Miroslav Koóš

Preparation and crystal and molecular structure of 6-O-[(2S)-2,3-epoxypropyl]-1, 2:3,4-di-O-isopropylidene-α-d-galactopyranose. Pyranoid ring conformation in 1,2:3,4-di-O-isopropylidene galactopyranose and related systems

Abstract The title compound was isolated by several recrystallisations from a 1:1 mixture of diastereomers which was obtained in 75% yield from the reaction of 1,2:3,4-di-O- isopropylidene-α- d -galactopyranose with epichlorohydrin. The absolute configuration of this isomer (30% yield) was established by X-ray crystallography. The conformation of the pyranoid ring in this compound is compared to those in related situations. In all these cases the pyranoid ring adopts a heavily distorted conformation which is described on average as between the screw-boat OS5 and the twist-boat (“skew”-boat) OT2 with deviations in the direction of the boat B2,5 in most cases. The puckering parameters for all such reported pyranoid rings were calculated or recalculated, and are given within expanded conventions of carbohydrate nomenclature.

Improved synthesis of an aldobiouronic acid related to hardwood xylans, and preparation of a derivative thereof suitable for linking to proteins

Treatment of 1,3,4-tri-O-acetyl-alpha-D-xylopyranose with methyl 2,3-di-O-benzyl-l-chloro-l-deoxy-4-O-methyl-alpha, beta-D-glucopyranuronate in the presence of silver trifluoromethanesulfonate was highly stereoselective to give the alpha-linked aldobiouronic acid derivative (4) in 86% yield, after hydrogenolysis of the crude product of the coupling and chromatography. Compound 4 was acetylated and the fully protected substance was converted to the corresponding glycosyl chloride. Reaction of the latter with p-nitrophenol under phase-transfer catalysis afforded, after deacetylation, p-nitrophenyl 2-O-(methyl 4-O-methyl-alpha-D-glucopyranosyluronate)-beta-D-xylopyranoside.

On hydrogen bonding in 1,6-anhydro-β-d-glucopyranose (levoglucosan): X-ray and neutron diffraction and DFT study

The geometry of hydrogen bonds in 1,6-anhydro-beta-D-glucopyranose (levoglucosan) is accurately determined by refinement of time-of-flight neutron single-crystal diffraction data. Molecules of levoglucosan are held together by a hydrogen-bond array formed by a combination of strong O-H...O and supporting weaker C-H...O bonds. These are fully and accurately detailed by the neutron diffraction study. The strong hydrogen bonds link molecules in finite chains, with hydroxyl O atoms acting as both donors and acceptors of hydroxyl H atoms. A comparison of molecular and solid-state DFT calculations predicts red shifts of O-H and associated blue shifts of C-H stretching frequencies due to the formation of hydrogen bonds in this system.

Synthesis and Molecular Structure of Methyl 4-O-methyl-α-D- glucopyranuronate

A method for the preparation of methyl 4-O-methyl-α-D-glucopyranuronate and its single crystal X-ray structure determination are reported. The molecule adopts an almost ideal 4C1 (OC3) conformation.

4-Amino-4-cyano-4,6-dideoxy sugar derivatives from methyl 6-deoxy-2,3-O-isopropylidene-α-l-lyxo-hexopyranosid-4-ulose via Strecker-type reaction

Abstract Application of the Strecker reaction to methyl 6-deoxy-2,3- O -isopropylidene- α - l - lyxo -hexopyranosid-4-ulose resulted in the formation of methyl 4-amino-4-cyano-4,6-dideoxy-2,3- O -isopropylidene- α - l -talopyranoside, methyl 4-amino-4-cyano-4,6-dideoxy-2,3- O -isopropylidene- β - d -allopyranoside and methyl 4-cyano-6-deoxy-2,3- O -isopropylidene- α - l -talopyranoside. Their proportionality and yields depend on the reaction conditions used. Additionally, 4-amino-4-cyano-4,6-dideoxy-2,3- O -isopropylidene- α - l -talopyranoside can be prepared favourably from preformed methyl 4-cyano-6-deoxy-2,3- O -isopropylidene- α - l -talopyranoside. The crystal structure of methyl 4-acetamido-4-cyano-4,6-dideoxy-2,3- O -isopropylidene- α - l -talopyranoside is also presented.

An efficient and versatile synthesis of apiose and some C-1-aldehyde- and/or 2,3-O-protected derivatives

Abstract The synthesis of 2,3- O -isopropylidene-β- d -apiofuranose (58% overall yield) from l -arabinose via 3- C -(hydroxymethyl)-2,3- O -isopropylidene- d - glycero -tetrose diethyl dithioacetal is reported. Starting from l -arabinose an alternative precursor of d -apiose, 3- C -(hydroxymethyl)-2,3- O -isopropylidene- d - glycero -tetrose dimethyl acetal, was prepared from 2,3- O -isopropylidene- l - threo -tetrodialdose dimethyl acetal and formaldehyde by the aldol-Cannizzaro reaction. Unprotected d -apiose is accessible from both precursors on acid hydrolysis.

