Beata Liberek

Hydrolysis of sulphonamides in aqueous solutions.

Hydrolysis is one of the most common reactions controlling abiotic degradation and is one of the main paths by which substances are degraded in the environment. Nevertheless, the available information on this process for many compounds, including sulphonamides (a group of antibiotic drugs widely used in veterinary medicine), is very limited. This is the first study investigating the hydrolytic stabilities of 12 sulphonamides, which were determined according to OECD guideline 111 (1st category reliability data on the basis of regulatory demands on data quality for the environmental risk assessment of pharmaceuticals). Hydrolysis behaviour was examined at pH values normally found in the environment. This was prefaced by a discussion of the acid-base properties of sulphonamides. All the sulphonamides tested were hydrolytically stable at pH 9.0, nine (apart from sulphadiazine, sulphachloropyridazine and sulphamethoxypyridazine) were stable in this respect at pH 7.0 and two (sulphadiazine and sulphaguanidine) at pH 4.0 (hydrolysis rate≤10%; t(0.5 (25°C))>1 year). The degradation products were identified, indicating two independent mechanisms of this process. Our results show that under typical environmental conditions (pH and temperature) sulphonamides are hydrolytically stable with a long half-life; they thus contribute to the on-going assessment of their environmental fate.

The use of tri-O-acetyl-D-glucal and -D-galactal in the synthesis of 3-acetamido-2,3-dideoxyhexopyranoses and -hexopyranosides.

Addition of hydrazoic acid to alpha,beta-unsaturated aldehydes derived from tri-O-acetyl-D-glucal and -D-galactal gave 3-azido-2,3-dideoxyhexopyranoses. These were converted into 1,4,6-tri-O-acetyl-3-azido-2,3-dideoxyhexopyranoses as well as methyl and ethyl glycosides. Hydrogenation of the proamine group in 3-azido-2,3-dideoxy derivatives provided different 3-amino and 3-acetamido sugars. The configuration and conformation of all products were established on the basis of the 1H and 13 C NMR, IR and polarimetric data.

X-ray diffraction and high-resolution NMR spectroscopy of methyl 3-azido-2,3-dideoxy-α-d-lyxo-hexopyranoside

The single-crystal X-ray diffraction and high-resolution 1H and 13C NMR spectral data for the title compound are reported. The influence of the ring oxygen atom on the J(1,2e) and J(4,5) coupling constants for 2-deoxy-D-lyxo- and -D-xylo-hexopyranosides is discussed.

Synthesis and conformational analysis of methyl 3-amino-2,3-dideoxyhexopyranosiduronic acids, new sugar amino acids, and their diglycotides

The synthesis of methyl 3-azido- and 3-amino-2,3-dideoxyhexopyranosiduronic acids and their methyl esters with the -alpha,beta-D-arabino-, -alpha,beta-D-ribo, and -alpha,beta-L-lyxo configurations is presented. The conformations of the synthesized sugar amino acids and their precursors are discussed on the basis of 1H NMR data. The influence of the 5-carboxyl group on the pyranose ring conformation is assessed, and the bonding of the monosugar amino acids into dimeric glycotides, using conventional solution-phase peptide syntheses, is reported.

Differently N-protected 3,4,6-tri-O-acetyl-2-amino-2-deoxy-D-glucopyranosyl chlorides and their application in the synthesis of diosgenyl 2-amino-2-deoxy-β-D-glucopyranoside.

Four differently N-protected 3,4,6-tri-O-acetyl-2-amino-2-deoxy-d-glucopyranosyl chlorides were synthesized and used as glycosyl donors in reactions with diosgenin. The following amine group protections were tested: trifluoroacetyl (TFA), 2,2,2-trichloroethoxycarbonyl (Troc), phthaloyl (Phth), and tetrachlorophthaloyl (TCP). Products of glycosylation were deprotected to yield diosgenyl 2-amino-2-deoxy-β-d-glucopyranoside. The efficiency of the procedures is discussed. Additionally, a single-crystal X-ray diffraction analysis for 3,4,6-tri-O-acetyl-2-deoxy-2-tetrachlorophthalimido-β-d-glucopyranosyl chloride is reported. Orientations of the pyranose substituents as well as the planarity of the acetoxy and phthalimide groups in the crystal lattice are discussed. Structural evidence is presented for a mesomeric effect in both groups. The preference of the cis over trans orientation of the acetoxy group is confirmed in the crystal lattice.

