In Vivo and In Vitro Photodynamic Studies with Benzochlorin Iminium Salts Delivered by a Lipid Emulsion

Benzochlorin iminium salts (Bis) are hydrophobic photosensitizers based on an octaethylbenzochlorin nucleus that absorb in the near-IR region of the visible spectrum. In these studies the photodynamic activities of the zinc, copper and metal-free BI derivatives were compared in vivo in C3H-HeJ mice bearing a mammary adenocarcinoma tumor line. In vitro studies were also performed with the radiation-induced fibrosarcoma tumor line. An argon-pumped Ti-sapphire laser tuned to deliver light between 710 and 800 nm or an Oriel arc-lamp filtered to deliver broadband light above 590 nm were used as light source. A lipid emulsion was used as the delivery system for sensitizers in all studies. A pronounced solvent dependence was observed for the Q band for each of all iminium salts examined. As an example, the metal-free (BI) derivative had an absorption maximum at 798 nm in dichloromethane and at 727 nm in serum. The action spectra showed a greater PDT response at blue-shifted wavelengths for each of the three iminium salts both in vivo and in vitro. Among the three derivatives, the zinc analog (ZnBI) produced the greatest tumor regression at the low drug/light dose of 0.7 (μ mole/kg and 200 J/cm². These results indicate that iminium salts have characteristics that may make them promising third-generation photosensitizers.     

IMINIUM SALT OF COPPER BENZOCHLORIN (CDS1), A NOVEL PHOTOSENSITIZER FOR PHOTODYNAMIC THERAPY: MECHANISM OF CELL KILLING

The mechanism of cell killing by CDS1, an iminium salt of octaethylbenzochlorin with copper in the aromatic ring, in combination with light from a noncoherent light source was investigated. Using a standard clonogenic assay and the AY-27 FANFT turnor line. photoactivation of CDS1 was shown to be cytotoxic. The photodynamic cell killing ability of CDS1 required the presence of molecular oxygen. The reactive species generated by light activation of CDS1 were effectively quenched by N.N' -diphenyl- p -phenylenediamine. Additionally, the photodynamic effect of CDS1 was not cnhanced by dcuterium oxide. To characterize the reactive oxygen species generated by the photoactivation of CDS1 the well-characterized erythrocyte ghost model was used. Superoxide dismutase and catalase were potcnt inhibitors of CDS1-induced lipid peroxidation of erythrocyte membranes. Sodium azide only partially inhibited lipid peroxidation. These findings differed from the known singlet oxygen generator, tin (II) etiopurpurin dichloride (SnET₂). Sodium azide was a potent inhibitor of SnET₂-induced lipid peroxidation, whereas superoxide dismutase and catalase were totally ineffective. Based on these results, we conclude that CDS1 requires the presence of molecular oxygen for cell killing to occur but appcars to act primarily through a non-singlet oxygen mechanism.     

OBSERVATIONS ON THE SYNTHESIS AND in vivo PHOTODYNAMIC ACTIVITY OF SOME BENZOCHLORINS

An improved synthesis of benzochlorins is reported. Demetallation of the meso-hydroxymethylvinyl derivative of octaethylporphyrin, followed by treatment with sulfuric acid results in cyclization to generate the corresponding octaethylbenzochlorin in high yield. Prolonged treatment with acid generates the sulfonated derivative. These sensitizers were shown to be efficient photodynamic agents in vivo. Animals bearing a transplanted N-[4-(5-nitro-2-furyl)-2-thiazoly]formamide induced urothelial tumor were treated with either the benzochlorin or its sulfonated derivative. Irradiation of tumors 24 h later resulted in a significant tumoricidal effect in a short term assay. We conclude that benzochlorins warrant further examination as potential agents for use in photodynamic therapy.     

COPPER BENZOCHLORIN, A NOVEL PHOTOSENSITIZER FOR PHOTODYNAMIC THERAPY: EFFECTS ON A TRANSPLANTABLE UROTHELIAL TUMOR

Abstract— An iminum salt of octaethylbenzochlorin with copper in the aromatic ring, CDSI, was tested for its tumoricidal effects on theA–27 N-[4-(5-notro-2-furyl)-2-thiazoly] formamide tumor line. CDSI was found to be an effective photosensitiz4r in vivo when used in combination with either a xenon arc lamp or a pulsed alexandrite laser. Hemodynamically, CDSI and light caused a rapid decrease in tumor blood flow. skin photosensitization was found to be minimal when drug-injected mice werwe illuminated in a solar simulator.     

