Controlled formation and topologies of thiophenolate-based macrocycles: rings, cylinders and bowls

The Schiff-base condensations of 1,3-diaminopropane with a protected thiophenol dialdehyde in the presence of Ni(2+), Pd(2+) or Zn(2+) can be controlled to yield either mononuclear acyclic, or 2 + 2 and 4 + 4 macrocyclic complexes by the choice of both metal cation and counteranion. The Ni(2+) complex of the 2 + 2 macrocycle contains two square-planar nickel ions and shows an arrangement similar to one observed previously: the mu-S atoms of the thiophenolate groups are pyramidal and lie on the same side of the plane defined by the four N atoms of the macrocycle to give a V-shaped molecule. By contrast, the Zn(2+) complex of the 2 + 2 macrocycle undergoes oligomerization to yield a bowl-shaped hexanuclear complex that includes a mu(3)-carbonate anion. Essential for this topology is the presence of three mu(3)-S-thiophenolato groups that link the three macrocyclic units to form a Zn(3)S(3) ring that seals the bottom part of the bowl. In this arrangement, one of the pyramidal mu(3)-S atoms in each dinuclear Zn(2+) complex is inverted relative to the arrangement observed for the dinickel complexes. Molecular modelling suggests that inversion about the mu-S atoms of the 2 + 2 macrocyclic complexes is readily accessible at room temperature and that the contrasting arrangements observed for the Ni(2+) and Zn(2+) complexes are those energetically most favourable for the respective metal ions. Rare 4 + 4 macrocyclic complexes are isolated as neutral dinuclear complexes for Ni(2+) and Pd(2+) and as a tetranuclear complex cation for Zn(2+). The topologies of these systems contrast significantly: those with two square-planar Ni(2+) or Pd(2+) ions form extended rings, while that with Zn(2+) forms a sulfur-lined cylinder which hosts acetonitrile molecules in the crystalline state. Reaction conditions can also be optimised to produce 2 + 1 acyclic ligands as their mononuclear Ni(2+) and Pd(2+) complexes, providing potentially useful building blocks for production of more complicated macrocyclic and supramolecular systems.     

Terphenyl-phenanthroline conjugate as a Zn(2+) sensor: H(2)PO(4)(-) induced tuning of emission wavelength

A new terphenyl-based macrocycle 5 incorporating phenanthroline as a fluorophore has been designed, synthesized and examined for its recognition ability toward various cations (Pb(2+), Hg(2+), Ba(2+), Cd(2+), Ag(+), Zn(2+), Cu(2+), Ni(2+), Co(2+), K(+), Mg(2+), Na(+) and Li(+)) by UV-vis, fluorescence and NMR spectroscopy. The receptor 5 showed highly selective 'Off-On' fluorescence signaling behavior for Zn(2+) ions in THF. Interestingly, the addition of H(2)PO(4)(-) ions to the [5-Zn] complex regulates the binding site for additional Zn(2+) ions and hence leads to a blue-shifted emission band.     

Chiral discrimination of a gemini-type surfactant with rigid spacer at the air-water interface

Spontaneous separation of chiral phases was observed in the monolayers of a racemate of gemini-type twin-tailed, twin-chiral amphiphiles, (2R,3R)-(+)-bis(decyloxy)succinic acid and (2S,3S)-(-)-bis(decyloxy)succinic acid. The pressure-area isotherms of the interfacial monolayers formed at the liquid-air interface, and the 2D lattice structures studied through surface probe measurements revealed that the racemate exhibits a homochiral discrimination of the enantiomers in two dimensions. An enantiomeric excess (e,e) of 20% was sufficient to break the chiral symmetry at the air-water interface for a homochiral interaction. Langmuir monolayers on ZnCl2 and CaCl2 subphases manifested chiral discrimination with Zn2+ evidencing homochiral interaction with a chelate-type complex, whereas Ca2+ resulted in a heterochiral interaction forming an ionic-type complex. For the chiral asymmetric units, oblique and rectangular unit cells of the racemic monolayer had exclusive requirements of homo- and heterochiral recognitions for Zn2+ and Ca2+ ions, respectively. Monolayers transferred from the condensed phase at 25 mN/m onto hydrophilic Si(100) and quartz substrates revealed the formation of bilayers through transfer-induced monolayer buckling. The emergence of homochiral discrimination was explained using the effective-pair-potential (EPP) approach.     

