Synthesis of conjugates based on chlorin and isosteviol building blocks

Conjugates containing ent-beyerane carbocyclic frameworks on the periphery of a porphyrin macrocycle were prepared by acylation of chlorin e₆ derivatives with hydroxyl and amino groups using ent-16-ketobeyeran19-oic acid chloride (diterpenoid isosteviol). Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 165-169, March-April, 2009.     

Novel types of boronated chlorin e6 conjugates via ‘click chemistry’

Conjugates of chlorin e₆ with closo‐dodecaborate and cobalt bis(dicarbollide) anions were synthesized for the first time in high yields using the advanced ‘click’ methodology. In vitro study on A549 human lung adenocarcinoma cells revealed that the synthesized boronated conjugates are able to penetrate and accumulate in cancer cells, but their intracellular concentration is not sufficient for effective photodynamic and boron neutron capture therapy of cancer. Copyright © 2009 John Wiley & Sons, Ltd.     

METABOLICALLY CONVERTIBLE LIPOPHILIC DERIVATIVES OF pH-SENSITIVE AMPHIPATHIC PHOTOSENSITIZERS

Abstract We propose the use of acetoxymethyl esters of pH-sensitive amphipathic photosensitizers (PS) for photodynamic therapy (PDT). These compounds may be applicable for PDT involving endocytosis of lipophilic carriers leading to lysosomal uptakc of the esterified PS by target cells. Partial and/or total enzymatic de-esterification may result in the extralysosomal distribution of the photoactive agents, possibly culminating in a multisite photochemical response. We report here the synthesis and properties of chlorin e₆ triacetoxymethyl ester (CAME) and pheophorbide a acetoxymethyl ester (PAME). Chlorin e₆ and pheophorbide a are photocytotoxic chlorins that possess free carboxylate groups and exhibit optimum wavelengths of excitation substantially red shifted relative to hematoporphyrin derivative. Acetoxymethyl esterification of chlorin e₆ and pheophorbide a was accomplished with bromomethyl acetate. High-performance liquid chromatography allowed for the purification of PAME, in 87% purity, and CAME, in 63% yield and 94% purity, as well as the detection of the presumed mono- and diesters of chlorin e₆ as transient intermediates in the synthesis of CAME. The ultraviolet-visible absorption, fluorescence excitation and emission, NMR and mass spectra of the chlorin e₆ tnester are consistent with those expected for CAME. The pH-sensitive amphipathicity of pheophorbide a and chlorin e₆ but not CAME was demonstrated using a water/1-octanol partition assay. The production of pheophorbide a from PAME and the sequential formation of the di- and monoesters and free chlorin e₆ from CAME, by the action of lysosomal esterases obtained from cancer cells, demonstrate the potential of cellular enzymes to convert the lipophilic esters to pH-sensitive amphipathic PS. It is expected that the product of the esterases' action in the acidic lysosome will be hydrophobic and tend to diffuse into the organelle membrane. Contact with the neutral pH of the adjacent cytosol will result in conversion of the PS to a more hydrophilic anionic species, presumably allowing for it lo diffuse into that compartment and partition throughout the lipophilic and aqueous compartments of the cell.     

Synthesis,photophysical properties,and photochemical activity of the water-soluble dyad based on fullerene С<Subscript>60</Subscript> and chlorin <Emphasis Type="Italic">e</Emphasis><Subscript>6</Subscript> derivatives

Chlorin e₆ derivative and water-soluble dyad resulting from covalent bonding of polyanionic fullerene С₆₀ derivative to chlorin e₆ derivative were synthesized and studied for spectral properties and photochemical activity. A considerable change in the absorption spectra and pronounced fluorescence quenching for the chlorin moiety included in the dyad were identified. The singlet excited state of chlorin is quenched via electron transfer from the excited chlorin to the fullerene core. A comparison of the photochemical activities of the test compounds in aqueous solutions showed a tenfold increase in the photochemical activity of the chlorin–fullerene dyad compared with free chlorin per absorbed light quantum.     

