A simple and efficient approach for the synthesis of fluorinated and nonfluorinated octaethylporphyrin-based benzochlorins with variable lipophilicity, their in vivo tumor uptake, and the preliminary in vitro photosensitizing efficacy

Starting from commercially available Ni(II)octaethylporphyrin (OEP), an efficient approach for the preparation of a series of fluorinated and nonfluorinated benzochlorins with variable lipophicity has been developed. Their spectroscopic properties, preliminary in vitro photosensitizing efficacy, and tumor selectivity were determined. Our methodology provides a facile approach for the preparation of the free-base and the related Zn(II) benzochlorins containing alkyl and alkyl ether side chains with variable carbon units. For the preparation of benzochlorins containing alkyl groups attached to the exocyclic phenyl ring, the Ni(II) meso-(2-formylvinyl)octaethyl porphyrin 2 was reacted with various reagents such as (trifluoromethyl)trimethylsilane (TMS-CF3) or the Grignard reagents of various fluorinated or nonfluorinated alkyl halides. The corresponding intermediates 3, 6a-6e, and 8 obtained via intramolecular cyclization under acidic conditions afforded the related benzochlorins 5, 7a-d, and 9 in good yields except for 7e which was obtained in poor yield (11.4%). The alcohol 10 obtained by reacting porphyrin 2 with ethynylmagnesium chloride did not produce the expected acetylenic benzochlorin; instead the corresponding acetyl derivative 11 was obtained as a major product, which under appropriate reaction conditions was converted into a series of alkyl ether derivatives 13a-13d. To obtain a benzochlorin bearing an ester functionality (15), porphyrin 2 was first reacted with ethyl acetate/LDA and the intermediate alcohol 14 was then cyclized with sulfuric acid. Unlike most of the natural and synthetic chlorins, the Zn(II) complexes of the benzochlorin analogues exhibited a significant bathochromic shift ( approximately 10 nm) in the electronic absorption spectra, and the long wavelength absorptions were observed in the range 671-677 nm (epsilon: 43270-50360). For investigating the in vitro efficacy of these analogues, Molt-4 cells were used. At a concentration of 2.5 microM, and a light dose of 4 J/cm2, all benzochlorins produced significant photosensitizing efficacy. The tumor (RIF) and muscle uptake in C3H mice of these photosensitizers was determined by in vivo reflectance spectroscopy. These results indicate that in this series increasing the length of the alkyl or alkyl ether carbon chains at the fused phenyl ring system produced a significant increase in tumor uptake.     

Photosensitizers derived from 132-oxo-methyl pyropheophorbide-a: enhanced effect of indium(III) as a central metal in in vitro and in vivo photosensitizing efficacy

The effects of an additional keto group on absorption wavelength and the corresponding metal complexes Zn(II), Cu(II) In(III) on singlet oxygen production and photodynamic efficacy were examined among the alkyl ether analogs of pyropheophorbide-a. For the preparation of the desired photosensitizers, the methyl 13(2)-oxo-pyropheophorbide-a obtained by reacting methyl pyropheophorbide-a with aqueous LiOH-THF was converted into a series of alkyl ether analogs. These compounds were evaluated for photophysical properties and in vitro (by means of the MTT assay and intracellular localization in RIF cells) and in vivo (in C3H mice implanted with RIF tumors) photosensitizing efficacy. Among the alkyl ether derivatives, the methyl 3-decyloxyethyl-3-devinyl-13(2)-oxo-pyropheophorbide-a was found to be most effective and the insertion of In(III) into this analog further enhanced its in vitro and in vivo photosensitizing efficacy. Fluorescence microscopy showed that, in contrast to the hexyl and dodecyl ether derivatives of HPPH (which localize in mitochondria and lysosomes, respectively), the diketo-analogs and their In(III) complexes localized in Golgi bodies. The preliminary in vitro and in vivo results suggest that, in both free-base and metalated analogs, the introduction of an additional keto group at the five-member exocyclic ring in pyropheophorbide-a diminishes its photosensitizing efficacy. This may be due to a shift in subcellular localization from mitochondria to the Golgi bodies. The further introduction of In(III) enhances photoactivity, but not by shifting the localization of the photosensitizer.     

