The meso-β-linkage as structural motif in porphyrin-based donor-acceptor compounds

Synthetic strategies for using the meso-β-linkage as a structural motif in electron transfer mimics have been tested. Exploratory syntheses of directly meso-β-linked bis- and trisporphyrins and the first representative X-ray structure of a meso-β-linked bisporphyrins are reported. The structure reveals a unique form of intramolecular π-π stabilization between one porphyrin and a meso-aryl substituent in a second porphyrin unit that accounts for the stability of different atropisomers in trimers. Using β-formyl porphyrins, dipyrromethanes, and suitable quinone precursor aldehydes, mixed condensations gave convenient access to porphyrin-porphyrin-quinone (P-P-Q) donor-acceptor systems consisting of a meso-β-linked bisporphyrin, a spacer, and a quinone acceptor.     

Regioselective [3+4] cycloaddition of an azomethine ylide to meso-meso, β-β, β′-β′ triply linked diporphyrins

Thermal reaction of meso-meso, β-β, β′-β′ triply linked diporphyrins with an azomethine ylide produced seven-membered cycloadducts via formal [3+4] cycloaddition at the bay-area. Bischlorin structures of the cycloadducts are characterized on the basis of spectroscopic data and confirmed by single crystal X-ray diffraction analysis. Interestingly, the stability of the cycloadducts depends on the central metal ions in the porphyrin core.     

Dissociation kinetics of cobalt and zinc β-octabromo-meso-tetraphenyl- and β-octaethyl-meso-tetraphenylporphyrin complexes

Kinetics of solvoprotolytic dissociation of zinc and cobalt porphyrin complexes with a porphyrin macrocycle distorted to different extents (β-octaethyl-meso-tetraphenylporphyrin and β-octabromo-meso-tetraphenylporphyrin) have been studied in binary proton-donating solvents. The main factor decreasing the stability of the porphyrin complexes is the distortion of the planar structure of the macrocycle. The reactivity of the cobalt porphyrins is governed by both structural and electronic effects.     

Soldier defense secretions of the south american termites Cortaritermes Silvestri, Nasutitermes SP N.D and Nasutitermes Kemneri

The defense secretions of the soldiers of the South American termites Cortaritermes silvestri, Nasutitermes sp. n.D. and Nasutitermes kemneri have been investigated. The secretion of C. silvestri was shown to contain α-pinene, β-pinene, limonene and cis-pin-3-en-yl acetate. Three of the four diterpenes in this secretion were identified as the triacetate, diacetate propionate and acetate dipropionate of 3α, 9β, 12α-trihydroxy-11(12), 15(17-trinervitadiene. The soldier secreation of Nasutitermes sp. n.D. and Nasutitermes kemneri were found to contain a mixture of monoterpene hydrocarbons and diterpenes. The major monoterpene in these two species was shown to be β-phellandrene and terpinolene, respectively. The major diterpene in Nasutitermes sp. n.D. was identified as 9β-hydroxy-1(15), 8(19)-trinervitadiene and, for Nasutitermes kemneri, 2α, 3β-dihydroxy-1(15), 8(9)- and 1(15), 8(19)-trinervitadiene were the major components.     

Synthesis and conformational studies of chiral meso-(α,β-unsaturated)-porphyrins

We describe a method to improve the yield and the kinetics of the difficult syntheses of α,β-unsaturated porphyrins, which enabled us to obtain a new chiral porphyrin derived from (S)-(−)-perillaldehyde in a 6% yield. Variable temperature NMR experiments on the free base, the zinc(II) and the nickel(II) complexes showed that two distinct and consecutive dynamic processes linked with the meso substituents rotation occurred. These processes can be analyzed as an evolution of the conformer composition upon temperature change. Higher values are found for the free energies of rotation of the substituent (measured by variable temperature ¹H NMR) compared to those of other equivalent porphyrins like meso-tetraphenyl porphyrin or meso-tetracyclohexyl porphyrin.     

