoxydiene through the oxidative rearrangement of a furfuryl alcohol to a pyranone, thereby establishing its absolute stereochemistry. From the common intermediate, a structurally related natural product (-)-1893A was also synthesized via the vinylogous aldol reaction.     

The influence of polytypic structures on the M011-->M101 solid-solid phase transition of n-C36H74: an application of the oblique infrared transmission method

The molecular displacements on the M011-->M101 phase transition of n-hexatriacontane (n-C36H74) have been investigated with an IR microscope designed for the oblique infrared transmission method. It has been clarified that two polytypic structures of the M011 modification, single-layered structure (Mon) and double-layered one (Orth II), both transform to the M101 modification of single-layered structure with their respective mechanisms. On the M011(Mon)-->M101 transition, the inclination direction of molecular axis is changed by 90 degrees through an intermediate state in which the molecular chain is set perpendicular to the basal plane of the single crystal. On the other hand, a polymorphic-polytypic composite structural change on the M011(Orth II)-->M101 transition is accomplished through two kinds of molecular displacements occurring alternately along the stacking direction of molecular layers.     

Vesicle formation in oleyldimethylamine oxide/sodium oleate mixtures

Vesicle formation in a mixture of oleyldimethylamine oxide (OleylDMAO) and sodium oleate (NaOl) was investigated by viscoelastic measurements and cryoscopic transmission electron micrograph (cryo-TEM) observations. The viscoelastic properties changed with increasing mole fraction of NaOl (X _NaOl) from the Maxwell behavior of OleylDMAO solutions (X _NaOl=0) suggesting a transient network of long flexible chains. For X _NaOl=0.2 and 0.4 mixtures, both the shear storage modulus G and the shear loss modulus G showed weak dependences on angular frequency with a relation G>G. From cryo-TEM observations, vesicles coexisted with threadlike micelles in mixtures of X _NaOl=0.2 and 0.3. As X _NaOl increased further (X _NaOl=0.5 and 0.6), threadlike micelles disappeared and the coexistence of vesicles and globular micelles was observed. At X _NaOl=0.5, the viscosity decreased remarkably, which was consistent with the disappearance of threadlike micelles. The results indicated that vesicles were formed by the addition of NaOl to OleylDMAO solutions, contrary to the expectation of a decrease of the packing parameter with the introduction of electric charges.     

Comparative studies on the analysis of glycosylation heterogeneity of sialic acid-containing glycoproteins using capillary electrophoresis

Frontal affinity chromatography is a method for quantitative analysis of biomolecular interactions. We reinforced it by incorporating various merits of a contemporary liquid chromatography system. As a model study, the interaction between an immobilized Caenorhabditis elegans galectin (LEC-6) and fluorescently labeled oligosaccharides (pyridylaminated sugars) was analyzed. LEC-6 was coupled to N-hydroxysuccinimide-activated Sepharose 4 Fast Flow (100 μm diameter), and packed into a miniature column (e.g., 10×4.0 mm, 0.126 ml). Twelve pyridylaminated oligosaccharides were applied to the column through a 2-ml sample loop, and their elution patterns were monitored by fluorescence. The volume of the elution front (V) determined graphically for each sample was compared with that obtained in the presence of an excess amount of hapten saccharide, lactose (V₀); and the dissociation constant, K_d, was calculated according to the literature [K. Kasai, Y. Oda, M. Nishikawa, S. Ishii, J. Chromatogr. 376 (1986) 33]. This system also proved to be useful for an inverse confirmation; that is, application of galectins to an immobilized glycan column (in the present case, asialofetuin was immobilized on Sepharose 4 Fast Flow), and the elution profiles were monitored by fluorescence based on tryptophan. The relative affinity of various galectins for asialofetuin could be easily compared in terms of the extent of retardation. The newly constructed system proved to be extremely versatile. It enabled rapid (analysis time 12 min/cycle) and sensitive (20 nM for pyridylaminated derivatives, and 1 μg/ml for protein) analyses of lectin–carbohydrate interactions. It should become a powerful tool for elucidation of biomolecular interactions, in particular for functional analysis of a large number of proteins that should be the essential issues of post-genome projects.     

Synthesis and characterization of 6-O-acyl-2-O-alpha-D-glucopyranosyl-L-ascorbic acids with a branched-acyl chain

We previously reported the chemical synthesis of a series of novel monoacylated vitamin C derivatives, 6-O-acyl-2-O-alpha-D-glucopyranosyl-L-ascorbic acids (6-Acyl-AA-2G) possessing a straight-acyl chain of varying length from C(4) to C(18), as effective skin antioxidants. In this paper, we describe branched type of 6-Acyl-AA-2G derivatives (6-bAcyl-AA-2G) synthesized by use of a 2-branched-chain fatty acid anhydride as an acyl donor. The stability of 6-bAcyl-AA-2G in neutral solution was much higher than that of 6-Acyl-AA-2G, while they were susceptible to enzymatic hydrolysis for exerting vitamin C effect. These branched derivatives as well as 6-Acyl-AA-2G increased the radical scavenging activity against 1, 1-diphenyl-2-picrylhydrazyl and the lipophilicity in octanol/water-partitioning systems with increasing length of their acyl group. In addition, the 6-bAcyl-AA-2G derivative with an acyl chain of C(12), 6-bDode-AA-2G had the excellent solubility to various solvents, suggesting easy handling in cosmetic use. These characteristics of 6-bAcyl-AA-2G may be available for skin care application as an effective antioxidant.     