The role of the peripheral benzodiazepine receptor in photodynamic activity of certain pyropheophorbide ether photosensitizers: albumin site II as a surrogate marker for activity

A study has been carried out to define the importance of the peripheral benzodiazepine receptor (PBR) as a binding site for a series of chlorin-type photosensitizers, pyropheophorbide-a ethers, the subject of a previous quantitative structure-activity relationship study by us. The effects of the PBR ligand PK11195 on the photodynamic activity have been determined in vivo for certain members of this series of alkyl-substituted ethers: two of the most active derivatives (hexyl and heptyl), the least active derivative (dodecyl [C12]) and one of intermediate activity (octyl [C8]). The photodynamic therapy (PDT) effect was inhibited by PK11195 for both of the most active derivatives, but no effect on PDT activity was found for the less active C12 or C8 ethers. The inhibitory effects of PK11195 were predicted by the binding of only the active derivatives to the benzodiazepine site on albumin, ie. human serum albumin (HSA)-Site II. Thus, as with certain other types of photosensitizers, it has been demonstrated with this series of pyropheophorbide ethers that in vitro binding to HSA-Site II is a predictor of both optimal in vivo activity and binding to the PBR in vivo.     

CHLORIN AND PORPHYRIN DERIVATIVES AS POTENTIAL PHOTOSENSITIZERS IN PHOTODYNAMIC THERAPY

In order to find a photosensitizer with better optical properties and pharmacokinetics than Photofrin II, a series of new photosensitizers related to methyl pheophorbide-a and chlorin-e6 were synthesized. These compounds absorb at substantially longer wavelengths (lambda max 660 nm) than does Photofrin II (630 nm) and show promise for use in photodynamic therapy. Among the porphyrins, we observed that long carbon chain ether derivatives are better photosensitizers than their ester analogs. These sensitizers were tested for in vivo photosensitizing activity vis-a-vis Photofrin II, using the standard screening system of DBA/2 mice bearing transplanted SMT/F tumors. Most of these photosensitizers were found to have better tumoricidal photosensitizing activity than Photofrin II and demonstrated more rapid attenuation of normal tissue photosensitivity with time after administration vis-a-vis Photofrin II.     

Functionalization of OEP-based benzochlorins to develop carbohydrate-conjugated photosensitizers. Attempt to target beta-galactoside-recognized proteins

meso-(2-Formylvinyl)octaethylporphyrin on reaction with cyanotrimethylsilane in the presence of various catalysts [copper triflate [Cu(OTf)(2)], indium triflate [In(OTf)(3)], or magnesium bromide diethyl etherate (MgBr(2).Et(2)O)] produced a mixture of the intermediate 3-hydroxy-3-cyanopropenoporphyrin, the corresponding trimethylsilyl ether derivative, and the unexpected propenochlorins. The yields of the reaction products were found to depend on the reaction conditions and the catalysts used. The intermediate porphyrins on treatment with concentrated sulfuric acid yielded the free-base cyanobenzochlorins in major quantity along with several other novel benzochlorins as minor products. Reduction of ethyl-3-hydroxy-1-pentenoate-porphyrin with DIBAL-H/NaBH(4) and subsequent acid treatment provided the corresponding free-base 10(3)-(2-hydroxyethyl)benzochlorin, which upon a sequence of reactions gave a free-base benzochlorin bearing a carboxylic acid functionality in good yield. It was then condensed with a variety of carbohydrates (glucosamine, galactosamine, and lactosamine), and the related conjugates were screened using the galectin-binding-ability assay. Among the carbohydrate conjugates investigated, the lactose and galactose analogues displayed the galectin-binding ability with an enhancement of about 300-400-fold compared to lactose. In preliminary studies, all photosensitizers (with or without carbohydrate moieties) were found to be active in vitro [radiation-induced fibrosarcoma (RIF) tumor cells]. However, the cells incubated with lactose (known to bind to beta-galactoside-recognized proteins) prior to the addition of the photosensitizers containing the beta-galactose moiety (e.g., galactose and lactose) produced a 100% decrease in their photosensitizing efficacy. Under similar experimental conditions, benzochlorin without a beta-galactoside moiety or the related glucose conjugate did not show any inhibition in its photosensitizing efficacy. These results in combination with the galectin-binding data indicate a possible beta-galactoside-recognized protein specificity of the galactose- and lactose-benzochlorin conjugates.     