Novel metal complexes of boronated chlorin e6 for photodynamic therapy

Various structural modifications of chlorins are aimed at optimization of biomedical characteristics of these plant-derived tetrapyrrolic compounds. In particular, conjugation with boron polyhedra improves the efficacy of chlorin e₆ derivatives as antitumor photosensitizers. To obtain the compounds that may possess several clinically favorable characteristics, we synthesized a series of metal chlorin e₆ conjugates with 1-carba-closo-dodecaborate anion that contain Pd(II), Sn(IV) or Zn(II) in the coordination sphere of the chlorin macrocycle. The compounds were synthesized by alkylation of amino group in chlorin e₆ metal complexes with 1-trifluoromethanesulfonylmethyl-1-carba-closo-dodecaborate cesium. The water soluble Pd(II) complex of chlorin e₆ 13(1)-N-{2-[N-(1-carba-closo-dodecaboran-1-yl)methyl]aminoethyl}amide-15(2), 17(3)-dimethyl ester (compound 6) evoked low dark cytotoxicity; in striking contrast, 6 potently sensitized human tumor cells to illumination with monochromatic red light. Confocal microscopic studies demonstrated that photoactivation of 6 rapidly (within minutes) changed the patterns of intracellular drug distribution from diffuse cytoplasmic to clustered perinuclear. Co-localization experiments revealed that 6 associated with lysosomes in illuminated cells. These events were paralleled by alteration of mitochondrial shape, a decrease of mitochondrial transmembrane electric potential and the loss of plasma membrane impermeability for propidium iodide, the latter being a hallmark of cell necrosis. Similar mechanisms of cell photodamage were found for structurally close Pd(II) complex of chlorin with neutral carborane and for Sn(IV) chlorin conjugated with the anionic carborane. Thus, metal complexes of carboranylchlorins are efficient photosensitizers capable of triggering rapid necrosis. These compounds are promising for further development as multipotent agents in which each moiety, i.e., metal, the chlorin macrocycle and the boron substituent, as well as the entire complex, can be useful in cancer diagnostics and treatment.     

Synthesis of amide derivatives of chlorin <Emphasis Type="Italic">e</Emphasis><Subscript>6</Subscript>

A number of secondary and tertiary chlorin e ₆-13-amides were synthesized in high yield by the action of primary and secondary amines on methylpheophorbide a under mild conditions. Unlike the secondary amides, tertiary 13-amides were shown to exist as two stereoisomers differing by orientation of the amide group plane with respect to the macroring. The reaction of methylpheophorbide a with 2-aminoethanol gave chlorin e ₆ derivatives containing one, two, and three hydroxy groups.     

Reaction of methylpheophorbides <Emphasis Type="Italic">d</Emphasis> and <Emphasis Type="Italic">b</Emphasis> with amines

A series of formyl analogs of chlorin e₆ 13-amides were synthesized in high yields by reaction under mild conditions of primary and secondary amines with methylpheophorides b and d. In contrast with the secondary 13-amides, tertiary 13-amides were found as two isomers differing in the orientation of the amide plane relative to the plane of the chlorin ring. Methylpheophorbides b and d were more reactive toward the amines than methylpheophorbide a.     

Chlorophyll and Its Derivatives,Chlorins and Porphyrins,as a Promising Class of Environmentally Friendly Dyes

The possibilities of using pheophorbid (a), chlorin e ₆, its copper complex, 6-N-(2-aminoethylamido)chlorin e ₆ dimethyl ester, and its complexes with Cu(II), Ni(II), Co(II), and Zn(II) as dyes for cellulose, acetate, and wool fibers were studied.     

The First Selenoanhydride in the Series of Chlorophyll a Derivatives,Its Stability and Photoinduced Cytotoxicity

In this work, we obtained the first selenium-containing chlorin with a chalcogen atom in exlocycle E. It was shown that the spectral properties were preserved in the target compound and the stability increased at two different pH values, in comparison with the starting purpurin-18. The derivatives have sufficiently high fluorescence and singlet oxygen quantum yields. The photoinduced cytotoxicity of sulfur- and selenium-anhydrides of chlorin p₆ studied for the first time in vitro on the S37 cell line was found to be two times higher that of purpurin-18 and purpurinimide studied previously. Moreover, the dark cytotoxicity increased four-fold in comparison with the latter compounds. Apparently, the increase in the dark cytotoxicity is due to the interaction of the pigments studied with sulfur- and selenium-containing endogenous intracellular compounds. Intracellular distributions of thioanhydride and selenoanhydride chlorin p₆ in S37 cells were shown in cytoplasm by diffusion distribution. The intracellular concentration of the sulfur derivative turned out to be higher and, as a consequence, its photoinduced cytotoxicity was higher as well.     

