Differentiating the 2,3-diols of glucopyranosides by 4,6-O-benzylidene-protected-1,2-D-glucopyranosylorthoesters strategy

A facile and efficient method to differentiate the 2,3-diols of glucopyranosides based on 1,2-orthoesters strategy was developed. Stable thioglucosides were employed as the starting materials to prepare the corresponding 1,2-orthoesters. When treated with HCl aqueous solution and followed with Et(3)N, differentiation of the 2,3-diols was efficiently achieved along with the generation of a convertible anomeric hydroxyl group. In addition, an easy and practical method based on NOE was proposed to determine whether the 1,2-orthoesters were endo-type or exo-type.     

Differentiating the 2,3-diols of glucopyranosides by 4,6-O-benzylidene-protected-1,2-d-glucopyranosylorthoesters strategy

A facile and efficient method to differentiate the 2,3-diols of glucopyranosides based on 1,2-orthoesters strategy was developed. Stable thioglucosides were employed as the starting materials to prepare the corresponding 1,2-orthoesters. When treated with HCl aqueous solution and followed with Et₃N, differentiation of the 2,3-diols was efficiently achieved along with the generation of a convertible anomeric hydroxyl group. In addition, an easy and practical method based on NOE was proposed to determine whether the 1,2-orthoesters were endo-type or exo-type.     

Rearrangement of sugar 1,2-orthoesters to glycosidic products: a mechanistic implication

The identification of cross-over products in the rearrangement of two structurally similar sugar 1,2-orthoesters to glycosidic products is reported.     

Preparation and mass-spectral analysis of O-hydroxy-ethyl derivatives of -glucose

Various hydroxyethyl ethers of -glucose have been prepared in good yield by treating -glucose derivatives with 2-bromoethyl tetrahydropyranyl ether in the presence of sodium hydride. The derived O-(hydroxyethyl)- -glucitol acetates exhibited characteristic mass-spectral fragments. The furanose and pyranose forms of 1,2-O-ethylene- -glucose derived from 2-O-(2-hydroxyethyl)- -glucose were identified by mass-spectral analysis.     

Characterization of N- and O-linked glycosylation of recombinant human bile salt-stimulated lipase secreted by Pichia pastoris

Recombinant human bile salt-stimulated lipase (hBSSL) was expressed in and secreted by Pichia pastoris, an organism exploited for the large-scale production of recombinant (glyco)proteins by bioprocessing technology. The 76.3-kDa glycoprotein was associated with 75-80 Man and a small amount of GlcNAc. hBSSL has one N-glycosylation site at Asn187, which was 38-40% occupied with a Man(10)GlcNAc(2) structure defined previously in Pichia as the oligosaccharide-lipid form of Man(9)GlcNAc(2) trimmed of the middle-arm terminal alpha 1,2-Man and elongated with Man alpha 1,2Man alpha 1,6-disaccharide attached to the lower-arm core alpha 1,3-Man (Trimble et al. [1991], J. Biol. Chem., 266, 22807-22817). The C-terminal 192 residues of hBSSL contain 16 Pro-rich 11-amino-acid repeats, which include 32 Ser/Thr residues as potential O-glycosylation sites. Using hBSSL as a platform to study Pichia's O-glycosylation capabilities, we found that nearly all of these sites were occupied by mannose-containing O-glycans, whose structures, after beta-elimination and purification, were assigned by (1)H NMR and, in some cases, by linkage-specific exoglycosidases and methylation analysis. The most abundant O-glycan was alpha 1,2-mannobiitol (55%), followed by alpha 1,2-mannotriitol (16%) and mannitol (10%) and a lesser amount was alpha 1,2-mannotetraitol. Unexpectedly, Man(5) and Man(6) O-glycans were present, which had the structure Man beta 1,2Man beta 1,2Man alpha 1,2(Man alpha 1,2)(1,2)mannitol. Also a small amount of a phosphorylated Man(6) O-glycan was characterized by MALDI-TOF MS postsource decay analysis as having the reducing-end mannitol disubstituted with a glycosidically linked phosphorylated Man and an unbranched Man(4) polymer elongated from a different mannitol carbon. This is the first report of the synthesis of beta-Man- and phosphate-containing O-linked constituents on glycoproteins synthesized by P. pastoris.     