A first comparative study of purpurinimide-based fluorinated vs. nonfluorinated photosensitizers for photodynamic therapy

A first report on the synthesis and comparative in vitro-in vivo photosensitizing efficacy of various fluorinated and the corresponding nonfluorinated, purpurinimide-based photosensitizers is discussed. In preliminary in vivo screening, compared with the nonfluorinated analogs, purpurinimides bearing trifluoromethyl substituents showed enhanced photosensitizing efficacy. Among compounds (isomers) with similar lipophilicity, the position of the substituents was found to play a decisive role in biological efficacy.     

Thermolysis of vic-dihydroxybacteriochlorins: effect of the nature of substrates in directing the formation of chlorin-chlorin dimers with fixed and flexible orientations and their preliminary in vitro photosensitizing efficacy

The thermolysis products obtained by refluxing a series of vic-dihydroxychlorins in o-dichlorobenzene are characterized. Depending on the nature of substrates, this methodology provides an access for novel carbon-carbon linked chlorin-chlorin dimers and chlorin-porphyrin dimers with fixed and flexible orientations. The configuration of the linkers in the symmetrical and unsymmetrical dimers was confirmed by extensive NMR (COSY, ROESY) and molecular modeling studies. The molecular modeling studies of the energy-optimized dimers with flexible orientation confirmed that one of the chlorin units of the dimeric structure is tilted toward the opposite ring as evident by the shielding effect in the resonances of some of the protons in the (1)H NMR spectroscopy. Among the dimers with fixed orientation, compared to the free-base analogues, the related mono- and di-Zn(II) complexes produced a decreased fluorescence intensity, suggesting a possibility of the faster energy transfer via intersystem crossing (ISC) in the metalated derivatives than the corresponding free-base analogues to produce the corresponding excited triplet states. The photosensitizing efficacy of the monomers and the related dimers was also compared in radiation-induced fibrosarcoma (RIF) tumor cells at variable drug/light doses. In preliminary screening, compared to monomers, the corresponding carbon-carbon linked dimers produced enhanced photosensitizing efficacy.     

Fluorinated photosensitizers: synthesis, photophysical, electrochemical, intracellular localization, in vitro photosensitizing efficacy and determination of tumor-uptake by F in vivo NMR spectroscopy

For in vivo NMR studies, starting from pyrroles, a series of fluorinated porphyrins were synthesized by following the MacDonald reaction conditions. Upon reaction with osmium tetroxide, a fluorinated porphyrin containing four trifluoromethyl groups (12 fluorine units) was converted into the related chlorin and bacteriochlorin which exhibited long-wavelength absorptions at 652 and 720 nm, respectively. All compounds produced good singlet oxygen production efficiency. A comparative study of nine porphyrins with and without fluorine substituents indicated no adverse effects of the presence of fluorinated groups in the photophysical properties of the porphyrins, chlorins or bacteriochlorins. The first and second one-electron reduction potentials (vs SCE) of the investigated compounds range between −1.29 and −1.49 V and between −1.66 and −1.84 V in PhCN containing 0.1 M TBAP. UV-visible spectroelectrochemical data suggested the formation of π-anion and π-cation radicals upon the first reduction and first oxidation. The in vivo ¹⁹F MR study of a representative fluorine labeled compound with twelve equivalent fluorines confirmed the presence of the fluorine labeled sensitizer in mouse (C3H/HeJ) implanted with RIF tumors on mouse foot dorsum by inoculating 2×10⁵ cells (the studies were repeated on four tumored mice to confirm the feasibility and reproducibility). All fluorinated compounds were found to be quite effective in vitro. In a comparative intracellular localization study with Rhodamine-123 in RIF tumor cells, the most soluble porphyrin containing two propionic ester side chains was found to localize in mitochondria as well as the related chlorin and bacteriochlorin.     

QUANTUM YIELD and EQUILIBRIUM POSITION OF THE CONFIGURATIONAL PHOTOISOMERIZATION OF BILIRUBIN BOUND TO HUMAN SERUM ALBUMIN*

Abstract— At low fluence rates it is possible to observe a photoequilibrium between Z,Z-bilirubin(BR) and its E isomers(collectively called PBR) bound to human serum albumin(HSA).For excitation centered at 465 nm, the fraction of PBR/HSA in the photoequilibrium mixture was observed to be 0.22 + 0.02. The quantum yield for conversion of BR/HSA to PBR/HSA was found to be 0.20 0.02. The equality of the quantum yield value and the fraction of PBR/HSA in the photoequilibrium mixture is consistent with a simple mechanism for the photoisomerization in which optically excited singlet states of BR and PBR convert rapidly and with virtually total efficiency to a common excited intermediate with twisted geometry that subsequently decays to BR and PBR in the ratio 4:1, respectively. Quantum yields for other photoprocesses of BR bound to HSA are much lower than that for configur-ational isomerization. The central role suggested for configurational isomerization in the phototherapy for neonatal hyperbilirubinemia is supported by these observations.     

