Synthesis of an amide cyclophane building block of shape-persistent triangular molecular wedges

The synthesis of an amide cyclophane, which can be considered as the first generation of a family of triangular shape-persistent molecular wedges is described.     

Synthesis of a core trisaccharide building block for the assembly of N-glycan neoconjugates

A short and high yielding synthesis of a core trisaccharide 1 as the key building block in the assembly of a library of N-glycan neoconjugates is presented. The β-d-Manp-(1→4)-d-GlcpNAc linkage was introduced by inversion of the C-2 position of a β-glucoside. The glucosyl donor was efficiently synthesised following a recently published one-pot strategy. 2-Naphthylmethyl and benzylidene-acetal protection in the terminal mannose permitted selective liberation of main branching sites for subsequent glycosylation. A C5 azido linker attached to the anomeric position, which is stable throughout the synthesis, will allow for the posterior immobilisation of deprotected glycans on a microarray surface.     

A stimulus-responsive shape-persistent micelle bearing a calix[4]arene building block: reversible pH-dependent transition between spherical and cylindrical forms

A series of cationic calix[4]arene-based lipids with alkyl chains of varying length were newly synthesized, and the ones with propyl and hexyl tails, denoted by CaL[4]C3 and C6, respectively, were found to form spherical micelles at low pH (protonated state of the amine headgroup). Upon deprotonation with increasing pH, CaL[4]C3 showed a sphere-to-cylinder transition, while CaL[4]C6 changed from sphere, to cylinder, to monolayer vesicle. Synchrotron small-angle X-ray scattering (SAXS) patterns from both spherical and cylindrical CaL[4]C3 micelles exhibited a sharp intensity minimum, indicating shape monodispersity. The monodispersity of the CaL[4]C3 spherical micelles was further confirmed by analytical ultracentrifugation (AUC). SAXS, AUC, and static light scattering agreeingly indicated an aggregation number of 6. In contrast, CaL[4]C6 exhibited polydispersity with an average aggregation number of 12. When the number of carbons of the alkyl chain was increased to 9 (CaL[4]C9), cylinder formed at low pH, while at high pH, no clear morphology could be observed. The present results indicate that a very precise combination of tail length, head volume, and rigidity of the building block is required to produce shape-persistent micelles and that the shape-persistence can be maintained upon a structural transition. An attempt to reconstruct a molecular model for the spherical CaL[4]C3 micelle was made with an ab initio shape determining program.     

A trans-AB-bacteriochlorin building block

Synthetic bacteriochlorins are of interest for fundamental studies in photochemistry because of their strong absorption in the near-infrared spectral region and close similarity with natural bacteriochlorophylls. A de novo route to 5-methoxybacteriochlorins entails self-condensation of a dihydrodipyrrin-acetal, which in turn is prepared from a 2-(2-nitroethyl)pyrrole species and an α,β-unsaturated ketone-acetal (e.g., 1,1-dimethoxy-4-methylpent-3-en-2-one). Here, four new results are reported concerning the synthesis of substituted bacteriochlorins. First, a new, scalable route to 1,1-dimethoxy-4-methylpent-3-en-2-one removes a significant previous impediment to the overall route. Second, the new route was employed to gain access to new α,β-unsaturated ketones and corresponding dihydrodipyrrins bearing alternative substituents in place of the dimethoxy unit. Third, a dihydrodipyrrin bearing a 1,3-dioxolan-2-yl moiety afforded the bacteriochlorin (30% yield) containing a 2-hydroxyethoxy substituent at the 5-position. Fourth, subsequent bromination proceeded regioselectively at the 15-position to give a trans-(5,15)-AB-bacteriochlorin building block. The linear 5,15-substitution pattern is attractive for a number of molecular designs. The results taken together afford deeper understanding of the scope and limitations of the de novo route and also advance the capabilities for tailoring synthetic bacteriochlorins.     

A novel building block for the synthesis of isofagomin analogues

The de novo synthesis of the novel potent building blocks phenyl (R)-3-acetoxymethyl-3,6-dihydro-2H-pyridine-1-carboxylate (−)-7 and phenyl (S)-3-butyryl-oxymethyl-3,6-dihydro-2H-pyridine-1-carboxylate (+)-8 starting from commercially available methyl-1-benzyl-4-oxo-3-piperidinecarboxylate is described. The key steps are the enantioselective esterification of the racemic alcohol 6 and the enantioselective hydrolysis of the racemic acetate 5, respectively, using lipase P from Pseudomonas caepacia.     

A versatile building block for pyrazole-pyrrole hybrid macrocycles

This contribution describes the synthesis of a novel pyrazole-pyrrole building block and its use in the formation of a non-aromatic, Schiff base-type macrocycle incorporating a chromophore and H-bonding donor and acceptor functionalities inside and outside of the macrocycle, which makes it predestined for molecular recognition systems.     

