New multivalent glycomimetics are synthesized to interact efficiently with the promising target D... more New multivalent glycomimetics are synthesized to interact efficiently with the promising target DC-SIGN.
A new application of flavins in visible light photocatalysis: excited alloxazine allows fast cycl... more A new application of flavins in visible light photocatalysis: excited alloxazine allows fast cycloaddition of both electron-poor and electron-rich dienes.
Chemical communications (Cambridge, England), Jan 11, 2014
The meta-iodo derivative, fixed in the cone conformation, enables the gram-scale preparation of a... more The meta-iodo derivative, fixed in the cone conformation, enables the gram-scale preparation of a meta-bridged calix[4]arene. This intermediate, possessing a fluorene moiety within the macrocyclic skeleton, can be regioselectively alkylated on the corresponding methylene bridge to form a unique substitution pattern in classical calixarene chemistry.
Eight meso-aryl calixphyrin derivatives were synthesized and their conformational equilibria and ... more Eight meso-aryl calixphyrin derivatives were synthesized and their conformational equilibria and transitions studied with temperature-dependent NMR spectroscopy. On the basis of density functional computations, several conformer species could be identified and observed changes in chemical shifts explained. In some compounds, the aryl group rotation and porphyrin ring flipping could be monitored independently, as their NMR coalescence temperatures were well-separated. Calculated relative conformer energies, transition barriers, and isotropic shieldings agree well with the experimental data. In the meso-substituted porhyrins (calixphyrins) the sp 3 carbon atoms perturb their π-electron system and significantly modify the molecular shape and the flexibility. Even when the conjugation of the π-electron system was destroyed by the nonplanarity, far-range electronic induction effects still exist and influence chemical shielding and molecular geometry. The aryl functional groups moderately modify the structure of the calixphyrin ring and thus can be used for finetuning of the mechanical and chemical properties of these compounds.
Calix[4]phyrins are convenient models for porphyrin metabolism intermediates. They also attract a... more Calix[4]phyrins are convenient models for porphyrin metabolism intermediates. They also attract attention as complexation agents in macromolecular chemistry. For the biological function and chemical properties, their flexibility plays an important role. In this study, we explore the inner hydrogen motion previously detected in some calix[4]phyrins as a slow chemical exchange in the NMR spectra (J. Am. Chem. Soc. 2004, 126, 13714). The potential energy surface of this motion is defined by two generalized coordinates and modeled at DFT levels. The transitional barriers thus obtained agree reasonably well with those calculated from dynamic 1 H NMR measurements. The transitions over both the sp 2 and sp 3 links are found to be possible. During the transfer, an intermediate is formed where the two hydrogen atoms are attached to the neighboring nitrogens. Surprisingly, the barriers channeling the sp 2 and sp 3 paths in significantly depend on the dispersion and other interactions between remote side chains. The results confirm the possibility of a fine-tuning of the calixphyrin core properties by distant substituents.
Proceedings of the National Academy of Sciences, 1991
A new class of compounds, 9-[(2RS)-3-fluoro-2-phosphonylmethoxypropyl] [(RS)-FPMP] derivatives of... more A new class of compounds, 9-[(2RS)-3-fluoro-2-phosphonylmethoxypropyl] [(RS)-FPMP] derivatives of purines, is described that has selective activity against a broad spectrum of retroviruses [including human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2)] but not other RNA or DNA viruses. This activity spectrum is completely different from that of the parental compounds, 9-[(2S)-3-hydroxy-2-phosphonylmethoxypropyl] [(S)-HPMP] derivatives of purines, which are active against a broad range of DNA viruses. The racemic (RS)-FPMP derivatives of adenine and 2,6-diaminopurine, termed (RS)-FPMPA and (RS)-FPMPDAP, respectively, are markedly more selective as in vitro antiretroviral agents than their 9-(2-phosphonylmethoxyethyl) (PME) counterparts, PMEA and PMEDAP. Also, (RS)-FPMPA and (RS)-FPMPDAP have a substantially higher therapeutic index in mice in inhibiting Moloney murine sarcoma virus-induced tumor formation and associated death and are markedly less inhibitory to human bone ...