A highly selective fluorescence-based polymer sensor incorporating an (R,R)-salen moiety for Zn(2+) detection

A chiral polymer incorporating an (R,R)-salen moiety was synthesized by the polymerization of (R,R)-1,2-diaminocyclohexane with 2,5-dibutoxy-1,4-di(salicyclaldehyde)-1,4-diethynyl-benzene by a nucleophilic addition-elimination reaction. The fluorescence responses of the (R,R)-salen-based polymer toward various metal ions were investigated by fluorescence spectra. Compared with other cations, such as Na(+), K(+), Mg(2+), Ca(2+), Mn(2+), Fe(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), Ag(+), Cd(2+), Hg(2+), and Pb(2+), Zn(2+) can lead to a pronounced fluorescence enhancement as high as 7.8-fold together with an obvious blue-shift change of the chiral polymer. More importantly, the fluorescent color of the polymer changed to bright blue instead of weak yellow after addition of Zn(2+), which can be easily detected by the naked eye. The results indicate that this kind of chiral polymer, incorporating an (R,R)-salen moiety as a receptor in the main chain backbone, can exhibit high sensitivity and selectivity for Zn(2+) recognition.     

Metal-induced chiral folding of depsipeptide dendrimers

The synthesis and metal complexation of chiral depsipeptide dendrimers 3 and 7 containing an ethylenediaminetetraacetic acid (EDTA) ester-derived core is reported. The EDTA ester cavity of these dendrimers selectively complexes Zn(2+) and Cu(2+) ions leading to diastereoselective folding. To elucidate the coordination motif in the resulting "foldamers" of 3-ZnCl(2), 7-ZnCl(2), 3-CuCl(2), and 7-CuCl(2), the coordination behavior of the tetramethyl ester of EDTA (8) has been investigated as a model case. The corresponding complexes 8-ZnCl(2) and 8-CuCl(2) have been structurally characterized by (1)H NMR spectroscopy and X-ray analysis. The complexes involve the inherently chiral octahedral cis-alpha coordination motif, in which 8 serves as a tetradentate ligand. In the case of the Zn(II) complex 8-ZnCl(2), both Deltacis-alpha(S,S,lambda) and Lambdacis-alpha(R,R,lambda) stereoisomers were found in the unit cell. For the Cu(II) complex 8-CuCl(2), only one stereoisomer, namely Deltacis-alpha(S,S,lambda) was found in the crystal under investigation. (1)H NMR spectroscopy has shown that the same coordination motif is diastereoselectively formed in the chiral Zn(2+) dendrimers 3-ZnCl(2) and 7-ZnCl(2). Likewise, the calculated CD spectrum of the Deltacis-alpha(S,S,lambda) stereoisomer of the model complex 8-CuCl(2) shows good agreement with the experimental spectrum of the Cu(II) dendrimers 3-CuCl(2) and 7-CuCl(2), allowing assignment of the absolute configurations of the preferred foldamers as Lambdacis-alpha(R,R,lambda) for 3-CuCl(2) and Deltacis-alpha(S,S,lambda) for 7-CuCl(2). This work represents the first example of metal-complexation-mediated diastereoselective folding of chiral dendrimers with known absolute configuration.     