The first total synthesis of (+/-)-linderol A, a tricyclic hexahydrodibenzofuran constituent of Lindera umbellata bark, with potent inhibitory activity on melanin biosynthesis of cultured B-16 melanoma cells

[reaction in text] The first total synthesis of (+/-)-linderol A, a hexahydrodibenzofuran isolated from Lindera umbellata bark, with potent inhibitory activity on melanin biosynthesis of cultured B-16 melanoma cells was achieved via a 20-step of reaction in 7.64% overall yield starting from 4,6-dimethoxysalicylaldehyde.     

A comparison of the adsorption of saliva proteins and some typical proteins onto the surface of hydroxyapatite

Adsorption of protein from saliva on hydroxyapatite was compared with adsorption of several typical proteins with different electric charges, i.e. lysozyme, human serum albumin, β-lactoglobulin and ovalbumin. Adsorbed amounts of these proteins were determined and electrophoretic mobilities of protein-covered hydroxyapatite particles were measured, at different values for the adsorbed mass and, therefore, at various degrees of surface coverage. Also, adsorption kinetics were investigated by streaming potential measurements of a hydroxyapatite surface in contact with a protein solution, allowing monitoring of changes in the zeta-potential of the protein-covered hydroxyapatite surface in real time. The adsorbed amounts show that, as compared to most of the other proteins, the saliva proteins have remarkably low adsorption affinity. The measured values for the electrophoretic mobilities indicate that the positively charged proteins in the saliva mixture preferentially adsorb onto the negatively charged hydroxyapatite surface; this is most pronounced at low protein concentration in solution (i.e. at low coverage of the surface by the protein). Preferential uptake of the positively charged saliva proteins during the initial stages of the adsorption process is also concluded from the results of the kinetics experiments. Preferential adsorption of positive proteins is somewhat suppressed by the presence of Ca²⁺ ions in the medium. The results suggest that an acquired pellicle on a tooth in an oral environment contains a significant fraction of positively charged proteins. The positively charged proteins in the pellicle reduce the zeta-potential at the tooth surface to low values; consequently, electrostatic forces are expected to play only a minor role in the interaction with other components (e.g. bacterial cells).     

Synthesis of 2'-O-[2-[(N,N-dimethylamino)oxy]ethyl] modified nucleosides and oligonucleotides.

A versatile synthetic route has been developed for the synthesis of 2'-O-[2-[(N,N-dimethylamino)oxy]ethyl] (abbreviated as 2'-O-DMAOE) modified purine and pyrimidine nucleosides and their corresponding nucleoside phosphoramidites and solid supports. To synthesize 2'-O-DMAOE purine nucleosides, the key intermediate B (Scheme 1) was obtained from the 2'-O-allyl purine nucleosides (13a and 15) via oxidative cleavage of the carbon-carbon bond to the corresponding aldehydes followed by reduction. To synthesize pyrimidine nucleosides, opening the 2,2'-anhydro-5-methyluridine 5 with the borate ester of ethylene glycol gave the key intermediate B. The 2'-O-(2-hydroxyethyl) nucleosides were converted, in excellent yield, by a regioselective Mitsunobu reaction, to the corresponding 2'-O-[2-[(1,3-dihydro-1,3-dioxo-2H-isoindol-2-yl)oxy]ethyl] nucleosides (18, 19, and 20). These compounds were subsequently deprotected and converted into the 2'-O-[2-[(methyleneamino)oxy]ethyl] derivatives (22, 23, and 24). Reduction and a second reductive amination with formaldehyde yielded the corresponding 2'-O-[2-[(N,N-dimethylamino)oxy]ethyl] nucleosides (25, 26, and 27). These nucleosides were converted to their 3'-O-phosphoramidites and controlled-pore glass solid supports in excellent overall yield. Using these monomers, modified oligonucleotides containing pyrimidine and purine bases were synthesized with phosphodiester, phosphorothioate, and both linkages (phosphorothioate and phosphodiester) present in the same oligonucleotide as a chimera in high yields. The oligonucleotides were characterized by HPLC, capillary gel electrophoresis, and ESMS. The effect of this modification on the affinity of the oligonucleotides for complementary RNA and on nuclease stability was evaluated. The 2'-O-DMAOE modification enhanced the binding affinity of the oligonucleotides for the complementary RNA (and not for DNA). The modified oligonucleotides that possessed the phosphodiester backbone demonstrated excellent resistance to nuclease with t(1/2) > 24 h.