Reactions of diphenyldithiophosphinic acid with <Emphasis Type="Italic">N</Emphasis>-alkyl-2-chloro-2-methylpropanimines

In contrast to O,O-dialkyldithiophosphoric acids, the reactions of more weak diphenyldithiophosphinic acid with N-alkyl-2-chloro-2-methylpropanimines at a 1 : 1 reagent ratio follow two pathways. The first route is nucleophilic substitution of the chlorine atom of the initially formed iminium salt with the diphenylthiophosphinylthio moiety and the second route is the reduction of the C–Cl bond of this iminium salt cation. The main reaction direction is nucleophilic substitution producing new iminium salts, namely, N-alkyl-2-(di phenyl thiophosphinylthio)-2-methylpropaniminium chlorides. These salts were used as the starting material to synthesize new organophosphorus compounds bearing aldehyde, imine, and acetal groups and 1,3-diazolidine cycle.     

A comparative mechanistic study of Cu-catalyzed oxidative coupling reactions with N-phenyltetrahydroisoquinoline

A comparative mechanistic study of Cu-catalyzed oxidative coupling reactions of N-phenyltetrahydroisoquinoline with different nucleophiles was conducted. Two previously reported combinations of catalyst and oxidant were studied, CuCl(2)·2H(2)O/O(2) and CuBr/tert-butyl hydroperoxide (TBHP). On the basis of a synthetic study with different nucleophiles, the electrophilicity of the intermediate iminium ion was estimated and differences between the two methods were revealed. The key intermediate in the aerobic method is shown to be an iminium ion, formed through oxidation by copper(II), which can react with any nucleophile of sufficient reactivity. The role of oxygen is the reoxidation of the reduced catalyst. In the CuBr/TBHP system, an α-amino peroxide is proposed as a true intermediate within the catalytic cycle, formed from the amine and TBHP by a Cu-catalyzed radical reaction pathway and acting as a precursor to the iminium ion intermediate.     

Photophysical Properties of Tin Ethyl Etiopurpurin I (SnET2) and Tin Octaethylbenzochlorin (SnOEBC) in Solution and Bound to Albumin

Abstract— The photophysical characteristics of two second-generation PDT photosensitizers, tin ethyl etiopurpurin I (SnET₂) and tin octaethylbenzochlorin (SnOEBC), have been measured in homogeneous solution and when bound to bovine serum albumin (BSA). The ground state and triplet state absorption spectra have been characterized, as have triplet lifetimes and quantum yields for intersys-tem crossing, singlet oxygen formation and photobleaching. In total, these parameters provide a complete set of data that can be used to quantitatively compare the photosensitizing efficiencies of these molecules. The photo-bleaching quantum yield of SnET₂ is increased dramatically when it is bound to BSA, thus limiting the production of singlet oxygen at incident fluences above 1 J/cm². In contrast, the quantum yield of photobleaching of SnOEBC is at least an order of magnitude lower than that of SnET₂ under these conditions and does not significantly limit the photosensitization process for typical in vivo or in vitro fluences. This difference is expected to play a significant role in determining the relative photosensitizing ability of these compounds in vivo.     

Determination of copper in urine by diffuse reflectance spectroscopy

A possibility of determining copper(II) after adsorption on polyacrylonitrile fiber filled with a KU-2 cation exchanger with immobilized 1-(2-pyridylazo)-2-naphthol (PANF–KU-2–PAN) is studied. The diffuse reflectance spectra of the carrier discs before and after the adsorption of copper in the batch mode are recorded. The dependences of the analytical signals of the copper complex on PANF–KU-2–PAN on adsorption conditions are studied. The conditions for determining 0.05–0.40 μg/mL of copper(II) by measuring diffuse reflection coefficient at 640 nm or visually by a color scale after the adsorption of copper from 20 mL of a solution containing 0.01 M of HCl are found. The determination of 0.1 μg/mL of copper does not interfered with equal amounts of Co, Zn, and Pb and double amounts of Ag, Fe(III), Cd, Mn(II), Bi(III), and Cr(III). The procedure is used for urine analysis. The following conditions of the preparation of urine samples for the determination of copper were selected: boiling with hydrogen peroxide followed by acidification to pH 2. A procedure for determining copper in urine with a limit of detection of 0.03 μg/mL was developed; the relative standard deviation does not exceed 25%; the duration of analysis of 5–6 samples is 30–35 min.     

Reaktionen von 2- und 3-phenylsubstituierten Alkylakyliden-iminium-Ionen in der Gasphase. 5. Mitteilung über stossinduzierte Fragmentierungen von felddesorbierten Kationen

Reactions of 2- and 3-Phenyl Substituted Alkylalkylidene Iminium Ions in the Gas Phase The collision-induced fragmentations of 2- and 3-phenyl substituted alkylalkylidene iminium ions are reported. Besides the homolytic cleavage of the azaallyl bond a nucleophilic attack of the unsubstituted phenyl group at the iminium function is observed in the gas phase, yielding carbonium ions such as cyclopropanspirobenzenium ( 3 ), indanylium ( 10 ) and indenylium ions ( 11 ).     

