Synthesis of fragments of the glycocalyx glycan of the parasite Schistosoma mansoni

The chemical synthesis of alpha-L-Fucp-(1 --> 3)-beta-D-GalpNAc-(1 --> 4)-beta-D-GlcpNAc-(1 --> 3)-alpha-D-GalpO(CH2)5NH2, beta-D-GalpNAc-(1 --> 4)-[alpha-L-Fucp-(1 --> 3)-]beta-D-GlcpNAc-(1 --> 3)-alpha-D-GalpO(CH2)5NH2, and alpha-L-Fucp-(1 --> 3)-beta-D-GalpNAc-(1 --> 4)-[alpha-L-Fucp-(1 --> 3)-]beta-D-GlcpNAc-(1 --> 3)-alpha-D-GalpO(CH2)5NH2 is described. These structures represent fucosylated oligosaccharide fragments of the glycocalyx glycan of the cercarial stage of the parasite Schistosoma mansoni, and in protein-conjugated form they are potential diagnostics in the search for antibodies raised against the glycan in the serum of infected humans.     

Synthesis of C-terminal fragments of bombesin and their analogues

With the aim of structural-functional studies in the bombesin series, a number of bombesin fragments and analogues have been synthesized. The synthesis was performed by the carbodiimide method and by the activated-ester method. Fragments with the sequences 7–14, 8–14, and 9–14 were obtained by 4+4, 3+4, and 2+4 schemes and a pentapeptide with the sequence 9–13 by a 3 + 2 scheme. Acetylation of the octapeptide BN(7–14) was carried out by the action of acetic anhydride in pyridine. Analogues of the C-terminal nonapeptide of bombesin [DPhe⁷]BN(6–14) and [Pro⁶, Gly⁷, DAla¹¹]BN(6–14) were synthesized by fragment condensation using the 5 + 4 scheme. The individuality of the compounds obtained was confirmed by their chromatographic behavior on plates coated with silica gel, and by the results of amino acid analysis, high-voltage electrophoresis, and high-performance liquid chromatography, and their structures were confirmed by the results of high-resolution¹H NMR spectroscopy (360 MHz). In experiments on rabbits, in a dose of 1 µg with central administration the full hypothermic effect of bombesin was shown by the preparation [AcGln⁷]BN(7–14), while the preparation [DPhe⁷]BN(6–14) and [Pro⁶,Gly⁷,DAla¹¹]BN(6–14) possessed only a slight effect (～1% of the activity of bombesin).     

Synthesis of C-terminal fragments of bombesin and their analogues

With the aim of structural-functional studies in the bombesin series, a number of bombesin fragments and analogues have been synthesized. The synthesis was performed by the carbodiimide method and by the activated-ester method. Fragments with the sequences 7–14, 8–14, and 9–14 were obtained by 4+4, 3+4, and 2+4 schemes and a pentapeptide with the sequence 9–13 by a 3 + 2 scheme. Acetylation of the octapeptide BN(7–14) was carried out by the action of acetic anhydride in pyridine. Analogues of the C-terminal nonapeptide of bombesin [DPhe⁷]BN(6–14) and [Pro⁶, Gly⁷, DAla¹¹]BN(6–14) were synthesized by fragment condensation using the 5 + 4 scheme. The individuality of the compounds obtained was confirmed by their chromatographic behavior on plates coated with silica gel, and by the results of amino acid analysis, high-voltage electrophoresis, and high-performance liquid chromatography, and their structures were confirmed by the results of high-resolution¹H NMR spectroscopy (360 MHz). In experiments on rabbits, in a dose of 1 µg with central administration the full hypothermic effect of bombesin was shown by the preparation [AcGln⁷]BN(7–14), while the preparation [DPhe⁷]BN(6–14) and [Pro⁶,Gly⁷,DAla¹¹]BN(6–14) possessed only a slight effect (1% of the activity of bombesin).Leningrad State University. Institute of Organic Synthesis, Latvian SSR Academy of Sciences, Riga. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 554–564, July–August, 1989.     

