ABSTRACT A series of substituted planar chiral flavinium salts with a phenyl “cap” have been prep... more ABSTRACT A series of substituted planar chiral flavinium salts with a phenyl “cap” have been prepared as potential catalysts for enantioselective sulfoxidation reactions with hydrogen peroxide by using an approach based on the synthesis of (arylamino)uracils and their condensation with substituted nitrosobenzenes. The effect of substituents at various positions on the ability of the catalyst to promote enantioselective sulfoxidation recations was investigated. Introduction of the tyrosine group into the side-chain of the flavinium species or substitution of the nitrogen N-3 of the flavin unit by o-isopropylphenyl has a remarkably positive effect on the enantioselectivity of the sulfoxidation reactions of aromatic and aliphatic substrates, respectively. On the other hand, substitution of the phenyl “cap” led to a substantial decrease in the efficiency of the catalyst. In summary, optimisation of the structures of the planar chiral flavinium catalysts led to enantioselectivities of up to 61 % ee for aromatic sulfides and of up to 65 % ee for tert-butyl methyl sulfide.
Regioselective derivatization via an organomercury intermediate allowed for the introduction of c... more Regioselective derivatization via an organomercury intermediate allowed for the introduction of carboxylic acid functionality into the meta position of the calix[4]arene skeleton. Intramolecular Friedel-Crafts cyclization led to a novel type of calixarene containing a ketone bridging moiety. Subsequent attack of the ketone by organometallic compounds occurred selectively from outside providing tertiary alcohols with the OH group oriented inside the cavity. These compounds can complex neutral molecules both in the solid state (X-ray) and in solution (NMR) using the cooperative effect of hydrogen bonding (OH) and CH-π interactions from within the cavity.
ABSTRACT Friedel–Crafts acylation of 25,27-dialkoxycalix[4]arenes has been studied. Direct acylat... more ABSTRACT Friedel–Crafts acylation of 25,27-dialkoxycalix[4]arenes has been studied. Direct acylation of de-tert-butylated calixarene using acyl chlorides and AlCl3 in 1,2-dichloroethane provided the corresponding diacyl derivatives regioselectively in high yields. Furthermore, ipso-substitution in the tert-butylated series under the same reaction conditions is possible, albeit in lower yields. As indicated by the unsuccessful application of this chemistry to O-acyl derivatives, the ipso-acylation reaction of calix[4]arenes proceeds by direct attack at the upper rim and not by a Fries rearrangement mechanism.
The structure of N,N',N''-tribenzylphosphorothioic triamide, C21H24N3PS, (I), and ana... more The structure of N,N',N''-tribenzylphosphorothioic triamide, C21H24N3PS, (I), and analysis of the bond-angle sums at the N atoms for this compound, and for 74 structures with a P(S)[N]3 skeleton and the N atom in a three-coordinate geometry found in the Cambridge Structural Database [CSD; Groom & Allen (2014). Angew. Chem. Int. Ed. 53, 662-671], are reported. For (I), the bond-angle sum at one of the N atoms [359 (1)°] shows a nearly planar configuration, while the other two show a nonplanar geometry with bond-angle sums of 342 (1) and 347 (1)°. The location of the atoms attached to the nonplanar N atoms suggests an anti orientation of the corresponding lone electron pairs (LEPs) on these N atoms with respect to the P=S group. For 74 structures with a P(S)[N]3 skeleton and with the N atom in a three-coordinate geometry, the bond-angle sums at the N atoms were found to be in the range 293-360°. Among 307 such three-coordinate N atoms, 39% (120 N atoms) have bond-angle sum...