Intramolecular iminium ene reaction with Cu(I) catalysts: facile formation of 4-amino-3-methylenechromans from O-propargyl salicylaldehydes and dialkylamines

Reaction of O-propargyl salicylaldehyde and related compounds with dialkylamines in the presence of copper(I) iodide gave 4-(alkylamino)-3-methylenechroman derivatives in good yields through the loss of one alkyl group of the dialkylamine. The reaction also worked well by employing 2-amino benzaldehyde derivatives to afford 4-(alkylamino)-3-methylene-1,2,3,4-tetrahydroquinolines. A deuterium-labeling experiment suggested that the α-hydrogen of the dialkylamine was transferred intramolecularly into the terminal methylene. This result indicated the reaction mechanism, which involved the formation of iminium ion between the aldehyde and the dialkylamine followed by ene-type C-C bond formation with inverse electron demand and hydrolysis.     

Photocytotoxicity of a new Rh2(II,II) complex: increase in cytotoxicity upon irradiation similar to that of PDT agent hematoporphyrin

A new type of heteroleptic dirhodium complex cis-[Rh(2)(mu-O2CCH3)2-(bpy)(dppz)]2+ (3) was synthesized and its potential as a photodynamic therapy (PDT) agent was investigated. Although 27% hypochromicity of the absorption of 3 in the near-UV and visible regions is observed in the presence of duplex DNA, relative viscosity measurements reveal that the complex does not intercalate between the DNA bases. The DNA photocleavage with visible light by 3 proceeds via both oxygen dependent and independent mechanisms, and it is more efficient than that of related complexes. The increase in the cytotoxicity of 3 towards human skin cells is similar to that of hematoporphyrin, a key ingredient in a PDT drug currently in use. This feature makes this complex a useful candidate for further PDT studies.     

Synthesis of 1-morpholino-1-(phenylethynyl)cycloalkanes from enamines and phenylacetylene in the presence of Cu(I) halides

1-Morpholino-1-(phenylethynyl)cyclopentane and 1-morpholino-1-(phenylethynyl)cyclohexane were obtained by reactions of enamines, derivatives of cyclic ketones, with phenylacetylene in the presence of CuI. A scheme for catalysis by Cu(I) compounds with the intermediate formation of copper phenylacetylide and iminium salts was suggested.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 169–170, January, 1994.     

Intramolecular Cyclization of 1-(ω-Phenylalkyl)-2-(nitromethylene)pyrrolidines in Triflic Acid

1-(ω-Phenylalkyl)-2-(nitromethylene)pyrrolidines in triflic acid undergo a C,O-diprotonation, followed by loss of water, to form conjugated iminium–hydroxynitrilium dications, which react with the tethered phenyl ring by electrophilic aromatic substitution to afford tricyclic iminium compounds as triflate salts. The scope and mechanism of this reaction are discussed.     

Enantioselective olefin epoxidation using novel biphenyl and binaphthyl azepines and azepinium salts

Homologous biphenyl and (diastereomeric) binaphthyl tertiary azepines and quaternary iminium salts were prepared from (S)- and (R)-3,3-dimethylbutan-2-amine. Both the amines and iminium ions behave as effective catalysts for the enantioselective epoxidation of unfunctionalized olefins (ee up to 87%).     

Computational study of iminium ion formation: effects of amine structure

Density functional calculations are used to explore the formation of iminium ions from secondary amines and acrolein and the subsequent reactivity of the resulting iminium ions. After establishing a feasible profile for this reaction in simulated experimental conditions, we focus on the effect of variation in amine structure on calculated barriers. This analysis shows that incorporation of a heteroatom (N or O) in the alpha-position to the reactive amine results in significantly reduced energy barriers, as does an electron-withdrawing group (carbonyl or thiocarbonyl) in the beta-position. Electron density analysis is used to monitor reactions at a detailed level, and to identify important intermolecular interactions at both minima and transition states. Barriers to reaction are linked to calculated proton affinities of secondary amines, suggesting that the relative ease of protonation-deprotonation of the amine is a key property of effective catalysts. Moreover, barriers for subsequent Diels-Alder reaction of iminium ions with cyclopentadiene are lower than for their formation, suggesting that formation may be the rate determining step in the catalytic cycle.     

Mechanism of Evolution of Koneramine Complexes from One‐Pot Reactions: Snapshots of Intermediates Offer Facile Routes to New Dipicolylamines

Koneramines (L^ROR′, R=Ph or Ts; R′=Me, iPr) and their complexes were found to emerge from the system of pyridine‐2‐carboxaldehyde and N‐phenyl/tosylethylenediamine when a primary or secondary alcohol was used as solvent. Imidazolidinylpyridines (L^R, R=Ph or Ts) became major emergents whereas hemi‐aminals (L^ROH, R=Ph or Ts) are minor emergents of the system when tertiary butanol was used as the solvent; the bulky tertiary butyl group prevented the addition of alcohol to the iminium ion that diverted the equilibrium towards imidazolidinylpyridines. By playing with the components of the reaction mixture, crystals of the metastable intermediates bound to copper(II) and/or zinc(II) were obtained and the structures were determined by X‐ray diffraction analysis. The reported results shed light on how to control the emergents of the multicomponent reaction mixture that forms koneramines. Reactivity studies of the intermediates pave the way for a new type of koneramine complexes that are new dipicolylamines where the two pyridine moieties of the resulting koneramine are not the same.     

