Asymmetric synthesis of a xanthine dehydrogenase inhibitor (S)-(−)-BOF-4272: Utility of chiral alkoxysulfonium salts

A practical synthetic method for a xanthine dehydrogenase inhibitor, (S)-(−)-BOF-4272, was established utilizing an asymmetric oxidation of diaryl sulfide BOF-4269. The oxidation of the sulfide with 1-chlorobenzotriazole carried out in the presence of 4-cyanopyridine and chiral 2-phenylcyclohexanol gave a high enantiomeric excess (73%ee). The sulfoxides in each enantiomerically pure form could be obtained by treating with alkaline hydrolysis or thermolysis of one the diastereomeric intermediate sulfonium salts (>99%de). Thus the transformation into the sulfoxides occur with virtually perfect inversion (alkaline hydrolysis) or retention (thermolysis). It is therefore possible to obtain the target sulfoxide, (S)-(−)-BOF-4272, from both the two diastereomeric sulfonium intermediates.     

Palladium‐Assisted “Aromatic Metamorphosis” of Dibenzothiophenes into Triphenylenes

Two new palladium‐catalyzed reactions of aromatic sulfur compounds enabled the conversion of dibenzothiophenes into triphenylenes in four steps. This transformation of one aromatic framework into another consists of 1) 4‐chlorobutylation of the dibenzothiophene to form the corresponding sulfonium salt, 2) palladium‐catalyzed arylative ring opening of the sulfonium salt with a sodium tetraarylborate, 3) an intramolecular S_N2 reaction to form a teraryl sulfonium salt, and 4) palladium‐catalyzed intramolecular C? S/C? H coupling through electrophilic palladation. Symmetrical as well as unsymmetrical triphenylenes of interest were synthesized in a tailor‐made fashion in satisfactory overall yields.     

Syntheses and Peculiar Behavior in Solutions of Optically Active Telluronium Salts

A diastereomeric (epimeric) mixture of ethylmethylphenyltelluronium (1S)-(+)-camphor-10-sulfonate (dia.-1) was optically resolved by fractional recrystallization into the diastereomerically pure isomers (R)(Te)-1 and (S)(Te)-1. The absolute configurations of the isomers were determined by the X-ray crystallographic analysis of (R)(Te)-1. Enantiomerically pure (R)-ethylmethylphenyltelluronium perchlorate, tetrafluoroborate, p-chlorobenzenesulfonate, bornane-10-sulfonate, tetraphenylborate, and picrylsulfonate (R)-2-7 were isolated, respectively, by anion-exchange reactions of diastereomerically pure (R)(Te)-1. The optically active telluronium salts were found to show peculiar optical properties on their specific rotations and circular dichroism spectra in solutions compared with those of the corresponding sulfonium and selenonium salts. On the basis of NMR studies, the behavior on the optical properties of the optically active telluronium salts was found to be caused by a strong solvation in polar solvents.     

Evidence for intermolecular interaction between sulfonium and sulfide sulfur atoms and its application to synthesis of cyclic bis(disulfide) dimer

On the basis of the remote Pummerer reaction of p-bis(alkylthio)-aromatic S-oxides, the intermolecular interaction between the sulfonium and sulfide sulfur atoms is described. (1) In marked contrast to the Pummerer reaction of 1b-d(3) with (CF(3)CO)(2)O (J. Org. Chem. 1999, 64, 3190-3195), the reaction of 3,3',5,5'-tetramesityl-4-(trideuteriomethylsulfinyl)-4'-(methylthio)biphenyl (1a-d(3)) as a sterically hindered analogue of 1b gave only 2a-d(2). (2) Both reactions of the two unsymmetrical regioisomers of 1-(ethylthio)-4-(methylthio)benzene S-oxide (5a and 5b) with (CF(3)CO)(2)O afforded a mixture of the mono-Pummerer products 6a and 6b, the bis-Pummerer product 7, and the bis-sulfide 8 in a similar ratio. The quenching at the initial stage of both reactions produced 5a, 5b, 8, and the bis-sulfoxide 10 in a similar ratio. These results indicate the equilibrium in the intermolecular interaction between the sulfur atoms. (3) The reaction of the p-bis(benzylthio)-aromatic S-oxide 16 with (CF(3)SO(2))(2)O gave the cyclic bis(disulfide) dimer 17 for the diphenyl sulfide and diphenylmethane spacers or the cyclic tetrakis(disulfide) tetramer 19 for the benzene and biphenyl spacers via the debenzylation of an intermolecular dithia dication. The cyclic bis(dithia dication) dimer A resulting from the intermolecular interaction between the sulfonium and sulfide sulfur atoms is proposed as an intermediate throughout the present reactions.     

