Enantioselective self-assembly,crystallographic structure and magnetic properties of the two enantiomers of the optically active canted antiferromagnet [Ru(bpy)3][Mn2(ox)3]

The two enantiomers of [Ru(bpy)₃][Mn₂(ox)₃] (bpy = 2,2′-bipyridine, ox = oxalate), namely [(Δ)-Ru(bpy)₃][(Δ)-Mn₂(ox)₃], (Δ-1) and [(Λ)-Ru(bpy)₃][(Λ)-Mn₂(ox)₃], (Λ-1), were obtained as single crystals using [(Δ)-Ru(bpy)₃]²⁺ and [(Λ)-Ru(bpy)₃]²⁺, respectively, as a chiral templating cation. Their structures were determined by single-crystal X-ray diffraction. The compounds crystallise in the enantiomeric chiral cubic space groups, P4₃32 (Δ-1) and P4₁32 (Λ-1), with a = 15.492(2) and 15.507(2) Å, respectively (Z = 4). Both structures include a three-dimensional 10-gon 3-connected (10,3) anionic network wrapped around the [Ru(bpy)₃]²⁺ cations. In both crystalline enantiomers, the resolved ruthenium template cation imposes both the topology and the absolute configuration of all the metal centres. The thermal variation of the magnetic susceptibility, measured on Δ-1 and Λ-1 crystals, reveals an antiferromagnetic coupling between the oxalate-bridged manganese ions in the paramagnetic region characterised by a negative Weiss constant Θ = −35 K. Below T_N = 13 K, Δ-1 and Λ-1 exhibit a canted antiferromagnetic order.     

Synthesis of optically active 4,4,4-trifluoro-3-{4-(4-methoxyphenyl)phenyl}butanoic acid and its application to chiral dopant for nematic liquid crystals

We synthesized an optically active 4,4,4-trifluoro-3-{4-(4-methoxyphenyl)phenyl}butanoic acid (5^*). New chiral dopants for nematic liquid crystals were derived from (R)-(−)-5^*, and their helical twisting power (HTP) values were measured. Their HTP values were largely influenced by the linkage between the asymmetric frame and the core moiety. The chiral dopant, (R)-(+)-4,4,4-trifluoro-1-(4-hexyloxyphenyl)-3-{4-(4-methoxyphenyl)phenyl}-1-butanone ((R)-(+)-7^*) showed the largest HTP value (−21.7 μm⁻¹).     

Synthesis of rigid and C2-symmetric 18-crown-6 type macrocycles bearing diamide–diester groups: enantiomeric recognition for α-(1-naphthyl)ethylammonium perchlorate salts

A series of rigid and chiral C₂-symmetric 18-crown-6 type macrocycles (S,S)-4, (S,S)-5, (S,S)-6 and (R,R)-2 bearing diamide–ester groups were synthesized. The binding properties of these macrocycles were examined for α-(1-naphthyl)ethylammonium perchlorates salts by an ¹H NMR titration method. Taking into account the host employed, important differences were observed in the K_a values of (R)- and (S)-enantiomers of guests for macrocycles (S,S)-4 and (S,S)-6, K_S/K_R = 3.6, and K_S/K_R = 0.1 (K_R/K_S = 10.3) ΔΔG = 3.19 and ΔΔG = ?5.77 kJ mol^?1, respectively. The results indicated excellent enantioselectivity of macrocyclic (S,S)-6 towards the enantiomers of α-(1-naphthyl)ethylammonium perchlorate salts.     

Enthalpic changes on mixing two couples of S- and R-enantiomers of benzyl-(1-phenyl-ethyl)-amine, 1-phenylethylamine, 1-phenyl-ethanol,butyric acid oxiranylmethyl ester, 4-methyl-[1,3]dioxolan-2-one, 2-chloro-methyloxirane and 3-hydroxyisobutyric acid methyl ester at T = 298.15 K

Enthalpies of mixing of (R)- and (S)-enantomers of liquid chiral compounds such as benzyl-(1-phenyl-ethyl)-amine (1), 1-phenylethylamine (2), 1-phenyl-ethanol (3), butyric acid oxiranylmethyl ester (4), 4-methyl-[1,3]dioxolan-2-one (5), 2-Chloromethyloxirane (6) and 3-hydroxyisobutyric acid methyl ester (7) have been measured over the whole range of mole fractions at 298.15 K, albeit very small values. Mixing of heterochiral liquids of R-1 + S-1, R-5 + S-5, and R-7 + S-7 realized enthalpic stabilization over the whole range of mole fractions, whereas that of R-2 + S-2, R-3 + S-3, R-4 + S-4, and R-6 + S-6 realized enthalpic destabilization over entire compositions. The extreme values of enthalpies of mixing and the intermolecular interaction obtained by the molecular mechanics calculations showed a linear correlation, except few the compounds measured.     