Supporting material-Experimental procedures 2-Allyloxy-2-phenylethyl tosylate (7b) was prepared a... more Supporting material-Experimental procedures 2-Allyloxy-2-phenylethyl tosylate (7b) was prepared according to Masami and Masaru 1. Allyl(2-bromo-1-phenylethyl)ether (6b) was prepared by the reaction of 7b with LiBr according to Dickman and Jones 2. Tosylate (7b) (3g, 9.42 mmol) and LiBr (4.1g, 47.2 mmol) were dissolved in 23 ml of acetone and the solution was refluxed for 20 h. The solvent was removed by evaporation under reduced pressure, the residue was diluted with 50 ml of water and washed twice with methylene chloride. The organic layer was dried with MgSO 4 , filtered and the solvent evaporated under reduced pressure. The crude product obtained (2.17g, 95.6 %) was purified by column chromatography on silica gel (eluent: CHCl 3). Ether 6b was obtained as a yellowish liquid (1.986g, 87.5 %) and identified by comparison of NMR spectra with published data 1. Allyl(2-bromo-2-phenylethyl)ether (6a) Allyl(2-hydroxy-2-phenylethyl)ether 3 (6g, 33,7 mmol) diluted with 6 ml of THF was added dropwise to 3.84 g (14.2 mmol, 26 % excess) phosphorus tribromide stirred in the atmosphere of dry nitrogen. The reaction mixture was externally cooled by ice water for 1 h. It was then left overnight at room temperature and thereafter diluted with 60 ml of diethyl ether, washed twice with cold water and dried with anhydrous MgSO 4. The dried extract was filtered. Evaporation of ether yielded 8.07 g (99%) crude product which was then vacuum distilled affording 5.16 g (63.5 %) of 6a, b.p. 88-92°C at 0.4 mbar, as a colourless liquid.
Table of Contents 1. Optimization of reaction conditions p. 1 2. Spectra of compounds p. 2-33 Com... more Table of Contents 1. Optimization of reaction conditions p. 1 2. Spectra of compounds p. 2-33 Compound 3b p. 3-7 Compound 2b p. 8-13 199 Hg spectra of 3b and 2b p. 13 Compound 6b p. 14-17 Compound 5b p. 18-21 Compound 3c p. 22-24 Compound 2c p. 24-26 Compound 3d p. 27-29 Compound 2d p. 30-33 3. Pirkle's alcohol p. 33 4. Crystallographic data p. 34-36 5. Quantum chemical calculations p. 37-46
NMR spectroscopy, X-ray diffraction analysis, and quantum chemical calculations were used for con... more NMR spectroscopy, X-ray diffraction analysis, and quantum chemical calculations were used for conformational behavior study of partially alkylated thiacalix[4]arenes bearing methyl (1), ethyl (2), or propyl (3) groups at the lower rim. The conformational properties are governed by two basic effects: (i) stabilization by intramolecular hydrogen bonds, and (ii) sterical requirements of the alkoxy groups at the lower rim. While the monosubstituted derivatives 1a and 3a adopt the cone conformation in solution, distally disubstituted compounds 1b, 1'b, 2b, 2'b, 3b, and 3'b exhibit several interesting conformational features. They prefer pinched cone conformation in solution, and, except for 3'b, they form also 1,2-alternate conformation, which is flexible and undergoes rather fast transition between two identical structures. The crystal structures of the compounds 1b, 2b, 2'b, and 3b revealed yet quite rare 1,2-alternate conformation forming molecular channels held together by pi-pi interactions. Different channels-with hexagonal symmetry, 0.26 nm wide-are formed in the crystal structure of the pinched cone conformation of 3b. An uncommon hydrogen bonding pattern was found in dimethoxy and dipropoxy derivatives 1'b and 3'b that adopt distorted cone conformations in crystal. Trialkoxy-substituted compounds 1c and 3c adopt the partial cone conformation in solution. A higher mobility of methyl derivative 1c enables also existence of the cone conformer.
