Yaroslav V. Tkachev

Toxicity of (22R,23R)-22,23-dihydroxystigmastane derivatives to cultured cancer cells.

Toxicity of eight 22,23-dihydroxystigmastane derivatives (four pairs of (22R,23R)- and (22S,23S)-isomers differing in steroid backbone structure) to human breast carcinoma MCF-7 cells was compared. For every pair of structurally related compounds, (22R,23R) isomer was found to be significantly more toxic than (22S,23S) isomer. Computational analysis showed that side chain of (22R,23R)-22,23-dihydroxystigmastane derivatives is rigid, whereas that of (22S,23S)-isomers is rather flexible. Structure of steroid backbone significantly affects cytotoxicity of (22R,23R)-22,23-dihydroxystigmastane derivatives to human breast carcinoma MCF-7 cells, human ovary carcinoma CaOv cells, and human prostate carcinoma LnCaP cells. (22R,23R)-3beta,22,23-trihydroxystigmast-5-ene and (22R,23R)-3beta,22,23-trihydroxystigmast-5-en-7-one, both comprising equatorial 3beta-hydroxyl group, exhibited the highest cytotoxicity, while the most polar 28-homobrassinolide and 28-homocastasterone, both comprising 2alpha,3alpha-dihydroxy groups, exhibited the lowest toxicity. Binding of (22R,23R)-22,23-dihydroxystigmastane derivatives to plasmatic membrane was suggested to be important for cytotoxicity.

Synthesis of 21-nitrogen substituted pregna-5,17(20)-dienes from pregnenolone

The facile synthesis of six [17(20)Z]- and [17(20)E]-isomeric 3β-hydroxy-pregna-5,17(20)-dien-21-oyl amides and three [17(20)E]-3β-hydroxy-2-[prergna-5,17(20)-dien-20-yl]-oxazolines from pregnenolone is presented. The synthetic scheme consists of transformation of pregnenolone into the known 17α-bromo-21-iodo-3β-acetoxypregn-5-en-20-one followed by reaction with ethanolamine, 2-methyl-2-aminopropanol, and (1-aminocyclohexyl)methanol resulted in mixture of [17(20)E]- and [17(20)Z]-pregna-5,17(20)-dien-21-(2-hydroxy)-oyl amides; separation of [17(20)E]- and [17(20)Z]-isomers; their cyclization into [17(20)E]-oxazolines under action of POCl(3) in pyridine, and removal of acetate protecting groups. Significantly different orientation of nitrogen containing substituents in [17(20)Z]- and [17(20)E]-isomers regarding to steroid backbone enables their configuration to be easily identified by NMR spectroscopy. All synthesized compounds did not exhibit marked toxic effects in three cell lines (MCF-7, Hep G2, and LNCaP). In androgen-sensitive LNCaP cells all testing compounds at concentrations of 50 nM potently stimulated proliferation.

[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.

Styrylmalonates as an Alternative to Donor–Acceptor Cyclopropanes in the Reactions with Aldehydes: A Route to 5,6-Dihydropyran-2-ones

A new strategy for modifying the reactivity of donor-acceptor cyclopropanes (DAC) has been suggested. It involves the use of isomeric styrylmalonates as alternative sources of reactive intermediates. The efficiency of the approach has been demonstrated in reactions with aromatic aldehydes. As a result, a new process for construction of the 5,6-dihydropyran-2-one skeleton has been developed. It efficiently occurs with high diastereoselectivity in the presence of BF3·Et2O; the products can be easily isolated by crystallization. The subsequent use of the resulting dihydropyranones in syntheses providing convenient access to various classes of compounds with broad molecular diversity has been demonstrated.

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 2H2O 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 1H- and 13C-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.

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

HIGHLIGHTSSynthesis of oxazolinyl and benzoxazolyl derivatives of [17(20)E]‐21‐norpregnene.Inhibition of CYP17A1 activity.Computational modeling of [17(20)E]‐21‐norpregnene oxazolinyl derivatives binding modes in CYP17A1 active site.Inhibition of prostate carcinoma PC‐3 and LNCaP cells growth. ABSTRACT 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 17&agr;‐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 3&bgr;‐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.

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-3β-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.

Cascade Cleavage of Three-Membered Rings in the Reaction of D–A Cyclopropanes with 4,5-Diazaspiro[2.4]hept-4-enes: A Route to Highly Functionalized Pyrazolines

A new cascade process for reactions of donor-acceptor cyclopropanes (DACs) with spiro[cyclopropanepyrazolines] in the presence of EtAlCl2 or Ga halides is reported. The action of a Lewis acid results in DAC activation and addition of the carbocationic intermediate to the azocyclopropane system of the pyrazoline with opening of the second three-membered ring and addition of a halide anion from the Lewis acid. A specific feature of this process is that one activated cyclopropane ring activates another one, and depending on the component ratio, the process can involve two DAC molecules and one pyrazoline molecule or one DAC molecule and two pyrazoline molecules. The process is tolerant to various functional groups and occurs with a wide range of substrates to give polyfunctionalized structures based on a 2-pyrazoline moiety.

Uniform EPR Spectra Analysis of Spin-Labeled Macromolecules by Temperature and Viscosity Dependences

© 2012 Tkachev and Timofeev, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Uniform EPR Spectra Analysis of Spin-Labeled Macromolecules by Temperature and Viscosity Dependences

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

Graphical abstract Figure. No Caption available. HighlightsTestosterone and epitestosterone chemically conjugated with pyropheophorbide a.Spectral properties and molecular models of conjugates are presented.Epitestosterone conjugates inhibit LNCaP and PC‐3 cells growth stronger.Conformationally rigid conjugates possess stronger anti‐proliferative activity. ABSTRACT Conjugates of 17&agr;‐substituted testosterone (1 and 2) and 17&bgr;‐substituted epitestosterone (3 and 4) with pyropheophorbide a were synthesized. The scheme consisted of synthesis of 17&agr;‐hydroxy‐3‐oxopregn‐4‐en‐21‐oic and 17&bgr;‐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.