Publications

Synthesis of novel heterocycles containing Se-O/Se-N linkages: Role of intramolecular coordination

The contrasting structure and reactivity of the mono ortho-coordinated aryl- and alkyl-selenium derivatives and 2,6-dibsubstituted aryl- and alkyl-selenium derivatives are described. The 2,6-disubstituted diaryl diselenides with Se$\ctdot$O intramole

CCDC 738429: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Fluoxetine, a selective serotonin reuptake inhibitor modulates inflammatory and neuropathic pain in the rat

The clinical usefulness of classical tricyclic antidepressants has been indicated in a variety of neuropathic pain. The role of selective serotonin reuptak

A Review on Benzoselenazoles: Synthetic Methodologies and Potential Biological Applications

Among the various organoselenium heterocycles, a new class of benzoselenazoles has attracted a great attention of scientists. The ever-growing interest for five-membered benzoselenazole heterocycles amongst the chemists has made commendable...

CCDC 2270525: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Regenerable Antioxidants—Introduction of Chalcogen Substituents into Tocopherols

To improve the radical‐trapping capacity of the natural antioxidants, alkylthio‐, alkylseleno‐, and alkyltelluro groups were introduced into all vacant aromatic positions in β‐, γ‐ and δ‐tocopherol. Reaction of the tocopherols with electrophilic chalcogen reagents generated by persulfate oxidation of dialkyl dichalcogenides provided convenient but low‐yielding access to many sulfur and selenium derivatives, but failed in the case of tellurium. An approach based on lithiation of the appropriate bromo‐tocopherol, insertion of chalcogen into the carbon‐lithium bond, air‐oxidation to a dichalcogenide, and final borohydride reduction/alkylation turned out to be generally applicable to the synthesis of all chalcogen derivatives. Whereas alkylthio‐ and alkylseleno analogues were generally poorer quenchers of lipid peroxyl radicals than the corresponding parents, all tellurium compounds showed a substantially improved radical‐trapping activity. Introduction of alkyltelluro groups into the tocopherol scaffold also caused a dramatic increase in the regenerability of the antioxidant. In a two‐phase lipid peroxidation system containing N ‐acetylcysteine as a water‐soluble co‐antioxidant the inhibition time was up to six‐fold higher than that recorded for the natural antioxidants.

Stable Selenenium Cations: Unusual Reactivity and Excellent Glutathione Peroxidase‐Like Activity

The syntheses of the three selenenium cations 17 – 19 derived from N ‐[ n ‐butyl‐(3‐nitrobenzylimino)]phenyl selenide ( 14 ) are described. Precursor 14 was synthesized by treating N ‐(2‐bromo‐3‐nitrobenzylimino)benzene ( 12 ) with in situ generated n BuSeNa. The selenenium cation 17 with chloride as counteranion was isolated when 14 was treated with sulfuryl chloride (SO 2 Cl 2 ) in the presence of triethylamine (Et 3 N). The selenenium cations with bromide ( 18 ) and tribromide ( 19 ) as counteranions, were synthesized by treating 14 with Br 2 in the presence of Et 3 N. Reaction of 19 with thiophenol afforded two unexpected products: the cyclic diselenide 20 and the bicyclic selenide 21 . Oxidation of 18 with hydrogen peroxide afforded the ebselen derivative, 2‐(4‐bromophenyl)‐7‐nitro‐1,2‐benzisoselenazol(2 H )‐3‐one Se ‐oxide ( 22 ). The presence of nonbonding Se ··· O/Se–N intramolecular interactions in 18 and 19 have been confirmed by single‐crystal X‐ray studies. Glutathione peroxidase‐like antioxidant activities of 17 – 19 and related compounds have been determined by the coupled reductase assay. It is proved that the high GPx‐like activities of cations involve the formation of corresponding intermediate selenoxide in the catalytic cycle. The isolated selenoxide 22 shows the highest GPx‐like activity among the series of compounds. The compounds have been further investigated by density functional theory calculations at the B3LYP level of theory using the 6‐31+G(d) basis set to identify nonbonding Se ··· O/N interactions. The second perturbation energy was obtained through natural bond orbital (NBO) analysis and NBO charges were calculated to ascertain the positive charge at the selenium atom. Nucleus‐independent chemical shifts (NICS) calculations have also been carried out.