Synthesis of oligosaccharide fragments of the glycosylinositolphospholipid of Trypanosoma cruzi: a new selenoglycoside glycosyl donor for the preparation of 4-thiogalactofuranosyl analogues

A new selenoglycoside, phenyl 2,3,5,6-tetra-O-acetyl-4-thio-1-selenogalactofuranose, has been synthesized. This 4-thiogalactofuranosyl donor was used in the syntheses of heteroatom analogues of the di-, tri-, and tetrasaccharides corresponding to the oligosaccharide β-d-Galf-(1→3)-α-d-Manp-(1→2)-(β-d-Galf-(1→3))-α-d-Manp. These compounds represent fragments of the terminal end of the glycosylinositolphospholipid oligosaccharide found in the protozoan Trypanosoma cruzi, the causative agent of Chagas disease, and are intended for use as inhibitors of the enzymes that construct the native oligosaccharides. The syntheses employed the selective activation of a phenyl 4-thio-1-selenogalactofuranoside glycosyl donor over ethyl 1-thioglycoside glycosyl acceptors with NIS/TfOH.     

Synthesis of apiose-containing oligosaccharide fragments of the plant cell wall: fragments of rhamnogalacturonan-II side chains A and B, and apiogalacturonan

Fragments of pectic polysaccharides rhamnogalacturonan-II (RG-II) and apiogalacturonan were synthesised using p-tolylthio apiofuranoside derivatives as key building blocks. Apiofuranose thioglycosides can be conveniently prepared by cyclization of the corresponding dithioacetals possessing a 2,3-O-isopropylidene group, which is required for preservation of the correct (3R) configuration of the apiofuranose ring. The remarkable stability of this protecting group in apiofuranose derivatives requires its replacement with a more reactive protecting group, such as a benzylidene acetal which was used in the synthesis of trisaccharide β-Rhap-(1→3')-β-Apif-(1→2)-α-GalAp-OMe. The X-ray crystal structure of the protected precursor of this trisaccharide has been elucidated.     

Synthesis and photochromism of indolinospirochromenes with condensed fragments in the indoline part of the molecules

Indoline spirochromenes with condensed fragments in the indoline part of the molecules were synthesized. All of the compounds have photochromic properties. The introduction of a condensed fragment into the indoline part of the molecule leads to a bathochromic shift of both the long-wave and short-wave absorption bands of the photomerocyanine; the rate of the dark reaction does not change.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 104–109, January, 1988.     

Synthesis of oligosaccharide fragments of the Streptococcus pneumoniae type 14 capsular polysaccharide and their neoglycoconjugates with bovine serum albumin

2-Aminoethyl glycosides of tetra-, hexa- and octasaccharide fragments of the bacteria Streptococcus pneumoniae type 14 capsular polysaccharide were synthesized within a project directed to the development of pneumococcal conjugated vaccine based on synthetic carbohydrate ligands. Squarate method was used to obtain neoglycoconjugates of the synthesized oligosaccharides with bovine serum albumin.     

Synthesis and biological evaluation of phosphono analogues of capsular polysaccharide fragments from Neisseria meningitidis A

Neisseria meningitidis type A (MenA) is a Gram-negative encapsulated bacterium that may cause explosive epidemics of meningitis, especially in the sub-Saharan region of Africa. The development and manufacture of an efficient glycoconjugate vaccine against Neisseria meningitidis A is greatly hampered by the poor hydrolytic stability of its capsular polysaccharide, which is made up of (1-->6)-linked 2-acetamido-2-deoxy-alpha-D-mannopyranosyl phosphate repeating units. Since this chemical lability is a product of the inherent instability of the phosphodiester bridges, here we report the synthesis of phosphonoester-linked oligomers of N-acetyl mannosamine as candidates for stabilised analogues of the corresponding phosphate-bridged saccharides. The installation of each interglycosidic phosphonoester linkage was achieved by Mitsunobu coupling of a glycosyl C-phosphonate building block with the 6-OH moiety of a mannosaminyl residue. Each of the synthesised compounds contains an O-linked aminopropyl spacer at its reducing end (alpha- or beta-oriented) to allow for protein conjugation. The relative affinities of the synthetic molecules were investigated by a competitive ELISA assay and showed that a human polyclonal anti-MenA serum can recognise both the phosphonoester-bridged fragments 1-3 and their monomeric subunits, glycosides 20 and 21. Moreover, the biological results suggest that the abilities of these compounds to inhibit the binding of a specific antibody to MenA polysaccharide are dependent on the chain lengths of the molecules, but independent on the orientations of the anomeric linkers.     

姜黄素类似物的合成及其生物活性的测定

实验合成了姜黄素的Knoevenagel缩合物4-(2-呋喃次甲基)姜黄素C1,氨基硫脲Schiff 碱配体E1,及其Schiff 碱配体的Zn(Ⅱ)配合物D1.采用DPPH法测定了产品清除自由基的能力,结果表明产品C1对DPPH自由基清除率为82.0%.在pH7.2的Tris-Hcl缓冲溶液中,采用紫外光谱和荧光光谱研究了C1与鲱鱼精DNA的相互作用,结果表明,C1与DNA是通过嵌插模式发生相互作用的,其键合常数为Kq =9.31×103.     

