N. V. Lukashev

Thiamin diphosphate‐dependent enzymes: from enzymology to metabolic regulation, drug design and disease models

Bringing a knowledge of enzymology into research in vivo and in situ is of great importance in understanding systems biology and metabolic regulation. The central metabolic significance of thiamin (vitamin B1) and its diphosphorylated derivative (thiamin diphosphate; ThDP), and the fundamental differences in the ThDP‐dependent enzymes of metabolic networks in mammals versus plants, fungi and bacteria, or in health versus disease, suggest that these enzymes are promising targets for biotechnological and medical applications. Here, the in vivo action of known regulators of ThDP‐dependent enzymes, such as synthetic structural analogs of the enzyme substrates and thiamin, is analyzed in light of the enzymological data accumulated during half a century of research. Mimicking the enzyme‐specific catalytic intermediates, the phosphonate analogs of 2‐oxo acids selectively inhibit particular ThDP‐dependent enzymes. Because of their selectivity, use of these compounds in cellular and animal models of ThDP‐dependent enzyme malfunctions improves the validity of the model and its predictive power when compared with the nonselective and enzymatically less characterized oxythiamin and pyrithiamin. In vitro studies of the interaction of thiamin analogs and their biological derivatives with potential in vivo targets are necessary to identify and attenuate the analog selectivity. For both the substrate and thiamin synthetic analogs, in vitro reactivities with potential targets are highly relevant in vivo. However, effective concentrations in vivo are often higher than in vitro studies would suggest. The significance of specific inihibition of the ThDP‐dependent enzymes for the development of herbicides, antibiotics, anticancer and neuroprotective strategies is discussed.

The chemoselective alkynylation of dihaloquinolines by the Sonogashira-Hagihara reaction

Conditions for the regioselective Sonogashira—Hagihara alkynylation of 4-chloro-6-iodo(bromo)quinolines were found and 6-alkynyl-4-chloroquinolines were obtained in 90—100% yields.

Successive substitution of halogen atoms in 4,6-dihaloquinolines in palladium-catalyzed reactions with amines and arylboronic acids

A procedure was developed for the synthesis of 4,6-diamino- and 4,6- or 6,4-arylaminoquinolines by palladium-catalyzed C-N- and/or C-C-cross-coupling of 6-bromo-4-chloroquinoline.

Specific inhibition by synthetic analogs of pyruvate reveals that the pyruvate dehydrogenase reaction is essential for metabolism and viability of glioblastoma cells

The pyruvate dehydrogenase complex (PDHC) and its phosphorylation are considered essential for oncotransformation, but it is unclear whether cancer cells require PDHC to be functional or silenced. We used specific inhibition of PDHC by synthetic structural analogs of pyruvate to resolve this question. With isolated and intramitochondrial PDHC, acetyl phosphinate (AcPH, KiAcPH = 0.1 μM) was a much more potent competitive inhibitor than the methyl ester of acetyl phosphonate (AcPMe, KiAcPMe = 40 μM). When preincubated with the complex, AcPH also irreversibly inactivated PDHC. Pyruvate prevented, but did not reverse the inactivation. The pyruvate analogs did not significantly inhibit other 2-oxo acid dehydrogenases. Different cell lines were exposed to the inhibitors and a membrane-permeable precursor of AcPMe, dimethyl acetyl phosphonate, which did not inhibit isolated PDHC. Using an ATP-based assay, dependence of cellular viability on the concentration of the pyruvate analogs was followed. The highest toxicity of the membrane-permeable precursor suggested that the cellular action of charged AcPH and AcPMe requires monocarboxylate transporters. The relevant cell-specific transcripts extracted from Gene Expression Omnibus database indicated that cell lines with higher expression of monocarboxylate transporters and PDHC components were more sensitive to the PDHC inhibitors. Prior to a detectable antiproliferative action, AcPH significantly changed metabolic profiles of the investigated glioblastoma cell lines. We conclude that catalytic transformation of pyruvate by pyruvate dehydrogenase is essential for the metabolism and viability of glioblastoma cell lines, although metabolic heterogeneity causes different cellular sensitivities and/or abilities to cope with PDHC inhibition.

Mitochondrial Impairment May Increase Cellular NAD(P)H: Resazurin Oxidoreductase Activity, Perturbing the NAD(P)H-Based Viability Assays.

