[4 + 2] Annulation of Donor-Acceptor Cyclopropanes with Acetylenes Using 1,2-Zwitterionic Reactivity.

A new process for the [4 + 2] annulation of donor-acceptor cyclopropanes with acetylenes under the effect of anhydrous GaCl3 using 1,2-zwitterion reactivity was elaborated. The reaction opens access to substituted dihydronaphthalenes, naphthalenes, and other fused carbocycles. The direction of the reaction can be efficiently controlled by temperature.

The role of active site tyrosine 58 in Citrobacter freundii methionine γ-lyase.

In the spatial structure of methionine γ-lyase (MGL, EC 4.4.1.11) from Citrobacter freundii, Tyr58 is located at H-bonding distance to the oxygen atom of the phosphate "handle" of pyridoxal 5'-phosphate (PLP). It was replaced for phenylalanine by site-directed mutagenesis. The X-ray structure of the mutant enzyme was determined at 1.96Å resolution. Comparison of spatial structures and absorption spectra of wild-type and mutant holoenzymes demonstrated that the replacement did not result in essential changes of the conformation of the active site Tyr58Phe MGL. The Kd value of PLP for Tyr58Phe MGL proved to be comparable to the Kd value for the wild-type enzyme. The replacement led to a decrease of catalytic efficiencies in both γ- and ß-elimination reactions of about two orders of magnitude as compared to those for the wild-type enzyme. The rates of exchange of C-α- and C-ß- protons of inhibitors in D2O catalyzed by the mutant form are comparable with those for the wild-type enzyme. Spectral data on the complexes of the mutant form with the substrates and inhibitors showed that the replacement led to a change of rate the limiting step of the physiological reaction. The results allowed us to conclude that Tyr58 is involved in an optimal positioning of the active site Lys210 at some stages of γ- and ß-elimination reactions. This article is part of a Special Issue entitled: Cofactor-dependent proteins: evolution, chemical diversity and bio-applications.

Donor-Acceptor Cyclopropanes as 1,2-Dipoles in GaCl3-Mediated [4 + 2]-Annulation with Alkenes: Easy Access to the Tetralin Skeleton.

A new process for (4 + 2)-annulation of donor-acceptor cyclopropanes (DACs) with unsaturated compounds in the presence of anhydrous GaCl3 has been developed. In this process, DACs act as sources of formal 1,2- and 1,4-dipoles to give polysubstituted tetralins in high yields and with high regio- and diastereoselectivity. Alkenes with both aryl and alkyl substituents at the double bond undergo this reaction equally readily. A most likely mechanism of the reaction has been proposed. It involves preliminary generation of a key 1,2-dipolar gallium complex and its subsequent participation in annulation with an alkene.

A new type of donor-acceptor cyclopropane reactivity: the generation of formal 1,2- and 1,4-dipoles.

A new type of donor-acceptor cyclopropane reactivity has been discovered. On treatment with anhydrous GaCl3 , they react as sources of even-numbered 1,2- and 1,4-dipoles instead of the classical odd-numbered 1,3-dipoles due to migration of positive charge from the benzyl center. This type of reactivity has been demonstrated for new reactions, namely, cyclodimerizations of donor-acceptor cyclopropanes that occur as [2+2]-, [3+2]-, [4+2]-, [5+2], [4+3]-, and [5+4]-annulations. The [4+2]-annulation of 2-arylcyclopropane-1,1-dicarboxylates to give polysubstituted 2-aryltetralins has been developed in a preparative version that provides exceedingly high regio- and diastereoselectivity and high yields. The strategy for selective hetero-combination of donor-acceptor cyclopropanes was also been developed. The mechanisms of the discovered reactions involving the formation of a comparatively stable 1,2-ylide intermediate have been studied.

Pregna-5,17(20)-dien-21-oyl amides affecting sterol and triglyceride biosynthesis in Hep G2 cells.

Synthesis of series [17(20)Z]- and [17(20)E]-pregna-5,17(20)-dien-21-oyl amides, containing polar substituents in amide moiety, based on rearrangement of 17α-bromo-21-iodo-3ß-acetoxypregn-5-en-20-one caused by amines, is presented. The titled compounds were evaluated for their potency to regulate sterol and triglyceride biosynthesis in human hepatoma Hep G2 cells in comparison with 25-hydroxycholesterol. Three [17(20)E]-pregna-5,17(20)-dien-21-oyl amides at a concentrations of 5 µM inhibited sterol biosynthesis and stimulated triglyceride biosynthesis; their regulatory potency was dependent on the structure of amide moiety; the isomeric [17(20)Z]-pregna-5,17(20)-dien-21-oyl amides were inactive.

