Helical Compounds Research Articles

Synthesis of some dipyrrolophenanthroline derivatives as novel macromolecules

Some N-heterocyclic compounds such as pyrazino(2,3-f)(1,10)phenanthroline and dipyrido(3,2- a: 2',3'-c)phenazine can react with dialkyl acetylenedicarboxylate to give new helical compounds, which exhibit nonplanarity enforced by the crowding of the pyrrole rings.

Tunable blue-emitting fluorophores—benzo[1,2- b:4,3- b′]dithiophene and trithia[5]helicene end-capped with electron-rich or electron-deficient aryl substituents

Light-emitting fluorophores 1– 10b based on aryl substituted benzo[1,2- b:4,3- b′]dithiophenes ( BDT) and trithia[5]helicenes ( T5H) have been synthesized using various combinations of Suzuki coupling, the Wittig, or McMurry reaction, and subsequent photocyclization of the dithienylethenes thus obtained. Photophysical properties of the helical compounds end-capped with different electron-rich and electron-deficient aryl moieties thus resulting were evaluated. Photocyclization of a dithienylethene derivative 10a was investigated, and the X-ray crystal structure of dinaphthyl-substituted BDT ( 4) was obtained. With this series of compounds 1– 10b, we demonstrate that the optical properties of all of the new compounds, and by extension many conjugated materials, can be tuned over the entire blue range (400–480 nm).

Interaction of bulged DNA with leucine-containing mimics of NCS-chrom

Synthesis of chiral spirocyclic helical compounds containing leucine that mimic the molecular architecture of the potent DNA bulge binder obtained from the natural product metabolite NCSi-gb has been accomplished. The interaction between the compounds and DNA was studied by circular dichroism (CD) method. The results suggested that the two synthetic diastereoisomers specifically targeted the bulge site of DNA and induced conformational change of bulged DNA greatly.

Spirocyclic helical compounds as binding agents for bulged RNA, including HIV-2 TAR

Based on fluorescence binding studies and 1D 1H NMR studies, designed synthetic analogues of NCSi-gb bind specifically with two-base bulged RNA, including HIV-2 TAR RNA, making them potential lead compounds for antiviral drug development.

Stimulation on DNA triplet repeat strand slippage synthesis by the designed spirocycles

The designed simpler chiral spirocyclic helical compounds that mimic the molecular architecture of the DNA bulge binder NCSi-gb have been prepared. It has been found that the synthesized spirocyclic compounds have strong stimulation effect on DNA slippage synthesis. Their stimulation activities on DNA strand slippage suggest that they may bind to or induce the formation of a non Watson–Crick structure during in vitro replication of DNA triplet repeats.

Stability and Properties of Polyhelicenes and Annelated Fused-Ring Carbon Helices: Models Toward Helical Graphites

The geometrical structures and properties of conjugated polyhelicenes and annelated fused-ring carbon helices with analogous frameworks were theoretically studied at the HF/6-31G and B3LYP/6-31G levels. These studies focused on the stability of the fused-ring structures with special emphasis on the helical geometrical arrangements. To elucidate bonding patterns, the orbitals, electron density contours, and the electrostatic potential of these helical compounds were analyzed. The structure of fused polynaphthalenes arranged in a helical spiral can be regarded as part of a locally helical graphite lattice that is expected to give rise to special electronic properties along the helically layered conjugated single sheet that can be regarded as a single extended pi system but also involving local layer-to-layer pi-pi interactions that are typical in ordinary graphite. This dual feature might lead to novel materials.

Synthesis and NMR Binding Study of a Chiral Spirocyclic Helical Analogue of a Natural DNA Bulge Binder

[reaction: see text] Synthesis of chiral spirocyclic helical compounds which mimic the molecular architecture of the potent DNA bulge binder obtained from the antitumor agent NCS-chrom has been accomplished. Structural analysis of the compounds by CD and NMR is presented. NMR titration study indicates binding of P,alpha-helimer (1d) at a two-base bulge site in a DNA oligomer, providing insight to the design of agents as specific probes of a bulged structure in nucleic acids.