A genomic library of bacterial strain Paenibacillus thiaminolyticus was constructed and the plasm... more A genomic library of bacterial strain Paenibacillus thiaminolyticus was constructed and the plasmid DNA of the clone, containing the gene encoding β-D-galactosidase with β-D-fucosidase activity, detected by 5-bromo-4-chloro-3indoxyl β-D-galactopyranoside, was sequenced. Cells of Escherichia coli BL21 (DE3) were used for production of the enzyme in the form of a histidine-tagged protein. This recombinant fusion protein was purified using Ni-NTA agarose affinity chromatography and characterized by using p-nitrophenyl β-D-fucopyranoside (K m value of 1.18 ± 0.06 mmol/L), p-nitrophenyl β-D-galactopyranoside (K m value of 250 ± 40 mmol/L), p-nitrophenyl β-Dglucopyranoside (K m value of 77 ± 6 mmol/L), and lactose (K m value of 206 ± 5 mmol/L) as substrates. Optimal pH and temperature were estimated as 5.5 and 65 • C, respectively. According to the amino acid sequence, the molecular weight of the fusion protein was calculated to be 68.6 kDa and gel filtration chromatography confirmed the presence of the enzyme in a monomeric form. In the following step, its ability to catalyze transfucosylation reactions was tested. The enzyme was able to catalyze the transfer of fucosyl moiety to different p-nitrophenyl glycopyranosides (producing p-nitrophenyl β-D-fucopyranosyl-(1,3)-β-Dfucopyranoside, p-nitrophenyl β-D-fucopyranosyl-(1,3)α-D-glucopyranoside, p-nitrophenyl β-D-fucopyranosyl-(1,3)-α-D-mannopyranoside, and p-nitrophenyl β-Dfucopyranosyl-(1,6)-α-D-galactopyranoside) and alcohols (producing methyl β-D-fucopyranoside, ethyl β-Dfucopyranoside, 1-propyl β-D-fucopyranoside, 2-propyl β-D-fucopyranoside, 1-octyl β-D-fucopyranoside, and 2-octyl β-D-fucopyranoside). These results indicate the possibility of utilizing this enzyme as a promising tool for enzymatic synthesis of β-D-fucosylated molecules.
6-Allyloxypurines readily undergo palladium-catalysed Claisen rearrangement under mild conditions... more 6-Allyloxypurines readily undergo palladium-catalysed Claisen rearrangement under mild conditions affording N 1-substituted hypoxanthines. In contrast with the previously reported protocol, the Claisen rearrangement can be performed using Pd(PPh3)4 or Pd(dba)2/dppf in dry THF at 60°C. The reaction can accommodate variously substituted allyl fragments to position N 1 of the hypoxanthine skeleton with high yields. Retention of the double bond configuration during rearrangement was observed.
Experimental procedures and characterizations p. 2-6 Spectra of compounds p. 7-21 Dynamic NMR mea... more Experimental procedures and characterizations p. 2-6 Spectra of compounds p. 7-21 Dynamic NMR measurements p. 22-25 Crystallographic data p. 26-27 Molecular packing (figures) p. 28-30
Acta Crystallographica Section E Structure Reports Online, 2009
The title compound, C 15 H 18 N 4 O 3 , was formed by the reaction of methanol with 5-ethyl-1,3-d... more The title compound, C 15 H 18 N 4 O 3 , was formed by the reaction of methanol with 5-ethyl-1,3-dimethylalloxazinium perchlorate. Its structure mimics those of possible flavin intermediates in flavoenzymes. The heterocyclic rings are substituted with methyl, ethyl and methoxy groups. The central tricyclic skeleton is bent due to the presence of an sp 3 C atom. There are weak intermolecular C-HÁ Á ÁO interactions in the structure, forming a three-dimensional network. Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: FB2153). organic compounds o1536 Ménová et al.
