A seleninic acid is an organoselenium compound and an oxoacid with the general formula RSeO2H, where R ≠ H. It is the second member of the family of organoselenium oxoacids, which also include selenenic acids and selenonic acids, which are RSeOH and RSeO3H, respectively. The parent member of this family of compounds is methaneseleninic acid (CH3SeO2H), also known as methylseleninic acid or "MSA".
- MeSeSeMe + H2O2 → 2MeSeO2H
- RSeC(O)R' + DMDO → RSeO2H
- RSeC(O)R' + excess DMDO → RSeO3H
- 2 RSeOH → RSeO2H + 1/2 RSeSeR
Structure, bonding, properties
Methaneseleninic acid, from decomposition of Se-methylselenocysteine Se-oxide but also available commercially, has been characterized by X-ray crystallography. The configuration about the selenium atom is pyramidal, with Se-C = 1.925(8) Å, Se-O = 1.672(7) Å, Se-OH = 1.756(7) Å, the angle OSeO = 103.0(3)°, the angle HO-Se-C = 93.5(3)°, and the angle OSeC = 101.4(3)°. The structure is isomorphous to that of methanesulfinic acid  Optical isomers of methaneseleninic acid can be isolated as chiral crystals by recrystallization from a mixture of methanol and toluene. The absolute configuration of one of the enantiomers was determined by X-ray crystallography. Optically active methaneseleninic acid was stable toward racemization in the solid state, although it racemized very rapidly in solution. Benzeneseleninic acid (C6H5SeO2H) had been previously characterized by X-ray methods and its optical resolution reported.
Reactions and applications in synthesis
Seleninic acids (particularly areneseleninic acids) are useful catalysts for hydrogen peroxide epoxidations, Baeyer–Villiger oxidations, oxidations of thioethers, etc.; peroxyseleninic acids (RSe(O)OOH) are thought to be the active oxidants.
Methaneseleninic acid shows "potent" anticancer activity and is considered to be an excellent compound for studying the anticancer effects of selenium in vitro. Methaneseleninic acid shows superior in vivo inhibitory efficacy toward human prostate cancer compared to selenomethionine or selenite (ion). It has recently been reported that methaneseleninic acid enhances the efficacy of paclitaxel for treatment of triple-negative breast cancer, that methaneseleninic acid functions as an aromatase inhibitor, of possible use in therapy for estrogen receptor-positive breast cancer in postmenopausal women, that methaneseleninic acid shows promise as a sensitizing agent for ABT-737-induced apoptosis of several cancer lines, and that methaneseleninic acid restricts tumor growth in the nude mouse model of metastatic breast cancer and Lewis lung carcinoma in mice.
Methaneselenol (CH3SeH) can be produced in vivo by reduction of methaneseleninic acid and may in fact be the key metabolite responsible for selenium’s anticancer activity through generation of superoxide. The reduction of methaneseleninic acid by mammalian thioredoxin reductase has been studied.
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