Characterization of Four New Distinct ω-Transaminases from <Emphasis Type="Italic">Pseudomonas putida</Emphasis> NBRC 14164 for Kinetic Resolution of Racemic Amines and Amino Alcohols

Four uncharacterized ω-transaminases (ωTAs) from Pseudomonas putida NBRC 14164 have been identified and cloned from the pool of fully sequenced genomes. The genes were functionally expressed in Escherichia coli BL21, and the enzymes were purified and characterized. Four TAs showed highly (S)-selective ωTA activity and converted (S)-α-methylbenzylamine and pyruvate to acetophenone and l-Ala. The maximum activity of cloned enzymes was in the pH range of 8.0–8.5 (Pp36420), 8.5–9.5 (Pp21050), 9.0–9.5 (PpspuC), and 9.5–10.5 (PpbauA), and the optimal temperatures were at 35 °C (Pp36420, Pp21050, and PpspuC) and 50 °C (PpbauA), respectively, with K _M of 161.3 mM (Pp21050), 136.7 mM (PpbauA), 398.5 mM (Pp36420), and 130.9 mM (PpspuC) and yielding a catalytic efficiency k _cat/K _M of 0.015, 0.003, 0.012, and 0.023 mM^?1 s^?1. Several racemic amines and amino alcohols were resolved by the cloned ωTAs; perfect conversions (48–50 %) were obtained by at least one enzyme, and the residual substrates were left with 97–99 % ee. Kinetic resolution of racemic phenylglycinol was done with PpspuC in a 100-mL scale. Enaniomeric excess of (S)-phenylglycinol reached 99 % with 45 % isolated yield. The high enantioselectivity and large substrate spectra of the cloned PpTAs showed an attractive potency for biotechnology application in production of chiral amines and amino alcohols.     

Recovery of host crystals from inclusion crystals of <Emphasis Type="Italic">p-tert-</Emphasis>butylcalix[4]arene and <Emphasis Type="Italic">p-tert</Emphasis>-butylthiacalix[4]arene by the treatment with a solvent and/or supercritical CO<Subscript>2</Subscript>

Upon stirring inclusion crystals of p-tert-butylthiacalix[4]arene (2) in solvents with heating, guest compounds were efficiently desorbed to yield guest-free crystals. More specifically, upon treatment with methanol, the exchange of guest compounds with methanol in the crystals, followed by the desorption of the methanol afforded metastable host crystals 2β, whereas, upon treatment with heptane, the dissolution of the inclusion crystals and simultaneous crystallization of compound 2 afforded stable host crystals 2α. Further, a host crystal of p-tert-butylcalix[4]arene (1) was recovered by the treatment of 2:1 (host/guest) inclusion crystals of compound 1 with supercritical carbon dioxide (scCO₂), and through the combination of the guest exchange of 1:1 inclusion crystals of compound 1 with hexane and scCO₂ treatment of the resulting 2:1 inclusion crystals 1₂·hexane. Although the recovered host crystal of compound 1 contained a small amount of CO₂, it could be reused for the inclusion of organic compounds.     

Synthesis,spectroscopic characterization,crystal structures,and theoretical studies of (<Emphasis Type="Italic">E</Emphasis>)-2-(2,4-dimethoxybenzylidene)thiosemicarbazone and (<Emphasis Type="Italic">E</Emphasis>)-2-(2,5-dimethoxybenzylidene)thiosemicarbazone

Two thiosemicarbazones, (E)-2-(2,4-dimethoxybenzylidene)thiosemicarbazone (24-MBTSC (1)) and (E)-2-(2,5-dimethoxybenzylidene)thiosemicarbazone (25-MBTSC (2)), derived from 2,4-dimethoxybenzaldehyde and 2,5-dimethoxybenzaldehyde, respectively, with thiosemicarbazide have been synthesized and their structures were characterized by elemental analyses, FT-IR, ¹H NMR spectroscopy, and X-ray single-crystal diffraction analysis. Molecular orbital calculations have been carried out for 1 and 2 by using an ab initio method (HF) and also density functional method (B3LYP) at 6-31G basis set. Compound 1 crystallizes in the monoclinic system, space group P2₁/c, with a = 8.1342(5) Å, b = 18.1406(10) Å, c = 8.2847(6) Å, β = 109.7258(17)°, V = 1150.75(12) Å³, and Z = 4, whereas compound 2 crystallizes in the orthorhombic system, space group Pbca, with a = 11.0868(6) Å, b = 13.1332(6) Å, c = 15.9006(8) Å, V = 2315.2(2) Å³, and Z = 8. The compounds 1 and 2 displays a trans-configuration about the C=N double bond.     

