Synthesis of disulfides via sulfenylation of alkyl and aryldithiopyridine n-oxides

Synthesis of unsymmetrical phosphorus disulfides

A sulfur-mediated umpolung strategy employing N-thiosuccinimides and (EtO)2P(O)SH has been developed to synthesize unsymmetrical organophosphorus disulfides (P(O)-S-S motif). A pronucleophile (EtO)2P(O)SH, Brønsted acid and phosphorothioate nucleophile, converts N-thiosuccinimides into unsymmetrical phosphorus disulfides. This protocol achieves catalyst- and additive-free reaction conditions, uses a renewable solvent (EtOH), and avoids harsh reagents.

Convenient Synthesis of Functionalized Unsymmetrical Vinyl Disulfides and Their Inverse Electron-Demand Hetero-Diels-Alder Reaction

The simple, convenient, and efficient methods for the preparation of unsymmetrical vinyl disulfides with additional functional groups under mild conditions with moderate to high yields were designed. The developed methods include the reaction of S-vinyl phosphorodithioate with thiotosylates or S-vinyl thiotosylate with thiols. The designed methods allow for the synthesis of unsymmetrical vinyl disulfides with additional functionalities such as hydroxy, carboxy, protected amino, or ester groups. Vinyl disulfides reacted with the generated transient o-iminothioquinones in an inverse electron-demand [4+2] cycloaddition to produce benzo[b][1,4]thiazine derivatives.

Impact of an unusual disulfide transformation on detection of isothermal amplification products

Detection of infectious pathogens such as HIV-1, HPV, and SARS-CoV-2 from biospecimens is critical to healthcare. Particularly sensitive and specific diagnostic techniques to accomplish this include molecular amplification and detection tests of nucleic acids from pathogens. Such tests are comprised of reagent compositions to facilitate hybridization of primers and probes that are complementary to specifically amplified sequences of the analyte target. One of these reagents from an isothermal molecular assay occasionally changed its physical appearance over time, generating interest into the cause of the transformation and suitability of the reagent in diagnostic testing. A preliminary hypothesis was that the 2,2′-dithiodipyridine component was the pre-chromophoric compound of its distinctly yellow reduced form, 2-thiopyridine. However, under oxidizing conditions, 2-thiopyridine is a minor constituent of hybridization reagents and not a major contributor to the yellow colour. Instead, a new yellow compound was isolated from coloured hybridization reagent, identified as 1-(2′-pyridyl)-2-thiopyridone and determined to be the result of an intramolecular cyclic rearrangement and sulfur extrusion from 2,2′-dithiodipyridine under acidic and oxidizing conditions. Neither the appearance of 1-(2′-pyridyl)-2-thiopyridone, nor the concomitant depletion of 2,2′-dithiodipyridine reduced the sensitivity or specificity of in vitro diagnostic screening assay results for detecting amplified nucleic acids from viral pathogens, ensuring the safety of tested blood transfusion products.

tBuOK-triggered bond formation reactions

Recently, inexpensive and readily available tBuOK has seen widespread use in transition-metal-free reactions. Herein, we report the use of tBuOK for S-S, S-Se, N[double bond, length as m-dash]N and C[double bond, length as m-dash]N bond formations, which significantly extends the scope of tBuOK in chemical synthesis. Compared with traditional methods, we have realized mild and general methods for disulfide, azobenzenes imine etc. synthesis.

Convenient and efficient synthesis of functionalized unsymmetrical Z-alkenyl disulfanes

We developed a simple and efficient method for the synthesis of functionalized unsymmetrical Z-alkenyl disulfanes under mild conditions in moderate to good yields. The designed method is based on the reaction of Z-alkenyl thiotosylates with thiols in the presence of base. The developed method allows the preparation of unsymmetrical Z-alkenyl disulfanes bearing additional hydroxy, carboxy, or amino functionalities.

Synthesis of mixed glycosyl disulfides/selenenylsulfides using benzyltriethylammonium tetrathiomolybdate as a sulfur transfer reagent

An easy and mild method has been developed for the synthesis of mixed glycosyl disulfides/selenenylsulfides from glycosyl halides and diaryl/dialkyl dichalcogenides in the presence of benzyltriethylammonium tetrathiomolybdate [(BnEt3N)2MoS4]. The salient feature of this method is the sulfur transfer from [BnEt3N]2MoS4 to form glycosyl disulfides which with excess tetrathiomolybdate further undergo exchange reaction with other dichalcogenides in a one-pot operation.

