Facile synthesis and optical resolution of inherently chiral fluorescent calix[4]crowns: enantioselective recognition towards chiral leucinol

A series of tri-O-alkylated inherently chiral fluorescent calix[4]crowns in the cone conformations and a series of tetra-O-alkylated inherently chiral fluorescent calix[4]crowns in the partial cone conformations have been synthesized. By condensing with chiral auxiliary (S)-BINOL, the resulting diastereomers could be separated via preparative TLC. We found that the size of the crown moiety effected the separation of the diastereomers. Further, removal of the BINOL unit by hydrolysis furnished pairs of enantiomers with optical purity. Moreover, we found that a tetra-O-alkylated inherently chiral fluorescent calix[4]crown-6 in the partial cone conformation 6c showed considerable enantioselective recognition capability towards chiral leucinol.     

Preparation of enantiopure inherently chiral calix[5]arenes

Enantiopure inherently chiral calix[5]arenes were successfully prepared by separation of their (R)-BINOL diastereomeric derivatives of the corresponding racemates by column chromatography instead of HPLC. A new type of inherently chiral calix[5]arene was obtained.     

Efficient synthesis of calix[6]tmpa: a new calix[6]azacryptand with unique conformational and host-guest properties

A new C(3v)-symmetrical calix[6]azacryptand, that is, calix[6]tmpa (11), was synthesized by efficient [1+1] macrocyclization reactions. Remarkably, both linear and convergent synthetic strategies that were applied lead to equally good overall yields. Calix[6]tmpa behaves as a single proton sponge and appeared reluctant to undergo polyprotonation, unlike classical tris(2-pyridylmethyl)amine (tmpa) derivatives. It also acts as a good host for ammonium ions. Interestingly, it strongly binds a sodium ion and a neutral guest molecule, such as a urea, an amide, or an alcohol, in a cooperative way. A (1)H NMR study indicated that the ligand, as well as its complexes, adopt a major flattened cone conformation that is the opposite of that observed with the previously reported calix[6]cryptands. Characterization of the monoprotonated derivative 11H(+) by X-ray diffraction also revealed the presence of a 1,3-alternate conformation, which is the first example of its kind in the calix[6]arene family. This conformer is probably also present in solution as a minor species. The important covalent constraint induced by the polyaromatic tmpa cap on the calixarene skeleton, and conversely from the calix core onto the tmpa moiety, is the likely basis for the unique conformational and chemical properties of this host.     

Preparation of both antipodes of enantiopure inherently chiral calix[4]crowns

Both antipodes of enantiopure inherently chiral calix[4]crown derivatives were successfully obtained through separation of their BINOL diastereomeric derivatives of corresponding racemates using preparative TLC instead of conventional HPLC methods. Such a result provides a basis for future study of chiral recognition and asymmetric catalysis with inherently chiral calixrene derivatives.     

Synthesis and chiral recognition properties of two novel chiral calix[4]arene tartaric ester derivatives

Two new chiral calix[4]arene derivatives containing tartaric acid ester moieties were synthesized. The chiral calix[4]arenes are in a ‘cone’ conformation according to NMR spectroscopy. The chiral recognition capabilities of 1–4 toward the guests, 1,2-propanediol and serine methyl ester hydrochloride (SerOMe), were investigated (¹H NMR spectroscopy). The extraction properties of compounds 1 and 2 toward selected α-amino acid methyl esters were also studied.     