Capillary electrophoresis: a superior miniaturized tool for analysis of the mono-, di-, and oligosaccharide constituents of glycan moieties in proteoglycans

Proteoglycans are a major family of glycoconjugates which participate in and regulate several cellular events and biological functions. Their glycan chains determine their physicochemical and biological properties. Capillary electrophoresis, because of its high resolving power and sensitivity, has been successfully used for the analysis of carbohydrates. The monosaccharide constituents, the disaccharide sulfation pattern, and the uronic acid distribution within glycan chains of proteoglycans determine their interactions with matrix effectors and are responsible for numerous effects. Determination of the chemical composition and identification of key structural components and domains of glycans are, therefore, essential in understanding the biological functions of proteoglycans. In this report an overview of the capillary electrophoresis methods used to analyze and characterize the structure of the glycan chains of proteoglycans is presented.     

Synthesis of the ABC and IJ ring fragments of yessotoxin

Synthesis of a 6/6/6 tricyclic ether system (3) corresponding to the ABC ring fragment of yessotoxin (1) has been achieved via coupling of a triflate and a 2-lithiofuran followed by intramolecular hetero-Michael addition. The IJ ring fragment (4) of 1 was readily synthesized via successive Sharpless epoxidation and 6-endo cyclization of the resulting vinyl epoxide.     

Parasitological and Biochemical Efficacy of the Active Ingredients of Allium sativum and Curcuma longa in Schistosoma mansoni Infected Mice

The active ingredients allicin and curcumin have a wide range of actions against fungi, bacteria, and helminths. Therefore, the study was aimed to evaluate the efficacy of allicin (AL) and curcumin (CU) as antischistosomal drugs and their biochemical effects in normal and Schistosoma mansoni-infected mice. Praziquantel (PZQ) was administrated for two successive days while AL or CU was given for two weeks from the week 7th postinfection (PI). The possible effect of different regimens on Schistosoma worms was evaluated by measuring the percentage of the recovered worms, tissue egg load, and oogram pattern. Serum alanine transaminase activity and levels of triglycerides, cholesterol, and uric acid were measured. Liver tissue malondialdehyde and reduced glutathione levels besides, the activities of glutathione-S-transferase, superoxide dismutase and catalase were assessed for the oxidative/antioxidant condition. DNA electrophoresis of liver tissue was used to indicate the degree of fragmentation. There was a significant reduction in the recovered worms and egg load, with a marked change of oogram pattern in all treated groups with PZQ, AL, and CU in comparison with infected-untreated mice. PZQ, AL, and CU prevented most of the hematological and biochemical disorders, as well as significantly improved the antioxidant capacity and enhanced DNA fragmentation in the liver tissue of schistosomiasis mice compared to the infected-untreated group. These promising results suggest that AL and CU are efficient as antischistosomal drugs, and it would be beneficial to test their combination to understand the mechanism of action and the proper period of treatment leading to the best result.     

Synthesis and antigenic analysis of the BclA glycoprotein oligosaccharide from the Bacillus anthracis exosporium

The glycoprotein BclA is an important constituent of the exosporium of Bacillus anthracis spores. This glycoprotein is substituted with an oligosaccharide composed of a beta-L-rhamnoside substituted with the previously unknown terminal saccharide, 2-O-methyl-4-(3-hydroxy-3-methylbutanamido)-4,6-dideoxy-D-glucopyranose, also referred to as anthrose. Anthrose has not been found in spores of B. cereus and B. thuringiensis, making it a potential species-specific marker for B. anthracis. In order to study the antigenicity of anthrose, efficient syntheses of an anthrose-containing trisaccharide and a series of structurally related analogues were developed. The analogues lacked either the methyl ether at C-2 or contained modified C-4 amino functionalities of anthrose. The synthetic compounds were equipped with an aminopropyl spacer to facilitate conjugation to the carrier proteins mariculture Keyhole Limpet Hemocyanin (mcKLH) and bovine serum albumin (BSA). Serum antibodies of rabbits immunized with live or irradiated spores of B. anthracis Sterne 34F(2) were able to recognize the synthetic trisaccharide-mcKLH conjugate. The specificity of the interaction was confirmed by competitive inhibition with the free- and BSA-conjugated trisaccharides. Inhibition using the trisaccharide analogues demonstrated that the isovaleric acid moiety of anthrose is an important structural motif for antibody recognition. These data demonstrate that 1) anthrose is a specific antigenic determinant of the B. anthracis Sterne spore; 2) this antigen is presented to the immune system of rabbits receiving the anthrax live-spore vaccine; 3) synthetic analogues of the oligosaccharide retain the antigenic structure; and 4) the antigenic region is localized to specific terminal groups of the oligosaccharide. Collectively these data provide an important proof-of-concept step in the synthesis and development of spore-specific reagents for detection and targeting of non-protein structures in B. anthracis.     

