Lóránt Jánossy
University of Debrecen
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Featured researches published by Lóránt Jánossy.
Carbohydrate Research | 1997
Erzsébet Farkas; Lóránt Jánossy; János Harangi; Lili Kandra; András Lipták
Abstract One-pot acetylation and subsequent partial acetolysis of α-, β- and γ-cyclodextrins resulted in crystalline peracetylated malto-hexaose, -heptaose, and -octaose, respectively. Prolonged acetolysis of β-cyclodextrin gave a mixture of acetylated maltooligosaccharides, from which peracetylated malto-triose, -tetraose, and -pentaose were isolated. The acetylated oligosaccharides were converted into α-acetobromo derivatives, and then transformed into 4-nitrophenyl and 2-chloro-4-nitrophenyl β-glycosides. From the 4-nitrophenyl glycosides 4,6-O-benzylidene derivatives were prepared, which were used together with the free glycosides as substrates of porcine pancreatic α-amylase. One-pot acetylation and subsequent partial acetolysis of cyclodextrins resulted in the peracetylated maltooligomers (dp 3–8), which were transformed into 4-nitrophenyl and 2-chloro-4-nitrophenyl β-glycosides, the 4.6-O-benzylidene derivatives of NP-glycosides were also prepared
Tetrahedron Letters | 2000
András Lipták; Anikó Borbás; Lóránt Jánossy; László Szilágyi
Abstract Dioxane- and dioxolane-type (2-naphthyl)methylene acetals of glycosides were prepared by acid-catalyzed transacetalization reactions. The acetals were cleaved using either AlH3 (LiAlH4:AlCl3=3:1), NaCNBH3–HCl or BH3 Me3N–AlCl3 reagents. Reaction of the 4,6-O-acetals with AlH3 yielded 4-ONAP ethers whereas the other two reagents gave 6-ONAP derivatives with excellent regioselectivity. In dioxolane-type acetals the direction of the cleavage with all three reagents is determined by the stereochemistry of the acetal center; equatorial ONAP/axial-hydroxy derivatives are obtained from the exo-naphthyl isomers; endo-naphthyl acetals, on the other hand, give rise to the formation of axial ONAP/equatorial-hydroxy compounds. The NAP ether and the (2-naphthyl)methylene acetal protecting groups can both be readily removed by treatment with DDQ.
Carbohydrate Research | 2001
Magdolna Csávás; Anikó Borbás; Lóránt Jánossy; Gyula Batta; András Lipták
Abstract For the characterization of the supposed epitope of an arabinogalactan, isolated from the extract of the cell-cultured Echinacea purpurea, the title hexasaccharide was synthesized. The whole synthetic route was based on the 6-O-(methoxydimethyl)methyl ether (MIP) protecting group strategy. 2-O-Benzyl-3,4-O-isopropylidene-6-O-(methoxydimethyl)methyl-β- d -galactopyranosyl-(1→6)-1,2:3,4-di-O-isopropylidene-α- d -galactopyranose was used to prepare the desired glycosyl donor and glycosyl acceptor both carrying a persistent O-benzyl group at position 2′. Reaction of the digalactose donor and the digalactose acceptor resulted in a β-(1→6)-linked galactose-containing tetrasaccharide in which OH-2′ and OH-2′′′ were substituted with benzyl groups. Hydrogenolytic removal of the benzyl groups of the tetragalactose compound gave the diol aglycon which was diarabinosylated in one step to furnish the protected target compound, whose deprotection led to the title hexasaccharide. All of the synthesized compounds were characterized by 1H and 13C NMR spectra, as well as by MALDI-TOF mass-spectrometry measurements.
Tetrahedron Letters | 2003
Magdolna Csávás; Anikó Borbás; Lóránt Jánossy; András Lipták
Abstract An arabinogalactan-type double-branched octa- and two isomeric nonasaccharides were synthesized using the (2-naphthyl)methyl (NAP) and the acid sensitive but base stable (methoxydimethyl)methyl (MIP) protecting groups. The β-(1→6)-linked hexagalactan skeleton was synthesized having a benzyl and a (2-naphthyl)methyl (NAP) group at positions 2 of the second and the penultimate galactopyranosyl units, and this made possible sequential introduction of α- l -arabinofuranosyl or α- l -arabinofuranosyl-(1→5)-α- l -arabinofuranosyl side chains.