Covalent catalysis by pyridoxal: evaluation of the effect of the cofactor on the carbon acidity of glycine

First-order rate constants for deprotonation of the alpha-imino carbon of the adduct between 5'-deoxypyridoxal (1) and glycine were determined as the rate constants for Claisen-type addition of glycine to 1 where deprotonation is rate determining for product formation. There is no significant deprotonation at pH 7.1 of the form of the 1-glycine iminium ion with the pyridine nitrogen in the basic form. The value of kHO for hydroxide ion-catalyzed deprotonation of the alpha-imino carbon increases from 7.5 x 10(2) to 3.8 x 10(5) to 3.0 x 10(7) M(-1) s(-1), respectively, with protonation of the pyridine nitrogen, the phenoxide oxyanion, and the carboxylate anion of the 1-glycine iminium ion. There is a corresponding decrease in the pKas for deprotonation of the alpha-imino carbon from 17 to 11 to 6. It is proposed that enzymes selectively bind and catalyze the reaction of the iminium ion with pKa = 17. A comparison of kB = 1.7 x 10(-3) s(-1) for deprotonation of the alpha-imino carbon of this cofactor-glycine adduct (pKa = 17 by HPO4(2-) with k(cat)/K(m) = 4 x 10(5) M(-1) s(-1) for catalysis of amino-acid racemization by alanine racemase shows that the enzyme causes a ca 2 x 10(8)-fold acceleration of the rate of deprotonation the alpha-imino carbon. This corresponds to about one-half of the burden borne by alanine racemase in catalysis of deprotonation of alanine.     

Bispidine copper(II) compounds: effects of the rigid ligand backbone

Approximative density-functional theory calculations indicate that the tetradentate ligand L (L = 2,4-bis-(2-pyridyl)-3,7-diaza-[3.3.1]-bicyclononane) enforces an unusual and strong binding of a co-ligand (substrate) to a copper(II) center. The co-ligand in [Cu(L)(Cl)](+) completes a square-pyramidal coordination around copper(II) and binds in the equatorial plane rather than on the apical position. This configuration is a stable geometric isomer for the model complex [Cu(NH3)2(imine)2(Cl)](+), but it is disfavored by approximately 10 kJ mol(-1) and not commonly observed for CuN4 chromophores with a monodentate co-ligand. The equatorial coordination increases the bond energy of the copper(II)-chloride bond by approximately 80 kJ mol(-1), and similar results are expected for other copper(II)-L-substrate complexes, some of which show strong catalytic activity or unusual stability. Despite the enforced configuration, L does not impose significant steric strain on the copper(II) center but is well preorganized for the Jahn-Teller labile ion in this unusual geometry. The preorganization extends to the orientation of the pyridine donors (torsion angle around the copper-pyridine bond), and this seems to be of importance in the reactivity of the copper-L complexes and their derivatives.     

PHOTOCHEMICAL OXIDATION OF VINDOLINE and 16-O-ACETYLVINDOLINE

Abstract— Photooxidation of 16-O-acetylvindoline in methanol using chlorpromazine-HCl as a photosensitizing agent produces nearly quantitative yields of an iminium derivative. The 16-O-acetylvindol-ine-iminium product was characterized spectrally by proton NMR and mass spectrometry; and by chemical reduction with sodium borodeuteride. Proton NMR and mass spectral analyses of the reduced product revealed that deuterium was stereospecifically incorporated into the 3-a-position. The iminium product formed by photochemical oxidation is identical to that produced by copper oxidases and peroxidase. Photochemical oxidation provides direct evidence for the involvement of free radicals in Aspidosperma alkaloid transformations.     

Alkynylation of ferrocene by terminal alkynes. Part I. A simple one-step synthesis of ferrocenylacetylenes

Ferrocene reacts with terminal alkynes in the presence of copper and iron salts to give 1-ferrocenyl-2-R-alkynes (R - substituent). This direct cross-coupling of ferrocenyl and alkynyl moieties allows for the preparation of ferrocenyl substituted alkynes in one step directly from ferrocene and a terminal alkyne avoiding prior preparation of other derivatives of ferrocene. This new synthetic reaction does not require special conditions, is promoted by the action of common iron and copper salts, and tolerates the presence of functional groups in the alkyne.