Selenol group

More recently, 4-methylbenzyl 25 and 4-methoxybenzyl (Mob) protection17 was proposed for the selenol group. The 4-methylbenzyl group is introduced by reacting selenocysteine with a-bromo-p-xylene following essentially the procedure for the preparation of the related cysteine derivative. 25 This type of protection is applied in combination with the Boc/Bzl strategy and its removal is achieved by HF treatment in the presence of 15% anisole and 2.5% ethyl methyl sulfide at 0°C in one hour. Unfortunately, experimental details were not reported by Oikawa et al. 25 ... 

TrxRs are homodimeric flavoproteins [80] that catalyze the NADPH-dependent reduction of thioredoxin (Trx), a ubiquitous 12 kDa protein that is the major protein disulfide reductase in cells [81], and belongs to the pyridine nucleotide-disulfide oxidoreductase family [82]. Each monomer includes an FAD prosthetic group, a NADPH binding site and an active site containing a redox-active selenol group. Electrons are transferred from NADPH via FAD to the active-site selenol of TrxR, which then reduces the substrate Trx [83]. The crystal structure of TrxR is shown in Fig. 13 [84],... 

The active site of GPx-ase contains a selenol group (SeH) which is oxidized to Se(=0)H with formation of one equivalent of water in the first step of the enzymatic cycle (equation 17b). Two equivalents of glutathione then react with... 

Serine and cysteine protease-catalyzed hydrolysis of esters and amides involves two steps (1) attack of the active site nucleophile on the carbonyl at the cleavage site to form an acyl-enzyme intermediate, and (2) hydrolysis of the acylated enzyme to regenerate the catalyst (Equation 1). We wondered whether a selenol group (-SeH) could assume the role of the active site nucleophile. We found that selenolsubtilisin, like thiolsubtilisin, is a poor amidase. Thus, i F-succinyl-Ala-Ala-Pro-Phe-p-nitro-anilide is not hydrolyzed at all by the selenol-containing enzyme even though it is an excellent substrate for subtilisin itself. Activated esters, on the other hand, are substrates. 

Insertion of a C=0 or C=S group between two thiol or two selenol functions of a 1,2- or 1,3-dithiol or diselenol results in formation of the corresponding five- or six-membered heterocycles. 

Treatment of tetrahydroberberine (26) with sodium benzenethiolate (48) or -selenolate (49) in the presence of ruthenium catalyst afforded the C-14—N bond cleavage products 51 or 52 with a phenylthio or phenylseleno group at C-14 (Scheme 12). The latter was converted to the 10-membered amino olefin 53 on treatment with m-chloroperbenzoic acid. 

Cd thiolates and selenolates tend to form q-S- or q-Se-bridged dinuclear species, even with bulky organic groups, e.g., 2,4,6-tri-t-butylphenyl.317 318 With some ligand combinations, heterocubanes with Cd4S4 core or oligonuclear species derived from heterocubanes are formed.319,320... 

Ono and Kamimura have found a very simple method for the stereo-control of the Michael addition of thiols, selenols, or alcohols. The Michael addition of thiolate anions to nitroalkenes followed by protonation at -78 °C gives anti-(J-nitro sulfides (Eq. 4.8).11 This procedure can be extended to the preparation of a/jti-(3-nitro selenides (Eq. 4.9)12 and a/jti-(3-nitro ethers (Eq. 4.10).13 The addition products of benzyl alcohol are converted into P-amino alcohols with the retention of the configuration, which is a useful method for anri-P-amino alcohols. This is an alternative method of stereoselective nitro-aldol reactions (Section 3.3). The anti selectivity of these reactions is explained on the basis of stereoselective protonation to nitronate anion intermediates. The high stereoselectivity requires heteroatom substituents on the P-position of the nitro group. The computational calculation exhibits that the heteroatom covers one site of the plane of the nitronate anion.14... 

The aim of this chapter is to review the chemistry of chalcogenolates in the last 10 years. The more recent reviews in this field included chalcogenolates of the s-block elements,13,14 early transition metal thiolates,15 metal complexes with selenolate and tellurolate ligands,16 copper(I), lithium and magnesium thiolates,17 functionalized thiolate complexes,18 19 pentafluorobenzenethiolate platinum group compounds,20 tellurium derivatives,21 luminescent gold compounds,22 and complexes with lanthanide or actinide.23... 

Only a few group 1 and 2 metal derivatives of selenolates have been structurally characterized. They are prepared with the same methods used for the thiolates.155,158 At present there are no crystal structures of lithium terphenyl selenolates. However, the potassium and rubidium salts, which are dimeric, have been structurally characterized.155 They are isomorphous, both to each other and to the closely related thiolate analogues.1533 Currently, there are no reported terphenylselenolates reported for the alkaline-earth metals. 

Nucleophilic additions of alcohols, amines, thiols, and selenols to Group 8 buta-trienylidene intermediates [M]=C=C=C=CR2 have also been used in the preparation of stable heteroatom-conjugated allenylidene complexes. Thus, activation of trimethylsilyl-l,3-butadiyne HC=C-C=CSiMe3 by the iron(II) complex [FeClCp (dppe)], in methanol and in the presence of NaBPh4, resulted in the high-yield formation of the methoxy-allenylidene [FeCp =C=C=C(OMe)Me ... 

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