Metal-binding ability of human prion protein fragment peptides analyzed by column switch HPLC

The structural conversion of the prion protein (PrP) from the normal cellular isoform (PrP(C)) to the posttranslationally modified form (PrP(Sc)) is thought to relate to Cu2? binding to histidine (H) residues. Traditionally, the binding of metals to PrP has been investigated by monitoring the conformational conversion using circular dichroism (CD). In this study, the metal-binding ability of 21 synthetic peptides representing regions of human PrP(C) was investigated by column switch high-performance liquid chromatography (CS-HPLC). The CS-HPLC system is composed of a metal chelate affinity column and an octadecylsilica (ODS) reversed-phase column that together enable the identification of metal-binding regardless of conformational conversion. Synthetic peptides were designed with respect to the position of H residues as well as the secondary structure of human PrP (hPrP). The ability of the octapeptide (PHGGGWGQ)-repeating region (OP-repeat) to bind metals was analyzed by CS-HPLC and supported by CD analysis, and indicated that CS-HPLC is a reliable and useful method for measuring peptide metal-binding. Peptides from the middle region of hPrP showed a high affinity for Cu2?, but binding to Zn2?, Ni2?, and Co2? was dependent on peptide length. C-Terminal peptides had a lower affinity for Cu2?, Zn2?, Ni2?, and Co2? than OP-repeat region peptides. Interestingly, hPrP193-230, which contained no H residues, also bound to Cu2?, Zn2?, Ni2?, and Co2?, indicating that this region is a novel metal-binding site in the C-terminal region of PrP(C). The CS-HPLC method described in this study is useful and convenient for assessing metal-binding affinity and characterizing metal-binding peptides or proteins.     

Novel cycloundecapeptides related to gramicidin S with both high antibiotic activity and low hemolytic activity

To find candidates with high antimicrobial and low hemolytic activities, many gramicidin S (GS) analogs of various ring sizes have been designed and synthesized. However, syntheses of antimicrobially active analogues of GS having a disordered symmetry structure from C(2) have almost never been reported, because the stable, amphiphilic β-sheet structure of GS with C(2) symmetry is considered essential for its strong antibacterial activity. In the present studies, novel thirteen cycloundecapeptides 1-13 related to GS were synthesized and examined. Among them, cyclo(-Va1(1)-Orn(2)-Leu(3)-D-Phe(4)-X(5)-Pro(6)-Val(7)-Orn(8)-Leu(9)-D-Phe(10)-Pro(11)-) (X=Lys (10), Orn (11), Arg (12) and Lys(Lys) (13)) resulted in high antibiotic activity against both Gram-positive and Gram-negative microorganisms tested. In addition, 11 showed low toxicity against sheep blood cells compared with that of GS. Further, circular dichroism (CD) spectra of 10-13 had a curve similar to each other, suggesting that the conformations of these analogues in methanol are similar to each other. However, CD spectra of 10-13 were different from that of GS in the 190-210 nm region. These results suggest that the presences of one added amino acid residue at position 5 of 10-13 might be partially effective through a structural change in the biological activity of 10-13. In addition, the structural modifications at position 5 lower the undesirable hemolytic activity and enhance the desirable antibiotic activity.     

Biomimetic one-pot preparation of a black tea polyphenol theasinensin A from epigallocatechin gallate by treatment with copper(II) chloride and ascorbic acid

Chromatographic separation of black tea polyphenols is too difficult to supply sufficient quantities of pure compounds for biological experiments. Thus, facile methods to prepare black tea constituents were desired. Treatment of epigallocatechin gallate with copper(II) chloride efficiently afforded an unstable quinone dimer, dehydrotheasinensin A, and subsequent treatment with ascorbic acid stereoselectively yielded theasinensin A. The latter is a dimer with an R-biphenyl bond, one of the major polyphenols found in black tea. The method is simpler and more effective than enzymatic preparation.     

Phase behaviour and molecular dynamics in the binary system of sodium perchlorate and 1,2-propanediamine

The phase and glass transition behaviour in a binary mixture of sodium perchlorate and 1,2-propanediamine {(NaClO₄)_x(12PDA)_1?x, x < 0.40} was investigated by differential scanning calorimetry and Raman scattering measurements. A eutectic point and a peritectic point were found at x = 0.17 and 0.19, respectively. The phase diagram indicates the existence of solvated compounds of (NaClO₄)₁(12PDA)₄ and (NaClO₄)₂(12PDA)₅. The concentration dependence of the glass transition point shows a sigmoid curve implying an underlying anomaly.     

