Trivalent sulfonium compounds (TSCs): Tetrahydrothiophene-based amphiphiles exhibit similar antimicrobial activity to analogous ammonium-based amphiphiles

Recent advances in the development of quaternary ammonium compounds (QACs) have focused on new structural motifs to increase bioactivity, but significantly less studied has been the change from ammonium- to sulfonium-based disinfectants. Herein, we report the synthesis of structurally analogous series of quaternary ammonium and trivalent sulfonium compounds (TSCs). The bioactivity profiles of these compounds generally mirror each other, and the antibacterial activity of sulfonium-based THT-18 was found to be comparable to the commercial disinfectant, BAC. The development of these compounds presents a new avenue for further study of disinfectants to combat the growing threat of bacterial resistance.

Sulfonium salts as leaving groups for aromatic labelling of drug-like small molecules with fluorine-18

Positron emission tomography (PET) is unique in that it allows quantification of biochemical processes in vivo, but difficulties with preparing suitably labelled radiotracers limit its scientific and diagnostic applications. Aromatic [(18)F]fluorination of drug-like small molecules is particularly challenging as their functional group compositions often impair the labelling efficiency. Herein, we report a new strategy for incorporation of (18)F into highly functionalized aromatic compounds using sulfonium salts as leaving groups. The method is compatible with pharmacologically relevant functional groups, including aliphatic amines and basic heterocycles. Activated substrates react with [(18)F]fluoride at room temperature, and with heating the reaction proceeds in the presence of hydrogen bond donors. Furthermore, the use of electron rich spectator ligands allows efficient and regioselective [(18)F]fluorination of non-activated aromatic moieties. The method provides a broadly applicable route for (18)F labelling of biologically active small molecules, and offers immediate practical benefits for drug discovery and imaging with PET.

Synthesis of triphenylsulfonium triflate bound copolymer for electron beam lithography

Photoacid generator (PAG) has been widely used as a key component in photoresist for high-resolution patterning with high sensitivity. A novel acrylic monomer, triphenylsulfonium salt methyl methacrylate (TPSMA), was synthesized and includes triphenylsulfonium triflate as a PAG. The poly(MMA-co-TPSMA) (PMT) as a polymer-bound PAG was synthesized with methyl methacrylate (MMA) and TPSMA for electron beam lithography. Characterization of PMT was carried out by NMR and FTIR. The molecular weight was analyzed by GPC. Thermal properties were studied using TGA and DSC. Thecharacterization results were in good agreement with corresponding chemical compositions and thermal stability. PMT was subsequently employed in electron beam lithography and its lithographic performance was confirmed by FE-SEM. This PMT was accomplished to improve the lithographic performance including sensitivity, line width roughness (LWR) and resolution. We found that PMT was capable of 20 nm negative tone patterns with better sensitivity than hydrogensilsesquioxane (HSQ) which is a conventional negative tone resist.

PolyNaSS grafting on titanium surfaces enhances osteoblast differentiation and inhibits Staphylococcus aureus adhesion

Titanium surface modifications to simultaneously prevent bacterial adhesion but promote bone-cell functions could be highly beneficial for improving implant osseointegration. In the present in vitro study, the effect of sulfonate groups on titanium surfaces was investigated with respect to both S. aureus adhesion and osteoblast functions pertinent to new bone formation. Commercial pure titanium (cpTi) squares were oxydized (Tiox), grafted with poly(sodium styrene sulfonate) groups (Tigraft) by covalent bonding using radical polymerization, and were characterized by infrared spectroscopy (HATR-FTIR) and colorimetry. Bacterial adhesion study showed that Tigraft exhibited high inhibition of S. aureus adhesion S at levels >90 %, when compared to cpTi (P < 0.05). In contrast osteoblasts adhesion was similar on all three titanium surfaces. While the kinetics of cell proliferation were similar on the three titanium surfaces, Alkaline phosphatase-specific activity of osteoblasts cultured on Tigraft surfaces was twofold higher than that observed on either on Tiox or cpTi surfaces (P < 0.01). More importantly, the amount and the distribution of calcium-containing nodules was different. The total area covered by calcium-containing nodules was 2.2-fold higher on the Tigraft as compared to either Tiox or cpTi surfaces (P < 0.01). These results provide evidence that poly(sodium styrene sulfonate) groups grafting on cpTi simultaneously inhibits bacteria adhesion but promote osteoblast function pertinent to new bone formation. Such modified titanium surfaces offer a promising strategy for preventing biofilm-related infections and enhancing osteointegration of implants in orthopaedic and dental applications.