The compound N,N',N''-tricyclohexylphosphorothioic triamide, C18H36N3PS or P(S)[NHC6H... more The compound N,N',N''-tricyclohexylphosphorothioic triamide, C18H36N3PS or P(S)[NHC6H11]3, (I), crystallizes in the space group Pnma with the molecule lying across a mirror plane; one N atom lies on the mirror plane, whereas the bond-angle sum at the other N atom has a deviation of some 8° from the ideal value of 360° for a planar configuration. The orientation of the atoms attached to this nonplanar N atom corresponds to an anti orientation of the corresponding lone electron pair (LEP) with respect to the P=S group. The P=S bond length of 1.9785 (6) Å is within the expected range for compounds with a P(S)[N]3 skeleton; however, it is in the region of the longest bond lengths found for analogous structures. This may be due to the involvement of the P=S group in N-H···S=P hydrogen bonds. In O,O'-diethyl (2-phenylhydrazin-1-yl)thiophosphonate, C10H17N2O2PS or P(S)[OC2H5]2[NHNHC6H5], (II), the bond-angle sum at the N atom attached to the phenyl ring is 345.1°, whereas, ...
Acta Crystallographica Section C Structural Chemistry, 2014
In the title salts, C12H14N2(2+)·2ClO4(-), (I), and C12H14N2(2+)·S2O8(2-), (II), the dication is ... more In the title salts, C12H14N2(2+)·2ClO4(-), (I), and C12H14N2(2+)·S2O8(2-), (II), the dication is organized around an inversion centre located at the centre of the -CH2CH2- bridge and the two pyridine segments are anti with respect to one another. The peroxodisulfate anion in (II) also exhibits inversion symmetry. Hirshfeld surface analysis shows closely similar Hirshfeld surface shapes for the dications in the two salts, reflecting similar intermolecular contacts and similar conformations. The two-dimensional fingerprint plots (FPs) are quite asymmetric, due to the presence of more than one component (cation and anion). The most striking of the complementary features for each of the FPs of the dications is the broad green spike in the region d(e) > d(i), without the presence of a corresponding spike in the region d(e) < d(i), reflecting the absence of O···H contacts. Moreover, H···O interactions (51% in the dications of both salts) outnumber other contacts in both crystal structures.
In this study isolation and structural elucidation of a homoisoflavonoid, 3-(3',4'-dihydr... more In this study isolation and structural elucidation of a homoisoflavonoid, 3-(3',4'-dihydroxybenzyl)-8-hydroxy-5,7-dimethoxychroman-4-one (Scillapersicone 1), is reported from Scilla persica HAUSSKN. The structure was solved by a single crystal X-ray analysis. The unit cell parameters are a=11.7676 (2)Å, b=20.1174 (4)Å, c=7.8645 (9)Å, β=93.544 (2)°, V=1858.23 (7)Å(3), monoclinic space group P21/c and four symmetry equivalent molecules in an unit cell. The structure was consistent with the UV, IR, 1D and 2D NMR, HRFAB-MS data. The optimized molecular geometry agrees closely that obtained from the single crystal X-ray crystallography. Furthermore, cytotoxicity of this compound was evaluated by MTT assay on AGS and WEHI-164 cancerous cell lines.
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.
ABSTRACT Chromium aminocarbene complexes [(CO)(5)Cr = C(N(CH3)(2))R], R = N-methyl-2-pyrrolyl, 2-... more ABSTRACT Chromium aminocarbene complexes [(CO)(5)Cr = C(N(CH3)(2))R], R = N-methyl-2-pyrrolyl, 2-thienyl and 2-furyl were prepared and structurally characterized. X-ray study indicated two stable rotamers in case of compounds containing 2-thienyl and 2-furyl substituents. DFT calculations well interpreted structural parameters of all studied complexes. Calculations of potential energy surfaces (PES) for neutral species confirmed existence of two energy minima on the potential energy surfaces. Calculated rotation barriers increase in the series 2-furyl, 2-thienyl and N-methyl-2-pyrrolyl, respectively. The PES scans for compounds in one-electron reduced states essentially reveal opposite behavior to the one observed for neutral complexes. Connection is drawn between the observed structural flexibility and electrochemical properties of the compounds.
Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, Jan 5, 2015
A series of new VO(IV) complexes of tetradentate N2O2 Schiff base ligands (L(1)-L(4)), were synth... more A series of new VO(IV) complexes of tetradentate N2O2 Schiff base ligands (L(1)-L(4)), were synthesized and characterized by FT-IR, UV-vis and elemental analysis. The structure of the complex VOL(1)⋅DMF was also investigated by X-ray crystallography which revealed a vanadyl center with distorted octahedral coordination where the 2-aza and 2-oxo coordinating sites of the ligand were perpendicular to the "-yl" oxygen. The electrochemical properties of the vanadyl complexes were investigated by cyclic voltammetry. A good correlation was observed between the oxidation potentials and the electron withdrawing character of the substituents on the Schiff base ligands, showing the following trend: MeO<H<Br<Cl. We also studied the thermodynamics of formation of the complexes and kinetic aspects of their thermal decomposition. The formation constants with various substituents on the aldehyde ring follow the trend 5-OMe>5-H>5-Br>5-Cl. Furthermore, the kinetic paramet...
ABSTRACT A new type of calixarene-based receptor designed for the recognition of chiral anions wa... more ABSTRACT A new type of calixarene-based receptor designed for the recognition of chiral anions was prepared by the introduction of (S)-2-methylbutan-1-ol moieties into the lower rim of calixarene. The immobilization of calixarene skeleton in the 1,3-alternate conformation enabled the construction of a cavity consisting of preorganised ureido functions and chiral substituents in close proximity. This cavity is capable of chiral discrimination of selected anions as demonstrated on d- and l-phenylalaninates.
To reveal the alternative ways for upper-rim thiacalixarene derivatization, the formylation react... more To reveal the alternative ways for upper-rim thiacalixarene derivatization, the formylation reactions (Gross and/or Duff conditions) of the corresponding tetrapropoxythiacalix[4]arene immobilized in the 1,3-alternate conformation were systematically studied. Surprisingly, albeit using an excess of the formylation agent, only two formyl groups were introduced exclusively into the meta positions of thiacalixarene skeleton. Unexpected regioselectivity of these reactions opens the door for a unique substitution pattern in thiacalixarene chemistry. The formation of meta-substituted aldehydes is another illustration showing remarkably different reactivity of the thiacalix[4]arene system compared with that of a classical calyx[4]arene analogue.
Diethyl 1-fluoro-1-phenylsulfonylmethanephosphonate (1) in the presence of cesium carbonate under... more Diethyl 1-fluoro-1-phenylsulfonylmethanephosphonate (1) in the presence of cesium carbonate undergoes efficient 1,4-addition to Michael acceptors having terminal double bonds such as α,β-unsaturated ketones, esters, sulfones, sulfoxides, and phosphonates to yield the corresponding adducts in good to excellent yields. In the presence of sodium hydride, 1 reacts with α,β-enones to provide γ-fluoro-γ-phenylsulfonylenol phosphates arising from 1,4-addition followed by phosphonate to phosphate rearrangement.
Five flavin (isoalloxazine) and alloxazine adducts with O-nucleophiles, 5-ethyl-4a-hydroxy-3,7,8,... more Five flavin (isoalloxazine) and alloxazine adducts with O-nucleophiles, 5-ethyl-4a-hydroxy-3,7,8,10-tetramethyl-4a,5-dihydroisoalloxazine (1a-OH), 5-ethyl-4a-hydroxy-3,10-dimethyl-4a,5-dihydroisoalloxazine (1b-OH), 5-ethyl-4a-methoxy-3,10-dimethyl-4a,5-dihydroisoalloxazine (1b-OMe), 5-ethyl-4a-hydroxy-1,3-dimethyl-4a,5-dihydroalloxazine (2a-OH) and 5-ethyl-4a-methoxy-1,3-dimethyl-4a,5-dihydroalloxazine (2a-OMe) were prepared from the corresponding salts, 5-ethyl-3,7,8,10-tetramethylisoalloxazinium (1a), 5-ethyl-3,10-dimethylisoalloxazinium (1b) and 5-ethyl-1,3-dimethylalloxazinium (2a) perchlorates by the addition of a nucleophile (water or methanol) and triethylamine as a base. The prepared adducts represent artificial analogs of flavin cofactor derivatives which are essential
ABSTRACT A series of substituted planar chiral flavinium salts with a phenyl “cap” have been prep... more ABSTRACT A series of substituted planar chiral flavinium salts with a phenyl “cap” have been prepared as potential catalysts for enantioselective sulfoxidation reactions with hydrogen peroxide by using an approach based on the synthesis of (arylamino)uracils and their condensation with substituted nitrosobenzenes. The effect of substituents at various positions on the ability of the catalyst to promote enantioselective sulfoxidation recations was investigated. Introduction of the tyrosine group into the side-chain of the flavinium species or substitution of the nitrogen N-3 of the flavin unit by o-isopropylphenyl has a remarkably positive effect on the enantioselectivity of the sulfoxidation reactions of aromatic and aliphatic substrates, respectively. On the other hand, substitution of the phenyl “cap” led to a substantial decrease in the efficiency of the catalyst. In summary, optimisation of the structures of the planar chiral flavinium catalysts led to enantioselectivities of up to 61 % ee for aromatic sulfides and of up to 65 % ee for tert-butyl methyl sulfide.