Substituent Effects in Chain‐Breaking Aryltellurophenol Antioxidants

2-Aryltellurophenols substituted in the aryltelluro or phenolic parts of the molecule were prepared by lithiation of the corresponding tetrahydropyran-protected 2-bromophenol, followed by reaction with a suitable diaryl ditelluride then deprotection. In a two-phase system containing N-acetylcysteine as a co-antioxidant in the aqueous phase, all of the compounds quenched lipid peroxyl radicals more efficiently than α-tocopherol, with three to five-fold longer inhibition times. Thus, these compounds offer better and longer-lasting antioxidant protection than recently prepared alkyltellurophenols. Compounds with electron-donating para substituents in the aryltelluro or phenolic part of the molecule showed the best results. The mechanism for quenching peroxyl radicals was considered and discussed with respect to the calculated O-H bond-dissociation energies, deuterium-labelling experiments and studies of thiol consumption in the aqueous phase.

Chain‐Breaking Phenolic 2,3‐Dihydrobenzo[<i>b</i>]selenophene Antioxidants: Proximity Effects and Regeneration Studies

Phenolic 2,3-dihydrobenzo[b]selenophene antioxidants bearing an OH-group ortho (9), meta (10, 11) and para (8) to the Se were prepared by seleno-Claisen rearrangement/intramolecular hydroselenation. meta-Isomer (11) was studied by X-ray crystallography. The radical-trapping activity and regenerability of compounds 8-11 were evaluated using a two-phase system in which linoleic acid was undergoing peroxidation in the lipid phase while regeneration of the antioxidant by co-antioxidants (N-acetylcysteine, glutathione, dithiothreitol, ascorbic acid, tris(carboxyethyl)phosphine hydrochloride) was ongoing in the aqueous layer. Compound 9 quenched peroxyl radicals more efficiently than α-tocopherol. It also provided the most long-lasting antioxidant protection. With thiol co-antioxidants it could inhibit peroxidation for more than five-fold longer than the natural product. Regeneration was more efficient when the aqueous phase pH was slightly acidic. Since calculated O-H bond dissociation energies for 8-11 were substantially larger than for α-tocopherol, an antioxidant mechanism involving O-atom transfer from peroxyl to selenium was proposed. The resulting phenolic selenoxide/alkoxyl radical would then exchange a hydrogen atom in a solvent cage before antioxidant regeneration at the aqueous lipid interphase.

Intramolecular C–C coupling of 2,6-disubstituted-1-bromoaryls for dihydrophenanthridines

The reaction of 2,6-disubstituted-1-bromoaryl imines with sodium borohydride under reflux condition leads to an intramolecular cyclization through C–Br and C–H coupling without any transition-metal catalyst, furnishing 5,6-dihydrophenanthridine and phenanthridine derivatives.

Review of <i>Water Science and Technology: An Introduction</i> , 4th Edition by Nick GrayCRC Press, Boca Raton, Florida; 2017; ISBN 9781498753456; 680 pp.; $79.95.

No abstract is provided for this article.

Photoluminescent selenospirocyclic and selenotetracyclic derivatives by domino reactions of amines and imines

Novel photoluminescent selenospirocyclic and selenotetracyclic compounds, stabilized by intramolecular secondary Se⋯O interactions with an ortho-nitro group, have been accessed successfully through domino reactions of amines and imines, respectively.

Regenerable Radical‐Trapping and Preventive Selenazolonamine Antioxidants

Selenazolonamines 10 a – d with free amine (‐NH 2 ) group, a new series of preventive and radical‐trapping antioxidants were synthesized from their corresponding diselenides. The radical‐trapping antioxidant capacity of compounds 10 a – d was determined in a chlorobenzene/water membrane‐like model system in which azo ‐initiated peroxidation of linoleic acid was carried out in the lipid phase. The regeneration occurred in the aqueous ascorbic acid as co‐antioxidant, which could regenerate the antioxidants and enhance their inhibition times. The best antioxidant 10 d substituted with para ‐NMe 2 a strong electron‐donating group quenched the peroxyl radicals more efficiently than α‐tocopherol almost 5.5‐fold longer inhibition time. The novel selenazolonamines 10 a – d and their derivatives exhibited good preventive i. e. glutathione peroxidase‐like activity in the coupled reductase assay. Based on 77 Se NMR spectroscopy, a catalytic cycle for 10 d , involving diselenide, selenosulfide, and selenol as intermediates was proposed. The mechanism for quenching of peroxyl radicals for 10 d was also considered to be involved via proton‐coupled electron transfer reaction.

Selective cyclooxygenase-2 inhibitors in inflammatory bowel disease

Synthesis and Characterization of Boron Complexes of Some Biologically Active Ligands

Boron complexes LB-O-B(OAc)2 and LB-O-BL with Schiff bases (LH2) having and donor systems have been prepared from oxybis(diacetoxy)borane. The compounds have been characterized by elemental analysis, molecular weight determination and conductivity measurements. The mode of bonding of the ligands with the boron atom has been determined on the basis of IR, 1H NMR, 11B NMR and electronic spectral studies.