Oxidative cross S–H/S–H coupling: selective synthesis of unsymmetrical aryl tert-alkyl disulfanes

Selective oxidative coupling between equivalent aryl and tert-alkyl mercaptans was achieved under mild condition. This protocol may provide an efficient process to synthesize the unsymmetrical aryl tert-alkyl disulfides.

DDQ-mediated synthesis of functionalized unsymmetrical disulfanes

We developed a simple and efficient method for the synthesis of functionalized unsymmetrical disulfanes under mild conditions in good yields.

Inhibition of glutathione peroxidase mediates the collateral sensitivity of multidrug-resistant cells to tiopronin

Multidrug resistance (MDR) is a major obstacle to the successful chemotherapy of cancer. MDR is often the result of overexpression of ATP-binding cassette transporters following chemotherapy. A common ATP-binding cassette transporter that is overexpressed in MDR cancer cells is P-glycoprotein, which actively effluxes drugs against a concentration gradient, producing an MDR phenotype. Collateral sensitivity (CS), a phenomenon of drug hypersensitivity, is defined as the ability of certain compounds to selectively target MDR cells, but not the drug-sensitive parent cells from which they were derived. The drug tiopronin has been previously shown to elicit CS. However, unlike other CS agents, the mechanism of action was not dependent on the expression of P-glycoprotein in MDR cells. We have determined that the CS activity of tiopronin is mediated by the generation of reactive oxygen species (ROS) and that CS can be reversed by a variety of ROS-scavenging compounds. Specifically, selective toxicity of tiopronin toward MDR cells is achieved by inhibition of glutathione peroxidase (GPx), and the mode of inhibition of GPx1 by tiopronin is shown in this report. Why MDR cells are particularly sensitive to ROS is discussed, as is the difficulty in exploiting this hypersensitivity to tiopronin in the clinic.

Precursors and formation of pyrithione and other pyridyl-containing sulfur compounds in drumstick onion, Allium stipitatum

Two novel, structurally unusual cysteine derivatives were isolated from the bulbs of Allium stipitatum (Allium subg. Melanocrommyum) and shown to be S-(2-pyridyl)cysteine N-oxide and S-(2-pyridyl)glutathione N-oxide. The former compound is the first example of a naturally occurring alliinase substrate that contains an N-oxide functionality instead of the S-oxide group. In addition, S-methylcysteine S-oxide (methiin) and S-(methylthiomethyl)cysteine 4-oxide (marasmin) were found in the bulbs. Presented data suggest that the previously reported identification of S-(2-pyridyl)cysteine S-oxide was most likely erroneous. The alliinase-mediated formation of pyridyl-containing compounds following disruption of A. stipitatum bulbs was studied by a combination of HPLC-MS, HPLC-PDA, DART-MS, and NMR techniques. It was found that no pyridyl-containing thiosulfinates are present in homogenized bulbs in detectable quantities. Instead, various pyridine N-oxide derivatives are formed, including N-hydroxypyridine-2(1H)-thione (pyrithione), 2-(methyldithio)pyridine N-oxide, 2-[(methylthio)methyldithio]pyridine N-oxide, di(2-pyridyl) disulfide N-oxide, and di(2-pyridyl) disulfide N,N'-dioxide. This represents the first report of pyrithione formation as a natural product.

Investigations into the origin of the molecular recognition of several adenosine deaminase inhibitors

Inhibitors of adenosine deaminase (ADA, EC 3.5.4.4) are potential therapeutic agents for the treatment of various health disorders. Several highly potent inhibitors were previously identified, yet they exhibit unacceptable toxicities. We performed a SAR study involving a series of C2 or C8 substituted purine-riboside analogues with a view to discover less potent inhibitors with a lesser toxicity. We found that any substitution at C8 position of nebularine resulted in total loss of activity toward calf intestinal ADA. However, several 2-substituted-adenosine, 8-aza-adenosine, and nebularine analogues exhibited inhibitory activity. Specifically, 2-Cl-purine riboside, 8-aza-2-thiohexyl adenosine, 2-thiohexyl adenosine, and 2-MeS-purine riboside were found to be competitive inhibitors of ADA with K(i) values of 25, 22, 6, and 3 μM, respectively. We concluded that electronic parameters are not major recognition determinants of ADA but rather steric parameters. A C2 substituent which fits ADA hydrophobic pocket and improves H-bonding with the enzyme makes a good inhibitor. In addition, a gg rotamer about C4'-C5' bond is apparently an important recognition determinant.