Synthesis of cobalt bis(dicarbollide) conjugates with natural chlorins by the Sonogashira reaction

Novel boron-containing conjugates based on the alkynylated cobalt bis(dicarbollide) anion and chlorin e ₆ and purpurinimide p-iodophenyl derivatives were synthesized by the Sonogashira reaction. These conjugates can accumulate in the cancer cell cytoplasm and can be considered as potential candidates for using in boron neutron capture therapy of tumors.     

Atropoisomerism of 13-N,N-dimethylamide-15,17-dimethyl ester of chlorin e6 from the data of X-ray, 1H NMR, and HPLC

Atropoisomerism of tertiary 13-amides of chlorin e ₆ was studied by the methods of X-ray analysis, ¹H NMR spectroscopy, and high performance liquid chromatography on the example of 13-N,N-dimethylamide-15,17-dimethyl ester of chlorin e ₆. The spatial structure of the major and minor atropoisomers was established. The possibility of reversible interconversion of the atropoisomers of the studied compound in solution was shown.     

Square‐Wave Voltammetry of Sodium Copper Chlorophyllin on Glassy‐Carbon and Paraffin‐Impregnated Graphite Electrode

Electrochemical oxidation of sodium copper chlorophyllin (CHL) has been investigated at a glassy‐carbon (GC) and paraffin‐impregnated graphite electrode (PIGE) using square‐wave voltammetry (SWV). Square‐wave voltammograms of other two chlorin‐type compounds, namely chlorin e₆ and chlorophyll a, have been studied as well. The measurements were performed in the pH range between 7 and 11. The square‐wave frequency was changed between 8 and 1000 Hz. The oxidation of studied chlorins is a complex, pH‐independent, reversible or quasireversible process, followed by the chemical transformation of the product. The product of the EC reaction of CHL is an electroactive π? π dimer, which strongly adsorbs on the electrode surface and undergoes further oxidation at more positive potential. The electrooxidation of the adsorbed dimer is a pH‐independent irreversible process with the formation of an electroinactive film. The voltammetric behaviour of chlorin e₆ on PIGE was qualitatively similar to that of CHL. The SW voltammograms of chlorin e₆ recorded on GCE and of chlorophyll a recorded on PIGE consisted of only one peak. The SW responses of studied compounds strongly depend on the stabilization of the reaction intermediate by adsorption to the electrode surface.     

Natural dyes based on chlorophyll and protoporphyrin derivatives

The utility of natural dyes (chlorophyll, protoporphyrin, and their derivatives) as ecologically pure new-generation dyes that are safer than common synthetic arene-based dyes is discussed. New dyes were obtained from chlorophyll and protoporphyrin derivatives such as pheophorbide (a+b), chlorin e₆, 6-N-(2-aminoethylamido)chlorin e₆ dimethyl ester, and 6-N-(2-aminoethylamido)deuteroporphyrin methyl ester and tested in coloration of wool, cotton, and acetate fibers.     

Synthesis of Derivatives of Chlorin P6 Trimethyl Ester

The Vilsmeier reaction of nickel(II) chlorin P₆ trimethyl ester with 3-dimethyl-aminoacrolein yielded nickel(II) chlorin P₆ 20-(2-formylvinyl) trimethyl ester and nickel(II) chlorin P₆ 3-(1-hydroxyethyl)-3-devinyl-20-(2-formylvinyl) trimethyl ester. Also, the outgrowths of nickel(II) chlorin P₆ 20-(2-formyl) trimethyl ester and nickel(II) chlorin P₆ 3-(2-formylvinyl)-3-devinyl-20-(2-formyl) trimethyl ester were obtained by Vilsmeier reaction with dimethylformamide. By treating the derivatives of nickel(II) 20-(2-formyl)-chlorin and nickel(II) 3-(2-formylvinyl)-20-(2-formyl)-chlorin with trifluoracetic acid, the removal of the central nickel(II) ion was accomplished. The derivatives of 20-(2-formyl)-chlorin and 3-(2-formylvinyl)-20-(2-formyl)-chlorin demonstrated considerable bathochromic shift of the major absorption band in the red region of the optical spectrum.     