Two new flavonoid diglycosides from Cephalotaxus sinensis

Two new acetylated flavonoid diglycosides, scutellarein-5-O-[a-L-rhamnopyranosyl-(1→ 4)-b-D-6-O-acetylglucopyranoside] (1), apigenin-5-O-[a-L-rhamnopyranosyl-(1→2)-b-D-3,6-di-O-acetylglucopyranoside] (2), were isolated from the leaves of Cephalotaxus sinensis. Their structures were determined by chemical and spectroscopic methods including HR-FAB-MS, 1H–1H COSY, HSQC and HMBC experiments.     

Ring-expanded chiral rhombamine macrocycles for efficient NMR enantiodiscrimination of carboxylic acid derivatives

Novel 46-membered chiral rhombamine macrocycles (R,R,R,R)-8a and 8b were synthesized by [2+2] cyclocondensation reactions of (R,R)-1,2-diaminocyclohexane with the corresponding dialdehydes and subsequent reduction with NaBH₄. The X-ray crystal structure of 1:4 dioxane complex with (R,R,R,R)-8a indicated a rhombus conformation of the chiral macrocycle. Compounds (R,R,R,R)-8a and 8b were tested as chiral shift reagents for a wide range of α-substituted carboxylic acids and amino acid derivatives. Enantiodiscrimination of ¹H NMR signals was observed with ΔΔδ values of up to 0.214 ppm.     

Switched enantioselectivity by solvent components and temperature in photocyclodimerization of 2-anthracenecarboxylate with 6~A,6~X-diguanidio-γ-cyclodextrins

A series of 6A,6X-diguanidio-g-cyclodextrins (CDs) were synthesized as chiral hosts for mediating the enantiodifferentiating[4+4] photocyclodimerization of 2-anthracenecarboxylic acid (AC). Variation of the temperature and the ammonia contents led to greatly enhanced head-to-head photodimers 3 and 4, companying by inversion of product chirality.     

The enantiomeric recognition of chiral organic ammonium salts by chiral pyridino-macrocycles bearing aminoalcohol subunits

Pyridine-based macrocycles were prepared by treating 2,6-bis[[2′6′-bis(bromomethyl)-4′-methylphenoxy]methyl]pyridine 3 with the appropriate chiral aminoalcohols. The enantiomeric recognition of these macrocycles bearing aminoalcohol subunits of the pyridinocrown type ligand was evaluated for chiral organic ammonium salts by UV titration. The important differences were observed in the K_a values of (R)-Am2 and (S)-Am2 for (S,S,S)-1, (S,S,S)-2 and (S,S,S)-3 hosts, K_S/K_R = 5.0, K_S/K_R = 2.4 and K_S/K_R = 5.0, respectively. There seems to be a general tendency for hosts to recognise (S)-enantiomers for both Am1 and Am2.     

Approaches to (R)- and (S)-1′-(1-aminoethyl)ferrocene-1-carboxylic acid derivatives

Lipase-catalyzed esterification of (±)-methyl 1′-(1-hydroxyethyl)ferrocene-1-carboxylate 4 afforded its (R)-acetate (−)-5 (ee = 99%) and (S)-(+)-4 (ee = 90%). Stereoretentive azidation/amination/acetylation of (R)-(−)-5 gave (R)-(+)-methyl 1′-(1-acetamidoethyl)ferrocene-1-carboxylate (R)-3 (ee = 98%). In a similar manner (S)-(+)-4 was converted into (S)-(−)-3 (ee = 84%). Both enantiomers of 3 were obtained in high chemical yields without a loss of enantiomeric purity. The title compounds can be coupled with natural amino acids and peptides on both C- and N-termini.     

Preparation of isoxazolidinyl nucleoside enantiomers by lipase-catalysed kinetic resolution

An efficient biocatalytic procedure to obtain chiral N,O-nucleoside derivatives consisting of a lipase-catalysed resolution of the corresponding racemates in organic solvent has been developed. Enantioselective esterification of thymine and cytosine derivatives, (±)-9a and (±)-9b, has been investigated by comparing the efficiency of different lipases and acyl donors. Since esterification of (±)-9a and (±)-9b, occurred with low enantioselectivity (E ? 14) in the presence of the lipases considered, for preparative purposes we resorted, with success, to a double sequential kinetic resolution, using Lipozyme IM as the best catalyst. This approach enables us to obtain all the enantiomers with ee ? 95%. The absolute configuration of the new chiral N-acetyl cytosine derivative 9b was established by circular dichroism spectroscopy.     