Chromatographic behavior of pyrithiones

Pyrithione biocides are currently viewed as a major prospect for the replacement of tributyltin antifoulants in ship paints. The chromatographic behavior of 1-hydroxy-2-pyridinethione (pyrithione, PT), bis(2-pyridinyl)disulfide 1,1'-dioxide (PT2), and the metal complexes zinc [Zn(PT)2], iron [Fe(PT)3] and copper [Cu(PT)2] pyrithione, were investigated by means of UV-vis spectroscopy, ESI-MSn, HPLC-DAD and HPLC-ESI-MSnD. This revealed transformations of the analytes, which affect the development of adequate methods for species or environmental analysis of pyrithiones. PT transforms into copper- or iron- containing complexes and/or the oxidation product PT2, depending on the type of the stationary phase used in chromatographic analysis. Speciation complicates direct chromatography of [Zn(PT)2] and [Fe(PT)3].

Callipeltoside a: total synthesis, assignment of the absolute and relative configuration, and evaluation of synthetic analogues

The total synthesis of the novel antitumor agent callipeltoside A, as well as several analogues, is accomplished and allows assignment of the stereochemistry not previously established. A convergent strategy is employed wherein the target is dissected into three units-the core macrolactone, the sugar callipeltose, and a cyclopropyl bearing chain. The strategy for the synthesis of the macrolactone derives from employment of diastereoselective aldol reactions that emanate from an 11 carbon piece. The stereochemistry of the latter derives from the chiral pool and two asymmetric reactions-a ketone reduction using CBS-oxazaborolidine and a Pd catalyzed asymmetric allylic alkylation (AAA). The novelty of the latter protocol is its control of regioselectivity as well as absolute configuration. The trisubstituted olefin is generated using an alkene-alkyne coupling to create a trisubustituted olefin with complete control of geometry. The excellent chemo- and regioselectivity highlights the synthetic potential of this new ruthenium catalyzed process. The macrolactonization employs in situ formation of an acylketene generated by the thermolysis of a m-dioxolenone. Two strategies evolved for attachment of the side chain-one based upon olefination and a second upon olefin metathesis. The higher efficiency of the latter makes it the method of choice. A novel one pot olefin metathesis-Takai olefination protocol that should be broadly applicable is developed. The sugar is attached by a glycosylation by employing the O-trichloroacetimidate. This route provided both C-13 epimers of the macrolactone by using either enantiomeric ligand in the Pd AAA reaction. It also provided both trans-chlorocyclopropane diastereomers of callipeltoside A which allows the C-20 and C-21 configuration to be established as S and R, respectively. The convergent nature of the synthesis in which the largest piece, the macrolatone, require only 16 linear steps imparts utility to this strategy for the establishment of the structure-activity relationship. Initial biological testing demonstrates the irrelevance of the chloro substituent and the necessity of the sugar.

Efficient syntheses of thiochromans via cationic cycloadditions

alpha-(Benzotriazolyl)methyl thioethers 1a-e reacted with styrenes under Lewis acid catalysis to give novel polysubstituted thiochromans (3,4-dihydro-2H-1-benzothiopyrans) 3-14 and 16-20 in generally high yields. Most thiochromans were isolated as one diastereomer following recrystallization. The configuration and conformation of the products are predicted on the basis of their NMR data. A stepwise reaction, proceeding via a [4(+) + 2] cationic polar cycloaddition mechanism, is proposed.

Picosecond radical kinetics. Rate constants for ring openings of 2-aryl-substituted cyclopropylcarbinyl radicals

The kinetics of ring openings of a series of eight (trans-2-arylcyclopropyl)methyl radicals (1) were studied by indirect kinetic methods using Barton's PTOC esters as radical precursors and reaction with PhSeH as the competition reaction. The substituents were CF3, F, Me, and OMe located on both the para and meta positions of the aromatic ring. Syntheses of the radical precursors and the products of the radical reactions are described. Kinetics were determined between -43 and 25°C in four cases (CF3 and OMe substituents) and at 0 and 25°C in the other four cases. The rate constants at 25°C ranged from 1.0 × 1011 s-1 (p-CH3) to 4.1 × 1011 s-1 (p-CF3). The relatively large acceleration of the p-CF3 group, ca. 2.5 times as fast as the parent system with Ar = Ph, correlates well with Adam's ΔD substituent parameters but not with other radical substituent parameters. These calibrated radical rearrangements provide a new set of ultrafast reactions that can be applied in mechanistic probe studies.Key words: cyclopropylcarbinyl radical, kinetics, PTOC esters, benzeneselenol.