Optically pure trans-2,3-disubstituted N-sulfinyl aziridines. Regio- and stereoselective opening mediated by the sulfinyl group

A new entry to optically pure trans-2,3-disubstituted N-sulfinyl aziridines starting from 1,2-aminosulfides, involving formation of a sulfonium salt intermediate followed by intramolecular nucleophilic attack by the sulfinamide nitrogen atom, is reported. The regio- and stereoselective opening of the aziridine ring can be achieved by anchimeric assistance of the sulfinyl group.     

Crystal and molecular structure of the levorotatory (1R,2S)-ephedrinium (S)-t-butylsulfinylacetate: a definitive proof of the absolute configuration of enantiomeric t-butyl methyl sulfoxides

The levorotatory enantiomer of t-butylsulfinylacetic acid 3 was obtained in the reaction of the α-carbanion of (+)-t-butyl methyl sulfoxide 1 with carbon dioxide. The same enantiopure form of the acid 3 was isolated from its diastereomerically pure levorotatory salt 5 with (−)-(1R,2S)-ephedrine. The structure of this salt was determined by X-ray analysis and the absolute configuration (S) at sulfur was ascribed to the t-butylsulfinylacetate anion. Consequently, the absolute configuration (S) was assigned to the acid (−)-3 and its precursor (+)-t-butyl methyl sulfoxide 1.     

Stereoselective addition of alpha-sulfinyl carbanions to N-p-tolylsulfinylketimines: synthesis of optically pure 1,2,2'-trialkyl-2-aminoethanols

The reactions of lithium carbanions derived from both enantiomers of methyl (1) and ethyl p-tolyl sulfoxide (2) with (S)-N-arylsulfinylketimines 3 and 4 took place in a highly stereoselective manner and good isolated yields. The configuration of the carbon bonded to nitrogen relies exclusively on the N-sulfinylimine configuration. When ethyl p-tolyl sulfoxide (2) is use as nucleophile, two chiral centers are created simultaneously, where the configuration of the carbon bonded to the sulfur is mainly controlled by 2. The asymmetric induction increases with the temperature, being total at room temperature in the case of the matched pair of reactants. A non-oxidative Pummerer reaction on the obtained aminosulfoxides allows a straightforward synthesis of optically pure 1,2-ethanolamines with one or two chiral centers, including amino alcohols with a bulky quaternary carbon bonded to the amine group.     

An optically active vinyl sulfoxide copolymer and the configuration of sulfoxide adjacent to radical or anionic sites

Optically active vinyl p-tolyl sulfoxide was synthesized and copolymerized with styrene to produce an optically active copolymer. The question of the configuration of sulfur in a sulfoxide when adjacent to a radical site is discussed. The configuration of sulfur in a sulfoxide is proven to be nonplanar when adjacent to an anionic site.     