Hydrazinolysis of monosaccharides: a two-step synthesis of chiral pentane-1,2,3-triols from pentoses and observations on the hydrazinolysis of glycoproteins and glycopeptides

1,2-Dideoxyalditols, the corresponding 1-alkenes, and 1-deoxyalditols are formed in various proportions from d-glucose, d-mannose, l-arabinose, and d-xylose by the action of refluxing hydrazine. Sequential hydrazinolysis, catalytic hydrogenation, and chromatography afford a route to 1,2-dideoxyalditols. For example, 1,2-dideoxy-l-erythro-pentitol is formed from l-arabinose in 42% yield, and d-xylose is a source of 1,2-dideoxy-d-threo-pentitol (50%). Under the conditions (anhydrous hydrazine at 100° for 30 h in the absence of air) used by Montreuil for the hydrazinolysis of glycoproteins and glycopeptides, no 1,2-dideoxyalditol was formed; degradation was incomplete, there being some aldose hydrazone present. Under Kochetkov's hydrazinolysis conditions (105° for 10 h with hydrazinium sulphate), less degradation occurred and the product from d-galactose was identified as 1-deoxy-d-tagatose hydrazone.     

Stereoselective glycosylations using benzoylated glucosyl halides with inexpensive promoters

Reactions of O-benzoylated glucopyranosyl halide (I, Br), isolated or generated in situ from per-benzoylated glucose (8a) and trimethylsilyl halide, with various alcohols were efficiently promoted by zinc halide (Cl, Br) or N-bromosuccinimide with a catalytic ZnI₂ to give the corresponding 1,2-trans-β-glucosides in good to high yields. When the anomeric halogenation of 8a was carried out in the presence of reactive alcohols, 1,2-cis--glucosides were selectively formed.     

Selective hydrogenolysis of raw glycerol to 1,2-propanediol over Cu–ZnO catalysts in fixed-bed reactor

The catalytic properties of Cu–ZnO catalysts for glycerol hydrogenolysis to 1,2-propanediol (1,2-PDO) were tested in a fixed-bed reactor at 250 °C and 2.0 MPa H₂. The relation between composition, surface properties, and catalytic performance of glycerol hydrogenation of Cu–ZnO catalysts was studied using nitrogen adsorption (BET methods), XRD, H₂ temperature-programmed reduction, and N₂O chemisorptions. It was found that there was a close link between the surface CuO amount of Cu–ZnO catalyst and the reactivity for glycerol hydrogenation. The Cu–ZnO catalyst (Cu/Zn = 1.86) which had the highest surface Cu amount showed the best catalytic activity for glycerol hydrogenolysis. Furthermore, Cu–ZnO catalyst presented good stability and remarkable catalytic activity for glycerol hydrogenolysis to 1,2-PDO using raw glycerol derived from the fat saponification as feedstock.     

Stereoselective C-glycosidation of unprotected D-glycals with trimethylsilyl cyanide

Unprotected glycals reacted with trimethylsilyl cyanide in the presence of a catalytic amount of a palladium compound to yield the 2,3-unsaturated glycosyl cyanides in high yield and in alpha-selectivity.     