Syntheses, structures and photoluminescent properties of silver(I) complexes with in situ generated hexahydropyrimidine derivatives

Two new linear and V-shaped tetradentate ligands, namely 1,4-bis(2-hexahydropyrimidyl)benzene (L) and 1,3-bis(2-hexahydropyrimidyl)benzene (L ′), and their silver(I) complexes, [Ag 2L(μ-ONO 2)](NO 3) · 2H 2O ( 1), [Ag 2L(μ-pn)](NO 3) 2 ( 2), [Ag 2L(μ-pn)](ClO 4) 2 ( 3) and [Ag 4L ′ 2(H 2O)](NO 3) 4 · 5H 2O ( 4) (pn=1,3-diaminopropane) have been synthesized in situ and structurally characterized by single-crystal X-ray diffraction. 1 and 2 were obtained from the same reaction solution but different crystallization conditions. 1 is an one-dimensional chain featuring cuboid tetranuclear silver(I) units interconnected through monoatomic nitrate bridges. Both 2 and 3 are ribbon-like helical compounds in which each L ligand acts in a tetradentate bridging mode to interconnect four metal atoms, and each pn ligand functions in a bidentate bridging mode to link a pair of metal atoms. 4 shows a truncated square-pyramidal tetranuclear motif arose by the V-shaped L ′ ligand. Close Ag⋯Ag separations (2.901–2.939 Å) assisted by bis(hexahydropyrimidine) bridges were observed in 1 and 4, indicating metal–metal interactions. Photoluminescence of 1– 4 has also been observed in the solid state and solution at room temperature and low temperature, respectively.

Chiral recognition in the binding of helicenediamine to double strand DNA: interactions between low molecular weight helical compounds and a helical polymer

Binding of a helicene, 5,8-bis(aminomethyl)-1,12-dimethylbenzo[ c]phenanthrene, to calf thymus DNA was studied using UV, CD, and fluorescence spectroscopy as well as calorimetry. The enantiomeric helicenes strongly bound to the double strand DNA possessing the right-handed helical structure. In addition, chiral recognition was observed in the binding, where the ( P)-helicene with the right-handed helicity formed more stable complex than the ( M)-helicene with the left-handed helicity. The binding studies of the helicenes and natural nucleosides by 1H NMR spectroscopy also revealed the higher affinity to the ( P)-helicene. Both monomeric and polymeric nucleic acids thus turned out to favor the ( P)-helicity.

Template Effects, Asymmetry, and Twinning in Helical Inclusion Compounds

Brasilianer- und Dauphineer-Zwillinge bei Kristallen von Einschlussverbindungen aus 2,12-Tridecandion und Harnstoff (siehe Bild) wurden durch kombinierte Anwendung von optischer Mikroskopie, Kristallographie und Synchrotron-Topographie mit weißer Röntgenstrahlung (SXRT) nachgewiesen und erstmals strukturell analysiert.

Pseudopolymorphic Clathrate Structures Formed by an Alicyclic Dialcohol Inclusion Host

Dialcohol host 2,7-dimethyltricyclo[4.3.1.03,8]undecane-syn-2,syn-7-diol 1 can form either ellipsoidal clathrate or helical tubulate inclusion compounds where only dispersion forces operate between the hosts and guests. The former (tetragonal space group I41/acd), built from two interpenetrating sublattices containing both diol enantiomers, encloses the guests in rugby ball-shaped cavities. The latter (trigonal space group P3121 or P3221), containing only one diol enantiomer, traps the guests within parallel tubes. Which inclusion type is produced is determined by the guest size and shape and, hence, control is possible over these structures. At room temperature, cyclohexane gives the tetragonal structure, but fluorocyclohexane yields the trigonal structure. Chloroform produces both pseudopolymorphs: the tetragonal form at higher and the trigonal form at lower temperatures. Powder and single-crystal structural X-ray data are reported for these clathrate compounds.

ChemInform Abstract: Fine-Control of Helical Tubuland Inclusion Properties Through the Pendant Group Approach.