蚕沙叶绿素的降解及二氢卟吩e6醚衍生物的合成

研究了蚕沙叶绿素降解为二氢卟吩e6的化学过程, 并以二氢卟吩e6单甲酯为原料合成了九种二氢卟吩e6醚衍生物, 用UV/Vis、IR、^1H NMR及FAB-MS谱分别确定了它们的结构。     

Thermal stability of chlorophyll <Emphasis Type="Italic">a</Emphasis> derivatives containing hydrophilic groups

Trends in thermal stability of aromatic macroheterocycles based of pheophorbide a and chlorin e ₆ containing hydrophilic groups have been revealed by means of thermogravimetric analysis at 298–1223 K under inert atmosphere. Methylpheophorbide a and 13(1)-N-methylamide of chlorin e ₆ are the most stable, the decomposition onset temperature being t _o 351 and 333°С. Their functional substitution leads t _o the reduction in thermal stability. Depending on the macrocycle structure the decrease in t _o can reach 20–200°С.     

Partialsynthese eines bacteriophäophorbid-C-methylesters

The partial synthesis of a bacteriophaeophorbide c methylester starting from the chlorophyll a derivative chlorin e₆ trimethyl-ester is described.     

DNA-binding properties and photocleavage activity of cationic water-soluble chlorophyll derivatives

Three cationic water-soluble chlorin e(6) derivatives, that is, 6a-,gammab-,7c-tris(2-trimethylammonioethyl)chlorin e(6) (1), 6a-,gammab-,7c-tris(3-methylpyridiniummethyl)chlorin e(6) (2), and 6a-,gammab-, 7c-tris(2-trimethylammonioethyl)-2-(3-trimethylammonioprop-1-enyl)chlorin e(6) (3), have been designed and synthesized to allow the study of their DNA-binding and -photocleavage activities. The DNA-unwinding assay, measurements of melting temperatures of double-stranded DNA, and the induced CD and visible absorption spectra have revealed that 1 and 3 are intercalated into the base pairs of the double-helical DNA, while 2 is bound to outside the minor groove of the double-helical DNA. The cationic water-soluble chlorin e(6) derivatives effectively cleave the double-helical DNA under photoirradiation and the DNA-photocleavage activity increases in the order 3>1>2. The DNA-binding and -photocleavage characteristics of the three cationic water-soluble chlorin e(6) derivatives are influenced by aspects of their molecular structure, such as the kind, number, and position of the cationic substituents.     

meso- and β-Pyrrole-Linked Chlorin-Bacteriochlorin Dyads for Promoting Far-Red FRET and Singlet Oxygen Production

A series of chlorin-bacteriochlorin dyads (derived from naturally occurring chlorophyll-a and bacteriochlorophyll-a), covalently connected either through the meso-aryl or β-pyrrole position (position-3) via an ester linkage have been synthesized and characterized as a new class of far-red emitting fluorescence resonance energy transfer (FRET) imaging, and heavy atom-lacking singlet oxygen-producing agents. From systematic absorption, fluorescence, electrochemical, and computational studies, the role of chlorin as an energy donor and bacteriochlorin as an energy acceptor in these wide-band-capturing dyads was established. Efficiency of FRET evaluated from spectral overlap was found to be 95 and 98 % for the meso-linked and β-pyrrole-linked dyads, respectively. Furthermore, evidence for the occurrence of FRET from singlet-excited chlorin to bacteriochlorin was secured from studies involving femtosecond transient absorption studies in toluene. The measured FRET rate constants, k_FRET, were in the order of 10¹¹ s⁻¹, suggesting the occurrence of ultrafast energy transfer in these dyads. Nanosecond transient absorption studies confirmed relaxation of the energy transfer product, ¹BChl*, to its triplet state, ³Bchl*. The ³Bchl* thus generated was capable of producing singlet oxygen with quantum yields comparable to their monomeric entities. The occurrence of efficient FRET emitting in the far-red region and the ability to produce singlet oxygen make the present series of dyads useful for photonic, imaging and therapy applications.     

具有叶绿素-a基本碳架的氯代二氢卟吩衍生物的合成

选择脱镁叶绿酸-a甲酯为起始原料, 经过化学结构修饰转换成其他叶绿素-a衍生物. 以过氧化氢/盐酸、N-氯代丁二酰亚胺(NCS)、氯化氢(或者浓盐酸)为氯化剂, 根据3-乙烯基和20-meso-位的不同化学反应活性, 通过亲电加成和亲电取代反应, 在二氢卟吩环上选择性地引进氯原子, 完成8种未见报道的具有叶绿素-a基本碳架的氯代二氢卟吩衍生物的合成. 所合成的新化合物均经UV, IR, 1H NMR及元素分析证明其结构.