Synthesis ofa trimeric lignin model compound composed ofol-O-4 and β-O-4 linkages under microwave irradiation

A trimeric lignin model compound composed of α-O-4 and β-O-4 linkages was prepared by the microwave-assisted synthesis, which consisted of three steps： （a） the synthesis of 3-methoxy-4- benzyloxyacetophenone （2） from acetovanillone （1）, （b） the bromination of compound 2 to produce 3- methoxy-4-benzyloxy-α-bromoacetophenone （3）, and （c） followed by a nucleophilic substitution of compound （3） to obtain 3-methoxy-4-benzyloxy-α-（3-methoxy-4-（1-propenyl）phenol）-acetophenone （4）. The target product was characterized by MS, 1H NMR and 13C NMR spectroscopy. It was found that the trimeric compound synthesized can be used as a preferable lignin model compound because it contains guaiacyl structural unit （3-methoxy-4-hydroxy phenyl propane） linked by α-O-4 and β-O-4 linkages. In addition, under the conditions of microwave irradiation, the reaction time of each step is significantly reduced, and the selectivity of target product is greatly improved. The yields of each step and the overall sequence are 95.31%. 87.3%. 90.6% and 75.4% （95.31%× 87.3% × 90.6%）. respectively.     

Synthesis and crystal structure of (S)-pindolol

Racemic 3-(4-indolyloxy)-1,2-propanediol 2 has been effectively resolved into (S)- and (R)-enantiomers by a preferential crystallization procedure. Non-racemic (S)-2 was converted into (S)-4-(2,3-epoxypropoxy)-1H-indole (S)-4 via a Mitsunobu reaction and then into (S)-pindolol (S)-1. The crystalline (S)-1 was studied by single crystal X-ray diffraction. A large number of symmetry independent molecules (Z′ = 6) led to a weakening of the system of strong intermolecular hydrogen bonds, which combined with a loose packing (PI = 64.6%), may be the cause of the abnormally low melting point of (S)-1 as compared with rac-1.     

A new C21-steroidal glycoside from Cynanchum stauntonii

A new C21-steroidal glycoside with two known compounds were isolated from the root of Cynanchum Stauntonii.Based on thespectral analysis,including MS,1H NMR,13C NMR,DEPT,1H-1H COSY,13C-1H COSY,HMQC and HMBC,their chemicalstructures were determinated as glaucogenin-C 3-O-a-L-cymaropyranosyl-(1→4)-b-D-digitoxopyranosyl-(1→4)-β-D-canaropyranoside(1),stigmasterol(2)and ursolic acid(3).     

Synthesis of some Mannich base derivatives and their antimicrobial activity study

A series of 2-(phenyl)-2-(morpholin-4-yl)-N-phenylacetamide I–VII were synthesized by Mannich base method. Synthesized compounds I–VII were confirmed by IR, ¹H NMR, ¹³C NMR, mass and elemental analyses. Synthesized compounds I–VII were screened for antibacterial activity against various bacterial strains and compared with standard Ciprofloxacin at concentration 100 μg/mL and for antifungal activity against various fungal strains and compared with Clotrimazole at concentration 100 μg/mL; particularly 3-(4-chlorophenyl)-3-(morp holin-4-yl)-N-phenylpropanamide lll that has high antibacterial activity against Streptococcus epidermidis was compared with standard Ciprofloxacin.     

A family of dodecanuclear Mn11Ln single-molecule magnets

A series of four isostructural dodecanuclear complexes [Mn^III₉Mn^II₂Ln^III(O)₈(OH)(piv)₁₆(NO₃)(CH₃CN)]·xCH₃CN·yC₇H₁₆ (piv = pivalate; x = ½, y = ¾, Ln = Tb (1); x = 2, y = ½, Ln = Dy (2), Ho (3), and Y (4)) has been prepared for which the structural motif described as ‘a lanthanide ion nested in a large manganese shell’ is observed. All compounds show out-of-phase signals in their ac susceptibilities, and their single-molecule magnet behaviour was confirmed by single-crystal micro-SQUID studies of 1-3 which show hysteresis loops of molecular origin at T < 1.0 K. The SMM behaviour observed in compounds 1-3 is more pronounced than that for 4, which contains the diamagnetic Y^III ion. This is principally the result of ferromagnetic coupling between the paramagnetic anisotropic Ln^III ions (Tb^III, Dy^III and Ho^III) and the manganese shell, which enhances the total spin ground state of the complexes.     