Lipophilic derivatives of natural chlorins: synthesis, mixed micelles with phospholipids, and uptake by cultured cells.

The chemical synthesis of six lipophilic conjugates of chlorins was carried out, in which lipophilic fragment (either hexadecyl- or cholest-5-en-3ß-yloxyethyl-) bound to 13(1)-, 15(2)-, 17(3)-positions of macrocycle by formation of related carboxamides. Structure of synthesized conjugates was studied by spectral methods and molecular modeling. Lipophilic conjugates of chlorins, being mixed with egg yolk phosphatidyl choline, formed mixed micelles stable in aqueous media under physiological conditions. Mixed micelles of conjugates with phosphatidyl choline differing in stoichiometric compositions were prepared and characterized by absorption spectra, electron microscopy and laser scattering. These micelles were found to bind and internalized by human breast carcinoma MCF-7 cells. The presented data reveal that modification of macrocycle with lipophilic substituents, solubilization of obtained conjugates in aqueous medium as mixed micelles with phospholipids, and transfer of mixed micelles to cells is simple approach for targeting of chlorin derivatives, which apparently may be used in photodynamic therapy.

Stereoselective double lewis acid/organo-catalyzed dimerization of donor-acceptor cyclopropanes into substituted 2-oxabicyclo[3.3.0]octanes.

A new approach for the dimerization of donor-acceptor cyclopropanes (2-arylcyclopropane-1,1-dicarboxylates) under double-catalysis conditions by treatment with 20 mol % of GaCl(3) and dimethyl 3,5-dimethyl-1-pyrazoline-3,5-dicarboxylate as a specific organocatalyst has been found. Under these conditions, the starting compounds are regio- and stereospecifically converted into polysubstituted 2-oxabicyclo[3.3.0]octanes. Two new rings, one C-O bond, and two C-C bonds are formed in this process, and four stereocenters are thus created. The reaction mechanism was thoroughly studied by NMR spectroscopy, and a number of intermediates were detected.

Stereospecificity of isotopic exchange of C-α-protons of glycine catalyzed by three PLP-dependent lyases: the unusual case of tyrosine phenol-lyase.

A comparative study of the kinetics and stereospecificity of isotopic exchange of the pro-2R- and pro-2S protons of glycine in (2)H(2)O under the action of tyrosine phenol-lyase (TPL), tryptophan indole-lyase (TIL) and methionine γ-lyase (MGL) was undertaken. The kinetics of exchange was monitored using both (1)H- and (13)C-NMR. In the three compared lyases the stereospecificities of the main reactions with natural substrates dictate orthogonal orientation of the pro-2R proton of glycine with respect to the cofactor pyridoxal 5'-phosphate (PLP) plane. Consequently, according to Dunathan's postulate with all the three enzymes pro-2R proton should exchange faster than does the pro-2S one. In fact the found ratios of 2R:2S reactivities are 1:20 for TPL, 108:1 for TIL, and 1,440:1 for MGL. Thus, TPL displays an unprecedented inversion of stereospecificity. A probable mechanism of the observed phenomenon is suggested, which is based on the X-ray data for the quinonoid intermediate, formed in the reaction of TPL with L-alanine. The mechanism implies different conformational changes in the active site upon binding of glycine and alanine. These changes can lead to relative stabilization of either the neutral amino group, accepting the α-proton, or the respective ammonium group, which is formed after the proton abstraction.

Chlorin e6-cholesterol conjugate and its copper complex. Simple synthesis and entrapping in phospholipid vesicles.

Synthesis of 13'[(cholest-5-en)-3beta-yloxyethoxycarbamoyl]-chlorin e6 starting from methylpheophorbide and 3beta(2-hydroxy)-ethoxycholest-5-ene is presented, as well as the preparation of related copper complex. Both conjugates obtained may be simply incorporated in phosphatidyl choline vesicles.

[17(20)E]- and [17(20)Z]-pregna-5,17(20)-dien-21-oylamides. Facile synthesis and primary evaluation for cancer cells proliferation.