Stereoelectronic effects determine oxacarbenium vs β-sulfonium ion mediated glycosylations

Activation of a glycosyl donor protected with a 2-O-(S)-(phenylthiomethyl)benzyl ether chiral auxiliary results in the formation of an anomeric β-sulfonium ion, which can be displaced with sugar alcohols to give corresponding α-glycosides. Sufficient deactivation of such glycosyl donors by electron-withdrawing protecting groups is, however, critical to avoid glycosylation of an oxacarbenium ion intermediate. The latter type of glycosylation pathway can also be suppressed by installing additional substituents in the chiral auxiliary.

Synthesis of analogues of salacinol containing a carboxylate inner salt and their inhibitory activities against human maltase glucoamylase

The syntheses of analogues of the naturally occurring glycosidase inhibitor, salacinol, containing a carboxylate inner salt are described. Salacinol is a sulfonium ion with an internal sulfate counterion. The synthetic strategy relies on the nucleophilic attack of 1,4-anhydro-2,3,5-tri-O-benzyl-4-thio-D- or L-arabinitol at the least hindered carbon of 4,5-anhydro-2,3-O-isopropylidene-D-ribonic acid benzyl ester to yield coupled adducts. Deprotection of the coupled products gives the target compounds. The compound derived from D-arabinitol inhibits recombinant human maltase glucoamylase, one of the key intestinal enzymes involved in the breakdown of glucose oligosaccharides in the small intestine, with a Ki value of 10+/-1 microM.

Synthesis of S-alkylated sulfonium-ions and their glucosidase inhibitory activities against recombinant human maltase glucoamylase

The syntheses of nine S-alkylated, cyclic sulfonium-ions with varying alkyl chain lengths, as mimics of N-alkylated imino sugars, and their glucosidase inhibitory activities are described. The target compounds were synthesized by alkylation of 2,3,5-tri-O-benzyl-1,4-anhydro-4-thio-d-arabinitol at the ring sulfur atom using various alkyl halides, followed by deprotection using boron trichloride. Enzyme inhibitory assays against recombinant human maltase glucoamylase (MGA), a critical enzyme in the small intestine involved in the breakdown of glucose oligosaccharides into glucose itself, shows that they are effective inhibitors of MGA with K(i) values ranging from 6 to 75 microM.

New electrophilic difluoromethylating reagent

A new electrophilic difluoromethylating reagent has been developed. The S-(difluoromethyl)diarylsulfonium tetrafluoroborate has been shown to be effective for the introduction of an electrophilic difluoromethyl group into the following nucleophiles: sulfonic acids, tertiary amines, imidazole derivatives, and phosphines. The reagent failed to transfer the difluoromethyl group to phenols, carbon nucleophiles, and primary and secondary amines.

S-Chiral Sulfinamides as Highly Enantioselective Organocatalysts

Easily accessible chiral sulfinamide 2 has been developed as the first highly efficient and enantioselective organocatalyst relying solely on a chiral sulfur center for stereochemical induction. In the presence of 20 mol % of 2, a broad range of N-aryl ketimines 1 were reduced by trichlorosilane to produce amines 3 in high yield and enantioselectivity. [reaction: see text]

Facile synthesis of sulfonium ion derivatives of 1,5-anhydro-5-thio-l-fucitol as potential α-l-fucosidase inhibitors

Five sulfonium ion derivatives with 1,5-anhydro-5-thio-L-fucitol as a core structure were efficiently synthesized as potential alpha-L-fucosidase inhibitors. The key unit, the tri-O-benzyl derivative of L-fucitol, was readily synthesized from methyl alpha-D-mannopyranoside. Alkylation with methyl iodide or 5-methoxycarbonyl-1-pentyl iodide in acetonitrile containing AgBF4 afforded the corresponding alkylated sulfonium tetrafluoroborates. Alternatively, ring opening of three 1,3-cyclic sulfates in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) containing K2CO3 afforded the corresponding zwitterionic sulfonium sulfates.