Furostanol saponins with inhibitory action against COX-2 production from Tupistra chinensis rhizomes

Two furostanol saponins were obtained from the n-butanol fraction of methanol extract from Tupistra chinensis rhizomes,a folk medicine of Shennongjia Forest District of Hubei Province.Their structures were determined as (25S)-26-O-(β-D-glucopyranosyl)- furost-1β,3β,22α,26-tetrol-3-O-β-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl-(1→2)-β-D-glucopyranoside (1) and (25R)- 26-O-(β-D-glucopyranosyl)-furost-1β,3β22α,26-tetrol 3-O-β-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl-(1→2)-β-D-glu- copyranoside (2),on basis of chemical and spectroscopic evidences.1 and 2 displayed marked inhibitory action towards COX-2 production in macrophages of the rat abdomen induced by LPS at 20μg/mL.     

New chemical and chemo-enzymatic routes for the synthesis of (RS)- and (S)-enciprazine

The chemo-enzymatic synthesis of racemic and enantiopure (RS)- and (S)-enciprazine 1, a non-benzodiazepine anxiolytic drug, is described herein. The synthesis started from 1-(2-methoxyphenyl) piperazine 3, which was treated with 2-(chloromethyl) oxirane (RS)-4 using lithium bromide to afford a racemic alcohol, 1-chloro-3-(4-(2-methoxyphenyl) piperazin-1-yl) propan-2-ol (RS)-6 in 85% yield. Intermediate (S)-6 was synthesized from racemic alcohol (RS)-6 using Candida rugosa lipase (CRL) with vinyl acetate as the acyl donor. Various reaction parameters such as temperature, time, substrate, enzyme concentration, and the effect of the reaction medium on the conversion and enantiomeric excess for the transesterification of (RS)-6 by CRL were optimized. It was observed that 10 mM of (RS)-6, 50 mg/mL of CRL in 4.0 mL of toluene with vinyl acetate (5.4 mmol) as acyl donor at 30 °C gave good conversion (C = 49.4%) and enantiomeric excess (ee_P = 98.4% and ee_S = 96%) after 9 h of reaction. Compound (S)-6 is a key intermediate for the synthesis of enantiopure (S)-1. The (RS)- and (S)-enciprazine drug 1 was synthesized by treating (RS)- and (S)-6 with 3,4,5-trimethoxyphenol 5 using MeCN as a solvent and K₂CO₃ as a base.     

Synthesis of chiral C/N-functionalized morpholine alcohols: study of their catalytic ability as ligand in asymmetric diethylzinc addition to aldehyde

A broad variety of chiral C/N-functionalized morpholine alcohols sharing a common structural motif in the 3-(hydroxymethyl)morpholine 6 were prepared from enantiomerically pure serine for the purpose of studying their catalytic ligand properties. The asymmetric addition of diethylzinc to benzaldehyde in the presence of 10 mol % of chiral C/N-functionalized morpholine alcohols gave 1-phenyl-1-propanol in 59–81% yield with 10–30% ee. The addition of 10 mol % of n-butyl lithium to the reaction mixture resulted in a significant enhancement of the stereoselectivity in the case of ligands bearing the two geminal phenyl substituents on the backbone. In the presence of n-butyl lithium and using (S)-3-(hydroxydiphenylmethyl)morpholine (S)-19 as the chiral promoter, (S)-1-phenyl-1-propanol was obtained in 81% yield with 76% ee. The geminal diphenyl-class of morpholine ligands was examined for the diethylzinc addition to four different aldehydes in the presence of n-butyl lithium. (S)-N-Benzyl-3-(hydroxydiphenylmethyl)morpholine (S)-27 was found to be most enantioselective in the case of 4-methoxybenzaldehyde to give (R)-alcohol in 87% yield with 80% ee. Catalysts (S)-19 and its N-methyl derivative (S)-26 gave alcohols with an (S)-absolute configuration while the N-benzylated derivative (S)-27 gave the opposite enantiomeric products. The tentative transition state models to account for the observed product stereoselectivity with morpholine ligands holding the geminal diphenyl group on the β-amino alcohol segment are proposed.     