Synthesis of the oligosaccharide moieties of musettamycin and marcellomycin,new antitumour antibiotics.

The total syntheses of the di and trisaccharide respective sugar-moieties of musettamycin and marcellomycin are reported.     

Synthesis and reactivity of the imido analogues of the uranyl ion

Addition of 1.5 equiv of I2 to a THF solution of UI3(THF)4, containing either 6 equiv of tBuNH2 or 2 equiv of RNH2 (R = Ph, 3,5-(CF3)2C6H3, 2,6-(iPr)2C6H3) and 4 equiv of NEt3, generates orange solutions containing U(NtBu)2I2(THF)2 (1) or U(NAr)2I2(THF)3 (Ar = Ph, 2; 3,5-(CF3)2C6H3, 3; 2,6-(iPr)2C6H3, 4), respectively, all of which can be isolated in good yields. Alternatively, 1 can be prepared by reaction of uranium metal with 3 equiv of I2 and 6 equiv of tBuNH2, also in good yield. Complexes 1-4 have been characterized by X-ray crystallography, and each of these complexes exhibits linear N-U-N linkages and short U-N bonds. Using density functional theory simulations of complexes 1 and 2, two triple bonds between the metal center and the nitrogen ligands were identified. Complexes 1 and 2 readily react with neutral Lewis bases such as pyridine or Ph3PO to form U(NR)2I2(L)2 (R = tBu, L = py, 5; Ph3PO, 7; R = Ph, L = py, 6; Ph3PO, 8), and with PMe3 to form U(NR)2I2(THF)(PMe3)2 (R = tBu, 9; Ph, 10). The solid-state molecular structures of 5, 7, and 9 have been determined by X-ray crystallography, and these complexes, like their parent compounds, exhibit linear N-U-N angles and short U-N bonds. Complexes 1 and 2 also react with AgOTf in CH2Cl2, forming U(NR)2(OTf)2(THF)3 (R = tBu, 11; Ph, 12) after recrystallization from THF. Crystals of 12 grown from CH2Cl2 were found to contain a dimer, [U(NPh)2(OTf)2(THF)2]2, a complex possessing bridging triflate groups.     

Synthesis of the 2,3,4-trisubstituted indole fragments of nosiheptide and glycothiohexide

Two routes to the protected 4-hydroxymethyl-3-methylindole-2-carboxylate fragment 17 of the thiopeptide antibiotic nosiheptide are described starting from methyl 4-methylindole-2-carboxylate 11, itself prepared in two steps, or from 3-amino-4-chlorobenzoic acid 26. The first route can be adapted to the synthesis of a fragment of the related antibiotic glycothiohexide-alpha, the 3,4-bis(hydroxymethyl)indole-2-carboxylate in which the two hydroxymethyl groups are differentiated as in indole 19 or the lactone 20.     

Synthesis and biological evaluation of analogues of the antibiotic pantocin B

Strains of the bacteria Erwinia herbicola produce antibiotics that effectively control E. amylovora, the bacterial pathogen responsible for the plant disease fire blight. Pantocin B was the first of these antibiotics to be characterized, and a flexible synthesis of various analogues is reported. Embedded in the "pseudo-tripeptide" backbone of pantocin B are a methylenediamine and a methyl sulfone, both unusual structural features in natural products. The peptidic nature of pantocin B facilitated a series of structure-activity relationship studies that probed the roles of these functional groups in determining the biological activity of pantocin B. A clear demarcation of the roles between the N- and C-terminal portions of the antibiotic was determined as a result of the structure-activity relationship studies. The N-terminal L-alanyl group is needed for cellular import but not for interaction with the intracellular target, the arginine biosynthetic enzyme N-acetylornithine aminotransferase. The methylenediamine and methyl sulfone portions were found to be essential for antibiotic activity, presumably due to extensive interactions with N-acetylornithine aminotransferase.