Abstract The helical tubulands are a family of alicyclic diols which crystallise in chiral space group P3121 and whose lattices can contain guest molecules enclosed within parallel tubes. New examples can be designed following a series of rules based on molecular structure and symmetry. In order to probe the latter requirement, and also to increase host–guest interactions, the behaviour of 2,5,8-trimethyltricyclo[5.3.1.13,9]dodecane-syn-2,syn-8-diol 4 was investigated using X-ray methods. Although molecules of 4 have no C2 symmetry they still form the helical tubuland lattice on crystallisation. In the pure apohost 4 their symmetry-breaking C5 methyl groups protrude into the tube volumes where they randomly adopt one of two equivalent orientations. Although the pendant methyl groups reduce the volume available for guest inclusion, they create irregular tube wall surfaces and interact more effectively with guest molecules. The helical tubulate inclusion compounds of 4 with diisopropyl ketone, benzene, toluene, and o-xylene show significant local methyl group ordering around a given guest molecule which performs a crucial templating role in formation of the product. In all cases, however, crystallographic C2 symmetry results in the solid through overall disorder of these diol orientations. Hence this, rather than strict molecular symmetry, is the true symmetry requirement of the P3121 helical tubuland lattice.

Chiral "metallo-spiralenes": helical molecules conformationally stabilised by an organometallic scaffold

The synthesis of a series of chiral cyclomanganated 2-[(eta 6-phenyl)-Cr(CO)3]pyridine complexes derived from (-)-beta-pinene enables, by a "spirogenic transformation", the preparation of four different chiral helical heterobimetallic syn-facial complexes or Cr0/Mn1-spiralenes, among which two possess a right-handed P molecular helicity and two other a left-handed M one. These organometallic helical molecules are synthesised by applying two different methods to the chiral cyclomanganated (eta 6-arene)tricarbonylchromium substrates. The first method is the so-called "Fischer route" which involves a sequential addition of PhLi and MeOTf. The second method based on reaction of the cyclomanganated complex with diphenyldiazomethane which has been tested on achiral bimetallic substrates is a reasonable neutral alternative to the "Fischer methodology" for the synthesis of Cr0/Mn1-spiralenes. The crystal structure of one of these heterobimetallic chiral helical compounds serves as a starting point in the configurational and structural assessment of the synthesised chiral (eta 6-arene)tricarbonylchromium complexes. Application of the "Fischer route" to a cyclomanganated chiral 2-phenylpyridine generates a single chiral eta 3-benzylic complex--or Mn1-spiralene--bearing a left-handed M helicity which has been characterized by X-ray diffraction analysis. Circular dichroic spectroscopic measurements underline the predominant contribution of the chiral and chirally induced aromatic chromophores to the sign of the Cotton effects and confirm the helical configurations of the considered heterobimetallic species.

Complexation of Ethanol by a Helical Tubuland Diol Host

The cage compound 4,7-dimethylpentacyclo[6.3.0.02,6.03,10.05,9]undecane-anti-4,anti-7-diol 3 and its 4,7-bis(d3-methyl) derivative 4 form 1:1 cocrystalline complexes with ethanol instead of the expected helical tubulate inclusion compounds. The X-ray crystal structure of (4)·(ethanol) [(C13H12D6O2)·(C2H6O), Cmca, a 19.049(2), b 14.932(2), c 10.117(1) A, Z 8, R 0.061] shows that the key supramolecular synthon is a hydrogen-bonded (O — H)6 cycle of hydroxy groups constructed from two ethanols (in ring positions 1 and 4) and four diols. This uncommon centrosymmetric motif permits efficient lattice packing of ethanol and both diol enantiomers into layers without requiring the self-resolution that would be mandatory in forming the helical tubulate structure.

Helical Tubuland Inclusion Diol Hosts: Fine-Tuning the Canals by Crystal Engineering

Application of crystal engineering techniques offers the possibility of increasing the host-guest interaction within canals of helical tubulate inclusion compounds and thereby enhancing guest selectivity. New helical tubuland hosts have been synthesised bearing small pendant groups, first to create an irregular canal wall surface and, secondly, to provide a non-hydrocarbon canal interior. The polar fluoromethyl substituent has been found to be particularly effective for these purposes.