Electroanalytical method of TCPP and its supramolecular system with cyclodextrins

In this paper, electroanalytical method of tetrakis (4-carboxylphenyl) porphyrin (TCPP) has been established. In a supporting electrolyte of KH₂PO₄-Na₂HPO₄ (pH 7.0), a sensitive second derivative reduction peak of TCPP was found by single-sweep oscillopolarography. The potential peak is −0.70 V (versus SCE).The relationship between peak height and the concentration of TCPP is linear from 1×10⁻⁷ to 2×10⁻⁵ mol l⁻¹, the relative standard deviation (R.S.D.) was 0.41% (n=8), and the recovery of TCPP varied from 95.8-105.4%.The interaction of cyclodextrins (CD) with TCPP in NH₃-NH₄Cl (pH 8.0) has been studied by polarography. The TCPP can form the 1:1 inclusion complex with β-CD, γ-CD, hydroxylpropyl-β-CD, sulfurbutylether-β-CD and trimethyl-β-CD. “Current method” has been used to determine the formation constants of TCPP with five CDs. The result shows that the inclusion ability of hydroxylpropyl-β-CD is very strong. Moreover, modified β-CD has stronger inclusion capacity than native β-CD. The formation constant of TCPP with γ-CD is much greater than that of TCPP with β-CD, because the γ-CD has a bigger cavity that can match with the size of the meso-phenyl of TCPP. The supramolecular data will provide useful information for further application of TCPP.     

The effect of chemical modification of the macrocycle on the complex formation between porphyrins and metal salts in organic solvents

The complex formation of β-octaethylporphyrin, β-octaethyl-meso-monophenylporphyrin, β-octaethyl-meso-tetraphenylporphyrin, meso-diphenylporphyrin, meso-triphenylporphyrin, and meso-tetraphenylporphyrin with Zn(II), Cu(II), Co(II), and Mn(II) acetates and chlorides in dimethylformamide, dimethylsulfoxide, pyridine, acetic acid, and a chloroform–methanol 1 : 1 mixture has been studied by means of spectrophotometry. The observed regulations are in line with the concept of chemical reactivity of the N–H bonds in porphyrins of different complexity.     

Stereoselective synthesis and characterization of novel trans-4-(thiophenyl)pyrazolyl-β-lactams and their C–3 functionalization

A stereoselective synthesis and C–3 functionalization of a long series of novel hybrid 4-(thiophenyl)pyrazolyl-β-lactams have been carried out. The divergent substrate scope and mechanistic insights were examined to delineate the generality of reaction that favored trans-β-lactams 4a-q almost exclusively in all cases. The C–3 functionalization was achieved by Lewis acid assisted nucleophilic substitution reaction of cis-3-chloro-β-lactams 6a-e to afford cis-3-monosubstituted-β-lactams 7a-e. The cis stereochemistry of β-lactams 7a-e was further established by stereospecific desulfurization with Raney-nickel, in representative cases (7a,b), leading to the formation of cis-β-lactams 8a,b. The structures and stereochemical assignments for synthesized β-lactams have been unambiguously confirmed using FT-IR, 1D NMR (¹H and ¹³C), 2D NMR (¹H–¹H COSY, ¹H–¹³C HSQC and ¹³C DEPT–135), elemental analysis (CHN), mass spectrometry (ESI-MS) and single crystal X-ray crystallography, in representative cases (4b,e). The cis and trans configuration of the hydrogen/chloro/nucleophile substituent at C–3 was assigned with respect C4–H of the β-lactam ring.     

β-Cyano meso-unsubstituted porphyrins for intramolecular charge transfer

β-Cyano meso-unsubstituted porphyrin 10, synthesized via a ‘3+1’ condensation using a bromotripyrrane, shows an effective charge transfer interaction across the porphyrin between electron-acceptor and -donor groups in β-positions.     

Size dependence of the electronic and magnetic properties of fullerenes (C60-C240)

We use the Gutzwiller method for studying various characteristic energies of fullerences in the free state (first and second ionization energy, electron affinity and singlet and triplet excitation energies). The stability of spin density wave (SDW) in fullerene has been investigated. The critical value of (U/β) (U intraatomic correlation energy, β transfer energy to stabilize SDW) is equal to 3 in C₆₀ and 4.25 in C₂₄₀ (icosahedrally symmetric C₂₄₀).     