Regioselective derivatization via an organomercury intermediate allowed for the introduction of c... more Regioselective derivatization via an organomercury intermediate allowed for the introduction of carboxylic acid functionality into the meta position of the calix[4]arene skeleton. Intramolecular Friedel-Crafts cyclization led to a novel type of calixarene containing a ketone bridging moiety. Subsequent attack of the ketone by organometallic compounds occurred selectively from outside providing tertiary alcohols with the OH group oriented inside the cavity. These compounds can complex neutral molecules both in the solid state (X-ray) and in solution (NMR) using the cooperative effect of hydrogen bonding (OH) and CH-π interactions from within the cavity.
ABSTRACT Friedel–Crafts acylation of 25,27-dialkoxycalix[4]arenes has been studied. Direct acylat... more ABSTRACT Friedel–Crafts acylation of 25,27-dialkoxycalix[4]arenes has been studied. Direct acylation of de-tert-butylated calixarene using acyl chlorides and AlCl3 in 1,2-dichloroethane provided the corresponding diacyl derivatives regioselectively in high yields. Furthermore, ipso-substitution in the tert-butylated series under the same reaction conditions is possible, albeit in lower yields. As indicated by the unsuccessful application of this chemistry to O-acyl derivatives, the ipso-acylation reaction of calix[4]arenes proceeds by direct attack at the upper rim and not by a Fries rearrangement mechanism.
The structure of N,N',N''-tribenzylphosphorothioic triamide, C21H24N3PS, (I), and ana... more The structure of N,N',N''-tribenzylphosphorothioic triamide, C21H24N3PS, (I), and analysis of the bond-angle sums at the N atoms for this compound, and for 74 structures with a P(S)[N]3 skeleton and the N atom in a three-coordinate geometry found in the Cambridge Structural Database [CSD; Groom & Allen (2014). Angew. Chem. Int. Ed. 53, 662-671], are reported. For (I), the bond-angle sum at one of the N atoms [359 (1)°] shows a nearly planar configuration, while the other two show a nonplanar geometry with bond-angle sums of 342 (1) and 347 (1)°. The location of the atoms attached to the nonplanar N atoms suggests an anti orientation of the corresponding lone electron pairs (LEPs) on these N atoms with respect to the P=S group. For 74 structures with a P(S)[N]3 skeleton and with the N atom in a three-coordinate geometry, the bond-angle sums at the N atoms were found to be in the range 293-360°. Among 307 such three-coordinate N atoms, 39% (120 N atoms) have bond-angle sum...