Binding of cyclic carboxylates to octa-acid deep-cavity cavitand

As part of the fourth statistical assessment of modeling of proteins and ligands (sampl.eyesopen.com) prediction challenge, the strength of association of nine guests (1–9) binding to octa-acid host was determined by a combination of ¹H NMR and isothermal titration calorimetry. Association constants in sodium tetraborate buffered (pH 9.2) aqueous solution ranged from 5.39 × 10² M^?1 in the case of benzoate 1, up to 3.82 × 10⁵ M^?1 for trans-4-methylcyclohexanoate 7. Overall, the free energy difference between the free energies of complexation of these weakest and strongest binding guests was ΔΔG° = 3.88 kcal mol^?1. Based on a multitude of previous studies, the anticipated order of strength of binding was close to that which was actually obtained. However, the binding of guest 3 (4-ethylbenzoate) was considerably stronger than initially estimated.     

Channel inclusion of primary alcohols in isostructural solvates of the antiretroviral nevirapine: an X-ray and thermal analysis study

X-ray structural and thermoanalytical data for a series of solvates 2–7 of the anti-HIV drug nevirapine containing primary alcohols CH₃(CH₂) _n OH with n = 2–7 are reported. The structures of 2–7 are based on a common isostructural framework comprising centrosymmetric hydrogen-bonded nevirapine dimers and contain a common channel parallel to the crystal b-axis whose repeat length spans a narrow range (~8.43–8.52 Å) in the series and accommodates the various solvent molecules in 2–7. Thermogravimetry yielded a guest–host ratio close to 0.5 for the 1-butanol solvate 3 and a steady decrease in this ratio from 0.43 to 0.32 for the solvates 4–7. This anomalous stoichiometric variation was resolved following successful X-ray analysis of solvate 3 which revealed that the length spanned by the disordered 1-butanol molecule is commensurate with the channel periodicity b, resulting in a stoichiometric compound. Instead, solvates 5–7, for which single crystal X-ray data were available, showed significant disorder for the solvent molecules, attributed to their increasing chain lengths being incommensurate with the parameter b.     

Synthesis and characterization of half-sandwich ruthenium(II) complexes with N-alkyl pyridyl-imine ligands and their application in transfer hydrogenation of ketones

A series of new arene ruthenium(II) complexes were prepared by reaction of ruthenium(II) precursors of the general formula [(η⁶-arene)Ru(μ-Cl)Cl]₂ with N,N′-bidentate pyridyl-imine ligands to form complexes of the type [(η⁶-arene)RuCl(C₅H₄N-2-CH=N-R)]PF₆, with arene = C₆H₆, R = iso-propyl (1a), tert-butyl (1b), cyclohexyl (1c), cyclopentyl (1d) and n-butyl (1e); arene = p-cymene, R = iso-propyl (2a), tert-butyl (2b). The complexes were fully characterized by ¹H NMR and ¹³C NMR, UV–Vis and IR spectroscopies, elemental analyses, and the single-crystal X-ray structures of 2a and 2b have been determined. The single-crystal molecular structure revealed both compounds with a pseudo-octahedral geometry around the Ru(II) center, normally referred to as a piano stool conformation, with the pyridyl-imine as a bidentate N,N ligand. The activity of all complexes in the transfer hydrogenation of cyclohexanone in the presence of NaOH and iso-propanol is reported, the compounds showing turnover numbers of close to 1990 and high conversions. Complex 2b was also shown to be very effective for a range of aliphatic and cyclic ketones, giving conversions of up to 100 %.     

Substitution of aqua ligands from <Emphasis Type="Italic">cis</Emphasis>-platinum(II) complexes bearing 2-(phenylthiomethyl)pyridine spectator ligands