Reaction of 17alpha-bromo-21-iodo-3beta-acetoxypregn-5-en-20-one with ammonia, primary, and secondary amines is simple and convenient method for preparation of [17(20)E]- and [17(20)Z]-pregna-5,17(20)-dien-21-oylamides. Synthesis and characteristics of 12 related amides are presented. Primary testing on cells proliferation indicated differing effects of synthesized compounds on androgen insensitive MCF-7 cells and androgen sensitive LNCaP cells.

New steroidal oxazolines, benzoxazoles and benzimidazoles related to abiraterone and galeterone.

Seven new oxazoline, benzoxazole and benzimidazole derivatives were synthesized from 3ß-acetoxyandrosta-5,16-dien-17-carboxylic, 3ß-acetoxyandrost-5-en-17ß-carboxylic and 3ß-acetoxypregn-5-en-21-oic acids. Docking to active site of human 17α-hydroxylase/17,20-lyase revealed that all oxazolines, as well as benzoxazoles and benzimidazoles comprising Δ16 could form stable complexes with enzyme, in which steroid moiety is positioned similarly to that of abiraterone and galeterone, and nitrogen atom coordinates heme iron, while 16,17-saturated benzoxazoles and benzimidazoles could only bind in a position where heterocycle is located nearly parallel to heme plane. Modeling of the interaction of new benzoxazole and benzimidazole derivatives with androgen receptor revealed the destabilization of helix 12, constituting activation function 2 (AF2) site, by mentioned compounds, similar to one induced by known antagonist galeterone. The synthesized compounds inhibited growth of prostate carcinoma LNCaP and PC-3 cells at 96 h incubation; the potency of 2'-(3ß-hydroxyandrosta-5,16-dien-17-yl)-4',5'-dihydro-1',3'-oxazole and 2'-(3ß-hydroxyandrosta-5,16-dien-17-yl)-benzimidazole was superior and could inspire further investigations of these compounds as potential anti-cancer agents.

Synthesis and cytotoxicity evaluation of 22,23-oxygenated stigmastane derivatives.

Starting from (22E)-3alpha,5alpha-cyclo-6beta-methoxystigmast-22-ene eighteen derivatives of (22S,23S)-22,23-oxidostigmastane, (22R,23R)-22,23-oxidostigmastane, and (22R,23R)-22,23-dihydroxystigmastane were synthesized and screened for cytotoxicity in human hepatoma Hep G2 cells and human breast carcinoma MCF-7 cells using MTT assay. Four compounds of this series exhibited high cytotoxicity in both cells; three compounds were selectively toxic in MCF-7 cells, one compound was toxic in Hep G2 cells, rather than in MCF-7 cells; four compounds at low concentrations increased MTT test values over the control.

Comparison of [17(20)E]-21-Norpregnene oxazolinyl and benzoxazolyl derivatives as inhibitors of CYP17A1 activity and prostate carcinoma cells growth.

Four new 4,5-dihydro-1,3-oxazole, and four new benzo-[d]-oxazole derivatives of [17(20)E]-21-norpregnene, differing in the structure of steroid moiety, were synthesized and evaluated for their potency to inhibit 17α-hydroxylase/17,20-lyase (CYP17A1) activity. Among new compounds, the only oxazolinyl derivative comprising 5-oxo-4,5-seco-3-yn- moiety potently inhibited CYP17A1. Binding modes of the oxazolinyl derivatives of [17(20)E]-21-norpregnene were analyzed by molecular dynamics simulations, and model of alternate, water-bridged type II interaction was proposed for these compounds. Eight new compounds, together with two CYP17A1-inhibiting oxazolinyl derivatives synthesized earlier, abiraterone and galeterone were evaluated for their potency to inhibit prostate carcinoma PC-3 and LNCaP cells growth. Oxazolinyl and benzoxazolyl derivatives comprising 3ß-hydroxy-5-ene moieties potently inhibited prostate carcinoma cell growth; inhibitory potencies of 3-oxo-4-en- and 5-oxo-4,5-seco-3-yn- derivatives were significantly lower.

Conjugates of 17-substituted testosterone and epitestosterone with pyropheophorbide a differing in the length of linkers.