Synthesis and spectral properties of N4, N3S, and N2S2 porphyrins containing one, two, three, and four meso-furyl groups

Porphyrins with N₄, N₃S, and N₂S₂ cores having one, two, three, and four furyl groups at the meso-positions were synthesized by following various methodologies and characterized by using mass spectrometry, NMR spectroscopy, elemental analysis, absorption, and fluorescence spectroscopic techniques. NMR studies indicated that by replacing the meso-aryl groups with meso-furyl groups, the β-pyrrole and β-thiophene protons of porphyrins experienced considerable downfield shifts, supporting the alteration of π-delocalization of porphyrins on the introduction of meso-furyl groups. The absorption and emission bands of porphyrins experienced red shifts on the introduction of meso-furyl groups and the magnitude of red shifts vary linearly with the number of meso-furyl groups. Thus, the spectral studies supported a systematic alteration in spectral properties on successive introduction of meso-furyl groups.     

Enantioselective synthesis of heterocyclic β-aminoalcohols catalysed by a samarium iodo binaphtholate

Enantioselective aminolysis of meso-epoxides including a heterocycle catalysed by a samarium iodo binaphtholate has been studied. New β-amino alcohols have been isolated with enantiomeric excesses up to 70%.     

Enantioselective formal synthesis of tridemethylisovelleral

A simple and efficient synthetic route to the bicyclic α,β-unsaturated β-keto ester methyl (3aS,7aS)-6-oxo-2,3,3a,6,7,7a-hexahydro-1H-indene-5-carboxylate, a versatile intermediate in the synthesis of biologically active unsaturated 1,4-dialdehydes, is described. The synthesis includes a chirality introducing nonenzymatic asymmetric desymmetrization (ADS) reaction of a cyclic meso-anhydride 4 and a modified Hofmann method for preparing exocyclic dienes. The ester was synthesized in a moderate overall yield (19%) from 6 and with an excellent enantioselectivity (>90%).     

Phytochemical investigation of ethyl acetate extract from Curcuma aromatica Salisb. rhizomes

Three phytochemicals, curcumin 1, demethoxycurcumin 2 and β-sitosterol-3-O-β-d-glucopyranoside 3 have been isolated from the ethyl acetate extract of rhizomes of Curcuma aromatica. Chemical structures of all the three isolates were determined using spectroscopic and chemical analyses. β-Sitosterol-3-O-β-d-glucopyranoside has been isolated for the first time from this plant.     

Synthesis of cis bis-β-lactams via Staudinger cycloaddition reaction using C2-symmetric 1,2-diamines

An efficient stereoselective synthesis of bis-β-lactams via cycloaddition reaction (Staudinger reaction) of ketenes with bisimines derived from C₂-symmetric 1, 2-diamines is described. The reaction provided diastereomeric mixture of meso and C₂-symmetric cis-bis-β-lactams with higher selectivity for meso-bis-β-lactams.     

A comparative spectroscopic,electronic structure and chemical shift investigations of o-Chloronitrobenzene,p-Chloronitrobenzene and m-Chloronitrobenzene

The structural characteristics and substituent effects of o-Chloronitrobenzene, m-Chloronitrobenzene and p-Chloronitrobenzene have been analysed by experimental FTIR, FT-Raman and FT-NMR spectroscopic studies. A detailed quantum chemical calculations have been performed using DFT/B3LYP method with 6-311++G^**, 6-31G^** and cc-pVTZ basis sets. Complete vibrational analyses of the compounds were performed. The temperature dependence of thermodynamic properties has been analysed. The atomic charges and charge delocalisation of the molecule have been performed by natural bond orbital (NBO) analysis. Molecular electrostatic surface potential (MESP), total electron density distribution and frontier molecular orbitals (FMOs) are constructed at B3LYP/6-311++G^** level to understand the electronic properties. The charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping electron density isosurface with electrostatic potential surfaces (ESPs). The electronic properties, HOMO and LUMO energies were measured by time-dependent TD-DFT approach. ¹H and ¹³C NMR spectra were recorded and ¹H and ¹³C nuclear magnetic resonance chemical shifts of the molecule were calculated. The ¹H and ¹³C nuclear magnetic resonance (NMR) chemical shifts of the molecules in chloroform solvent were calculated by using the Gauge-Independent Atomic Orbital (GIAO) method and are found to be in good agreement with experimental values.     