Cis-Pt(II) complexes, namely [Pt{2-(phenylthiomethyl)pyridine}(H₂O)₂](CF₃SO₃)₂ Pt(pyS ^Ph ), [Pt{2-(4-tert-butylphenylthiomethyl)pyridine}(H₂O)₂](CF₃SO₃)₂ Pt(pyS ^{Ph( t -But)} ) and [Pt{2-(4-fluorophenylthiomethyl)pyridine}(H₂O)₂](CF₃SO₃)₂ Pt(pyS ^PhF ), were synthesised and characterised. The pK _a1 and pK _a2 values of the complexes were determined titrimetrically. Substitution of the aqua ligands from these complexes by thiourea nucleophiles was studied at a pH of 2 and ionic strength of 0.1 M under pseudo-first-order conditions using stopped-flow and UV–visible spectrophotometric techniques. Substitution of the aqua ligands depends on both the nature and concentration of the incoming ligand, with low enthalpy and negative entropy of activation values. Substitution of the first and second aqua ligands occurs sequentially and fits the rate laws: k _{obs (1/2)} = k _(1/2) [Nu]. The second-order rate constant, k ₁, relates to the substitution trans to sulphur, while k ₂ is the second-order rate constant for the subsequent substitution of the aqua ligand trans to pyridine. The rate of substitution of the first aqua ligand decreases in the order: Pt(pyS ^{Ph( t -But)} ) > Pt(pyS ^PhF ) > Pt(pyS ^Ph ), while that of the second decreases in the order: Pt(pyS ^{Ph( t -But)} ) > Pt(pyS ^Ph ) > Pt(pyS ^PhF ), reflecting the influence of the substituents on the spectator ligands. ¹⁹⁵Pt NMR spectra of aged solutions of complexes with the thiourea nucleophile suggest a subsequent but rapid concentration-independent ring opening of the N,S-bidentate ligand to form a PtS ₄ species. The crystal structure of Pt(pyS ^PhF )Cl ₂ was elucidated by X-ray diffraction analysis.     

Directed assembly of cobalt(II) 1-H-indazole-3-carboxylic acid coordination networks by bipyridine and its derivatives: structural versatility,electrochemical properties,and antifungal activity

This paper describes the hydrothermal synthesis, full characterization, and architectural diversity of three intriguingly bioactive cobalt–organic frameworks, namely, 3D [Co(HL ^? )₂(BPY)] _n ·4nH₂O (1), 2D [Co(HL ^? )₂(BPE)] _n (2), and 2D [Co(HL ^? )₂(DPP)] _n (3) coordination polymers, synthesized through a mixed ligand strategy using H ₂ L (1-H-indazole-3-carboxylic acid) as a main structural block and the flexible bipyridine and its derivatives (BPY = 4,4′-bipydine, BPE = 1,2-bis(4-pyridyl)ethane, DPP = 1,3-bis(4-pyridyl)propane) as auxiliary ligand sources. Complexes 1–3 were isolated as air stable and slightly soluble crystalline solids and characterized using elemental analysis, FT-IR, electrochemical technique, thermogravimetric analysis, powder X-ray diffractometer, and single-crystal X-ray crystallography. The bipyridine derivatives played key roles in defining the structural space group and dimensionality feature of the obtained networks. The abundant H-bonding and π–π stacking interactions in complexes 1–3 gave rise to their intricate metal–organic structures of 3D (1), 2D (2), and 2D (3). In addition, the solutions of complexes 1–3 showed profound antifungal activities against the selected strain of Colletotrichum musae compared with the controlled group using benomyl as a traditional agrochemical fungicide.     

2-Propylamino-5-[4-(2-hydroxy-3,5-dichlorobenzylideneamino) phenyl]-1,3,4-thiadiazole: X-ray and DFT-calculated structures

2-Propylamino-5-[4-(2-hydroxy-3,5-dichlorobenzylideneamino) phenyl]-1,3,4-thiadiazole, formulated as C₁₈H₁₆Cl₂N₄OS (I), was synthesized. The crystal and molecular structure of (I) have been determined by ¹H-NMR, IR, and X-ray single crystal diffraction. The compound (I) crystallizes in the monoclinic, space group P2(1)/c with unit cell parameters a = 9.0576(2) Å, b = 24.3382(8) Å, c = 9.0585(2) Å, M _r = 407.31, V = 1851.13(9) Å³, Z = 4, R ₁ = 0.036, and wR ₂ = 0.096. Molecular geometry from X-ray experiment of (I) in the ground state has been compared using the density functional method (B3LYP) with 6-31G(d) basis set. To determine conformational flexibility, molecular energy profile of (I) was obtained by semi-empirical (PM3) calculations with respect to selected degree of torsional freedom, which was varied from ?180° to +180° in steps of 10°. The results are indicative that the Schiff base, which contains a thiadiazole ring, prefers to be in E-configuration. In addition, molecular electrostatic potential, frontier molecular orbitals, and natural bond orbitals analysis were performed by the B3LYP/6-31G(d) method.     