Synthesis of a sulfonium ion analogue of the glycosidase inhibitor swainsonine

The synthesis of a bicyclic sulfonium ion analogue of a naturally occurring indolizidine alkaloid, swainsonine, in which the bridgehead nitrogen atom is replaced by a sulfonium ion, has been achieved by a multistep synthesis starting from (2S,3S,4R)-2,3-dibenzyloxy-4-formaldehyde-thiolane. The synthetic strategy relies on the intramolecular displacement of a leaving group on a pendant acyclic chain by a cyclic thioether. This bicyclic sulfonium salt provides a candidate with which to further probe the hypothesis that a sulfonium salt carrying a permanent positive charge would be an effective glycosidase inhibitor.

Catalytic enantioselective sulfinyl transfer using cinchona alkaloid catalysts

[reaction: see text] Practical reaction conditions for the catalytic enantioselective synthesis of sulfinate esters are reported. Commercially available cinchona alkaloids were found to be superior catalysts for the sulfinyl transfer reaction of tert-butanesulfinyl chloride and a variety of benzyl alcohols. Sulfinyl transfer with 2,4,6-trichlorobenzyl alcohol and 10 mol % of the commercially available, inexpensive catalyst quinidine provided the pure sulfinate ester product in 92% isolated yield and with 90% ee.

Synthesis of Sulfonium Sulfate Analogues of Disaccharides and Their Conversion to Chain-Extended Homologues of Salacinol: New Glycosidase Inhibitors

Four chain extended homologues of salacinol, a naturally occurring glycosidase inhibitor, were prepared for evaluation as inhibitors of glucosidase enzymes involved in the breakdown of carbohydrates. The syntheses involved the reactions of 1,4-anhydro-2,3,5-tri-O-benzyl-4-thio-D-arabinitol with cyclic sulfate derivatives of different monosaccharides. Debenzylation of the products afforded the novel sulfonium sulfate derivatives of D-glucose, D-galactose, D-arabinose, and D-xylose that are of interest in their own right as glycosidase inhibitors. Reduction to the corresponding alditols then afforded the homologues of salacinol containing polyhydroxylated, acyclic chains of 5- and 6-carbons, differing in stereochemistry at the stereogenic centers. Three of the chain-extended homologues inhibited recombinant human maltase glucoamylase, one of the key intestinal enzymes involved in the breakdown of glucose oligosaccharides in the small intestine, with Ki values in the low micromolar range, of approximately the same magnitude as salacinol, thus providing lead candidates for the treatment of Type 2 diabetes.

Synthesis and Conformational Analysis of Bicyclic Sulfonium Salts. Structures Related to the Glycosidase Inhibitor Australine

The syntheses of eight sulfonium compounds with structures related to the naturally occurring pyrrolizidine alkaloid, australine, in which the bridgehead nitrogen atom is replaced by a sulfonium ion, are described. The synthetic strategy relies on the intramolecular attack of a cyclic thioether across a terminal double bond in the presence of a suitable electrophile. We postulate that these compounds, having a permanent positive charge on the sulfur atom, will mimic the highly unstable oxacarbenium ion transition state in a glycosidase-catalyzed hydrolysis reaction. The conformational preferences of these compounds, based on analysis of 1H-1H vicinal coupling constants and 1D-NOESY data, are attributed to both steric and electrostatic interactions. These compounds will be used in the study of structure-activity relationships with glycosidase enzymes.