A versatile route to 2,3-unsaturated sugar derivatives via corresponding 3-acetoxy-1-nitro-1-alkenes

Abstract Reduction of 3-O-acetylated sugar 1-nitro-1-alkenes with zinc and acetic acid afforded corresponding 2,3-unsaturated sugar oximes in high yields from which either free deprotected sugars or further useful 2,3-unsaturated sugar derivatives can be prepared.

Synthesis and antimicrobial activity of some 2-alkyl-2H-1,4-benzothiazin-3(4H)-ones and 2-alkylbenzo[d]imidazolo[2,1-b]-thiazolidin-3-ones

SummarySodium 2-aminothiophenoxide (1) reacts with ethyl 2-bromoalkanoates (2) under direct cyclization to form 2-alkyl-2H-1,4-benzothiazin-3(4H)-ones (3). Reaction of the sodium salt of 2-mercaptobenzimidazole (4) with2 or 2-bromoalkanoic acids (5) affords only S-alkylated products (6 or7, respectively). The cyclization products — 2-alkylbenzo[d]imidazolo[2,1-b]thiazolidin-3-ones (8) — can be obtained only from the corresponding 2-(2-benzimidazolylthio)alkanoic acids (7) by the action of acetic anhydride. Both compounds3 and8 exhibit only moderate antimicrobial activity against some gram-positive bacteria.ZusammenfassungBei der Reaktion von Natrium-2-aminothiophenolat mit 2-Bromoalkansäure-ethylestern (2) entstehen als Cyclisierungsprodukte 2-Alkyl-2H-1,4-benzothiazin-3(4H)-one (3). Die Umsetzung von Natriumbenzimidazol-2-thiolat mit2 oder mit 2-Bromoalkansäuren (5) liefert nur S-Alkylierungsprodukte (6 oder7). Die Cyclisierungsprodukte — 2-Alkylbenzo[d]imidazolo[2,1-b]thiazolidin-3-one (8) — sind nur durch Umsetzung von entsprechenden 2-(2-Benzimidazolylthio)-alkansäuren (7) mit Acetanhydrid erhältlich. Die Verbindungen3 und8 weisen nur mäßige antimikrobielle Wirkung gegen einige gram-positive Bakterien aus.

Three isomeric forms of hydroxyphenyl-2-oxazoline: 2-(2-hydroxyphenyl)-2-oxazoline, 2-(3-hydroxyphenyl)-2-oxazoline and 2-(4-hydroxyphenyl)-2-oxazoline

Crystal structures are reported for three isomeric compounds, namely 2-(2-hydroxyphenyl)-2-oxazoline, (I), 2-(3-hydroxyphenyl)-2-oxazoline, (II), and 2-(4-hydroxyphenyl)-2-oxazoline, (III), all C9H9NO2 [systematic names: 2-(4,5-dihydro-1,3-oxazol-2-yl)phenol, (I), 3-(4,5-dihydro-1,3-oxazol-2-yl)phenol, (II), and 4-(4,5-dihydro-1,3-oxazol-2-yl)phenol, (III)]. In these compounds, the deviation from coplanarity of the oxazoline and benzene rings is dependent on the position of the hydroxy group on the benzene ring. The coplanar arrangement in (I) is stabilized by a strong intramolecular O-H...N hydrogen bond. Surprisingly, the 2-oxazoline ring in molecule B of (II) adopts a 3T4 (C2TC3) conformation, while the 2-oxazoline ring in molecule A, as well as that in (I) and (III), is nearly planar, as expected. Tetramers of molecules of (II) are formed and they are bound together via weak C-H...N hydrogen bonds. In (III), strong intermolecular O-H...N hydrogen bonds and weak intramolecular C-H...O hydrogen bonds lead to the formation of an infinite chain of molecules perpendicular to the b direction. This paper also reports a theoretical investigation of hydrogen bonds, based on density functional theory (DFT) employing periodic boundary conditions.

Synthesis of saccharide precursors for preparation of potential inhibitors of glycosyltranferases

Ethyl 6-O-tert-butyldimethylsilyl-3,4-di-O-acetyl-2-thio-α-D-fructofuranoside (Va), its β-analog (Vb); as well as benzyl 6-O-tert-butyldimethylsilyl-3,4-di-O-acetyl-2-thio-α-D-fructofuranoside (Xa) and its β-analog (Xb), having an unprotected OH group at C-1, were prepared by sequential synthesis starting from commercially available D-fructose. These compounds represent suitable nucleophiles for the preparation of model carbohydrate mimetics of a glycosyltransferase inhibitor type in transition state. The structures of all compounds were confirmed by NMR spectral data and elemental analyses.