JBIC Journal of Biological Inorganic Chemistry, 1998
The stability constants of the 1 : 1 complexes formed between Mg 2c and the anions of the N1, N3,... more The stability constants of the 1 : 1 complexes formed between Mg 2c and the anions of the N1, N3, and N7 deaza derivatives of 9-[2-(phosphonomethoxy)ethyl]adenine (PA 2-), i.e., of Mg(H;PA) c and Mg(PA), were determined by potentiometric pH titration in aqueous solution (25 7C; Ip0.1 M, NaNO 3) and compared with previous results [Sigel H, et al. (1992) Helv Chim Acta 75 : 2634-2656], obtained under the same conditions, for the corresponding complexes of 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA 2-) and (phosphonomethoxy)ethane (PME 2-). Based on the analysis of a microconstant scheme it is concluded that in the monoprotonated complexes, Mg(H;PA) c , Mg 2c is coordinated to a significant part at the nucleobase, H c being at the phosphonate group. By making use of log K Mg Mg(R-PO 3) versus pK H H(R-PO 3) straight-line plots (also obtained previously; see above) for simple phosphonates and phosphate monoesters, it is shown that all the Mg(PA) complexes, including those with PMEA 2and PME 2-, are more stable than expected on the basis of the basicity of the UPO 2P
The preparation of galactofuranosyl-containing disaccharidic parts of natural glycoconjugates was... more The preparation of galactofuranosyl-containing disaccharidic parts of natural glycoconjugates was performed according to a chemo-enzymatic synthesis. Our goals were firstly to develop an alternative approach to standard chemical strategies by limiting the number of reaction and purification steps, and secondly to evaluate the scope of the Araf51 biocatalyst to transfer a galactofuranosyl moiety to a set of pyranosidic acceptors differing from each other by the series, the anomeric configuration as well as the conformation. The study of binding mode of the resulting disaccharides was also performed by molecular modeling and showed significant differences between (1→2)-and (1→6)-linked disaccharides.
New multivalent glycomimetics are synthesized to interact efficiently with the promising target D... more New multivalent glycomimetics are synthesized to interact efficiently with the promising target DC-SIGN.
A new application of flavins in visible light photocatalysis: excited alloxazine allows fast cycl... more A new application of flavins in visible light photocatalysis: excited alloxazine allows fast cycloaddition of both electron-poor and electron-rich dienes.
Chemical communications (Cambridge, England), Jan 11, 2014
The meta-iodo derivative, fixed in the cone conformation, enables the gram-scale preparation of a... more The meta-iodo derivative, fixed in the cone conformation, enables the gram-scale preparation of a meta-bridged calix[4]arene. This intermediate, possessing a fluorene moiety within the macrocyclic skeleton, can be regioselectively alkylated on the corresponding methylene bridge to form a unique substitution pattern in classical calixarene chemistry.
Eight meso-aryl calixphyrin derivatives were synthesized and their conformational equilibria and ... more Eight meso-aryl calixphyrin derivatives were synthesized and their conformational equilibria and transitions studied with temperature-dependent NMR spectroscopy. On the basis of density functional computations, several conformer species could be identified and observed changes in chemical shifts explained. In some compounds, the aryl group rotation and porphyrin ring flipping could be monitored independently, as their NMR coalescence temperatures were well-separated. Calculated relative conformer energies, transition barriers, and isotropic shieldings agree well with the experimental data. In the meso-substituted porhyrins (calixphyrins) the sp 3 carbon atoms perturb their π-electron system and significantly modify the molecular shape and the flexibility. Even when the conjugation of the π-electron system was destroyed by the nonplanarity, far-range electronic induction effects still exist and influence chemical shielding and molecular geometry. The aryl functional groups moderately modify the structure of the calixphyrin ring and thus can be used for finetuning of the mechanical and chemical properties of these compounds.