Two new mononuclear cobalt(II) complexes of pyrazole-based ligands: synthesis,structures and magnetic studies

We have synthesized two mononuclear cobalt(II) complexes (1 and 2) of pyrazole-based bidentate (NN) and tridentate (NNN) tripodal ligands. X-ray crystal structure determination reveals that complex 1 has a tetrahedral geometry, while complex 2 has a trigonal–bipyramidal geometry. Both the complexes have been characterized by variable-temperature magnetic measurements between 2 and 300 K. A weak ferromagnetic exchange interaction (J = +1.5 cm^?1) is observed for complex 2. Due to the presence of supramolecular CH···Cl and π···π interactions, a good magnetostructural correlation was found between the D parameter and angular distortion (δ) for complex 1 and related complexes reported in the literature.     

Conformational and configurational diversity of solvent inclusion complexes of some calix[4]pyrroles and their anion recognition properties

Sterically hindered meso-tetramethyl-meso-tetraarylcalix[4]pyrroles 1-4 where aryl is p-fluorophenyl 1, p-chlorophenyl 2, and p-methylphenyl 3, 4 (configurational isomers) are synthesized and purified by the recrystallization technique. They are characterized by IR, ¹H and ¹³C NMR, and mass spectroscopy. Configurational isomers ααββ (3) and αααα (4) of meso-tetramethyl-meso-tetramethylphenylcalix[ 4]pyrroles are assigned by the ¹H NMR studies and confirmed by the X-ray diffraction analysis. The single crystal X-ray diffraction analysis reveals that the ethanol adduct of 1, the acetone adduct of 2 and 3 adopt the 1,2-conformation while the acetone-water adduct of 1 and the acetone adduct of 4 adopt partial cone and cone conformations respectively. The conformational diversity is due to non-covalent interactions among the encapsulated guest, pyrrolic NH protons, and meso- substituents. Anion binding studies (F^–, Cl^–, CH₃COO^–, HSO ₄ ^? ) are carried out through ¹H NMR titrations; the binding constants are evaluated using the EQNMR program, displaying that they are more selective towards fluoride rather than other anions with the 1:1 stoichiometry. The configuration of compounds drastically influences the ion-recognition processes.     

New water-soluble iminecalix[4]arene with a deep hydrophobic cavity

We report the synthesis of a new water-soluble iminecalix[4]arene host 4c with a deep hydrophobic cavity. The negatively charged four carboxylate functions on the top of the cavity play a major role in the recognition of charged molecular species. The ¹H NMR titration experiments revealed that host 4c binds with cationic (10-12) and neutral guests (6-9) in water with high binding constants in the order of 10⁴-10⁵ M⁻¹. Cationic guest 9 showed highest binding constant of 2.81 × 10⁵ M⁻¹ with host 4c amongst all tested guests. Selectivity over anionic guests (13-17) is established by the presence of negative charges at the top of the deep hydrophobic cavity, as guests 15 and 17 were not recognized by host 4c. Neutral pyridine derivatives with hydrophobic chains at para positions showed high binding constants of 6.02 × 10⁴-2.23 × 10⁵ M⁻¹. The data obtained for the recognition of the guests by host 4c revealed that the ionic as well as the hydrophobic-hydrophobic interactions are crucial in the molecular recognition in aqueous medium.     

Synthesis,antifungal and insecticidal activity of novel [1,2,4]triazolo[4,3-<Emphasis Type="Italic">a</Emphasis>]pyridine derivatives containing a sulfide substructure

A series of [1,2,4]triazolo[4,3-a]pyridine derivatives bearing a sulfide substructure was designed, synthesized and characterized via ¹H·NMR, ¹³C·NMR, IR and elemental analyses. Bioassay Results indicated some of the derivatives displayed good fungicidal activity on Rhizoctonia cerealis, moderated insecticidal activity against Plutella xylostella and good insecticidal activity on Helicoverpa armigera. The inhibitory effects of compounds 4g and 4u against Rhizotonia cerealis were 70.9% at 50 μg mL^?1; the IC₅₀ values of compounds 4d and 4s against Plutella xylostella were 43.87 and 50.75 μg mL^?1, respectively. And the IC₅₀ values of compounds 4d, 4q, and 4s on Helicoverpa armigera were 58.3, 77.14 and 65.31 μg mL^?1, respectively, which were better than that of commercial chlorpyrifos (103.77 μg mL^?1).     