腈类物降解菌多样性和产腈水合酶研究进展

腈水合酶催化反应在有机合成领域已有广泛的应用。作为一类重要的催化剂,腈水合酶可以将腈类物质转化为相应的酰胺。由于这种酶具有固有的立体和区域选择性,在精细化工领域已成为绿色、温和、对同分异构体具有选择性的催化剂。同时腈水合酶在生物修复和环境保护中也起着重要作用。综述了目前国内外腈水合酶的研究进展,包括降解腈类的微生物多样性、腈水合酶的催化特性、产腈水合酶菌株的改造以及腈水合酶相关基因的克隆与研究。对固定化酶和腈水合酶的应用也进行了叙述。     

C(2)-Symmetric dialkoxyphosphoramide and dialkoxythiophosphoramide derivatives of (1R, 2R)-1,2-diaminocyclohexane as chiral ligands for the titanium(IV) alkoxide-promoted asymmetric addition reactions of diethylzinc to arylaldehydes.

C(2)-Symmetric chiral diethoxyphosphoramide 4, diethoxythiophosphoramide 5, and diisopropoxyphosphoramide 6 of (1R, 2R)-1,2-diaminocyclohexane were prepared by the reactions of diethoxyphosphinic chloride, diethoxythiophosphinic chloride, and diisopropoxyphosphinic chloride with (1R, 2R)-1,2-diaminocyclohexane, respectively. They were used as catalytic chiral ligands in the asymmetric addition reactions of diethylzinc to aldehydes in the presence of titanium(IV) isopropoxide to give the corresponding sec-alcohols with 43-70% ee. Chiral ligands 4 and 5 gave the sec-alcohols with opposite absolute configuration.     

Controlled synthesis of O-glycopolypeptide polymers and their molecular recognition by lectins

The facile synthesis of high molecular weight water-soluble O-glycopolypeptide polymers by the ring-opening polymerization of their corresponding N-carboxyanhydride (NCA) in very high yield (overall yield > 70%) is reported. The per-acetylated-O-glycosylated lysine-NCA monomers, synthesized using stable glycosyl donors and a commercially available protected amino acid in very high yield, was polymerized using commercially available amine initiators. The synthesized water-soluble glycopolypeptides were found to be α-helical in aqueous solution. However, we were able to control the secondary conformation of the glycopolypeptides (α-helix vs nonhelical structures) by polymerizing racemic amino acid glyco NCAs. We have also investigated the binding of the glycopolypeptide poly(α-manno-O-lys) with the lectin Con-A using precipitation and hemagglutination assays as well as by isothermal titration calorimetry (ITC). The ITC results clearly show that the binding process is enthalpy driven for both α-helical and nonhelical structures, with negative entropic contribution. Binding stoichiometry for the glycopolypeptide poly(α-manno-O-lys) having a nonhelical structure was slightly higher as compared to the corresponding polypeptide which adopted an α-helical structure.     

Use of new phosphonylating and coupling agents in the synthesis of oligodeoxyribonucleotides via the H-phosphonate approach.

New phosphonylating and coupling agents for the synthesis of oligodeoxyribonucleotides via H-phosphonate approach have been developed. Tris(1,1,1,3,3,3-hexafluoro-2-propyl) phosphite, prepared by the reaction of lithium salt of 1,1,1,3,3,3-hexafluoro-2-propoxide with PCl3, reacts with deoxyribonucleosides in the presence of a catalytic amount of triethylamine to produce in the high yield the corresponding deoxyribonucleoside 3'-H-phosphonate units. The use of a new coupling reagent, 1,3-dimethyl-2-chloro-imidazolinium chloride (DMCI) for the internucleotidic H-phosphonate bond formation via the H-phosphonate approach is also discussed in detail.     

Catalytic asymmetric synthesis of 19,20-dihydroakuammicine

An enantiocontrolled total synthesis of 19,20-dihydroakuammicine using a catalytic asymmetric Michael addition of dimethyl malonate to cyclohexenone as the key step is described. The above catalytic asymmetric Michael addition proceeds quite efficiently in the presence of a heterobimetalic asymmetric catalyst (ALB-KO-t-Bu-MS 4A, 0.3 mol%), giving the corresponding Michael adduct in 94% yield and 99% ee.     