Conjugates of 17α-substituted testosterone (1 and 2) and 17ß-substituted epitestosterone (3 and 4) with pyropheophorbide a were synthesized. The scheme consisted of synthesis of 17α-hydroxy-3-oxopregn-4-en-21-oic and 17ß-hydroxy-3-oxopregn-4-en-21-oic acids, and their coupling with pyropheophorbide a by means of either ethylene diamine, or 1,5-diamino pentane linkers. Mutual influence of steroidal and macrocyclic fragments in conjugates molecules was dependent on configuration of C17 and length of linker, that was established by analysis of 1H NMR spectra and molecular models of conjugates. Studies of interaction of conjugates with prostate carcinoma cells revealed that their uptake and internalization were independent on the androgen receptor activity, but dependent on the structure of conjugates, decreasing in the following row: 3 > 4 ≥ 1 > 2. Conjugates significantly decreased the LNCaP and PC-3 cells growth at 96 h incubation. Epitestosterone derivatives 3 and 4 also showed superior anti-proliferative activity versus testosterone ones. Conformationally more rigid conjugates 1 and 3, comprising short linkers, were more active than those with long linkers; conjugate 3 was the most potent.

Novel side chain modified Delta8(14)-15-ketosterols.

Synthesis of five novel Delta8(14)-15-ketosterols comprising modified side chains starting from ergosterol is described. Ergosteryl acetate was converted into (22E)-3beta-acetoxy-5alpha-ergosta-8(14),22-dien-15-one through three stages in 32% overall yield; further transformations of the product obtained led to (22E)-3beta-hydroxy-5alpha-ergosta-8(14),22-dien-15-one, (22S,23S)-3beta-hydroxy-22,23-oxido-5alpha-ergost-8(14)-en-15-one, (22R,23R)-3beta-hydroxy-22,23-oxido-5alpha-ergost-8(14)-en-15-one, (22R,23R)-5alpha-ergost-8(14)-en-15-on-3beta,22,23-triol and (22R,23R)-3beta-hydroxy-22,23-isopropylidenedioxy-5alpha-ergost-8(14)-en-15-one. New Delta8(14)-15-ketosterols were evaluated for their cytotoxicity and effects on sterol biosynthesis in human hepatoma Hep G2 cells in comparison with known 3beta-hydroxy-5alpha-cholest-8(14)-en-15-one. Among the compounds tested, (22R,23R)-3beta-hydroxy-22,23-oxido-5alpha-ergost-8(14)-en-15-one was found to be the most potent inhibitor of sterol biosynthesis (IC(50)=0.6+/-0.2microM), whereas (22R,23R)-5alpha-ergost-8(14)-en-15-on-3beta,22,23-triol exhibited the highest cytotoxicity (TC(50)=12+/-3microM at a 24h incubation).

Oxazolinyl derivatives of [17(20)E]-21-norpregnene differing in the structure of A and B rings. Facile synthesis and inhibition of CYP17A1 catalytic activity.

Five 4,5-dihydro-1,3-oxazole derivatives of [17(20)E]-21-norpregnene, comprising 3ß-hydroxy-5-ene (1), 3,6-dioxo-4-ene (2), 3-oxo-4-ene (3), 3α,5α-cyclo-6-oxo (4), 3ß-hydroxy-6-oxo (5) fragments were synthesized. Synthesis was conducted with improved procedure, based on reaction of suitably protected [17(20)E]-pregnen-21-oic acids with ethanolamine in presence of triphenyl phosphine, carbon tetrachloride, and triethyl amine. Potency of the compounds 1-5 to inhibit 17α-hydroxylase/17,20-lyase (CYP17A1) activity was studied by highly sensitive electrochemical method, using the enzyme immobilization technique. Compounds 1 and 3 were found to be potent CYP17A1 inhibitors, compounds 2 and 5 were not active, compound 4 strongly and irreversibly suppressed the enzyme activity. Molecular docking of compounds 1-5 in the active site of CYP17A1 showed that positions of all compounds in the enzyme active site were similar.

The role of the fast motion of the spin label in the interpretation of EPR spectra for spin-labeled macromolecules.