Synthesis and crystal structures of (2.2.2-cryptand)rubidium chloride and bromide hydrates

Two complexes, (2.2.2-cryptand)rubidium chloride and bromide hydrates [Rb(Crypt-222]Hal · 3.5H₂O (Hal = Cl (I) and Br (II)), are synthesized. The structures of isomorphic crystals of compounds I and II are studied by X-ray diffraction analysis. The crystals are trigonal: space group P \(\overline 3 \), Z = 2; I: a = 11.810 Å, c = 11.302 Å; II: a = 11.890 Å, c = 11.402 Å. The structures are solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.060 (I) and 0.077 (II) for 2650 (I) and 2700 (II) independent reflections (CAD-4 automated diffractometer, λMoK _α radiation). In crystals of complexes I and II, the [Rb(Crypt-222)]⁺ cation of the host-guest type lies on the crystallographic axis 3 and has the approximate symmetry D ₃. In complexes I and II, the coordination polyhedron of the Rb⁺ cation is a two-base-centered trigonal prism somewhat distorted to an antiprism. The crystals of compounds I and II contain H-bonded disordered cubes of the water molecules and Cl^? or Br^? anions.     

Host–guest complexation in the β-glycyrrhizic acid–2,8-dimethyl-5-[2´-(6″-methylpyridin-3″-yl)ethyl]-2,3,4,5-tetrahydro-1<Emphasis Type="Italic">H</Emphasis>-pyrido[4,3-<Emphasis Type="Italic">b</Emphasis>]indole system

Electronic, IR, and NMR spectroscopy methods were used to study the interaction in the β-glycyrrhizic acid (GA)–2,8-dimethyl-5-[2´-(6″-methylpyridin-3″-yl)ethyl]-2,3,4,5-tetra-hydro-1H-pyrido[4,3-b]indole (Dim) system in an alcoholic medium. The complete assignment of signals in the ¹H and ¹³C NMR spectra of Dim and GA in CD₃OD was made for the individual components and for thier mixtures at different ratios. These data suggest the formation of a host–guest complex in this system. It is hypothesized that associates of GA molecules interact with Dim through Δ^12,13–carbonyl group conjugated bonds in the triterpene moiety of GA that interact with the aromatic systems of the indole and pyridine moieties of Dim, as well as via an acid-base mechanism involving mainly the carboxy groups of glucuronic acid residues in the carbohydrate part of GA and the nitrogen atom of the tetrahydropyridine ring of Dim.     

Palladacycles incorporating a carboxylate-functionalized phosphine ligand: syntheses,characterization and their catalytic applications toward Suzuki couplings in water

A series of acetato-bridged [C^X]-type (C = aryl carbanion, X = N, P) palladacycles (1–5) of the general formula [Pd(μ-CH₃COO)(C^X)]₂ were synthesized as metal precursors via slightly modified procedures. However, in the case of complex 5 with Dpbp (Dpbp = 2′-(diphenylphosphino-κP)[1,1′-biphenyl]-2-yl-κC) as the supporting C^P ligand, an unexpected dinuclear complex [Pd(μ-CO₂)(Dpbp)]₂ (6) was obtained as a by-product and structurally determined by X-ray crystallography. The reactions of complexes 1–4 with 2-(diphenylphosphino)benzoic acid conveniently afforded four carboxylate-functionalized phosphine complexes [Pd(C^N)(Dpb)] (Dbp = 2-(diphenylphosphino-κP)benzoato-κO, 7–10), two of which (9/10) are newly synthesized in the present work and have been fully characterized. A comparative catalytic study revealed that complex [Pd(Ppy)(Dpb)] (7) (Ppy = 2-(2-pyridinyl-κN)phenyl-κC) is the best performer in Suzuki cross-couplings in H₂O. In addition, complex 7 exhibits much better catalytic activity compared to the non-functionalized phosphine equivalent [Pd(OAc)(PPh₃)(Ppy)] (11), which clearly indicates the superiority of incorporating a carboxylate-functionalized phosphine ligand into the palladacycles. A preliminary mechanistic study uncovered a different precatalyst initiation pathway compared to other known analogues of catalyst precursors.     