Calix[4]phyrins are convenient models for porphyrin metabolism intermediates. They also attract a... more Calix[4]phyrins are convenient models for porphyrin metabolism intermediates. They also attract attention as complexation agents in macromolecular chemistry. For the biological function and chemical properties, their flexibility plays an important role. In this study, we explore the inner hydrogen motion previously detected in some calix[4]phyrins as a slow chemical exchange in the NMR spectra (J. Am. Chem. Soc. 2004, 126, 13714). The potential energy surface of this motion is defined by two generalized coordinates and modeled at DFT levels. The transitional barriers thus obtained agree reasonably well with those calculated from dynamic 1 H NMR measurements. The transitions over both the sp 2 and sp 3 links are found to be possible. During the transfer, an intermediate is formed where the two hydrogen atoms are attached to the neighboring nitrogens. Surprisingly, the barriers channeling the sp 2 and sp 3 paths in significantly depend on the dispersion and other interactions between remote side chains. The results confirm the possibility of a fine-tuning of the calixphyrin core properties by distant substituents.
Proceedings of the National Academy of Sciences, 1991
A new class of compounds, 9-[(2RS)-3-fluoro-2-phosphonylmethoxypropyl] [(RS)-FPMP] derivatives of... more A new class of compounds, 9-[(2RS)-3-fluoro-2-phosphonylmethoxypropyl] [(RS)-FPMP] derivatives of purines, is described that has selective activity against a broad spectrum of retroviruses [including human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2)] but not other RNA or DNA viruses. This activity spectrum is completely different from that of the parental compounds, 9-[(2S)-3-hydroxy-2-phosphonylmethoxypropyl] [(S)-HPMP] derivatives of purines, which are active against a broad range of DNA viruses. The racemic (RS)-FPMP derivatives of adenine and 2,6-diaminopurine, termed (RS)-FPMPA and (RS)-FPMPDAP, respectively, are markedly more selective as in vitro antiretroviral agents than their 9-(2-phosphonylmethoxyethyl) (PME) counterparts, PMEA and PMEDAP. Also, (RS)-FPMPA and (RS)-FPMPDAP have a substantially higher therapeutic index in mice in inhibiting Moloney murine sarcoma virus-induced tumor formation and associated death and are markedly less inhibitory to human bone ...
Supporting material-Experimental procedures 2-Allyloxy-2-phenylethyl tosylate (7b) was prepared a... more Supporting material-Experimental procedures 2-Allyloxy-2-phenylethyl tosylate (7b) was prepared according to Masami and Masaru 1. Allyl(2-bromo-1-phenylethyl)ether (6b) was prepared by the reaction of 7b with LiBr according to Dickman and Jones 2. Tosylate (7b) (3g, 9.42 mmol) and LiBr (4.1g, 47.2 mmol) were dissolved in 23 ml of acetone and the solution was refluxed for 20 h. The solvent was removed by evaporation under reduced pressure, the residue was diluted with 50 ml of water and washed twice with methylene chloride. The organic layer was dried with MgSO 4 , filtered and the solvent evaporated under reduced pressure. The crude product obtained (2.17g, 95.6 %) was purified by column chromatography on silica gel (eluent: CHCl 3). Ether 6b was obtained as a yellowish liquid (1.986g, 87.5 %) and identified by comparison of NMR spectra with published data 1. Allyl(2-bromo-2-phenylethyl)ether (6a) Allyl(2-hydroxy-2-phenylethyl)ether 3 (6g, 33,7 mmol) diluted with 6 ml of THF was added dropwise to 3.84 g (14.2 mmol, 26 % excess) phosphorus tribromide stirred in the atmosphere of dry nitrogen. The reaction mixture was externally cooled by ice water for 1 h. It was then left overnight at room temperature and thereafter diluted with 60 ml of diethyl ether, washed twice with cold water and dried with anhydrous MgSO 4. The dried extract was filtered. Evaporation of ether yielded 8.07 g (99%) crude product which was then vacuum distilled affording 5.16 g (63.5 %) of 6a, b.p. 88-92°C at 0.4 mbar, as a colourless liquid.