Synthesis of C-5-thioglycopyranosides and their sulfonium derivatives from 1-C-(2′-oxoalkyl)-5-S-acetylglycofuranosides

1-C-(2'-oxoalkyl)-5-S-acetylglycofuranosides of L-arabinose, D-ribose, and D-xylose were converted to 1-C-(2'-oxoalkyl)-5-thioglycopyranosides by base treatment. The transformation was achieved through beta-elimination to an acyclic alpha,beta-conjugated aldehyde (ketone or ester), followed by an intramolecular hetero-Michael addition by the 5-thiol group. The cycloaddition was highly stereoselective in favor of an equatorial 1-C-substitution. The resultant C-5-thioglycopyranosides were further converted to the sulfonium salts by treatment with cyclic sulfate and methyl iodide. Two sulfonium isomers were obtained due to the presence of both S-axial and S-equatorial substitutions. We observed that the chemical shifts of both C-1 and C-5 in the S-axial substituted sulfonium sugars are always shifted up-field (5-10 ppm) in comparison to those in the S-equatorial substitutions (deltaC 49-53 ppm vs 42-45 ppm at C-1 and 37-42 ppm vs 32-35 ppm at C-5), which provides an easy way for determination of the stereochemistry.

Insight into the Polar Reactivity of the Onium Chalcogen Analogues ofS-Adenosyl-l-methionine†

S-Adenosyl-L-methionine (AdoMet) is one of Nature's most diverse metabolites, used not only in a large number of biological reactions but amenable to several different modes of reactivity. The types of transformations in which it is involved include decarboxylation, electrophilic addition to any of the three carbons bonded to the central sulfur atom, proton removal at carbons adjacent to the sulfonium, and reductive cleavage to generate 5'-deoxyadenosyl 5'-radical intermediates. At physiological pH and temperature, AdoMet is subject to three spontaneous degradation pathways, the first of which is racemization of the chiral sulfonium group, which takes place in a pH-independent manner. The two remaining pathways are pH-dependent and include (1) intramolecular attack of the alpha-carboxylate group onto the gamma-carbon, affording L-homoserine lactone (HSL) and 5'-methylthioadenosine (MTA), and (2) deprotonation at C-5', initiating a cascade that results in formation of adenine and S-ribosylmethionine. Herein, we describe pH-dependent stability studies of AdoMet and its selenium and tellurium analogues, Se-adenosyl-L-selenomethionine and Te-adenosyl-L-telluromethionine (SeAdoMet and TeAdoMet, respectively), at 37 degrees C and constant ionic strength, which we use as a probe of their relative intrinsic reactivities. We find that with AdoMet intramolecular nucleophilic attack to afford HSL and MTA exhibits a pH-rate profile having two titratable groups with apparent pK(a) values of 1.2 +/- 0.4 and 8.2 +/- 0.05 and displaying first-order rate constants of <0.7 x 10(-6) s(-1) at pH values less than 0.5, approximately 3 x 10(-6) s(-1) at pH values between 2 and 7, and approximately 15 x 10(-6) s(-1) at pH values greater than 9. Degradation via deprotonation at C-5' follows a pH-rate profile having one titratable group with an apparent pK(a) value of approximately 11.5. The selenium analogue decays significantly faster via intramolecular nucleophilic attack, also exhibiting a pH-rate profile with two titratable groups with pK(a) values of approximately 0.86 and 8.0 +/- 0.1 with first-order rate constants of <7 x 10(-6) s(-1) at pH values less than 0.9, approximately 32 x 10(-6) s(-1) at pH values between 2 and 7, and approximately 170 x 10(-6) s(-1) at pH values greater than 9. Degradation via deprotonation at C-5' proceeds with one titratable group displaying an apparent pK(a) value of approximately 14.1. Unexpectedly, TeAdoMet did not decay at an observable rate via either of these two pathways. Last, enzymatically synthesized AdoMet was found to racemize at rates that were consistent with earlier studies (Hoffman, J. L. (1986) Biochemistry 25, 4444-4449); however, SeAdoMet and TeAdoMet did not racemize at detectable rates. In the accompanying paper, we use the information obtained in these model studies to probe the mechanism of cyclopropane fatty acid synthase via use of the onium chalcogens of AdoMet as methyl donors.