A Two-Step Synthesis Of (±)-Blastmycinolactol Using Acylurea

A convenient synthesis of natural (±)-blastmycino-lactol from the aldol addition reaction of n-pentanoylurea and (±)-2-benzyloxypropionaldehyde is described.     

Superhigh-Rate Epitaxial Silicon Thick Film Deposition from Trichlorosilane by Mesoplasma Chemical Vapor Deposition

Homoepitaxial Si thick films have been deposited by mesoplasma chemical vapor deposition (CVD) with SiHCl₃ (TCS)–H₂–Ar gas mixtures. The addition of a small amount of H₂ has been found to not only modify the film structure from polycrystalline to epitaxial but also effectively improve the deposition efficiency and film purity by removing Cl in the form of HCl. However, an excess introduction of H₂ decreases the deposition efficiency owing to the shrinkage of the plasma flame. On the other hand, an increase in TCS flow rate increases the epitaxial deposition rate despite exhibiting a saturating tendency, while the material yield tends to decrease gradually due possibly to an increase in the Cl atoms. Also, we observed a critical limit in the TCS flow rate for epitaxial growth, beyond which a polycrystalline film resulted. However, when RF input power was increased, not only the upper limit of TCS flow rate for epitaxy was extended but also the deposition yield was improved so that the deposition rate reached ~700 nm/s with the material yield of >50 % at 30 kW input power with an H₂/TCS ratio of 1.5. Additionally, high input power is found to be beneficial to decrease Cl atom incorporation into the film and improve the Hall mobility of the films. An epitaxial film with a Cl atom concentration of less than 3 × 10¹⁶ cm^?3 and a Hall mobility as high as 250 cm²/(V·s) was obtained at 30 kW input power.     

An Unusual Behavior of Methyl or Benzyl 3-Azido-5-O-Benzoyl-3,6-Di-Deoxy-α-L-Talofuranoside with (Dimethylamino)Sulfur Trifluoride; Migration of the Alkoxyl Group from the C-1 to the C-2 Position

The reaction of methyl or benzyl 3-azido-5-0-benzoyl-3,6-di-deoxy-α-L-talofuranoside with (diethylamino)sulfur trifluoride (DAST) in toluene at 60°C resulted in the formation of 3-azido-5-0-benzoyl-3,6-dideoxy-2-0-methyl (or 2-0-benzyl)-3β-L-galactofuranosyl fluoride in good yield. In this reaction the alkoxyl group at C-1 migrated to the C-2 position and a fluorine atom entered into the C-1 position. The furanosyl fluoride was converted, via reduction of the azido group followed by N-trifluoroacetylation, acetolysis, and O-deacetylation, into 3,6-dideoxy-2-0-methyl-3-trifluoroacet-amido-L-galactopyranose (2-methoxy-Daunosamine derivative).     

Synthetic Studies on Sialoglycoconjugates 66: First Total Synthesis of a Cholinergic Neuron-Specific Ganglioside GQ1bα1

Abstract

A first total synthesis of a cholinergic neuron-specific ganglioside, GQ1bα (IV³Neu5Acα, III⁶Neu5Acα, II³Neu5Acα₂-Gg₄Cer) is described. Regio- and stereo-selective monosialylation of the hydroxyl group at C-6 of the GalNAc residue in 2-(trimethylsilyl)ethyl O-(2-acetamido-2-deoxy-3,4-O-isopropylidene-β-d-galactopyranosyl)-(1→4)-O-(2,6-di-O-benzyl-β-dgalactopyranosyl)-(1→4)- O-2,3,6-tri-O-benzyl-β-dglucopyranoside (4) with methyl (phenyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-d glycero-d galacto-2-nonulopyranosid) onate (5), and subsequent dimericsialylation of the hydroxyl group at C-3 of the Gal residue with methyl [phenyl 5-acetamido-8-O-(5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d glycero-α-d galacto-2-nonulopyranosylono-1′,9-lactone)-4, 7-di-O-acetyl-3,5-dideoxy-2-thio-d glycero-d galacto-2-nonulopyranosid]onate (7), using N-iodosuccinimide (NIS)-trifluoromethanesulfonic acid (TfOH) as a promoter, gave the desired hexasaccharide 8 containing α-glycosidically-linked mono- and dimeric sialic acids. This was transformed into the acceptor 9 by removal of the isopropylidene group. Condensation of methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d glycero-α-d galacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-dgalactopyranoside (10) with 9, using dimethyl(methylthio)sulfonium triflate (DMTST) as a promoter, gave the desired octasaccharide derivative 11 in high yield. Compound 11 was converted into α-trichloroacetimidate 14, via reductive removal of the benzyl groups, O-acetylation, removal of the 2-(trimethylsilyl)ethyl group, and treatment with trichloroacetonitrile, which, on coupling with (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (15), gave the β-glycoside 16. Finally, 16 was transformed, via selective reduction of the azido group, coupling with octadecanoic acid, O-deacylation, and hydrolysis of the methyl ester group, into the title ganglioside 18 in good yield.     