Correlation between Site ll-Specific Human Serum Albumin (HSA) Binding Affinity and Murine in vivo Photosensitizing Efficacy of Some Photofrin Components

Human serum albumin (HSA) is one of the key components in human blood that may influence drug distribution. As such, it is important to know the affinity of any drug for albumin. Previously, Photofrina mixture of monomeric, dimeric and oligomeric porphyrins, has been subjected to HSA binding studies. However, due to its complex nature, binding studies on Photofrin or other hematoporphyrin derivatives with HSA are inconclusive. In this report, the binding properties of some components (dimers and trimers) of Photofrin® and the relationship between murine photosensitizing efficacy and those binding properties were investigated. The interaction of these porphyrins with HSA was investigated by direct ultrafiltration and fluorescent titration techniques with fluorescent probes such as dansyl-L-proline (DP), which is known to interact selectively with site II on HSA. Porphyrins also were tested for antitumor activity in a mouse model following intravenous administration and exposure to laser light. Together, the results suggest that the photosensitizers that were preferentially bound to site II of HSA were most effective at controlling murine tumor regrowth     

CONFIGURATIONAL PHOTOISOMERIZATION OF BILIRUBIN IN VITRO—I. QUENCHING OF Z→E ISOMERIZATION BY TWO-WAVELENGTH IRRADIATION

Abstract A simple rate-equation theory of configurational photoisomerization of bilirubin (BR) is presented and used to discuss the Z→E photoisomerization of BR in HSA solutions irradiated with laser light in the blue-green spectral region. The analytical expression of Z, E -BR:HSA (PBR) concentration at photoequilibrium (PE) is used to derive the PBR concentration from the spectrophotometric data on absorbance difference spectra. The PBR values are in good agreement with those recently reported in the case of 10 nm-bandwidth filtered light. Both sets of data give a best-fit value of the BR, PBR quantum yield ratio equal to 2.3 in the case of BR:HSA ratio equal to 1:2.
Successive irradiation of BR/HSA solutions with different wavelengths (457/488/457 nm) provides further support for the reversibility of the photoreaction. However, differences between the intermediate PE values have been found, and may reveal departures from the simple Z,Z→Z,E isomerization in BR/HSA solutions.
The possibility of controlling the formation of Z, E -BR/HSA has been demonstrated using simultaneous irradiation with blue (457 nm) and green (514 nm) laser beams. The two-wavelength scheme takes advantage of the reversibility of the BRIPBR reaction, and of the differences between BR/PBR absorption spectra and quantum yields. Efficient quenching of PE PBR is achieved when green substantially exceeds (10–40 times) blue light intensity. This experiment may simulate what actually occurs during clinical phototherapy with white and green fluorescent lamps, where the quenching of PBR at the formation sites may prevent diffusion of this slowly excreted isomer and, at the same time, increase the formation of the more rapidly excretable structural, non-reversible isomers, such as lumirubin.     

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.     

The Structural Basis of Mycobacterium tuberculosis RpoB Drug-Resistant Clinical Mutations on Rifampicin Drug Binding

Tuberculosis (TB), caused by the Mycobacterium tuberculosis infection, continues to be a leading cause of morbidity and mortality in developing countries. Resistance to the first-line anti-TB drugs, isoniazid (INH) and rifampicin (RIF), is a major drawback to effective TB treatment. Genetic mutations in the β-subunit of the DNA-directed RNA polymerase (rpoB) are reported to be a major reason of RIF resistance. However, the structural basis and mechanisms of these resistant mutations are insufficiently understood. In the present study, thirty drug-resistant mutants of rpoB were initially modeled and screened against RIF via a comparative molecular docking analysis with the wild-type (WT) model. These analyses prioritized six mutants (Asp441Val, Ser456Trp, Ser456Gln, Arg454Gln, His451Gly, and His451Pro) that showed adverse binding affinities, molecular interactions, and RIF binding hinderance properties, with respect to the WT. These mutant models were subsequently analyzed by molecular dynamics (MD) simulations. One-hundred nanosecond all-atom MD simulations, binding free energy calculations, and a dynamic residue network analysis (DRN) were employed to exhaustively assess the impact of mutations on RIF binding dynamics. Considering the global structural motions and protein–ligand binding affinities, the Asp441Val, Ser456Gln, and His454Pro mutations generally yielded detrimental effects on RIF binding. Locally, we found that the electrostatic contributions to binding, particularly by Arg454 and Glu487, might be adjusted to counteract resistance. The DRN analysis revealed that all mutations mostly distorted the communication values of the critical hubs and may, therefore, confer conformational changes in rpoB to perturb RIF binding. In principle, the approach combined fundamental molecular modeling tools for robust “global” and “local” level analyses of structural dynamics, making it well suited for investigating other similar drug resistance cases.     