Asymmetric synthesis of cyclopropyl phosphonates using chiral terpenyl sulfonium and selenonium ylides

The asymmetric cyclopropanation of a vinylphosphonate using optically active sulfonium and selenonium ylides derived from (−)-menthol and (+)-limonene was developed. The ylides were generated in situ by the reaction of the corresponding sulfonium or selenonium salt in the presence of potassium carbonate or DBU as a base. The transfer of the CHPh and CHCO₂Et groups into the cyclopropane ring showed moderate diastereoselectivity and excellent enantioselectivity (up to 99:1) for the trans- and cis-products. The absolute configuration of phenyl cyclopropyl was assigned based on comparison to their tolyl analogues.     

Synthesis of (S)-Propranolol by Chemicoenzymatic Approach

(S)-Propranolol, [1-isopropylamino-3-(1-naphthoxy)-2-propanol], which possesses important β-adrenergic blocking activity, has been synthesized by a chemicoenzymatic approach. The 2S-absolute configuration was created by the enzyme-mediated asymmetric hydrolysis of the (±)-2-acetoxy-1-chloro-3-(1-naphthoxy)-2-naphthoxy)-2-propanol. The enzymatically produced chiral intermediate was then chemically converted to optically pure (S)-propranolol.     

The first total synthesis of (+)-spatol with natural configuration

The first total synthesis of (+)-spatol (1) with natural configuration is described. The important step utilizes the carbon-carbon bond formation with simultaneous epoxide formation by the reaction of optically pure sulfonium ylide (4) and optically pure epoxy aldehyde (5).     

Modeling substrate- and inhibitor-bound forms of liver alcohol dehydrogenase: chemistry of mononuclear nitrogen/sulfur-ligated zinc alcohol,formamide, and sulfoxide complexes

Using a mixed nitrogen/sulfur ligand possessing a single internal hydrogen bond donor (N,N-bis-2-(methylthio)ethyl-N-(6-amino-2-pyridylmethyl)amine (bmapa)), we prepared and structurally and spectroscopically characterized a series of zinc complexes possessing a single alcohol ([(bmapa)Zn(MeOH)](ClO(4))(2) (1)), formamide ([(bmapa)Zn(DMF)](ClO(4))(2) (3), [(bmapa)Zn(NMF)](ClO(4))(2) (4)), or sulfoxide ([(bmapa)Zn(DMSO)](ClO(4))(2) (7), [(bmapa)Zn(TMSO)](ClO(4))(2) (8)) ligand. X-ray crystallographic characterization was obtained for 1.MeOH, 3, 4, 7.DMSO, and 8. To enable studies of the influence of the single hydrogen bond donor amino group of the bmapa ligand on the chemistry of zinc/neutral oxygen donor binding interactions, analogous alcohol ([(bmpa)Zn(MeOH)](ClO(4))(2) (2)), formamide ([(bmpa)Zn(DMF)](ClO(4))(2) (5), [(bmpa)Zn(NMF)](ClO(4))(2) (6)), and sulfoxide ([(bmpa)Zn(DMSO)](ClO(4))(2) (9), [(bmpa)Zn(TMSO)](ClO(4))(2) (10)) complexes of the bmpa (N,N-bis-2-(methylthio)ethyl-N-(2-pyridylmethyl)amine) ligand system were generated and characterized. Of these, 2, 5, 6, and 9.2DMSO were characterized by X-ray crystallography. Solution spectroscopic methods ((1)H and (13)C NMR, FTIR) were utilized to examine the formamide binding properties of 3-6 in CH(3)CN and CH(3)NO(2) solutions. Conclusions derived from this work include the following: (1) the increased donicity of formamide and sulfoxide donors (versus alcohols) makes these competitive ligands for a cationic N/S-ligated zinc center, even in alcohol solution, (2) the inclusion of a single internal hydrogen bond donor, characterized by a heteroatom distance of approximately 2.80-2.95 A, produces subtle structural perturbations in N/S-ligated zinc alcohol, formamide, or sulfoxide complexes, (3) the heteroatom distance of a secondary hydrogen-bonding interaction involving the oxygen atom of a zinc-coordinated alcohol, formamide, and sulfoxide ligand is reduced with increasing donicity of the exogenous ligand, and (4) formamide displacement on a N/S-ligated zinc center is rapid, regardless of the presence of an internal hydrogen bond donor. These results provide initial insight into the chemical factors governing the binding of a neutral oxygen donor to a N/S-ligated zinc center.     