N-containing boronic esters as self-complementary building blocks for the assembly of 2D and 3D molecular networks

The combination of two heteroaromatic boronic acids with pentaerythritol gave self-complementary tectons which were suitable for the generation of 2D and 3D molecular networks.     

A new titanium building block for early-late heterometallic complexes; preparation of a new tetrameric metallomacrocycle by self assembly

The new titanium dicarboxylate complex Cp*TiMe(OOC)2py (2) [Cp*=eta5-C5Me5; (OOC)2py = 2,6-pyridinedicarboxylate] has been synthesized. The reaction of complex 2 with water renders [Cp*Ti(OOC)2py]2O (3). The molecular structure of 3 has been studied by X-ray diffraction methods. Complex 2 reacts with isocyanides to yield the respective iminoacyl derivatives Cp*Ti(eta2-MeCNR)(OOC)2py [R=tBu (4), 2,6-dimethylphenyl (xylyl) (5)]. The molecular structure of complex4 has been established by X-ray diffraction. Compound 2 has been employed as a new building block for the preparation of new early-late heterometallic compounds; it reacts with [M(mu-OH)(COD)]2 (M = Rh, Ir) to give the corresponding tetranuclear metallomacrocycle derivatives [Cp*Ti{(OOC)(2)py}(mu-O)M(COD)]2 [M = Rh (6); Ir (7)]. The molecular structure of 6 has been established by X-ray diffraction.     

A shape-persistent polymeric crystallization template for CaCO3

Alanyl-alanine-derived poly(isocyanide)s possess a helical structure that persists even in aqueous media. These rigid macromolecules possess a regular distribution of carboxylic acid-terminated side chains which for the first time allows the study of the templating process involved in biomineralization using a shape-persistent polymeric template. It is demonstrated that in the case where the polymer derived from l-Ala-d-Ala is used the formation of apple core-type calcite crystals is controlled both by nucleation of the (01.1) face and subsequent adsorption of the polymer to the {hk.0} faces of the growing crystal. A small change in the secondary structure of the template that is introduced by using the polymer derived from l-Ala-l-Ala is directly reflected in the lower degree of control over the crystallization process.     

A building block method for the synthesis of higher cycloamides.

Series of cyclic amides containing optically active helicene, (P)-1,12-dimethylbenzo[c]phenanthrene, are synthesized using a building block method. The building block consists of one (P)-helicene unit and one dianiline unit with its amino-terminal-protected with benzyloxycarbonyl and its acid terminal activated as acid chloride. The coupling with (P,P....)-[(n - 3) + (n - 2)]diamine followed by deprotection gives (P,P....)-[(n - 1) + n]diamine, which possesses n - 1 parts of (P)-helicene and n parts of dianiline. Cyclization of the (P,P....)-[(n - 1) + n]diamine with helicenediacid dichloride gives (P,P....)-[n + n]cycloamide. All the members of (P,P)-[2 + 2]cycloamide to (P,P,P,P,P,P,P,P,P,P)-[10 + 10]cycloamide are synthesized using this method, and are compared spectroscopically.     

A principle for the assembly of novel mononuclear building blocks for supramolecular chemistry

Abstract

The controlled assembly of supramolecular coordination oligomers may be achieved by the use of multinucleating ligands which contain two or more metal-binding domains. Examples of such ligands commonly consist of discrete metal-binding sites linked by appropriate spacers. We now show that a consideration of the donor properties of a ligand and the acceptor properties of a metal ion may be used to induce multinucleating behaviour in oligopyridine ligands which conventionally chelate to single metal centres. Such species are key building blocks for the assembly of a variety of supramolecular species in which the non-coordinated donor atoms may later interact with other metal centres. The crystal structure of the complex [Ru(bpy-N,N′)₂(tpy-N,N′)][PF₆]₂ ( P 1, a = 8.367(2), b = 11.821(4), c = 19.398(5)Å, α = 93.83(2), β = 92.25(2), γ = 89.62(2)°, Z = 2, d _c = 1.63 g cm^?3, 5084 unique observed reflections with I < 1.5σ(I), R = 0.0745) which contains a bidentate tpy ligand is presented.     

Synthesis, resolution, and applications of 1,16-dihydroxytetraphenylene as a novel building block in molecular recognition and assembly

This paper concerns the synthesis of 1,16-dihydroxytetraphenylene (DHTP) (2) by employing a novel NBS bromination route. (+/-)-DHTP 2 was successfully resolved into its optical antipodes and converted to (+/-)-1,16-bis(diphenylphosphino)tetraphenylene (BPTP) (26), whose platinum complex BPTP-PtCl(2) (27) was also obtained. As a hydrogen bond donor, racemic and optically active DHTP 2 was allowed to assemble with 4,4'-bipyridine to form single crystals of good quality. X-ray Diffraction studies of these crystals revealed that the crystallographic packing of the hydrogen bonded complex between (+/-)-2 and 4,4'-bipyridine was different from the one formed from (S)-2 and 4,4'-bipyridine. It was found that an infinite zigzag chain with alternate chirality was formed in the assembly of (+/-)-2 and 4,4'-bipyridine, while (S)-2 and 4,4'-bipyridine failed to show the same assembly pattern. The reason (+/-)-2 formed an alternate and zigzag chain with 4,4'-bipyridine was most likely due to the inherent stability of this supramolecular assembly. The chiral recognition between 2 and optically active BINAP under the direction of platinum(II) has also been examined. (1)H and (31)P NMR spectroscopic studies demonstrated that there was an obvious discrimination of 2 between the enantiomers of BINAP-PtCO(3).     