The compound N,N',N''-tricyclohexylphosphorothioic triamide, C18H36N3PS or P(S)[NHC6H... more The compound N,N',N''-tricyclohexylphosphorothioic triamide, C18H36N3PS or P(S)[NHC6H11]3, (I), crystallizes in the space group Pnma with the molecule lying across a mirror plane; one N atom lies on the mirror plane, whereas the bond-angle sum at the other N atom has a deviation of some 8° from the ideal value of 360° for a planar configuration. The orientation of the atoms attached to this nonplanar N atom corresponds to an anti orientation of the corresponding lone electron pair (LEP) with respect to the P=S group. The P=S bond length of 1.9785 (6) Å is within the expected range for compounds with a P(S)[N]3 skeleton; however, it is in the region of the longest bond lengths found for analogous structures. This may be due to the involvement of the P=S group in N-H···S=P hydrogen bonds. In O,O'-diethyl (2-phenylhydrazin-1-yl)thiophosphonate, C10H17N2O2PS or P(S)[OC2H5]2[NHNHC6H5], (II), the bond-angle sum at the N atom attached to the phenyl ring is 345.1°, whereas, ...
Acta Crystallographica Section C Structural Chemistry, 2014
In the title salts, C12H14N2(2+)·2ClO4(-), (I), and C12H14N2(2+)·S2O8(2-), (II), the dication is ... more In the title salts, C12H14N2(2+)·2ClO4(-), (I), and C12H14N2(2+)·S2O8(2-), (II), the dication is organized around an inversion centre located at the centre of the -CH2CH2- bridge and the two pyridine segments are anti with respect to one another. The peroxodisulfate anion in (II) also exhibits inversion symmetry. Hirshfeld surface analysis shows closely similar Hirshfeld surface shapes for the dications in the two salts, reflecting similar intermolecular contacts and similar conformations. The two-dimensional fingerprint plots (FPs) are quite asymmetric, due to the presence of more than one component (cation and anion). The most striking of the complementary features for each of the FPs of the dications is the broad green spike in the region d(e) &amp;amp;amp;amp;amp;amp;gt; d(i), without the presence of a corresponding spike in the region d(e) &amp;amp;amp;amp;amp;amp;lt; d(i), reflecting the absence of O···H contacts. Moreover, H···O interactions (51% in the dications of both salts) outnumber other contacts in both crystal structures.
In this study isolation and structural elucidation of a homoisoflavonoid, 3-(3',4'-dihydr... more In this study isolation and structural elucidation of a homoisoflavonoid, 3-(3',4'-dihydroxybenzyl)-8-hydroxy-5,7-dimethoxychroman-4-one (Scillapersicone 1), is reported from Scilla persica HAUSSKN. The structure was solved by a single crystal X-ray analysis. The unit cell parameters are a=11.7676 (2)Å, b=20.1174 (4)Å, c=7.8645 (9)Å, β=93.544 (2)°, V=1858.23 (7)Å(3), monoclinic space group P21/c and four symmetry equivalent molecules in an unit cell. The structure was consistent with the UV, IR, 1D and 2D NMR, HRFAB-MS data. The optimized molecular geometry agrees closely that obtained from the single crystal X-ray crystallography. Furthermore, cytotoxicity of this compound was evaluated by MTT assay on AGS and WEHI-164 cancerous cell lines.
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.
ABSTRACT Chromium aminocarbene complexes [(CO)(5)Cr = C(N(CH3)(2))R], R = N-methyl-2-pyrrolyl, 2-... more ABSTRACT Chromium aminocarbene complexes [(CO)(5)Cr = C(N(CH3)(2))R], R = N-methyl-2-pyrrolyl, 2-thienyl and 2-furyl were prepared and structurally characterized. X-ray study indicated two stable rotamers in case of compounds containing 2-thienyl and 2-furyl substituents. DFT calculations well interpreted structural parameters of all studied complexes. Calculations of potential energy surfaces (PES) for neutral species confirmed existence of two energy minima on the potential energy surfaces. Calculated rotation barriers increase in the series 2-furyl, 2-thienyl and N-methyl-2-pyrrolyl, respectively. The PES scans for compounds in one-electron reduced states essentially reveal opposite behavior to the one observed for neutral complexes. Connection is drawn between the observed structural flexibility and electrochemical properties of the compounds.
Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, Jan 5, 2015
A series of new VO(IV) complexes of tetradentate N2O2 Schiff base ligands (L(1)-L(4)), were synth... more A series of new VO(IV) complexes of tetradentate N2O2 Schiff base ligands (L(1)-L(4)), were synthesized and characterized by FT-IR, UV-vis and elemental analysis. The structure of the complex VOL(1)⋅DMF was also investigated by X-ray crystallography which revealed a vanadyl center with distorted octahedral coordination where the 2-aza and 2-oxo coordinating sites of the ligand were perpendicular to the "-yl" oxygen. The electrochemical properties of the vanadyl complexes were investigated by cyclic voltammetry. A good correlation was observed between the oxidation potentials and the electron withdrawing character of the substituents on the Schiff base ligands, showing the following trend: MeO<H<Br<Cl. We also studied the thermodynamics of formation of the complexes and kinetic aspects of their thermal decomposition. The formation constants with various substituents on the aldehyde ring follow the trend 5-OMe>5-H>5-Br>5-Cl. Furthermore, the kinetic paramet...
ABSTRACT A new type of calixarene-based receptor designed for the recognition of chiral anions wa... more ABSTRACT A new type of calixarene-based receptor designed for the recognition of chiral anions was prepared by the introduction of (S)-2-methylbutan-1-ol moieties into the lower rim of calixarene. The immobilization of calixarene skeleton in the 1,3-alternate conformation enabled the construction of a cavity consisting of preorganised ureido functions and chiral substituents in close proximity. This cavity is capable of chiral discrimination of selected anions as demonstrated on d- and l-phenylalaninates.
To reveal the alternative ways for upper-rim thiacalixarene derivatization, the formylation react... more To reveal the alternative ways for upper-rim thiacalixarene derivatization, the formylation reactions (Gross and/or Duff conditions) of the corresponding tetrapropoxythiacalix[4]arene immobilized in the 1,3-alternate conformation were systematically studied. Surprisingly, albeit using an excess of the formylation agent, only two formyl groups were introduced exclusively into the meta positions of thiacalixarene skeleton. Unexpected regioselectivity of these reactions opens the door for a unique substitution pattern in thiacalixarene chemistry. The formation of meta-substituted aldehydes is another illustration showing remarkably different reactivity of the thiacalix[4]arene system compared with that of a classical calyx[4]arene analogue.
Diethyl 1-fluoro-1-phenylsulfonylmethanephosphonate (1) in the presence of cesium carbonate under... more Diethyl 1-fluoro-1-phenylsulfonylmethanephosphonate (1) in the presence of cesium carbonate undergoes efficient 1,4-addition to Michael acceptors having terminal double bonds such as α,β-unsaturated ketones, esters, sulfones, sulfoxides, and phosphonates to yield the corresponding adducts in good to excellent yields. In the presence of sodium hydride, 1 reacts with α,β-enones to provide γ-fluoro-γ-phenylsulfonylenol phosphates arising from 1,4-addition followed by phosphonate to phosphate rearrangement.
Five flavin (isoalloxazine) and alloxazine adducts with O-nucleophiles, 5-ethyl-4a-hydroxy-3,7,8,... more Five flavin (isoalloxazine) and alloxazine adducts with O-nucleophiles, 5-ethyl-4a-hydroxy-3,7,8,10-tetramethyl-4a,5-dihydroisoalloxazine (1a-OH), 5-ethyl-4a-hydroxy-3,10-dimethyl-4a,5-dihydroisoalloxazine (1b-OH), 5-ethyl-4a-methoxy-3,10-dimethyl-4a,5-dihydroisoalloxazine (1b-OMe), 5-ethyl-4a-hydroxy-1,3-dimethyl-4a,5-dihydroalloxazine (2a-OH) and 5-ethyl-4a-methoxy-1,3-dimethyl-4a,5-dihydroalloxazine (2a-OMe) were prepared from the corresponding salts, 5-ethyl-3,7,8,10-tetramethylisoalloxazinium (1a), 5-ethyl-3,10-dimethylisoalloxazinium (1b) and 5-ethyl-1,3-dimethylalloxazinium (2a) perchlorates by the addition of a nucleophile (water or methanol) and triethylamine as a base. The prepared adducts represent artificial analogs of flavin cofactor derivatives which are essential
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