Synthesis of tetrasubstituted Zn(II)-phthalocyanines carrying four carboranyl-units as potential BNCT and PDT agents

The synthesis of two tetrasubstituted zinc(II)phthalocyanines carrying four carbon-carbon linked o-carboranyl-units (40 boron atoms, 27.5% boron by weight) is presented. In an in vitro model test the new compounds showed a good photosensitizing efficiency, that encourages further studies for their evaluation as possible BNCT-PDT sensitizers.     

Diphenyl disulfide and sodium in NMP as an efficient protocol for in situ generation of thiophenolate anion: selective deprotection of aryl alkyl ethers and alkyl/aryl esters under nonhydrolytic conditions

Aryl methyl ethers, methyl esters, aryl esters, and aryl sulfonates are chemoselectively deprotected under nonhydrolytic conditions by treatment with Ph(2)S(2) (0.6 equiv) and Na (1.6 equiv) in NMP under reflux or at 90 degrees C. Quantitative utilization of the 'PhS' moiety as the effective nucleophilic species represents conservation of atom economy. Other solvents such as HMPA, DMPU, DMEU, and DMF afforded comparable results. Chloro, nitro, aldehyde, alpha,alpha-diketone, and alpha,beta-unsaturated ketone functionalities remain unaffected. The deprotection was found to take place in the order aryl ester > alkyl ester > aryl alkyl ether. Substrates bearing strong electron-withdrawing groups react at a faster rate than those not having such substitution. The differences in rate of reaction has been exploited for selective deprotection for intramolecular competition. An aryl acetate/benzoate is deprotected selectively in preference to a methyl ester or aryl methyl ether. Selective deprotection of a methyl ester is observed in the presence of an aryl alkyl ether.     

Cd（Ⅱ）与HSA或BSA的结合平衡研究

用平衡透析法详细研究了生理pH(7.43)条件下Cd(Ⅱ)与HSA或BSA的结合平衡.通过非线性最小二乘法拟合Bjerrum方程,首次报道了Cd(Ⅱ)-HSA和Cd(Ⅱ)-BSA体系的逐级稳定常数值,其K_1～K_3的数量级均为10~4;Hill系数和自由能偶合定量分析表明Cd(Ⅱ)与HSA或BSA的结合均产生在类似体系中少见的强的正协同效应,且Cd(Ⅱ)与HSA结合产生的正协同效应大于BSA;Scatchard图分析表明,Cd(Ⅱ)在HSA和BSA中均有3个强结合部位.通过Cd(Ⅱ)与Cu(Ⅱ),Zn(Ⅱ)或Ca(Ⅱ)等竞争结合HSA或BSA的结果,进一步讨论了Cd(Ⅱ)在HSA或BSA中强结合部位的可能位置和(或)配体.     