Enantiomeric Self-Resolution through Dimethylsulfoxide Complexation

The alicyclic diol 2 is known to adopt five different types of crystallattice: the pure solid, cocrystalline compounds with water or certainphenols, and two different types of lattice inclusion system (helicaltubulates and ellipsoidal clathrates). Self-resolution only occurs onforming the helical tubulate inclusion compounds. Its close analogue2,7-bis(trifluoromethyl)tricyclo[4.3.1.13,8]un-decane-syn-2,syn-7-diol 4 was synthesised to examine the influence ofreplacing CH3- by CF3-groups. It no longer formslattice inclusion compounds but does form a cocrystalline solid withdimethyl sulfoxide (DMSO). Crystal structures of 4[C13H16O2F6,P21/c, a 7.8636(6), b 13.1020(7), c 25.319(2) A, β101.526(4)°, Z 8, R 0.044] and (4)V_2.VD/MSO[(C13H16O2F6)2⋅C2H6SO,P212121, a 7.249(1), b 16.064(3),c 25.347(4) A, Z 4, R 0.033] were determined. In solid diol 4 themolecules are linked through (–-O–-H)4 rings toproduce layers of chirally pure enantiomers but the net crystal structure,which comprises layers of alternating handedness, is achiral. In contrast,complexation of 4 with DMSO by means of two -–O-–H.O=Shydrogen bonds induces complete enantiomeric self-resolution.

Helical Tubulate Inclusion Compounds: Size, Shape, and Stoichiometry

Abstract The X-ray crystal structures of helical tubulate inclusion compounds of the diol host 1 reveal considerable variation in canal size depending on the specific guest entrapped. Examination of this data reveals how such flexibility is achieved through changes in the host orientation and hydrogen bonding angles. The sum of these effects makes 1 a potent inclusion host for a wide range of small molecules and depends little on the guest functional group. Representative helical tubulate stoichiometries, packing, and interactions are explored. The guest-free diol exists with the same lattice type as an empty microporous solid.

Helical tubulate inclusion compounds

Abstract The inclusion properties of the first helical tubuland diol hosts 1–5 have been surveyed and are reported. Bicyclic diol 1 forms helical tubulate inclusion compounds with most small solvent molecules, but with certain phenols hydrogen bonded co-crystalline materials are produced instead. Diol 2 yields helical tubulates with larger guest molecules, but if smaller solvents are used then an alternative host system is obtained. This has the guests trapped in ellipsoidal cavities located along constricted canals and is termed the ellipsoidal clathrate type. In some cases both inclusion types can be produced from 2 by varying the experimental conditions. The free volume present in the helical tubuland lattices of 3 and 5 is insufficient for guest inclusion. Diol 4 has the largest void space and can form inclusion compounds with large molecules such as ferrocene and squalene. X-ray crystal structures of representative examples of these compounds are discussed.

Formation and Stability of the Helical Tubuland Diol Inclusion Lattice

Abstract Alicyclic oil 's of specific design crystallise with a lattice enclosing a series of parallel helical canals which trap a wide range of guest molecules. Typical structures of these helical tubulate compounds are presented. The canal sizes and geometries vary considerably depending on the actual diol utilised. Lattices with smaller canals retain the helical tubuland structure in the absence of guests, whereas those with larger canals collapse to a close-packed structure.

Helices, Supramolecular Chemistry, and Metal‐directed Self‐Assembly

Their synthetic applications and potential as models, as well as simple aesthetic pleasure, are the main reasons for interest in helical compounds. The preparation of several double‐helical molecules made up of complexed metal ions was previously reported. Now a triple‐helical molecule, in which two metal ions with a preference for octahedral coordination are complexed with three bis‐(bidentate) ligands, has been synthesized by Williams et al. The geometry dictated by the ligands in this triple helix keep the two metal atoms 8 Å apart (see also p. 1490).