Benzotrithiophene--a planar, electron-rich building block for organic semiconductors

Several functionalized benzo[1,2-b:3,4-b':5,6-d']trithiophenes have been synthesized and characterized. The fully planar and highly electron-rich material shows great promise as the donor constituent in donor-acceptor type copolymers for use in organic electronics. As a proof of concept, a copolymer with the electron acceptor, 2,1,3-benzothiadiazole, has been prepared. Side-chain modifications have been employed to adjust both the electron-rich character of the monomer and the solubility and processability of the polymer.     

C-pentyltetra(3-pyridyl)cavitand: a versatile building block for the directed assembly of hydrogen-bonded heterodimeric capsules

Hydrogen-bond-directed assembly of heterodimeric cavitand-based capsules is of considerable interest. Herein, we report the synthesis and single-crystal X-ray structure determination of a pyridyl-functionalized cavitand that contains suitable hydrogen-bond acceptor moieties for the construction of asymmetric cavitand-based capsules. [structure: see text]     

A stable fullerene-azide building block for the construction of a fullerene-porphyrin conjugate

A stable C₆₀ derivative bearing an azide functional group was prepared and used as a building block under the copper-mediated Huisgen 1,3-dipolar cycloaddition conditions for the preparation of a fullerene-porphyrin conjugate.     

A simple synthesis of truxene,a building block for optoelectronics and fullerene fragments

Truxene was efficiently synthesized by reduction of truxenone with excess hydrazine hydrate in diethylene glycol at 180 °C without added base, a variation of the Huang-Minlon Wolff–Kishner reduction. The proposed mechanism highlights hydrazine as a nucleophile and a base, extracting protons from the hydrazone and diazene intermediates.     

Pyridine-substituted oligopeptides as scaffolds for the assembly of multimetallic complexes: variation of chain length

This paper presents the synthesis and characterization of pyridine-substituted artificial oligopeptides with an aminoethylglycine backbone of varying length, which are designed to act as scaffolds for the self-assembly of multimetallic structures. The identities and purities of the oligopeptides are confirmed with mass spectrometry, (1)H NMR, HPLC, and pH titrations. The acid dissociation constants for the oligopeptides were determined and were found to decrease with increasing pyridine units. Titrations of the oligopeptides with Cu(II) and Pt(II) complexes containing the tridentate ligands 2,2':6',2'-terpyridine and pyridine 2,6-dicarboxylic acid were monitored using UV-visible absorption spectroscopy and showed stoichiometric binding based on the number of pyridines on the peptide strand. Metal titrations performed using an analogous oligopeptide with methyl substituents (in place of the pyridine ligands) showed very weak or no binding. In the case of the oligopeptides containing bound Pt(terpyridine)(2+) complexes, cyclic voltammetry reveals two sequential one-electron reductions at formal potentials that do not vary as a function of oligopeptide length. The measured diffusion coefficients were measured with chronoamperometry and were found to decrease with increasing oliopeptide length.     

Synthesis of an elongated linear oligo(phenylene ethynylene)-based building block for application in DNA-programmed assembly

The synthesis of an elongated linear oligonucleotide-functionalised module (ELOM) is described. The ELOM structure is based on an oligo(phenylene ethynylene) backbone substituted with two decyloxy groups. The two termini constitute two salicylaldehyde moieties acting as chemical cross-linkers. Before incorporation into an oligonucleotide sequence the organic part of the module, the elongated linear module (ELM), is functionalised with a dimethoxytrityl group and a phosphoramidite group. This enables incorporation into the middle of 30-mer oligonucleotide sequences by automated DNA synthesis. The obtained ELOMs were characterised by polyacrylamide gel electrophoresis and MALDI-TOF mass spectrometry. In analogy with previously reported LOM and TOM structures the coupling reactions of the ELOM modules were tested.     

Reanalysis of lindenatriene,a building block for the synthesis of lindenane oligomers

Lindenane oligomers isolated from Chloranthus pose significant challenges for chemical synthesis. The structure of a proposed biosynthetic monomer, lindenatriene, was recently called into question. Its attempted synthesis produced a compound whose ¹H NMR spectrum differed significantly from the spectrum of a monomer produced by oligomer pyrolysis. Here we propose that the original structural assignment after pyrolysis was correct and instead the spectra of synthetic materials were misinterpreted. Reanalysis of 2D NMR data suggest that lindenatriene isomerizes (formal [1,7]-hydrogen shift) upon treatment with base.