Table of Contents 1. Optimization of reaction conditions p. 1 2. Spectra of compounds p. 2-33 Com... more Table of Contents 1. Optimization of reaction conditions p. 1 2. Spectra of compounds p. 2-33 Compound 3b p. 3-7 Compound 2b p. 8-13 199 Hg spectra of 3b and 2b p. 13 Compound 6b p. 14-17 Compound 5b p. 18-21 Compound 3c p. 22-24 Compound 2c p. 24-26 Compound 3d p. 27-29 Compound 2d p. 30-33 3. Pirkle's alcohol p. 33 4. Crystallographic data p. 34-36 5. Quantum chemical calculations p. 37-46
NMR spectroscopy, X-ray diffraction analysis, and quantum chemical calculations were used for con... more NMR spectroscopy, X-ray diffraction analysis, and quantum chemical calculations were used for conformational behavior study of partially alkylated thiacalix[4]arenes bearing methyl (1), ethyl (2), or propyl (3) groups at the lower rim. The conformational properties are governed by two basic effects: (i) stabilization by intramolecular hydrogen bonds, and (ii) sterical requirements of the alkoxy groups at the lower rim. While the monosubstituted derivatives 1a and 3a adopt the cone conformation in solution, distally disubstituted compounds 1b, 1'b, 2b, 2'b, 3b, and 3'b exhibit several interesting conformational features. They prefer pinched cone conformation in solution, and, except for 3'b, they form also 1,2-alternate conformation, which is flexible and undergoes rather fast transition between two identical structures. The crystal structures of the compounds 1b, 2b, 2'b, and 3b revealed yet quite rare 1,2-alternate conformation forming molecular channels held together by pi-pi interactions. Different channels-with hexagonal symmetry, 0.26 nm wide-are formed in the crystal structure of the pinched cone conformation of 3b. An uncommon hydrogen bonding pattern was found in dimethoxy and dipropoxy derivatives 1'b and 3'b that adopt distorted cone conformations in crystal. Trialkoxy-substituted compounds 1c and 3c adopt the partial cone conformation in solution. A higher mobility of methyl derivative 1c enables also existence of the cone conformer.
A genomic library of bacterial strain Paenibacillus thiaminolyticus was constructed and the plasm... more A genomic library of bacterial strain Paenibacillus thiaminolyticus was constructed and the plasmid DNA of the clone, containing the gene encoding β-D-galactosidase with β-D-fucosidase activity, detected by 5-bromo-4-chloro-3indoxyl β-D-galactopyranoside, was sequenced. Cells of Escherichia coli BL21 (DE3) were used for production of the enzyme in the form of a histidine-tagged protein. This recombinant fusion protein was purified using Ni-NTA agarose affinity chromatography and characterized by using p-nitrophenyl β-D-fucopyranoside (K m value of 1.18 ± 0.06 mmol/L), p-nitrophenyl β-D-galactopyranoside (K m value of 250 ± 40 mmol/L), p-nitrophenyl β-Dglucopyranoside (K m value of 77 ± 6 mmol/L), and lactose (K m value of 206 ± 5 mmol/L) as substrates. Optimal pH and temperature were estimated as 5.5 and 65 • C, respectively. According to the amino acid sequence, the molecular weight of the fusion protein was calculated to be 68.6 kDa and gel filtration chromatography confirmed the presence of the enzyme in a monomeric form. In the following step, its ability to catalyze transfucosylation reactions was tested. The enzyme was able to catalyze the transfer of fucosyl moiety to different p-nitrophenyl glycopyranosides (producing p-nitrophenyl β-D-fucopyranosyl-(1,3)-β-Dfucopyranoside, p-nitrophenyl β-D-fucopyranosyl-(1,3)α-D-glucopyranoside, p-nitrophenyl β-D-fucopyranosyl-(1,3)-α-D-mannopyranoside, and p-nitrophenyl β-Dfucopyranosyl-(1,6)-α-D-galactopyranoside) and alcohols (producing methyl β-D-fucopyranoside, ethyl β-Dfucopyranoside, 1-propyl β-D-fucopyranoside, 2-propyl β-D-fucopyranoside, 1-octyl β-D-fucopyranoside, and 2-octyl β-D-fucopyranoside). These results indicate the possibility of utilizing this enzyme as a promising tool for enzymatic synthesis of β-D-fucosylated molecules.