Fully acetylated 1,5-anhydro-2-deoxypent-1-enitols and 1,5-anhydro-2,6-dideoxyhex-1-enitols in DFT level theory conformational studies

Geometry optimizations at the B3LYP level of density functional theory (DFT) are reported for the (4)H(5) and (5)H(4) conformations of four glycals: 3,4-di-O-acetyl-1,5-anhydro-2-deoxy-D-erythro-pent-1-enitol (3,4-di-O-acetyl-D-arabinal), its D-threo isomer (3,4-di-O-acetyl-D-xylal), 3,4-di-O-acetyl-1,5-anhydro-2,6-dideoxy-D-arabino-hex-1-enitol (3,4-di-O-acetyl-D-rhamnal), and its D-lyxo isomer (3,4-di-O-acetyl-D-fucal). The Gibbs free energies, relative Gibbs free energies and geometry parameters are presented for all the optimized structures. Conformational analysis of both the acetoxy groups and 1,2-unsaturated pyranoid ring is performed. It is demonstrated that the acetoxy group is planar and adopts two conformations with regard to the Ac-O bond rotations, one of which is strongly preferred. One of the hydrogen atoms of the methyl group is always oriented synperiplanarly whereas the remaining two anticlinally with respect to the carbonyl oxygen. With regard to the AcO-R bond rotations some of the orientations are forbidden. The calculations indicate that 3,4-di-O-acetyl-D-arabinal adopts mainly the (4)H(5) conformation, whereas 3,4-di-O-acetyl-D-xylal prefers the (5)H(4) form, owing to the vinylogous anomeric effect (VAE). Competition between the VAE and quasi 1,3-diaxial interactions means that both 3,4-di-O-acetyl-D-rhamnal and 3,4-di-O-acetyl-D-fucal remain in the (4)H(5)⇄(5)H(4) conformational equilibrium, shifted in the (4)H(5) direction. It seems that the orientation of the 4-OAc group influences the quasi 1,3-diaxial interactions between 3-OAc and 5-CH(3) groups. Theoretical results are compared with assignments based on (1)H NMR studies.

Methyl 3-amino-2,3,6,-trideoxy-L-hexopyranosides in DFT level theory conformational studies.

Geometry optimizations at the B3LYP level of density functional theory are reported for the (1)C4 and (4)C1 conformations of four theoretically possible alpha and beta methyl 3-amino-2,3,6-trideoxy-L-hexopyranosides. The Gibbs free energies, relative Gibbs free energies, and geometry parameters are presented for all the optimized structures. Conformational analysis of the pyranose ring is performed for each stereoisomer on the basis of calculated rotamer populations. It is demonstrated that the alpha/beta-L-arabino, alpha/beta-L-lyxo, and alpha-L-ribo stereoisomers adopt the (1)C4 conformation, whereas beta-L-ribo and alpha/beta-L-xylo stereoisomers remain in (1)C4 <==> (4)C1 conformational equilibrium. The preference of the alpha over the beta anomers is due to the endo-anomeric effect. The factors affecting the stability of pyranose ring conformations are discussed, as is the influence of hydrogen bonds on the orientation of the hydroxyl and amino groups. Figures of the most stable conformers are presented.

Flavonol-based fluorescent indicator for determination of β-glucosidase activity

A novel fluorescent probe, based on the excited-state intramolecular proton transfer (ESIPT) phenomenon, for evaluation of β-glucosidase activity was designed. The synthesis of the probe was optimized. The conditions for the monitoring of enzymatic cleavage of the probe were developed and discussed from the point of view of reaction kinetics and simplicity of the method.

N-Alkyl derivatives of diosgenyl 2-amino-2-deoxy-β-D-glucopyranoside; synthesis and antimicrobial activity

Summary Diosgenyl 2-amino-2-deoxy-β-D-glucopyranoside is a synthetic saponin exhibiting attractive pharmacological properties. Different pathways tested by us to obtain this glycoside are summarized here. Moreover, the synthesis of N-alkyl and N,N-dialkyl derivatives of the glucopyranoside is presented. Evaluation of antibacterial and antifungal activities of these derivatives indicates that they have no inhibitory activity against Gram-negative bacteria, whereas many of the tested N-alkyl saponins were found to inhibit the growth of Gram-positive bacteria and human pathogenic fungi.

Acetylated methyl 1,2-dideoxyhex-1-enopyranuronates in density functional theory conformational studies.

Geometry optimizations at the B3LYP level and single point calculations at the MP2 level are reported for the (4)H(5) and (5)H(4) conformations of methyl 3,4-di-O-acetyl-1,2-dideoxy-d-arabino-hex-1-enopyranuronate (methyl 3,4-di-O-acetyl-D-glucuronal), and methyl 3,4-di-O-acetyl-1,2-dideoxy-D-lyxo-hex-1-enopyranuronate (methyl 3,4-di-O-acetyl-D-galacturonal). Energy and geometry parameters are presented for the most stable optimized geometries. Conformational analysis of the acetoxy and methoxycarbonyl groups as well as the 1,2-unsaturated pyranoid ring is performed. It is demonstrated that both the acetoxy and methoxycarbonyl groups are planar and prefer cis over trans orientations with respect to the CO-O bond rotations. With regard to the AcO-R bond rotations some of the orientations are forbidden. The (4)H(5)⇌(5)H(4) conformational equilibrium in both methyl 3,4-di-O-acetyl-D-glucuronal (shifted towards (5)H4) and methyl 3,4-di-O-acetyl-D-galacturonal (shifted towards (4)H(5)) is the outcome of the competition between the vinylogous anomeric effect and quasi 1,3-diaxial interactions. It is demonstrated that the orientation of the 4-OAc group influences the strength of the quasi 1,3-diaxial interactions between 3-OAc and 5-COOCH(3) groups. Theoretical results are compared with assignments based on (1)H NMR studies.