Asymmetric synthesis of cyclic alpha-amino phosphonates using masked oxo sulfinimines (N-sulfinyl imines)

Five-, six-, and seven-membered cyclic alpha-amino phosphonates, amino acid surrogates, are prepared in enantiomerically pure form via the highly diastereomeric addition of metal phosphonates to masked oxo sulfinimines. Hydrolysis of the resulting masked oxo alpha-amino phosphonates followed by reduction of the intermediate cyclic imino phosphonates affords the title compounds in good yield.

Ruthenium Porphyrin Catalyzed Tandem Sulfonium/Ammonium Ylide Formation and [2,3]-Sigmatropic Rearrangement. A Concise Synthesis of (±)-Platynecine

meso-Tetrakis(p-tolyl)porphyrinatoruthenium(II) carbonyl, [Ru(II)(TTP)(CO)], can effect intermolecular sulfonium and ammonium ylide formation by catalytic decomposition of diazo compounds such as ethyl diazoacetate (EDA) in the presence of allyl sulfides and amines. Exclusive formation of [2,3]-sigmatropic rearrangement products (70-80% yields) was observed without [1,2]-rearrangement products being detected. The Ru-catalyzed reaction of EDA with disubstituted allyl sulfides such as crotyl sulfide produced an equimolar mixture of anti- and syn-2-(ethylthio)-3-methyl-4-pentenoic acid ethyl ester. The analogous "EDA + N,N-dimethylcrotylamine" reaction afforded a mixture of anti- and syn-2-(N,N-dimethylamino)-3-methyl-4-pentenoic acid ethyl esters with a diastereoselectivity of 3:1. The observed catalytic activity of [Ru(II)(TTP)(CO)] for the ylide [2,3]-sigmatropic rearrangement is comparable to the reported examples involving [Rh(2)(CH(3)CO(2))(4)] and [Cu(acac)(2)] as catalyst. Similarly, cyclic sulfonium and ammonium ylides can be produced by intramolecular reaction of a diazo group tethered to allyl sulfides and amines under the [Ru(II)(TTP)(CO)]-catalyzed reaction conditions. The subsequent [2,3]-sigmatropic rearrangement of the cyclic ylides furnished 2-allyl-substituted sulfur and nitrogen heterocycles in good yields (>90%). By employing [Ru(II)(TTP)(CO)] as catalyst, the cyclic ammonium ylide [2,3]-sigmatropic rearrangement reaction was successfully applied for the total synthesis of (+/-)-platynecine starting from cis-2-butenediol.

Synthesis of Alkylated Deoxynojirimycin and 1,5-Dideoxy-1,5-iminoxylitol Analogues: Polar Side-Chain Modification, Sulfonium and Selenonium Heteroatom Variants, Conformational Analysis, and Evaluation as Glycosidase Inhibitors

The syntheses of N-alkylated deoxynojirimycin and 1,5-dideoxy-1,5-iminoxylitol derivatives having either a D- or an L-erythritol-3-sulfate functionalized N-substituent are reported. The alkylating agent used was a cyclic sulfate derivative, whereby selective attack of the nitrogen atom at the least hindered primary center afforded the desired ammonium salt. In aqueous solution, these salts were configurationally labile at the ammonium center. Sulfonium and/or selenonium analogues of the ammonium salts were prepared by analogous reactions. The chalcogen salts were obtained as mixtures of diastereomers, separable in some cases, differing only in the stereochemistry at the configurationally stable sulfur or selenium atoms. Proof of configuration and conformation of each compound was obtained by detailed NMR experiments. The compounds are six-membered ring analogues of salacinol, a known sulfonium-salt glucosidase inhibitor. Evaluation of the target compounds for enzyme inhibition of the glucosidase enzyme glucoamylase G2 indicated that these compounds were either inactive or, at best, only weak inhibitors of maltose hydrolysis.