Novel chiral N4S2- and N6S3-donor macrocyclic ligands: synthesis,protonation constants,metal-ion binding and asymmetric catalysis in the Henry reaction

New hydrophobic chiral macrocyclic ligands L1-L3 with chiral diamino and thiophene moieties have been synthesized by the Schiff base condensation approach. Protonation constants of L1 and L2 were determined by potentiometry titration. Metal-ion binding experiments exhibited that L1 and L3 are pronounced in selective recognition, Ag+, Cu2+ and Ca2+ ions among the surveyed metal ions (Cu2+, Co2+, Ni2+, Zn2+, Cd2+, Pb2+, Ag+, Li+, Na+, K+, and Ca2+). L1 was found to spectroscopically detect the presence of Cu2+ and Ca2+ to function as a multiple readout sensor. The detection limit for Ca2+ ions was found to be 9.8 x 10(-5) M in CH2Cl2-MeOH solution. The trimeric chiral ligand L3 has been shown to be an efficient auxiliary in a Zn(II)-mediated enantioselective Henry reaction.     

Syntheses,Crystal Structures and Luminescent Properties of Two Schiff Base Complexes

Two new transition metal complexes based on chiral Schiff base ligand, namely Zn(L_1)_2(1) and Cd(L_2)2(2)(L 1=(R,E)-3-(2-hydroxy-3-methoxybenzylideneamino)propane-1,2-diol, L2=(R,E)-2-((2-hydroxy-1-phenylethylimino)methyl)-6-methoxyphenol), have been synthesized and characterized. Single-crystal X-ray diffractions reveal that both 1 and 2 crystallize in the same monoclinic space group C_2. 1 is four-coordinated, while 2 is six-coordinated. Complexes 1 and 2 show fluorescent emission at 479 and 580 nm, respectively. Moreover, 1 and 2 exhibit selective and sensitive recognition toward Zn~(2+)/Cd~(2+) ions in the methanol solution.     

Histidine-rich peptide: evidence for a single zinc-binding site on H5WYG peptide that promotes membrane fusion at neutral pH

The histidine-rich peptide H5WYG (GLFHAIAHFIHGGWHGLIHGWYG) was found to induce membrane fusion at physiologic pH in the presence of zinc chloride. In this study, we examined the ion selectivity of the interaction of Zn(2+) with H5WYG. This investigation was conducted by using adsorption at air/water interface and mass spectrometry. We found that a peptide-metal complex is formed with Zn(2+) ions. Electrospray ionisation-mass spectrometry (ESI-MS) reveals that the [H5WYG + Zn + 2H](4+), [H5WYG + Zn + H](3+) and [H5WYG + Zn](2+) ions, appearing by increasing the amount of Zn(2+) equivalent, correspond to a monomolecular H5WYG - Zn(2+) complex. Tandem mass spectrometry (MS/MS) provides evidence for the binding of the single Zn(2+) ion to the H(11) and H(19) and probably H(15) residues.     

Heterodinuclear metal arrangement in a flat macrocycle with two chemically-equivalent metal chelating sites

A phenanthroline-based macrocycle 1 has been newly developed which has two chemically equivalent metal chelating sites within the spatially restricted cavity for dinuclear metal arrangement. The macrocycle 1 reacts with Zn(CF(3)CO(2))(2) or ZnCl(2) to form homodinuclear Zn(II)-complexes. A single-crystal X-ray structural analysis of the resulting Zn(2)1(CF(3)CO(2))(4) determined the complex structure in which two Zn(II) ions are bound by two phenanthroline sites and two CF(3)CO(2)(-) ions bind to each Zn(II) ion in a tetrahedral geometry. Similarly, a homodinuclear Cu(I)-macrocycle was formed from 1 and Cu(CH(3)CN)(4)BF(4). Notably, from 1 and an equimolar mixture of Cu(CH(3)CN)(4)BF(4) and Zn(CF(3)CO(2))(2), a heterodinuclear Cu(I)-Zn(II)-macrocycle was exclusively formed in high yield (>90%) because of the relatively low stability of the dinuclear Cu(I)-macrocycle. A heterodinuclear Ag(I)-Zn(II)-macrocycle was similarly formed with fairly high selectivity from a mixture of Ag(I) and Zn(II) ions. Such selective heterodinuclear metal arrangement was not observed with other combinations of M-Zn(II) (M = Li(I), Mg(II), Pd(II), Hg(II), La(III), and Tb(III)).     