Decoding the Gut-Brain Axis in Alzheimer's Disease: Emerging Perspectives

Abstract: Alzheimer';s disease (AD) is a leading source of dementia, evidenced by cognitive debility, tau neurofibrillary tangles, and amyloid-β plaques. Recent studies emphasize the gut-brain axis as a vital element in the pathogenesis of Alzheimer';s disease, involving microbial, neuronal, immunological, and hormonal mechanisms. The composition of gut microbiota dysbiosis is determined by growth in intestinal barrier permeability and activation of immune cells, which causes impaired function of the blood-brain barrier that stimulates neural injury, neuronal loss, neuroinflammation, and eventually AD. Various studies have reported that the gut microbiota plays a crucial role in brain function and changes in individual behavior, as well as in bacterial amyloid formation. Growing experimental and clinical data specify the conspicuous role of intestinal dysbiosis and microbiota- host interactions in AD. The importance of this paper is the focus on the potential association of AD and gut microbiota and also a discussion of the therapeutic modalities of inhibiting gut dysbiosis.

In Search of Catalytic Antioxidants—(Alkyltelluro)phenols, (Alkyltelluro)resorcinols, and Bis(alkyltelluro)phenols

The quenching of peroxyl radicals by ortho-(alkyltelluro)phenols occurs by a more complex mechanism than formal H-atom transfer. In an effort to improve on this concept, we have prepared (alkyltelluro)resorcinols and bis(alkyltelluro)phenols and evaluated their catalytic chain-breaking and preventive antioxidative properties. The in situ formed trianion produced from 2-bromophenol and 3 equiv of tert-butyllithium was allowed to react with dialkyl ditellurides to provide ortho-(alkyltelluro)phenols in low yields. 2-Bromoresorcinols after treatment with 4 equiv of tert-butyllithium similarly afforded 2-(alkyltelluro)resorcinols. Bis(alkyltelluro)phenols were accessed by allowing the trianion produced from the reaction of 2,6-dibromophenol with 5 equiv of tert-butyllithium to react with dialkyl ditellurides. The novel phenolic compounds were found to inhibit azo-initiated peroxidation of linoleic acid much more efficiently than α-tocopherol in a two-phase peroxidation system containing excess N-acetylcysteine as a stoichiometric thiol reducing agent in the aqueous phase. Whereas most of the (alkyltelluro)phenols and resorcinols could inhibit peroxidation for only 89-228 min, some of the bis(alkyltelluro)phenols were more regenerable and offered protection for >410 min. The novel (alkyltelluro)phenols were also evaluated for their capacity to catalyze reduction of hydrogen peroxide in the presence of thiophenol (glutathione peroxidase-like activity). (Alkyltelluro)resorcinols 7a-c were the most efficient catalysts with activities circa 65 times higher than those recorded for diphenyl diselenide.

Synthesis of intramolecularly coordinated cyclic selenenate/thioselenenate esters and their glutathione peroxidase-like activity

The syntheses and characterization of selenenate esters, thioselenenate ester and related derivatives are described. The reactions of n-butyl-4-tert-2,6-di(formyl)phenyl selenide (23) or bis(2,6-diformyl-4-tert-butylphenyl)diselenide (24) with bromine affords a new selenenate ester, 5-tert-butyl-7-(formyl)benzoxaselenol-3-one (25), stabilized by ortho-formyl group along with 3,3′-oxybis(5-tert-butyl-3H-benzo[c][1,2]oxoselenole-7-carbaldehyde) (16). Oxidation of (25) with H2O2 gives 5-tert-butyl-7-(carboxylic)benzoxaselenol-3-one-Se-oxide (26). However, the direct oxidation of (23) with H2O2 affords 5-tert-butyl-7-(butylcarboxylate)benzoxaselenol-3-one (27). The synthesis of 5-tert-butyl-7-(methylcarboxylate) benzothiaselenol-3-one (28) has been accomplished by the reaction of (26) with thionyl chloride (SOCl2) with a catalytic amount of N, N-dimethylformamide. Attempted thionation of 7-nitro-1,2-benzisoselenole(3H)-Se-oxide (20) leads to the isolation of bis(2-chloromethyl-6-nitrophenyl)diselenide (29). The presence of intramolecular secondary Se···O interactions in all the esters is confirmed by single crystal X-ray diffraction studies and computational studies. Glutathione peroxidase-like activity of (16), (25)-(29) has been determined by the coupled reductase assay.