Novel synthetic approach for optical resolution of cryptophanol-A: a direct access to chiral cryptophanes and their chiroptical properties

The separation by crystallization of the pair of cryptophane diastereomers 1 a and 1 b, obtained in 1:1 ratio by treating racemic anti cryptophanol-A (2) with (-)-camphanic acid chloride, provided a substantial amount of optically pure material (diastereomeric excess>98 %). Subsequent hydrolysis afforded the optically pure cryptophanol-A enantiomers (+)-2 and (-)-2, which were submitted to nucleophilic substitution reactions to provide cryptophane-A (+)-3 and cryptophane monoester (-)-4 in optically pure form. The chiroptical properties of the new cryptophanes 1-4 were investigated by using circular dichroism spectroscopy, and the absolute configuration of the molecules was clearly established. These new cryptophanes represent additional interesting examples for studying the Cotton effect of interacting multichromophoric systems. Moreover, this novel approach presents numerous advantages over the other methods developed so far to obtain optically pure cryptophanes, and compounds (-)-2, (+)-2, and (-)-4 can give access to new enantiopure functionalized cryptophanes with host-guest properties similar to those of cryptophane-A.     

Electrophilic Reaction of Phenyl Bis(Phenylthio) Sulfonium Cation as an Active Species for the Oxidative Polymerization of Diphenyl Disulfide

Computer modeling predicts that the methyl bis(methylthio) sulfonium cation can act as an efficient electrophile for sulfide bond formation in which the sulfur atoms at the side position of the cation react with the phenyl ring of an aromatic molecule. The electrophilic reaction mechanism of phenyl bis-(phenylthio) sulfonium cation with anisole was examined using computer simulation. The reaction between phenyl bis- (phenylthio) sulfonium cation, which is a homogeneous structure of thecation, and anisole shows the efficient formation of 4-phenylthioanisole with diphenyl disulfide as a by-product. In the oxidative polymerization of diphenyl disulfide, the formation process of polyp-phenylene sulfide) includes an elementary reaction between the phenylthio group at each side position of the phenyl bis(phenylthio) sulfonium cation and the carbon at the para position of the phenyl ring.     

(4-苯硫基-苯基)二苯基硫鎓六氟磷酸盐的合成研究

以P₂O₅为脱水剂,甲烷磺酸为溶剂,二苯亚砜与二苯硫醚反应制备了(4-苯硫基-苯基)二苯基硫六氟磷酸盐.对产物进行了元素分析、紫外光谱、红外光谱、气-质联用和核磁共振的结构确证.该硫盐对环氧树脂具有良好的固化性能.     

4-Hydroxy-2-quinolones. 38. Synthesis, structure, and anticonvulsant activity of optically active 1-phenylethylamides of 1-R-4-hydroxy-2-oxo-3-quinolinecarboxylic acids

A synthesis is reported for optically pure antipodes of 1-phenylethylamides of 1-R-4-hydroxy-2-oxo-3-quinolinecarboxylic acids. An attempt was made to establish the absolute configuration of these products by X-ray diffraction crystallographic analysis. The anticonvulsant activity of the S-enantiomers was studied.For Communication 37, see ref. [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 55–63, January, 2000.     