Spontaneous resolution of a novel chiral coordination polymer through supramolecular interactions and solvent symmetry breaking

The spontaneous resolution reaction of racemic trans-2,3-dihydro-2,3-dipyridyl-benzo[e]indole 1 with Cd(ClO₄)₂·6H₂O in the presence of 2-butanol under solvothermal reaction conditions favors the formation of crystal 2 [P-Cd(R,R,-1)₂(ClO₄)₂], while a similar reaction in the presence of ethanol only favors the formation of crystal 3 [M-Cd(S,S,-1)₂(ClO₄)₂]. The crystal structural determination shows that both 2 and 3 crystallize in chiral enantiomorphous space groups (P6₁22 and P6₅22) and their structures are 1D infinite chain, and are just enantiomorphous pairs most like. The spontaneous resolution process displays estimated ee values of ca. +0.6 for 2-butanol and ca. −0.4 for ethanol. Enantiomerically pure (S,S)-trans-2,3-dihydro-2,3-dipyridyl-benzo[e]indole (S,S,-1) can be obtained through the decomposition of mechanically separated 3. Additionally (S,S,-1) also crystallizes in a chiral space group (P2₁). The CD (circular dichroism) spectra of both 2 and 3 in the solid state are also approximately enantiomorphous pairs. However, their fluorescent spectra in the solid state display a moderate difference in maximum emission peaks (Δλ = 19 nm). Crystal data for 2: C₄₄H₃₄Cl₂N₆O₈Cd, M = 958.07, hexagonal, P6₁22, a = 10.5488(5), c = 68.256(4) Å, α = γ = 90°, β = 120°, V = 6577.8(6) Å³, Z = 6, D_c = 1.451 mg m⁻³, R₁ = 0.0498, wR₂ = 0.1124, μ = 0.679 mm⁻¹, S = 0.623, Flack χ = −0.02(6). For space group P6₅22, R₁ = 0.0670, wR₂ = 0.1602, S = 0.725 with a Flack value of 1.03(7); Crystal data for 3, C₄₄H₃₄Cl₂N₆O₈Cd, M = 958.07, hexagonal, P6₅22, a = 10.5446(3), c = 68.265(3) Å, V = 6573.3(4) Å³, Z = 6, D_c = 1.452 mg m⁻³, R₁ = 0.0444,wR₂ = 0.1002, μ = 0.679 mm⁻¹, S = 0.558, Flack χ = 0.01(5). For space group P6₁22, R₁ = 0.0501, wR₂ = 0.1178, S = 0.599 with a Flack value of 1.00(5). The low Flack parameter indicates that the absolute configurations of 2 and 3 are stated; Crystal data for (S,S)-1, C₂₂H₁₇N₂, M = 323.39, orthorhombic, P2₁2₁2₁, a = 9.2598(7), b = 9.4617(8), c = 19.1452(16) Å, V = 1677.4(2) Å³, Z = 4, D_c = 1.281 mg m⁻³, R₁ = 0.0417, wR₂ = 0.1191, T = 293 K, μ = 0.077 mm⁻¹, S = 0.862.     

Reactions of a hydrido(hydrosilylene)tungsten complex with oxiranes

Reactivity of a hydrido(hydrosilylene)tungsten complex, Cp¹(CO)₂(H)WSi(H)[C(SiMe₃)₃] (1), toward oxiranes was investigated. Treatment of 1 with racemic mono-substituted oxiranes with a substituent R (R = Ph, vinyl, ^tBu, or ⁿBu) at room temperature produced dihydrido(vinyloxysilyl)tungsten complexes, (E)- and/or (Z)-Cp¹(CO)₂(H)₂W{Si(H)(OCHCHR)[C(SiMe₃)₃]} [(E/Z)-2: R = Ph, (E)-3: R = vinyl, (E)-4: R = ^tBu, (E/Z)-5: R = ⁿBu] in high yields via regioselective ring-opening of oxiranes. When the substituent R on oxirane was relatively large, (E)-isomers (2, 3, and 4) were obtained predominantly (87–97%), while the substituent was a relatively small ⁿBu group, an approximately 1:1 mixture of (E)- and (Z)-isomers [(E/Z)-5] was obtained. Reaction of 1 with 2,2-dimethyloxirane afforded the corresponding complex, Cp¹(CO)₂(H)₂W{Si(H)(OCHCMe₂)[C(SiMe₃)₃]} (6), quantitatively. A reaction mechanism is also discussed.