The spin label method was used to observe the nature of the fast motions of side chains in protein monocrystals. The EPR spectra of spin-labeled lysozyme monocrystals (with different orientations of the tetragonal protein crystal in relation to the direction of the magnetic field) were interpreted using the method of molecular dynamics (MD). Within the proposed simple model, MD calculations of the spin label motion trajectories are performed in a reasonable real time. The model regards the protein molecule as frozen as a whole and the spin-labeled amino acid residue as unfrozen. To calculate the trajectories in vacuum, a model of spin-labeled lysozyme was assembled, and the parameters of the force fields were specified for atoms of the protein molecule, including the spin label. The calculations show that the protein environment sterically limits the area of the possible angular reorientations for the NO reporter group of the nitroxide (within the spin label), and this, in turn, affects the shape of the EPR spectrum. However, it turned out that the spread in the positions of the reporter group in the angle space strictly adheres to the Gaussian distribution. Using the coordinates of the spin label atoms obtained by the MD method within a selected time range and considering the distribution of the spin label states over the ensemble of spin-labeled macromolecules in a crystal, the EPR spectra of spin-labeled lysozyme monocrystals were simulated. The resultant theoretical EPR spectra appeared to be similar to experimental ones.

Novel oxazolinyl derivatives of pregna-5,17(20)-diene as 17α-hydroxylase/17,20-lyase (CYP17A1) inhibitors.

New oxazolinyl derivatives of [17(20)E]-pregna-5,17(20)-diene: 2'-{[(E)-3ß-hydroxyandrost-5-en-17-ylidene]methyl}-4',5'-dihydro-1',3'-oxazole 1 and 2'-{[(E)-3ß-hydroxyandrost-5-en-17-ylidene]methyl}-4',4'-dimethyl-4',5'-dihydro-1',3'-oxazole 2 were evaluated as potential CYP17A1 inhibitors in comparison with 17-(pyridin-3-yl)androsta-5,16-dien-3ß-ol 3 (abiraterone). Differential absorption spectra of human recombinant CYP17A1 in the presence of compound 1 (λmax=422 nm, λmin=386 nm) and compound 2 (λmax=416 nm) indicated significant differences in enzyme/inhibitors complexes. CYP17A1 activity was measured using electrochemical methods. Inhibitory activity of compound 1 was comparable with abiraterone 3 (IC50=0.9±0.1 µM, and IC50=1.3±0.1 µM, for compounds 1 and 3, respectively), while compound 2 was found to be weaker inhibitor (IC50=13±1 µM). Docking of aforementioned compounds to CYP17A1 revealed that steroid fragments of compound 1 and abiraterone 3 occupied close positions; oxazoline cycle of compound 1 was coordinated with heme iron similarly to pyridine cycle of abiraterone 3. Configuration of substituents at 17(20) double bond in preferred docked position corresponded to Z-isomers of compounds 1 and 2. Presence of 4'-substituents in oxazoline ring of compound 2 prevents coordination of oxazoline nitrogen with heme iron and worsens its docking score in comparison with compound 1. These data indicate that oxazolinyl derivative of [17(20)E]-pregna-5,17(20)-diene 1 (rather than 4',4'-dimethyl derivative 2) may be considered as potential CYP17A1 inhibitor and template for development of new compounds affecting growth and proliferation of prostate cancer cells.

Synthesis and molecular modeling of (4'R)- and (4'S)- 4'-substituted 2'-{[(E)-androst-5-en-17-ylidene]-methyl}oxazolines.

Synthesis of four novel (4'R)- and (4'S)- 2'-{[(E)-3ß-hydroxyandrost-5-en-17-ylidene]-methyl} oxazolines, comprising 4'-hydroxymethyl (1 and 2) and 4'-methoxycarbonyl (3 and 4) substituents is presented. Reaction of 17α-bromo-21-iodo-3ß-acetoxypregn-5-en-20-one with either (L)-serine methyl ester, or (D)-serine methyl ester resulted in methyl N-[3ß-acetoxy-21-oxopregna-5,17(20)-dien-21-yl]-(L)-serinate and methyl N-[3ß-acetoxy-21-oxopregna-5,17(20)-dien-21-yl]-(D)-serinate (as mixtures of related [17(20)E]- and [17(20)Z]-isomers). Cyclization of obtained amides led to methyl 2'-{[(E)-3ß-acetoxyandrost-5-en-17-ylidene]methyl}-(4'S)-4',5'-dihydro-1',3'-oxazole-4'-carboxylate and methyl 2'-{[(E)-3ß-acetoxyandrost-5-en-17-ylidene]methyl}-(4'R)-4',5'-dihydro-1',3'-oxazole-4'-carboxylate which were transformed to titled compounds 1-4. The molecular docking of compounds 1-4 to ligand binding site of nuclear receptor LXRß revealed significant differences due to stereochemical configuration of 4' atom and structure of 4'-substituent.