Pulse Radiolytic Studies of 1-Halo-2-(methylthio)ethanes in Hexane and 1,2-Dichloroethane: Formation of an Intermolecular Species with a Three-Electron Bond between Sulfur and Iodine

1-Iodo-2-(methylthio)ethane was synthesized via a ring-opening reaction of thiirane with MeI in MeCN. The S-centered radical cation of this compound undergoes an intermolecular stabilization with the I substituent of a second unattacked substrate molecule to yield an bonded radical cation. The oxidation was initiated by solvent radical cations in irradiated 1,2-dicloroethane and hexane solutions. The 2ρ/ρ* three-electron-bonded species exhibits an optical absorption band at 410 nm, detectable by pulse radiolysis. During its decay, a new, longer-lived absorption band is formed at 380 nm which is assigned to . The latter is suggested to result from anchimeric assistance in the generation of a cyclic sulfonium salt. The radical cations of 1-bromo-and 1-chloro-2-(methylthio)ethane are assumed to undergo raped cyclization to the sulfonium salt without stabilization in any intermolecular S-Br or S-Cl interaction.     

Synthesis and antifungal activities of a series of (1,2-disubstituted vinyl)imidazoles.

A series of vinylimidazoles containing a hetero atom such as sulfur or oxygen at a beta-position of the vinyl group was prepared and the antifungal activities were tested. It was found that sulfur-substituted derivatives such as (E)-1-[2-(methylthio)-1-[2-(pentyloxy)phenyl]ethenyl]-1H-imidazole (5a-5) and (E)-1-[1-[2-(hexyloxy)phenyl]-2-(methylthio)ethenyl]-1H-imidazole (5a-6) showed excellent antifungal activities against dermatophytes and yeast cells. The stereochemistry of the hydrochloride salt of 5a-5 was determined by X-ray crystallography. The structure-activity relationships were discussed.     

Bis(methylthio)tetracenes: synthesis, crystal-packing structures, and OFET properties

5,12-Bis(methylthio)tetracene (2) and 5,11-bis(methylthio)tetracene (3) were synthesized. DFT calculations indicate that the HOMO and LUMO energy levels of 2 and 3 are lowered by 0.13-0.24 eV and their HOMO-LUMO energy gaps are reduced by 0.1 eV relative to those of tetracene. X-ray crystallographic data revealed that 2 is arranged as a result of a 1-D slipped-cofacial π-stacking with S-S and S-π interactions, similar to the packing arrangement of 6,13-bis(methylthio)pentacene (1), whereas 3 exhibits a herringbone packing arrangement without S-S interactions. The OFET devices fabricated using spin-coated films of soluble 1 and 2, with a bottom-contact device configuration, exhibited hole mobilities as high as 1.3 × 10(-2) and 4.0 × 10(-2) cm(2) V(-1) s(-1) with current on/off ratios of over 10(5) and 10(4), respectively.     

Interactions of Omeprazole and Precursors with beta-Cyclodextrin Host Molecules

β-Cyclodextrin (β-CD) was mixed with omeprazoleand some of its precursors in aqueous or water/ethanol solutions, and theresulting crystalline products have been characterized by elemental analysis,thermogravimetry, powder X-ray diffraction (XRD), FTIR and ¹³C CP MAS NMRspectroscopy. In the case of2-chloromethyl-4-methoxy-3,5-dimethylpyridine...HCl, itwas found that the solid product always consisted of pure β-CD hydrate. On the other hand, a 2 : 1(host-to-guest) inclusion complex was obtained between β-CD and2-methoxy-2-mercaptobenzimidazole. The thioether intermediate5-methoxy-2-[(3,5-dimethyl-4-methoxy-2-pyridine)methylthio]-1H-benzimidazoleand its sulfoxide derivative (omeprazole) both formed 1 : 1 inclusion complexes with β-CD. Powder XRD indicates that the crystal packing of β-CDhost molecules is herringbone-type for the 2 : 1 complex, and channel-typefor the 1 : 1 complexes. Ab initio calculations were carried out toinvestigate thehost–guest interactions. It was found that the interactionwith the pyridine fragment is wholly repulsive, due to the presence of severalring substituents. On the other hand, the inclusion of the benzimidazole fragmentis energetically favored, but highly dependent on the orientation of thesubstituent methoxy group.