Activation of the Si-Si σ-bond of 1,2-divinyldisilane catalyzed by Ru(II) complexes

In the presence of a catalytic amount of RuHCl(CO)(PR₃)_n (R=ⁱPr, n=2; R=Ph, n=3), 1,1,2,2-tetramethyl-1,2-divinyldisilane (1) undergoes unexpected and clean isomerization via the Si-Si bond cleavage to yield a mixture of 6- and 5-membered cyclic compounds, 1,1,4,4-tetramethyl-1,4-disilacyclohex-2-ene and 1,1,2,3,3,-pentamethyl-1,3-disilacyclopent-4-ene, the former being the major product.     

Asymmetric oxidation of racemic 2-substituted 1,3-oxathianes

Racemic 2-substituted 1,3-oxathianes were oxidized with good to high enantiomer-differentiation by using urea hydrogen peroxide addition compound as oxidant in the presence of a catalytic amount of di-mu-oxo Ti(salen) complex, giving the corresponding sulfoxides diastereoselectively.     

Synthesis of a cyanoethylidene derivative of 3,6-anhydro-d-galactose and its application as glycosyl donor

Starting from 1,2,4-tri-O-acetyl-3,6-anhydro-alpha-d-galactopyranose, 4-O-acetyl-3,6-anhydro-1,2-O-(1-cyanoethylidene)-alpha-d-galactopyranose (7) was synthesized by treatment with cyanotrimethylsilane. Additionally, 3,4-di-O-acetyl-1,2-O-(1-cyanoethylidene)-6-O-tosyl-alpha-d-galactopyranose was prepared from the corresponding bromide and both cyanoethylidene derivatives were used as donors in glycosylation reactions. The coupling with benzyl 2,4,6-tri-O-acetyl-3-O-trityl-beta-d-galactopyranoside provided exclusively the beta-linked disaccharides in approximately 30% yield. The more reactive methyl 2,3-O-isopropylidene-4-O-trityl-alpha-l-rhamnopyranoside gave with donors 3 and 7 the corresponding disaccharides in nearly 60% yield. Furthermore, the synthesis of 3,6-anhydro-4-O-trityl-1,2-O-[1-(endo-cyano)ethylidene]-alpha-d-galactopyranose, which can be used as a monomer for polycondensation reaction is described.     

Syntheses and reactions of 5-O-acetyl-1,2-anhydro-3-O-benzyl-alpha-D-ribofuranose and beta-D-lyxofuranose, 5-O-acetyl-1,2-anhydro-3,6-di-O-benzyl- and 1,2-anhydro-5,6-di-O-benzoyl-3-O-benzyl-beta-D-mannofuranose, and 6-O-acetyl-1,2-anhydro-3,4-di-O-benzyl-alpha-D-glucopyranose and -beta-D-talopyranose

The title compounds 5-O-acetyl-1,2-anhydro-3-O-benzyl-alpha-D-ribofuranose and 5-O-acetyl-1,2-anhydro-3-O-benzyl-beta-D-lyxofuranose, and 6-O-acetyl-1,2-anhydro-3,4-di-O-benzyl-alpha-D-glucopyranose and 6-O-acetyl-1,2-anhydro-3,4-di-O-benzyl-beta-D-talopyranose, and 5-O-acetyl-1,2-anhydro-3,6-di-O-benzyl-beta-D-mannofuranose and 1,2-anhydro-5,6-di-O-benzoyl-3-O-benzyl-beta-D-mannofuranose have each been synthesized from the corresponding 2-O-tosylate and 1-free hydroxyl intermediates by base-initiated intramolecular S(N)2 ring closure in almost quantitative yields. Acetyl and benzoyl groups were not affected in the ring closure reactions. Condensation of 6-O-acetyl-1,2-anhydro-3,4-di-O-benzyl-alpha-D-glucopyranose and 5-O-acetyl-1,2-anhydro-3,6-di-O-benzyl-beta-D-mannofuranose with 1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranose in the presence of ZnCl2 as the catalyst afforded the 1,2-trans-linked 6-O-acetyl-3,4-di-O-benzyl-beta-D-glucopyranosyl-(1-->6)-1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranose and 5-O-acetyl-3,6-di-O-benzyl-alpha-D-mannofuranosyl-(1-->6)-1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranose as the sole products in satisfactory yields, while condensation of 5-O-acetyl-1,2-anhydro-3-O-benzyl-beta-D-lyxofuranose with 3-O-benzyl-1,2-O-isopropylidene-alpha-D-xylofuranose yielded the 1,2-trans-linked 5-O-acetyl-3-O-benzyl-alpha-D-lyxofuranosyl-(1-->5)-3-O-benzyl-1,2-O-isopropylidene-alpha-D-xylofuranose as the sole product in a good yield. The 6-O-acetyl group in the glycosyl donor, 6-O-acetyl-1,2-anhydro-3,4-di-O-benzyl-alpha-D-glucopyranose, did not influence the stereoselectivity of the ring-opening-coupling reaction.     