Synthesis and properties of BF2- & PO2-complexes of mono meso-heterocycle substituted 25-oxasmaragdyrins and derivatives

BF₂- and PO₂-smaragdyrins containing one five membered heterocycle such as pyrrole, thiophene and furan at one of the meso-position of corresponding 25-oxasmaragdyrins were synthesized by treating the appropriate mono meso-heterocycle substituted 25-oxasmaragdyrin with BF₃.OEt₂ and POCl₃ respectively in CH₂Cl₂ under mild reaction conditions. All macrocycles were thoroughly characterized by HR-MS and 1D and 2D NMR spectroscopy. The presence of a five membered heterocycle in place of a six membered aryl group significantly alters the electronic properties of the smaragdyrin macrocycle as reflected in their spectral and electrochemical properties. The meso-pyrrole BF₂-smaragdyrin was subjected to a Vilsmeier-Haack reaction to prepare meso-(α-formyl pyrrolyl) BF₂-smaragdyrin which was subsequently used to prepare meso-(α-dipyrromethanyl pyrrolyl) BF₂-smaragdyrin. The further use of meso-heterocycle substituted BF₂- and PO₂-oxasmaragdyrins was demonstrated by treating meso-pyrrolyl BF₂-smaragdyrin with pentafluorobenzaldehyde in CHCl₃ under mild acid catalysed conditions to afford an unusual dipyrromethanyl bridged BF₂-smaragdyrin dyad which exhibits excellent photophysical properties.     

Thyonosides A and B, two new saponins isolated from the holothurian Thyone aurea

The structures of two saponins, thyonosides A and B, isolated from the holothurian Thyone aurea collected in Namibia, were elucidated by 1D and 2D NMR (¹H, ¹³C, ¹H-¹H COSY, ¹H-¹H J-resolved, TOCSY, HMQC, HMBC and NOESY). The two compounds have the same aglycon but different oligosaccharidic chains. Thyonoside A has a 3-O-methyl-β-d-xylopyranosyl-(1→3)-6-O-sodium sulphate-β-d-glucopyranosyl-(1→4)-β-d-quinovopyranosyl-(1→2)-4-O-sodium sulphate-β-d-xylopyranosyl chain, and thyonoside B a 3-O-methyl-β-d-xylopyranosyl-(1→4)-β-d-xylopyranosyl-(1→4)-β-d-quinovopyranosyl-(1→2)-4-O-sodium sulphate-β-d-xylopyranosyl chain. The holostane-type aglycon features an endocyclic double bond at position 7-8, a double bond at position 25-26 and a β-acetoxy group at C16.     

Self-assembly via intermolecular hydrogen-bonding between o-/m-/p-NH2 and BF2 groups on dipyrromethenes

Boron difluoride dipyrromethenes bearing configurationally different amine groups on a meso-phenyl ring were prepared and crystallized. The ortho- and para-amino groups allow the phenyl group to inductively release greater electron density into the dipyrromethenes resulting in relatively strong intermolecular hydrogen-bonding with the terminal BF₂ groups, whereas the meta-analog formed weaker hydrogen-bonds. The intensities of the ¹H NMR peaks in concentrated solutions all increased with F-decoupling.     

meso-Tetraaryl-7,8-dihydroxydithiachlorins: first examples of heterochlorins

Osmium tetraoxide-mediated dihydroxylation of meso-tetraaryldithiaporphyrins generates the corresponding meso-tetraaryldithia-7,8-dihydroxychlorins and meso-tetraaryldithia-7,8,17,18-tetrahydroxybacteriochlorins. The products are spectroscopically characterized and the substitution positions were unequivocally determined. The UV-vis of the heterochlorins and heterobacteriochlorins are chlorin- and bacteriochlorin-like, respectively. However, the chlorin spectra are surprisingly hypsochromically shifted as compared to the corresponding all-aza chlorins, whereas the bacteriochlorin is bathochromically shifted. meso-Tetraaryldithia-7,8-dihydroxychlorins are susceptible to oxidative ring-opening reactions to form the corresponding meso-tetraaryldithia-7-oxo-8-oxa-dithiaporphyrin (dithiaporpholactone). These derivatives are the first examples of heterochlorins and β-modified dithiaporphyrins.