Carbohydrate Research | 1999
Anikó Borbás; Lóránt Jánossy; Andreas Liptak
Abstract For the characterisation of the anticipated epitope of an arabinogalactan, isolated from the extract of Echinacea purpurea, the trisaccharide α- l -Ara f -(1→2)-β- d -Gal p -(1→6)- d -Gal was synthesized. The easily available 3,4- O -isopropylidene-6- O -(methoxydimethyl)methyl-β- d -galactopyranosyl-(1→6)-1,2:3,4-di- O -isopropylidene-α- d -galactopyranose having the OH-2′ free served as aglycone upon direct arabinosylation at the 2′ position under Helferich conditions. The formed HgBr 2 cleaved the acid sensitive protecting group at position 6′, but under basic conditions the desired, fully protected trisaccharide, or its symmetrical dimerization derivative linked 6′- to 6′-position via an isopropylidene bridge, could be obtained. An alternative route involved arabinosylation of a hepta-O-acetylated digalactose with free OH-2′. Two other oligosaccharides, namely, α- l -Ara f -(1→6)-β- d -Gal p -(1→6)- d -Gal and (α- l -Ara f ) 2 -(1→2,6)-β- d -Gal p -(1→6)- d -Gal were also synthesized and characterised.
Acta Biologica Hungarica | 2008
J. E. Kerrigan; Chandran Ragunath; Lili Kandra; Gyöngyi Gyémánt; András Lipták; Lóránt Jánossy; J. B. Kaplan; Narayanan Ramasubbu
Bacteria in a biofilm are enmeshed in a self-synthesized extracellular polysaccharide matrix (PGA), which is a linear polymer of beta(1,6)-linked N-acetylglucosamine (GlcNAc) residues. Dispersin B (DspB), a soluble glycoside hydrolase produced by the periodontal pathogen Actinobacillus actinomycetemcomitans degrades PGA. The enzyme DspB is an alpha/beta TIM-barrel protein and belongs to family 20 glycosyl hydrolases members. The enzyme activity of DspB with regard to its substrate specificity towards beta(1,6)-linked GlcNAc polymers and its endo/exo character was investigated through ligand docking and the hydrolysis of synthetic oligosaccharides. Ligand docking analysis suggested that beta(1,6)-linked GlcNAc oligosaccharide bound to the active site better that beta(1,4)-linked GlcNAc oligosaccharide. Our combined results indicate that DspB is an exo-acting enzyme that hydrolyzes beta(1,6)-linked N-acetylglucosamine oligomers.
Carbohydrate Research | 2002
András Lipták; Lóránt Jánossy; Anikó Borbás; József Szejtli
Abstract The proton-catalyzed addition of 2-methoxypropene to α-, β- and γ-cyclodextrins resulted in hexakis-, heptakis-, and octakis[2,6-di -O- (methoxydimethyl)methyl]-α-, β- and γ-cyclodextrins, but no reaction was observed of CD-s with 2,2-dimethoxypropane. The mixed acetal-type compounds can be alkylated under basic conditions. The preparation of hexakis(3 -O- benzyl)-α-cyclodextrin demonstrates the synthetic value of this methodology.
Journal of Carbohydrate Chemistry | 1998
Zoltán Szurmai; Lóránt Jánossy; Zoltán Szilágyi; Károly Vékey
Abstract For the construction of N-glycoprotein glycan chains, valuable potential glycosyl donors, O-α-D-mannopyranosyl-(1→2)-α-D-mannopyranose octaacetate (19) and O-α-D-mannopyranosyl-(1→2)-O-α-D-mannopyranosyl-(1→2)-α-D-mannopyranose undeca-acetate (20) were obtained in gram-scale by the acetylation and subsequent partial acetolysis of bakers yeast, without the isolation of mannan. The acetolytic products were investigated by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Octaacetates of mannobiose (1→3) (11) and (1→6) (17) were chemically synthesized.
Organic Letters | 2003
András Lipták; Ferenc Sajtos; Lóránt Jánossy; Diethmar Gehle; László Szilágyi
Archive | 1984
József Szejtli; András Lipták; Pál Nánási; Péter Fügedi; Ildikó Jodál; Lili Kandra; Lóránt Jánossy