Lanthanide complexes of the chiral hexaaza macrocycle and its meso-type isomer: solvent-controlled helicity inversion

Lanthanide(III) complexes of the enantiopure chiral hexaaza tetraamine macrocycle L, 2(R),7(R),18(R),23(R)-1,8,15,17,24,31-hexaazatricyclo[25.3.1.1.0.0]-dotriaconta-10,12,14,26,28,30-hexaene, as well as of its meso-type 2(R),7(R),18(S),23(S)-isomeric macrocycle L1, have been synthesized and characterized by spectroscopic methods. The 2D NMR spectra confirm the identity of these complexes and indicate C2 symmetry of the [LnL]3+ and Cs symmetry of the [LnL1]3+ complexes. The crystal structures of the [PrL(NO3)(H2O)2](NO3)2, [EuL(NO3)(H2O)2](NO3)2, [DyL(NO3)2]2[Dy(NO3)5] x 5CH3CN, [YbL(NO3)2]2[Yb(NO3)5] x 5CH3CN, [YbL(H2O)2](NO3)3 x H2O, and [EuL1(NO3)(H2O)2]0.52[EuL1(NO3)2]0.48(NO3)1.52 x 0.48H2O complexes have been determined by single-crystal X-ray diffraction. In all complexes, the lanthanide(III) ions are coordinated by six nitrogen atoms of the macrocycle L or L1, but for each type of complex, the conformation of the macrocycle and the axial ligation are different. The crystallographic, NMR, and CD data show that the [YbL]3+ complex exists in two stable forms. Both forms of the Yb(III) complex have been isolated, and their interconversion was studied in various solvents. The two forms of [YbL]3+ complex correspond to two diastereomers of ligand L, which differ in the sense of the helical twist and the configuration at the stereogenic amine nitrogen atoms. In one of the stereoisomers, the macrocycle L of (RRRR) configuration at the stereogenic cyclohexane carbon atoms adopts the (RSRS) configuration at the amine nitrogen atoms, while in the other stereoisomer, the macrocycle L of (RRRR) configuration at the stereogenic cyclohexane carbon atoms adopts the (SSSS) configuration at the amine nitrogen atoms. The (RRRR)(RSRS) isomer is quantitatively converting to the (RRRR)(SSSS) isomer in water solution, while the reverse process is observed for an acetonitrile solution, thus representing the rare case of helicity inversion controlled by the solvent.     

Dinuclear manganese complexes containing chiral 1,4,7-triazacyclononane-derived ligands and their catalytic potential for the oxidation of olefins, alkanes, and alcohols

Five new 1,4,7-triazacyclononane-derived compounds, sodium 3-(4,7-dimethyl-1,4,7-triazacyclononan-1-yl)propionate (Na[LMe2R']) as well as the enantiopure derivatives (S)-1-(2-methylbutyl)-4,7-dimethyl-1,4,7-triazacyclononane (S-LMe2R'), SS-trans-2,5,8-trimethyl-2,5,8-triazabicyclo[7.4.01,9]tridecane (SS-LBMe3), (S)-1-(2-hydroxypropyl)-4,7-dimethyl-1,4,7-triazacyclononane (S-LMe2R), and (R)-1-(2-hydroxypropyl)-4,7-dimethyl-1,4,7-triazacyclononane (R-LMe2R), have been synthesized. Reaction of manganese dichloride with the chiral macrocycles S-LMe2R and R-LMe2R in aqueous ethanol gives, upon oxidation with hydrogen peroxide, the brown dinuclear Mn(III)-Mn(IV) complexes which are enantiomers, [Mn2(S-LMe2R)2(mu-O)2]3+ (S,S-1) and [Mn2(R-LMe2R)2(mu-O)2]3+ (R,R-1). The single-crystal X-ray structure analyses of [S,S-1][PF6]3.0.5(CH3)2CO and [R,R-1][PF6]3.0.5(CH3)2CO show both enantiomers to contain Mn(III) and Mn(IV) centers, each of which being coordinated to three nitrogen atoms of a triazacyclononane ligand and each of which being bridged by two oxo and by two chiral hydroxypropyl pendent arms of the macrocycle. The enantiomeric complexes S,S-1 and R,R-1 were found to catalyze the oxidation of olefins, alkanes, and alcohols with hydrogen peroxide. In the epoxidation of indene the enantiomeric excess values attain 13%. The bond selectivities of the oxidation of linear and branched alkanes suggest the crucial step in this process to be the attack of a sterically hindered high-valent manganese-oxo species on the C-H bond.     