Optically pure calix[6]tris-ammoniums: syntheses and host-guest properties toward neutral guests

[reaction: see text] Optically pure calix[6]arenes bearing chiral amino arms 4, 7, and 10 have been synthesized in high yields from the known symmetrically 1,3,5-trismethylated calix[6]arene. For both compounds 7 and 10, the key step consists of an efficient selective alkylation on the narrow rim of the calix[6]arene with Ba(OH)2 as the base. All of these chiral calix[6]tris-amines possess a similar flattened cone conformation with the cavity occupied by the methoxy groups. In contrast to 4 and 7, upon protonation, the enantiopure calix[6]arene 10 can switch to the opposite flattened cone conformation through self-assembly of its ammonium arms in an ion-paired cap which closes the cavity. As shown by NMR host-guest studies and an X-ray structure, the obtained polarized host (10 x 3H+) behaves as a remarkable endo-receptor for small polar neutral molecules. Thanks to the tris-cationic chiral binding site of 10 x 3H+, it was shown that the guests experience a chiral environment upon inclusion. Finally, the first example of enantioselective molecular recognition inside the cavity of a calix[6]arene has been evidenced with a racemic 1,2-diol guest.     

Synthesis and chiral recognition abilities of new calix[6]arenes bearing amino alcohol moieties

Herein the synthesis and recognition abilities towards amino acids and amino alcohols of new d-/l-phenylalaninol substituted p-tert-butylcalix[6]arenas are reported. These compounds, 6 and 7 have been synthesized via nucleophilic substitution reactions involving 5,11,17,23,29,35-tert-butyl-37,38-dimethoxy-39,40,41,42-(p-tosylethoxy)calix[6]arene 5 with d-/l-phenylalaninol in dry THF. The extraction properties of 6 and 7 towards some selected amino acid methylesters and amino alcohols have been studied by liquid–liquid extraction. These results show that chiral calix[6]arene derivatives exhibit a good affinity towards all amino acids and amino alcohols.     

Synthesis of novel chiral Schiff base and amino alcohol derivatives of calix[4]arene and chiral recognition properties

In the present study, the synthesis and liquid phase extraction properties towards some amino acid methylesters and amino alcohols of Schiff base and amino alcohol substituted calix[4]arene are reported. The Schiff base substituted calix[4]arene 5 has been synthesized via condensation reaction involving 5,17-diformyl-11,23-di-tert-butyl-25,27-di[3-(4-formylphenoxy)propoxy]-26,28 dihydroxycalix[4]arene 4 and (R)-(?)-2-phenylglycine methyl ester in CHCl₃:MeOH. To give the amino alcohol substituted calix[4]arene 6, the synthesized chiral compound 5 was reduced by LiAlH₄. The new chiral Schiff base and amino alcohol derivatives of calix[4]arene have been characterized by a combination of FT-IR, ¹H NMR, ¹³C NMR, FAB-MS and elemental analysis. Also, the extraction behaviors of 5 and 6 towards some selected amino acid methylesters and amino alcohols have been studied by liquid–liquid extraction.     

Design of a novel inherently chiral calix[4]arene for chiral molecular recognition

A newly designed inherently chiral calix[4]arene was synthesized and resolved to an optically pure form. Enantiomeric recognition ability of the chiral calix[4]arene was examined using 1H NMR experiments with mandelic acid. In addition, the chiral calix[4]arene was applied to asymmetric reactions, as an organocatalyst.     

First synthesis of enantiopure 1,6-difunctionalized dodecahydrobenz[f]indenes

An enantiospecific route to the previously unreported 1,6-difunctionalized dodecahydrobenz[f]indene ring system is described. Optically pure Hajos-Parrish ketone is used as the building block for preparation of a 6-methyleneinden-5-ol. This allylic alcohol is then utilized in a Claisen rearrangement under Johnson's conditions to introduce a side chain that is further modified and cyclized to produce the benz[f]indene ring system.     

A new approach to enantiopure inherently chiral calix[4]arenes: determination of their absolute configurations

A new approach to the synthesis of meta-substituted enantiopure inherently chiral calix[4]arenes by introducing L-Boc-proline as dual functions of the chiral auxiliary has been described. Moreover, the absolute configurations of the enantiomers were determined by CD spectra, X-ray crystallographic analysis, and the chemical derivative method.     