Evaluation of the binding of oxovanadium(IV) to human serum albumin

The understanding of the biotransformations of insulin mimetic vanadium complexes in human blood and its transport to target cells is an essential issue in the development of more effective drugs. We present the study of the interaction of oxovanadium(iv) with human serum albumin (HSA) by electron paramagnetic resonance (EPR), circular dichroism (CD) and visible absorption spectroscopy. Metal competition studies were done using Cu(II) and Zn(II) as metal probes. The results show that V(IV)O occupies two types of binding sites in albumin, which compete not only with each other, but also with hydrolysis of the metal ion. In one of the sites the resulting V(IV)O-HSA complex has a weak visible CD signal and its X-band EPR spectrum may be easily measured. This was assigned to amino acid side chains of the ATCUN site. The other binding site shows stronger signals in the CD in the visible range, but has a hardly measurable EPR signal; it is assigned to the multi metal binding site (MBS) of HSA. Studies with fatted and defatted albumin show the complexity of the system since conformational changes, induced by the binding of fatty acids, decrease the ability of V(IV)O to bind albumin. The possibility and importance of ternary complex formation between V(IV)O, HSA and several drug candidates - maltol (mal), picolinic acid (pic), 2-hydroxypyridine-N-oxide (hpno) and 1,2-dimethyl-3-hydroxy-4(1H)-pyridinone (dhp) was also evaluated. In the presence of maltol the CD and EPR spectra significantly change, indicating the formation of ternary VO-HSA-maltol complexes. Modeling studies with amino acids and peptides were used to propose binding modes. Based on quantitative RT EPR measurements and CD data, it was concluded that in the systems with mal, pic, hpno, and dhp (V(IV)OL(2))(n)(HSA) species form, where the maximum value for n is at least 6 (mal, pic). The degree of formation of the ternary species, corresponding to the reaction V(IV)OL(2) + HSA -->/<-- V(IV)OL(2)(HSA) is hpno > pic ≥ mal > dhp. (V(IV)OL)(n)(HSA) type complexes are detected exclusively with pic. Based on the spectroscopic studies we propose that in the (V(IV)OL(2))(n)(HSA) species the protein bounds to vanadium through the histidine side chains.     

Reactions of nitroxides with metalloporphyrin alkyls bearing beta hydrogens: Aliphatic carbon-carbon bond activation by metal centered radicals

Nitroxide-induced beta-hydrogen atom abstraction and beta-elimination of rhodium porphyrin alkyls have been observed. Rhodium(II) porphyrin radical were proposed intermediates to form first and subsequently reacted via aliphatic carbon-carbon bond activation with alkyl substituted nitroxides to yield rhodium porphyrin alkyl complexes.     

Binding equilibrium study between Mn( Ⅱ ) and HSA or BSA

The binding of Mn( Ⅱ ) to human serum albumin (HSA) or bovine serum albumin (BSA) has been studied by equilibrium dialysis at physiological pH (7. 43). The Scatchard analysis indicates that there are 1.8 and 1.9 strong binding sites of Mn( Ⅱ ) in HSA and BSA, respectively. The successive stability constants which are reported for the first time are obtained by non-linear least-squares methods fitting Bjerrum formula. For both Mn( Ⅱ )-HSA and Mn( Ⅱ )-BSA systems, the order of magnitude of K1 was found to be 104. The analyses of Hill plots and free energy coupling show that the positive cooperative effect was found in both Mn( Ⅱ )-HSA and Mn( Ⅱ )-BSA systems . The results of Mn ( Ⅱ ) competing with Cu ( Ⅱ ) 、 Zn(Ⅱ)、Cd( Ⅱ) or Ca( Ⅱ ) to bind to HSA or BSA further support the conjecture that there are two strong binding sites of Mn( Ⅱ) in both HSA and BSA. One is most probably located at the tripeptide segment of N- terminal sequence of HSA and BSA molecules involving four groups composed of n     

3,3'-Diphosphoryl-1,1'-bi-2-naphthol-Zn(II) complexes as conjugate acid-base catalysts for enantioselective dialkylzinc addition to aldehydes

A highly enantioselective dialkylzinc (R(2)(2)Zn) addition to a series of aromatic, aliphatic, and heteroaromatic aldehydes (5) was developed based on conjugate Lewis acid-Lewis base catalysis. Bifunctional BINOL ligands bearing phosphine oxides [P(=O)R(2)] (7), phosphonates [P(=O)(OR)(2)] (8 and 9), or phosphoramides [P(=O)(NR(2))(2)] (10) at the 3,3'-positions were prepared by using a phospho-Fries rearrangement as a key step. The coordination of a NaphO-Zn(II)-R(2) center as a Lewis acid to a carbonyl group in a substrate and the activation of R(2)(2)Zn(II) with a phosphoryl group (P=O) as a Lewis base in the 3,3'-diphosphoryl-BINOL-Zn(II) catalyst could promote carbon-carbon bond formation with high enantioselectivities (up to >99% ee). Mechanistic studies were performed by X-ray analyses of a free ligand (7) and a tetranuclear Zn(II) cluster (21), a 31P NMR experiment on Zn(II) complexes, an absence of nonlinear effect between the ligand (7) and Et-adduct of benzaldehyde, and stoichiometric reactions with some chiral or achiral Zn(II) complexes to propose a transition-state assembly including monomeric active intermediates.