Racemic atropisomeric N,N-chelate ligands for recognizing chiral carboxylates via Zn(II) coordination: structure, fluorescence, and circular dichroism

Two racemic atropisomeric N,N'-chelate ligands, bis{3,3'-[N-Ph-2-(2'-py)indolyl]} (1) and bis{3,3'-N-4-[N-2-(2'-py)indolyl]phenyl-2-(2'-py)indolyl} (2), have been found to be able to distinguish the enantiomers of Zn((R)-BrMeBu)2 and Zn((S)-BrMeBu)2 where BrMeBu = O2CCH(Br)CHMe2, with a distinct and intense CD spectral response at approximately the 10 microM concentration range. Computational studies established that the (R)-1-Zn((R)-BrMeBu)2 or (S)-1-Zn((S)-BrMeBu)2 diastereomer is more stable than (R)-1-Zn((S)-BrMeBu)2 or (S)-1-Zn((R)-BrMeBu)2. In addition, computational studies showed that the CD spectra of (S)-1-Zn((S)-BrMeBu)2 and (S)-1-Zn((R)-BrMeBu)2 are similar. (1)H NMR spectra confirmed that these two diastereomers exist in solution in about a 2:1 ratio for both complexes of 1 and 2. The distinct CD response of the racemic ligands 1 and 2 toward the chiral zinc(II) carboxylate is therefore attributed to the preferential formation of one diastereomer. The binding modes of the zinc(II) salt with ligands 1 and 2 were established by the crystal structures of the model compounds 1-Zn(tfa)2 and 2-Zn(tfa)2 (tfa = CF3CO2(-)), where the Zn(II) ion is chelated by the two central pyridyl groups in the ligand. Fluorescent titration experiments with various zinc(II) salts showed that the fluorescent spectrum of the atropisomeric ligand displays an anion-dependent change. The zinc(II) binding strength to the N,N'-chelate site of the atropisomeric ligand has been found to play a key role in the selective recognition of different chiral zinc(II) carboxylate derivatives by the racemic atropisomeric ligands.     

Core/shell oligometallic template synthesis of macrocyclic hexaoxime

A 36-membered macrocyclic hexaoxime was quantitatively obtained by [3 + 3] condensation of dialdehyde 2 with diamine 3 using La3+ (core metal) and Zn2+ (shell metal) as a novel core/shell template, while the yield was very low in the absence of the metal ions. The high yield can be attributed to the efficient formation of a 3:3:1 complex of dialdehyde 2, Zn2+, and La3+, which readily gives the macrocycle keeping the Zn3La core/shell tetranuclear cluster structure.     

光学活性3-(1′-羟基乙基)-4-乙酰氧基-β-内酰胺的立体选择性合成

(1′R,3R,4R)-N-取代-3-(1′-羟基乙基)-4-乙酰氧基-β-内酰胺(3)是合成青霉烯和碳青霉烯类β-内酰胺抗生素的关键中间体.以廉价的L-抗坏血酸为原料,制得S-缩异丙氧叉甘油醛(5),与胺反应定量转变成相应的手性亚胺(6a～6d),6与双烯酮[2+2]环加成反应,高立体选择性地合成3(S)-乙酰基-β-内酰胺(Sa～8d),其非对映体过量由类似反应的80％提高到接近100％.8a经四步反应得到目标化合物3a.     