Assessing the inhibitory potency of galectin ligands identified from combinatorial (glyco)peptide libraries using surface plasmon resonance spectroscopy

Combinatorial (glyco)peptide libraries offer the possibility to define effective inhibitors of protein (lectin)-glycan interactions. If a (glyco)peptide surpasses the inhibitory potency of the free sugar, then the new peptide-lectin contacts underlying the affinity enhancement may guide further rational drug design. Focusing on the adhesion/growth regulatory human galectins 1 and 3, a screening of three combinatorial solid-phase (glyco)peptide libraries, containing Gal(β1-O)Thr, Gal(β1-S)Cys/Gal(β1-N)Asn, and Lac(β1-O)Thr, with the fluorescently labeled lectins had led to a series of lead compounds. To define the inhibitory potency of a selection of resynthesized (glyco)peptides systematically, a surface plasmon resonance-based inhibition assay with immobilized asialofetuin was set up. (Glyco)Peptides with up to 66-fold potency relative to free lactose as inhibitor were characterized. The presence of lactose in the most effective glycopeptides indicated the presence of affinity-enhancing peptide-lectin contacts. In addition to drug design, they may be helpful for fine-structural analysis of the binding sites.     

Role of the two catalytic domains of DSR-E dextransucrase and their involvement in the formation of highly alpha-1,2 branched dextran

The dsrE gene from Leuconostoc mesenteroides NRRL B-1299 was shown to encode a very large protein with two potentially active catalytic domains (CD1 and CD2) separated by a glucan binding domain (GBD). From sequence analysis, DSR-E was classified in glucoside hydrolase family 70, where it is the only enzyme to have two catalytic domains. The recombinant protein DSR-E synthesizes both alpha-1,6 and alpha-1,2 glucosidic linkages in transglucosylation reactions using sucrose as the donor and maltose as the acceptor. To investigate the specific roles of CD1 and CD2 in the catalytic mechanism, truncated forms of dsrE were cloned and expressed in Escherichia coli. Gene products were then small-scale purified to isolate the various corresponding enzymes. Dextran and oligosaccharide syntheses were performed. Structural characterization by (13)C nuclear magnetic resonance and/or high-performance liquid chromatography showed that enzymes devoid of CD2 synthesized products containing only alpha-1,6 linkages. On the other hand, enzymes devoid of CD1 modified alpha-1,6 linear oligosaccharides and dextran acceptors through the formation of alpha-1,2 linkages. Therefore, each domain is highly regiospecific, CD1 being specific for the synthesis of alpha-1,6 glucosidic bonds and CD2 only catalyzing the formation of alpha-1,2 linkages. This finding permitted us to elucidate the mechanism of alpha-1,2 branching formation and to engineer a novel transglucosidase specific for the formation of alpha-1,2 linkages. This enzyme will be very useful to control the rate of alpha-1,2 linkage synthesis in dextran or oligosaccharide production.