6-Allyloxypurines readily undergo palladium-catalysed Claisen rearrangement under mild conditions... more 6-Allyloxypurines readily undergo palladium-catalysed Claisen rearrangement under mild conditions affording N 1-substituted hypoxanthines. In contrast with the previously reported protocol, the Claisen rearrangement can be performed using Pd(PPh3)4 or Pd(dba)2/dppf in dry THF at 60°C. The reaction can accommodate variously substituted allyl fragments to position N 1 of the hypoxanthine skeleton with high yields. Retention of the double bond configuration during rearrangement was observed.
Experimental procedures and characterizations p. 2-6 Spectra of compounds p. 7-21 Dynamic NMR mea... more Experimental procedures and characterizations p. 2-6 Spectra of compounds p. 7-21 Dynamic NMR measurements p. 22-25 Crystallographic data p. 26-27 Molecular packing (figures) p. 28-30
Acta Crystallographica Section E Structure Reports Online, 2009
The title compound, C 15 H 18 N 4 O 3 , was formed by the reaction of methanol with 5-ethyl-1,3-d... more The title compound, C 15 H 18 N 4 O 3 , was formed by the reaction of methanol with 5-ethyl-1,3-dimethylalloxazinium perchlorate. Its structure mimics those of possible flavin intermediates in flavoenzymes. The heterocyclic rings are substituted with methyl, ethyl and methoxy groups. The central tricyclic skeleton is bent due to the presence of an sp 3 C atom. There are weak intermolecular C-HÁ Á ÁO interactions in the structure, forming a three-dimensional network. Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: FB2153). organic compounds o1536 Ménová et al.
JBIC Journal of Biological Inorganic Chemistry, 1998
The stability constants of the 1 : 1 complexes formed between Mg 2c and the anions of the N1, N3,... more The stability constants of the 1 : 1 complexes formed between Mg 2c and the anions of the N1, N3, and N7 deaza derivatives of 9-[2-(phosphonomethoxy)ethyl]adenine (PA 2-), i.e., of Mg(H;PA) c and Mg(PA), were determined by potentiometric pH titration in aqueous solution (25 7C; Ip0.1 M, NaNO 3) and compared with previous results [Sigel H, et al. (1992) Helv Chim Acta 75 : 2634-2656], obtained under the same conditions, for the corresponding complexes of 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA 2-) and (phosphonomethoxy)ethane (PME 2-). Based on the analysis of a microconstant scheme it is concluded that in the monoprotonated complexes, Mg(H;PA) c , Mg 2c is coordinated to a significant part at the nucleobase, H c being at the phosphonate group. By making use of log K Mg Mg(R-PO 3) versus pK H H(R-PO 3) straight-line plots (also obtained previously; see above) for simple phosphonates and phosphate monoesters, it is shown that all the Mg(PA) complexes, including those with PMEA 2and PME 2-, are more stable than expected on the basis of the basicity of the UPO 2P
The preparation of galactofuranosyl-containing disaccharidic parts of natural glycoconjugates was... more The preparation of galactofuranosyl-containing disaccharidic parts of natural glycoconjugates was performed according to a chemo-enzymatic synthesis. Our goals were firstly to develop an alternative approach to standard chemical strategies by limiting the number of reaction and purification steps, and secondly to evaluate the scope of the Araf51 biocatalyst to transfer a galactofuranosyl moiety to a set of pyranosidic acceptors differing from each other by the series, the anomeric configuration as well as the conformation. The study of binding mode of the resulting disaccharides was also performed by molecular modeling and showed significant differences between (1→2)-and (1→6)-linked disaccharides.
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Papers by Hana Dvorakova