Supramolecular structure,spectroscopic, thermal studies and antimicrobial activities of Schiff base complexes

Metal(II) complexes of 4-(((2-hydroxynaphthalen-1-yl)methylene)amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (HL) were prepared, and their compositions and physicochemical properties were characterized on the basis of elemental analysis, with¹HNMR, UV–Vis, IR, mass spectroscopy and thermogravimetric analysis. All results confirm that the novel complexes have a 1:1 (M:HL) stoichiometric formulae [M(HL)Cl₂] (M = Cu(II)(1), Cd(II)(5)), [Cu(L)(O₂NO)(OH₂)₂](2), [Cu(HL)(OSO₃)(OH₂)₃]2H₂O(3), [Co(HL)Cl₂(OH₂)₂]3H₂O(4), and the ligand behaves as a neutral/monobasic bidentate/tridentate forming a five/six-membered chelating ring towards the metal ions, bonding through azomethine nitrogen, exocyclic carbonyl oxygen, and/or deprotonated phenolic oxygen atoms. The XRD studies show that both the ligand and Cu(II) complex (1) show polycrystalline with monoclinic crystal structure. The molar conductivities show that all the complexes are non-electrolytes. On the basis of electronic spectral data and magnetic susceptibility measurements, a suitable geometry has been proposed. The trend in g values (g _ll > g _⊥ > 2.0023) suggest that the unpaired electron on copper has a \(d_{{x^{2} - y^{2} }}\) character, and the complex (1) has a square planar, while complexes (2) and (3) have a tetragonal distorted octahedral geometry. The molecular and electronic structures of the ligand (HL) and its complexes (1–5) have been discussed. Molecular docking was used to predict the binding between HL ligand and the receptors of the crystal structure of Escherichia coli (E. coli) (3t88) and the crystal structure of Staphylococcus aureus (S. aureus) (3q8u). The activation thermodynamic parameters, such as activation energy (E _a), enthalpy (ΔH), entropy (ΔS), and Gibbs free energy change of the decomposition (ΔG) are calculated using Coats–Redfern and Horowitz–Metzger methods. The ligand and its metal complexes (1–5) showed antimicrobial activity against bacterial species such as Gram positive bacteria (Bacillus cereus and S. aureus), Gram negative bacteria (E. coli and Klebsiella pneumoniae) and fungi (Aspergillus niger and Alternaria alternata); the complexes exhibited higher activity than the ligand.     

Syntheses,crystal structures and in vitro anticancer activities of oxovanadium(IV) complexes of amino acid Schiff base and 1,10-phenanthroline ligands

Four oxovanadium(IV) complexes, namely [VO(desa-met)(phen)]·MeOH·2H₂O (1) (desa-met = Schiff base derived from 4-(diethylamino)salicylaldehyde and dl-methionine, phen = 1,10-phenanthroline), [VO(o-van-met) (phen)]·MeOH·CH₂Cl₂·3H₂O (2) (o-van-met = Schiff base derived from o-vanillin and dl-methionine), [VO(dtbs-napa)(phen)]·2H₂O (3) (dtbs-napa = Schiff base derived from 3,5-di-tert-butyl salicylaldehyde and 3-(1-naphthyl)-l-alanine) and [VO(hyna-napa)(phen)]·1.5H₂O (4) (hyna-napa = Schiff base derived from 2-hydroxy-1-naphthaldehyde and 3-(1-naphthyl)-l-alanine), were synthesized and characterized by IR, HRMS, UV–vis spectra, molar conductance and single-crystal X-ray diffraction (XRD). X-ray structural analysis showed that the V(IV) atoms in all four complexes are six-coordinated in a distorted octahedral environment. In the crystals of complexes 1 and 2, π–π stacking interactions together with hydrogen bonds connect the molecular units into 2D networks. Meanwhile, CH–π stacking interactions are observed between the aromatic rings in the crystals of 1 and 4, while the π–π stacking interactions between aromatic rings in the crystals of 2 and 3 are arranged with a face-to-face mode. The in vitro anticancer activities of these complexes against A-549 and HeGp2 cells were tested by MTT assay.     

Spectroscopic characterizations,X-ray studies,and electronic circular dichroism calculations of two alkaloid triterpenoids

Two alkaloid triterpenoids formulated as C₂₆H₃₅NO₃ (1) and C₃₀H₄₅NO₂ (2) were isolated from the timer tree Aphanamixis grandifolia. The structure of 1 and 2 was determined by IR, HRESIMS, 1D, and 2D-NMR. Compound 1 was confirmed by X-ray single crystal diffraction. Compound 1 crystallizes in the monoclinic, space group C₂ with unit cell parameters a = 53.195(4) Å, b = 7.6339(8) Å, c = 11.202(2) Å, β = 94.6520(2)°. Intermolecular hydrogen bonding and π–π stacking were presented in the molecular packing of 1. The absolute configurations of 1 and 2 were established by comparison of experimental circular dichroism properties with their electronic circular dichroism predicted by molecular modeling DFT calculations.