Cellular NAD(P)H-dependent oxidoreductase activity with artificial dyes (NAD(P)H-OR) is an indicator of viability, as the cellular redox state is important for biosynthesis and antioxidant defense. However, high NAD(P)H due to impaired mitochondrial oxidation, known as reductive stress, should increase NAD(P)H-OR yet perturb viability. To better understand this complex behavior, we assayed NAD(P)H-OR with resazurin (Alamar Blue) in glioblastoma cell lines U87 and T98G, treated with inhibitors of central metabolism, oxythiamin, and phosphonate analogs of 2-oxo acids. Targeting the thiamin diphosphate (ThDP)-dependent enzymes, the inhibitors are known to decrease the NAD(P)H production in the pentose phosphate shuttle and/or upon mitochondrial oxidation of 2-oxo acids. Nevertheless, the inhibitors elevated NAD(P)H-OR with resazurin in a time- and concentration-dependent manner, suggesting impaired NAD(P)H oxidation rather than increased viability. In particular, inhibition of the ThDP-dependent enzymes affects metabolism of malate, which mediates mitochondrial oxidation of cytosolic NAD(P)H. We showed that oxythiamin not only inhibited mitochondrial 2-oxo acid dehydrogenases, but also induced cell-specific changes in glutamate and malate dehydrogenases and/or malic enzyme. As a result, inhibition of the 2-oxo acid dehydrogenases compromises mitochondrial metabolism, with the dysregulated electron fluxes leading to increases in cellular NAD(P)H-OR. Perturbed mitochondrial oxidation of NAD(P)H may thus complicate the NAD(P)H-based viability assay.

Pd-catalyzed alkylation of halogen-substituted steroids with organozinc compounds

A general procedure has been developed for the introduction of hydrophobic alkyl groups into positions 6, 3, and 17 of steroid molecules via palladium-catalyzed Negishi reaction of halogen-substituted steroids with benzyl- and alkylzinc halides.

Palladium-catalyzed amination in the synthesis of nitrogen and oxygen heterocycles containing fragments of cholane and quinoline

By Mitsunobu reaction from 3,24-cholanediol and 2-hydroxy-8-chloroquinoline 24-(8-chloroquinolinyl-2-oxy)cholan-3-ol and 3,24-di(8-chloroquinolinyl-2-oxy)cholane were synthesized. These compounds were brought into reactions of palladium-catalyzed amination with propanediamine, oxaalkane diamines, and N,N′-bis(3-aminopropyl)ethylenediamine to obtain macrocycles of various structures, linear mono- and bis(steroid) derivatives of trioxaalkane diamine, and also cholane bis(oxaalkandiamine) derivative. The dependence was demonstrated of macrocyles and cyclooligomers yield on the polyamine nature. 4-Hydroxy-7-chloroquinoline afforded only 24-(7-chloroquinolinyl-4-oxy)cholan-3-ol.

Synthesis of nitrogen- and oxygen-containing macrocycles by palladium-catalyzed amination of 3,24-bis(6-chloropyridin-2-yloxy)cholane

Abstract3,24-Bis(6-chloropyrdin-2-yloxy)cholane prepared from cholane-3,24-diol by the Mitsunobu reaction was successfully used to synthesize various polyaza macrocycles via palladium-catalyzed amination with linear polyamines. The contribution of side formation of cyclic oligomers was found to depend on the polyamine nature.

Palladium-catalyzed amination in the synthesis and modification of acyclic oxadiamino cholane derivatives

Palladium-catalyzed reactions of 24-(haloaryloxy)cholanes and 3,24-bis(haloaryloxy)cholanes with excess oxadiamines gave the corresponding mono- and bis(oxadiamino)-substituted cholanes which were subjected to palladium-catalyzed arylation with 1,3-dibromobenzene, 2,6-dibromopyridine, 1,8-dichloroanthracene, 9-bromoanthracene, 1-chloroanthracene, and 1-chloroanthraquinone. The results of these reactions were found to strongly depend on the haloarene nature. The arylation with 1,3-dibromobenzene and 2,6-dibromopyridine led to the formation of new macrocyclic compounds containing one cholane, one arene, and two oxadiamine fragments.

Some problems of the teaching of organic chemistry in universities of Russia

Original Russian Text