Synthesis and characterization of copper-, zinc-, manganese-, and cobalt-substituted dimeric heteropolyanions, [(alpha-XW9O33)2M3(H2O)3](n-) (n = 12, X =As(III), Sb(III), M = Cu(2+), Zn(2+); n = 10, X = Se(IV), Te(IV), M = Cu(2+) and [(alpha-AsW9O33)2WO(H2O)M2(H2O)2](10-) (M = Zn(2+), Mn(2+), Co(2+)

Interaction of the lacunary [alpha-XW9O33](9-) (X = As(III), Sb(III)) with Cu(2+) and Zn(2+) ions in neutral, aqueous medium leads to the formation of dimeric polyoxoanions, [(alpha-XW9O33)2M3(H2O)3](12-) (M = Cu(2+), Zn(2+); X = As(III), Sb(III)), in high yield. The selenium and tellurium analogues of the copper-containing heteropolyanions are also reported: [(alpha-XW9O33)2Cu3(H2O)3](10-) (X = Se(IV), Te(IV)). The polyanions consist of two [alpha-XW9O33] units joined by three equivalent Cu(2+) (X = As, Sb, Se, Te) or Zn(2+) (X = As, Sb) ions. All copper and zinc ions have one terminal water molecule resulting in square-pyramidal coordination geometry. Therefore, the title anions have idealized D3h symmetry. The space between the three transition metal ions is occupied by three sodium ions (M = Cu(2+), Zn(2+); X = As(III), Sb(III)) or potassium ions (M = Cu(2+); X = Se(IV), Te(IV)) leading to a central belt of six metal atoms alternating in position. Reaction of [alpha-AsW9O33](9-) with Zn(2+), Co(2+), and Mn(2+) ions in acidic medium (pH = 4-5) results in the same structural type but with a lower degree of transition-metal substitution, [(alpha-AsW9O33)2WO(H2O)M2(H2O)2](10-) (M = Zn(2+), Co(2+), Mn(2+)). All nine compounds are characterized by single-crystal X-ray diffraction, IR spectroscopy, and elemental analysis. The solution properties of [(alpha-XW9O33)2Zn3(H2O)3](12-) (X = As(III), Sb(III)) were also studied by 183W-NMR spectroscopy.     

A highly selective and sensitive in vivo fluorosensor for zinc(II) without cytotoxicity

A highly selective and sensitive fluorescent Zn(2+) sensor, 2,6-bis(2-hydroxy-benzoic acid hydrazide)-4-methylphenol (1), was designed and synthesized. In aqueous THF (4 : 6 v/v) ligand 1 induces a 2 : 1 complex formation with respect to Zn(2+) at physiological pH. This probe features visible light excitation(390 nm) and emission (490 nm) profiles, excellent selectivity responses for Zn(2+)over other competing biological metal ions with K(d) < 1 pM(2), LOD < 1 ng L(-1) and about 680 fold enhancement in fluorescent intensity upon Zn(2+) binding. It also exhibits cell permeability and intracellular Zn(2+) sensing in A375 human melanoma cancer cell.     

A new enantiopure unsaturated dicarboxylate as a 4-connected unit in a flexible homochiral PtS-type framework

Metal cation mediated chiral ligand transformation of (S)-camphanic acid leads to a new enantiopure unsaturated dicarboxylate that links tetrahedral Zn(2+) sites into 3-D homochiral 4-connected PtS-type framework structures, Zn(tced) (1, H(2)tced=1,2,2-trimethyl-3-cyclopentene-1,3-dicarboxylic acid) and Zn(4)(tced)(4)(4,4'-bipy) (2, 4,4'-bipy=4,4'-bipyridine).     