Synthetic Studies on Sialoglycoconjugates 81: Synthesis of Positional Isomers of Sialyl Lewis X Epitope Containing 1-Deoxy-d Glucose in Place of N-Acetylglucosamine,and Their Inhibitory Activity to Selectin-Mediated Adhesion

Abstract

Three sialyl-Le^x epitope analogs, which carry fucose and α-sialyl-(2→3)-galactose residues at O-2 and O-3, O-3 and O-2, and O-4 and O-6 positions of 1-deoxy-D-glucose backbone, respectively, have been synthesized. Glycosylation of 1,5-anhydro-4,6-O-benzylidene-D-glucitol (1) or 1,5-anhydro-6-O-benzoyl-2,3-di-O-benzyl-d-glucitol (4) prepared from 1,5-anhydro-d-glucitol, with methyl 2,3,4-tri-O-benzyl-1-thio-β-L-fucopyranoside (5) using dimethyl(methylthio)sulfonium triflate (DMTST) as a promoter, afforded the corresponding fucosyl 1,5-anhydro-d-glucitol derivatives 7, 8 and 9. Glycosylation of 7, 8 or 10 derived from 9, with methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d-glyceroα-d-galacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-d-galactopyranoside (11) in the presence of DMTST gave the expected tetrasaccharide derivatives 12, 16 and 20. Hydrolysis of the benzylidene group in 12 and 16 gave compounds 13 and 17. Finally 13, 17 and 20 were transformed, by reductive removal of the benzyl groups, O-deacylation and subsequent hydrolysis of the methyl ester, into the sialyl-Le^x epitope analogs 15, 19 and 22, respectively.     

Synthetic Studies on Sialoglycoconjugates 48: Total Synthesis of Gangliosides Gm1 and Gd1a

Abstract

A stereo controlled, facile total synthesis of gangliosides GM₁ and GD_1a, in connection with systematic synthesis of ganglio-series of ganglioside, is described. Glycosylation of 2-(trimethylsilyl) ethyl O-(2-acetamido-6-O-benzoyl-2-deoxy-(β-D-galactopyranosyl)-(l→4)-O-[(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacro-2–nonulopyranosylonate)-(2→3)]-O-2,6-di-O-benzyl-β-D-galacto-pyranosyl)-(l→40)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (4), with methyl 2,4,6-tri-O-benzoyl-3-O-benzyl-l-thio-β-D-galactopyranoside (8) or methyl O-(methyl 5-acetamido -4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacro-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-l-thio-β-D-galactopyranoside (9) by use of N-iodosuccinimide (NIS)-trifluoromethanesulfonic acid (TfOH) or dimethyl(methylthio)sulfonium triflate (DMTST) as a promoter, gave the corresponding [β-glycoside 10 and 18 in 66 and 62% yields, which were converted, via reductive removal of the benzyl groups, O-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group, and subsequent imidate formation, into the α-trichloroacetimidates 13 and 21. Glycosylation of (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-l,3-diol (14) with 13 or 21 by use of trimethylsilyl trifluoromethanesulfonate gave the corresponding β-glycoside 15 and 22, which on channeling through selective reduction of die azido group, coupling of the thus formed amino group with octadecanoic acid, O-deacylation, and saponification of the methyl ester group, gave the tital gangliosides GM₁ and GD_1a.