New water-soluble host molecules derived from calix[6]arene

4-Sulfonate derivatives of calix[6]arene and O-n-hexylcalix[6]arene (1a and 1b, respectively) were synthesized. Measurements using fluorescence and absorption spectral probes indicated that the cavity of calix-[6]arene can accept a naphthalene molecule but not a pyrene molecule and that (1b) has a hydrophobic cavity constructed from the aggregate of the hexyl groups while (1a) provides a reaction field apparently more polar than water. This is the first example for water-soluble host molecules derived from calix[6]arene.     

A novel calix[4]arene-based neutral semicarbazone receptor for anion recognition

A series of novel calix[4]arene-based neutral semicarbazone and thiosemicarbazone receptors have been synthesized and characterized. The molecular receptor 4a recognizes in preference to other anions (Cl⁻, Br⁻, I⁻, , and ) through a 1:1 binding-stoichiometry.     

脱氧胆酸手性分子钳的微波合成及其对中性分子的识别性能研究

在微波辐射条件下,以脱氧胆酸甲酯为间隔基,高产率合成了5个脱氧胆酸手性分子钳人工受体,其结构经IR,1HNMR,MS及元素分析确证。用差紫外光谱法测定了其对中性分子的识别性能。实验结果表明,这类分子钳人工受体对所考察的客体分子有良好的识别作用,主客体间形成1∶1型主客体配合物,受体5d对苯胺的结合常数高达14171.39 M-1。     

Efficient synthesis and host-guest properties of a new class of calix[6]azacryptands

Two members of a new class of calix[6]azacryptands, namely, calix[6]tampo and calix[6]tamb, have been synthesized through an efficient [1 + 1] macrocyclization reaction--reduction sequence. One of them has been obtained in a remarkably high overall yield from the known X(6)H(3)Me(3). In comparison to all the other calix[6]azacryptands, they possess unique conformational properties since they present a rigidified cone conformation with a partial filling of the cavity by the methoxy groups. In contrast to calix[6]tampo, the fully protonated derivative of calix[6]tamb behaves as a remarkable molecular receptor toward polar neutral guests. NMR studies have shown that the intracavity binding process is governed by a conformational flip of the aromatic walls of the calixarene core.     

Binding of neutral molecules by p-nitrophenylureido substituted calix[4]arenes

Although originally designed for anion recognition, bis(N′-p-nitrophenylureido)calix[4]arenes immobilised in the 1,3-alternate conformation can act as receptors for small neutral molecules, such as sulfoxides and ketones. Their binding ability was studied both in solution and in the solid state using the combination of UV/vis, NMR, and X-ray crystallography.     

Synthesis and structures of novel enantiopure inherently chiral calix[4]arene-derived salphen ligands and their transition-metal complexes

Synthesis and structures of two pairs of novel enantiopure inherently chiral calix[4]arene-derived salphen ligands were described. Several Zn²⁺, Ni²⁺, and Cu²⁺ complexes of the chiral ligands were also prepared, and their structures were characterized by NMR, IR, CD, and HRMS spectra.     

Synthesis and anion recognition of neutral receptors based on multiamide calix[4]arene

Two multiamide calix[4]arenes (5, 6) were synthesized and characterized by NMR, MS and elemental analysis. The binding properties of receptors with some anions (π-O₂NPhOPO₃²⁻, π-O₂NPhO⁻, H₂PO₄⁻, Ac⁻, Cl⁻, Br⁻ and I⁻) were studied by UV-Vis spectra. The results indicate that the tetraamide calix[4]arenes (5, 6) have a good selectivity to the anions containing aromatic ring (π-O₂NPhOPO₃ ²⁻, π-O₂NPhO⁻). The 1 : 1 complexes between host and guest were formed through multiple hydrogen bonding and π-π interactions. The hosts 5 and 6 also show a definite binding ability for the anions (H₂PO₄⁻, Ac⁻, Cl⁻) that have no ultraviolet absorption, which provides a simple method of spectrum detection for these anions.