Incorporation of triazole into a quinoline-rhodamine conjugate imparts iron(iii) selective complexation permitting detection at nanomolar levels

Two new rhodamine based probes 1 and 2 for the detection of Fe(3+) were synthesized and their selectivity towards Fe(3+) ions in the presence of other competitive metal ions tested. The probe 1 formed a coloured complex with Fe(3+) as well as Cu(2+) ions and revealed the lack of adequate number of coordination sites for selective complexation with Fe(3+). Incorporation of a triazole unit to the chelating moiety of 1 resulted in the probe 2, that displayed Fe(3+) selective complex formation even in the presence of other competitive metal ions like Li(+), Na(+), K(+), Cu(2+), Mg(2+), Ca(2+), Sr(2+), Cr(3+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Zn(2+), Cd(2+), Hg(2+) and Pb(2+). The observed limit of detection of Fe(3+) ions (5 × 10(-8) M) confirmed the very high sensitivity of 2. The excellent stability of 2 in physiological pH conditions, non-interference of amino acids, blood serum and bovine serum albumin (BSA) in the detection process, and the remarkable selectivity for Fe(3+) ions permitted the use of 2 in the imaging of live fibroblast cells treated with Fe(3+) ions.     

Role of anions on the crystal structures of copper(II) and zinc(II) complexes of a tunable butterfly cyclophane macrocycle

Three crystal structures of a ditopic cyclophane ligand (L) in which two 1,5,8,12-tetraamine molecules have been attached through methylene spacers to the ortho positions of a benzene ring are reported. The first one (1) corresponds to the tetraprotonated free macrocycle (H4L4+) having two tetrachlorozincate(II) counteranions (C24H54O2N8Cl8Zn2, a = 9.1890(2) A, b = 14.0120(3) A, c = 15.3180(3) A, alpha = 89.2320(7) degrees , beta = 82.0740(6) degrees , gamma = 83.017(1) degrees , Z = 2.00, triclinic, P); the second one (2) is of a binuclear Cu2+ complex having coordinated chloride anions and perchlorate counteranions (C24H58O14N8Cl4Cu2 a = 9.9380(2) A, b = 30.2470(6) A, c = 53.143(1) A, orthorhombic, F2dd, Z = 18), and the third one (3) corresponds to an analogous Zn2+ complex that has been crystallized using triflate as counteranion (C26H(51.2)O(6.6)N8Cl2F6S2Zn2 a = 8.472(5) A, b = 9.310(5), c = 13.745(5) A, alpha = 84.262(5) degrees , beta = 77.490(5) degrees , gamma = 73.557(5) degrees , triclinic, P, Z = 2). The analysis of the crystallographic data clearly shows that the conformation of the macrocycle and, in consequence, the overall architecture of the crystals are controlled by the anions present in the moiety, pi-pi-stacking associations, and hydrogen bonding interactions. The protonation and stability constants for the formation of the Cu2+ and Zn2+ complexes in aqueous solution have been determined potentiometrically in 0.15 mol dm(-3) NaClO4 at 298.1 K. Intramolecular hydrogen bonding defines the protonation behavior of the compound. Positive cooperativity is observed in the formation of the Cu2+ complexes.     

Facile route to 3,5-disubstituted morpholines: enantioselective synthesis of O-protected trans-3,5-bis(hydroxymethyl)morpholines

[reaction: see text] (3R,5R)-1 R1 & R2 = TBDPS, (3S,5R)-2 R1 = Bn,R2 = TBDPS, (3S,5S)-3 R2 & R2 = Bn. trans-3,5-Bis(benzyl/tert-butyldiphenylsilyloxymethyl)morpholines, promising candidates for the C(2)-symmetric class of chiral reagents, were prepared with excellent optical purity. A key step in the synthesis is the coupling of a serinol derivative with 2,3-O-isopropylideneglycerol triflate or its equivalent. This methodology was extended to the synthesis of chiral trans-3-(benzyloxymethyl)-5-(tert-butyldiphenylsilyloxymethyl)morpholine, a potentially useful chiral building block.