The organoselenium and organotellurium compounds have been described as promising pharmacological agents in view of their unique biological properties. Glutathione peroxidase mimic, antioxidant activity and thioredoxin reductase inhibition are some of the properties reviewed here. On the other hand, little is known about the molecular toxicological effects of organoselenium and organotellurium compounds. Most of our knowledge arose from research on inorganic selenium and tellurium. However, the ability to oxidize sulfhydryl groups from biological molecules can be involved both in their pharmacological properties and in their toxicological effects. In fact, exposition to high doses of organoselenium or to low doses of organotellurium causes the depletion of endogenous reduced glutathione in a variety of tissues. Thus, the design of compounds that cause low depletion of glutathione and react with specific targeted proteins, controlling specific metabolic pathways, will represent an important progress in understanding the field of organochalcogen compounds. Furthermore, the development of new organochalcogens with higher thiol-peroxidase activity that can use other non-toxic thiol reducing agents, such as N-acetylcysteine instead of glutathione, will permit the investigation of the co-administration of organochalcogens and thiols as a formulation for antioxidant therapy.

Organoselenium and Organotellurium Compounds: Toxicology and Pharmacology

Ligand environment and the structure of schiff base adducts and tetracoordinated metal-chelates

In 1836 the first organoselenium compound, diethyl selenide, was prepared by Löwig,1 and it was isolated in the pure form in 1869.2 Early selenium chemistry involved the synthesis of simple aliphatic compounds such as selenols (RSeH), selenides (RSeR), and diselenides (RSeSeR); however, because of their malodorous nature, these compounds were difficult to handle. This, combined with the instability of certain derivatives and difficulties in purification, meant that selenium chemistry was slow to develop. By the 1950s, the number of known selenium compounds had increased significantly, but it was not until the 1970s, when several new reactions leading to novel compounds with unusual properties were discovered, that selenium chemistry began to attract more general interest.3-9 Aryl-substituted compounds were synthesized that were found to be less volatile and more pleasant to handle than the earlier aliphatic compounds. Compounds containing selenium in high oxidation states are relatively easy to manipulate using modern techniques.4c Organoselenium chemistry has now become a well-established field of research, and recent advances have been brought about by the potential technical applications of selenium compounds. Today selenium compounds find application in many areas including organic synthesis,4 biochemistry,5 xerography,6 the synthesis of conducting materials7 and semiconductors,8 and ligand chemistry.4c,9 Many of these aspects of selenium chemistry are wellcovered elsewhere in the literature; however, the subject of hypervalency has not attracted much attention and is the focus of this review.10

Organoselenium chemistry: role of intramolecular interactions.

Publisher Summary This chapter discusses the important reactions of the hydroxyl group. Knowledge of the relative reactivities of hydroxyl groups in carbohydrates is fundamental to a thorough understanding of carbohydrate chemistry. The chapter explains esterification, which forms the largest part of the literature since 1953 on selective reactions of carbohydrates. The common methods of esterification utilize an acid chloride or an acid anhydride as the reagent, but other acid derivatives often show different selectivities. An investigation pertinent to the subject of favored reactivity concerned the reactions of certain acyl halides with ethanol, in acetone or chloroform solution. The mixed-order nature of some of these reactions suggested that every rate-determining transition-state contained the substrate, the nucleophile (ethanol), and an acceptor— X—for hydrogen bonding, suitable acceptors being an acetone molecule, a chloride ion, or another ethanol molecule. The possibility that intramolecular hydrogen-bonding does not persist in pyridine and that the advantage of a bonded hydroxyl group would be lost, invalidates the explanation of favored reactivity. But if the hydrogen-bonding to pyridine is hindered in the transition state, intramolecular hydrogen-bonding could conceivably assume importance.

Relative Reactivities of Hydroxyl Groups in Carbohydrates

The enthalpy changes of 47 five-membered heterocyclic compounds (ZH) [33 substituted 2,3-dihydro-2-phenylbenzo[d]imidazoles (1H-5H), 9 substituted 2,3-dihydro-2-phenylbenzo[d]thiazoles (6H), and 5 substituted 2,3-dihydro-2-phenylbenzo[d]oxazoles (7H)] as a class of very important organic hydride donors to release hydride anion were determined by using titration calorimetry. The result shows that the enthalpy change scale of the 47 ZH in acetonitrile ranges from 49.0 to 93.4 kcal/mol. Such a long energy scale evidently shows that the 47 ZH can construct a large and useful library of organic hydride donors, which can provide various organic hydride donors that the hydride-releasing enthalpies are known. The enthalpy changes of the 47 ZH to release hydrogen atom and the 47 ZH+• to release proton and hydrogen atom were also evaluated by using relative thermodynamic cycles according to Hess' law. The results show:  (1) the enthalpy change scale of the 47 ZH to release hydrogen atom covers a range from 71.8 to ...

Hydride, Hydrogen Atom, Proton, and Electron Transfer Driving Forces of Various Five-Membered Heterocyclic Organic Hydrides and Their Reaction Intermediates in Acetonitrile

Data on the problem of competitive coordination, obtained mainly during the last 10 years, are surveyed and treated systematically. The competitive binding of metals in complexes of bi- and poly-dentate ligand systems — simple diatomic and triatomic compounds (N2, O2, CO, CO2, CS2, etc.), ambident anions (CN-, NCX-, NO2-, SO32-, etc.), and neutral aliphatic, aromatic, and heterocyclic compounds, including chelating organic ligands — is examined. Attention is specially concentrated on nontraditional ways in which typical ligand systems are coordinated and on regioselective synthesis as a method for the specific synthesis of metal complexes with a specified location of the coordinate bond. The bibliography includes 575 references.

http://iopscience.iop.org/article/10.1070/RC1997v066n05ABEH000258/pdf

Competitive coordination : ambident ligands in the modern chemistry of metal complexes

Molecular and crystal structure of ortho-tellurated azomethines with intramolecular N → Te coordination

Numerous new data on the effect of intramolecular hydrogen bonds on the reactivity of organic compounds are reviewed systematically. The bibliography comprises 200 references.

https://iopscience.iop.org/article/10.1070/RC1970v039n03ABEH001950/pdf

The Intramolecular Hydrogen Bond and the Reactivity of Organic Compounds

Chemical consequences of intramolecular Te ← N coordination in tellurium-containing aromatic azomethine derivatives

The characteristic features of the reactivity of the principal classes of organic compounds of tellurium(II) and tellurium(IV) are examined and compared with the analogous compounds of sulfur and selenium. The factors determing the specific features of the chemical behaviour of orgamotellurium compounds are characterised. It is shown that the possibility of the convenient introduction of tellurium-containing functional groups, their structural modification, elimination, the low-temperature elimination of the tellurium atom as a result of the low energy of the C-Te bond, and the high nucleophilicity of the tellurolate anions and diorganyl tellurides together with other properties create preconditions for the development of a new methodology in organic synthesis. The bibliography includes 446 references.

https://iopscience.iop.org/article/10.1070/RC1995v064n06ABEH000162/pdf

Igor D. Sadekov

Papers

Competitive coordination : ambident ligands in the modern chemistry of metal complexes

Molecular and crystal structure of ortho-tellurated azomethines with intramolecular N → Te coordination

The Intramolecular Hydrogen Bond and the Reactivity of Organic Compounds

Chemical consequences of intramolecular Te ← N coordination in tellurium-containing aromatic azomethine derivatives

Specific features of the reactivity of organotellurium compounds