Synthesis of a novel class of sulfonium ions as potential inhibitors of UDP-galactopyranose mutase

Two sulfonium salts of 1,4-anhydro-4-thio-D-galactitol, with structures related to the known sulfonium salt glycosidase inhibitor, salacinol, have been synthesized as potential inhibitors of UDP-galactopyranose mutase. The synthetic strategy relies on the alkylation reaction of 1,4-anhydro-2,3,5,6-tetra-O-benzyl-4-thio-D-galactitol at the sulfur atom with 2,4-O-benzylidene-D- or -L-erythritol-1,3-cyclic sulfate. In each case, the reaction proceeded stereoselectively to yield only one stereoisomer at the stereogenic sulfur atom. The effect of the polar solvent, 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), in promoting high-yielding reactions is highlighted. The target compounds are then obtained by hydrogenolysis.

Improved asymmetric synthesis of aziridine 2-phosphonates using (S)-(+)-2,4,6-trimethylphenylsulfinamide

The aza-Darzens reaction of lithium diethyl iodomethylphosphonate with enantiopure N-(2,4,6-trimethylphenylsulfinyl)imines affords a single diastereomeric N-sulfinylaziridine 2-phosphonate which, on treatment with MeMgBr, gives the corresponding NH-aziridine 2-phosphonate chiral building blocks. An improved asymmetric synthesis of (S)-(+)-2,4,6-trimethylphenylsulfinamide is also given.

A new class of glycosidase inhibitor: synthesis of salacinol and its stereoisomers

Salacinol (4) is one of the active principles in the aqueous extracts of Salacia reticulata that are traditionally used in Sri Lanka and India for the treatment of diabetes. The syntheses of salacinol (4), the enantiomer of salacinol (5), and a diastereomer (7) are described. The synthetic strategy relies on the selective nucleophilic attack of 2,3,5-tri-O-benzyl-1,4-anhydro-4-thio-D- or L-arabinitol at C-1 of 2,4-O-benzylidene D- or L-erythritol-1,3-cyclic sulfate. The work serves to resolve the ambiguity about the exact structure of salacinol and establishes conclusively the structure of the natural product.

Synthesis and antiallergic activity of dimethyl-2-(phenylcarbamoyl)ethylsulfonium p-toluenesulfonate derivatives

The derivatives of dimethyl-2-(phenylcarbamoyl)ethylsulfonium p-toluenesulfonates were synthesized and evaluated for antiallergic activity. The 2,3-dihydroxyethoxy group was introduced to the phenyl ring from the standpoint of lipophilicity and electronic effects of substituent. The IgE-induced rat passive cutaneous anaphylaxis (PCA) was inhibited by oral administration of several substituted 2-[(4-propoxyphenyl)carbamoyl]ethyldimethylsulfonium p-toluenesulfonate derivatives. Among them (+/-)-2-[N-[4-(3-ethoxy-2-hydroxypropoxy)phenyl]carbamoyl]ethyldimeth ylsulfonium p-toluenesulfonate (1a, IPD-1151T) was found to possess considerable activity in the PCA test, and it was launched as Suplatast tosilate in Japan.

Cardioselective ammonium, phosphonium, and sulfonium analogues of alpha-tocopherol and ascorbic acid that inhibit in vitro and ex vivo lipid peroxidation and scavenge superoxide radicals

Analogues of alpha-tocopherol and ascorbic acid with permanently cationic substituents, i.e., phosphonium (8, 9), sulfonium (11), acylhydrazinium (13, 14), and ammonium (1, 16, 21), were synthesized, and the 2R and 2S enantiomers of the alpha-tocopherol analogues 1, 8, 11, and 13 were separated. The compounds were found to scavenge lipoperoxyl and superoxide radicals in vitro and accumulate in heart tissue (cardioselectivity) as demonstrated by measurement of ex vivo inhibition of lipid peroxidation in mouse heart homogenates and confirmed by HPLC determination of drug concentrations for 1 and 11. The 2R and 2S enantiomers of 1 inhibited ex vivo lipid peroxidation to an equal extent. Thus the in vivo uptake into myocytes (cardioselectivity) is independent of the geometry at the chiral center and common to permanently cationic compounds.

The interaction of ammonium, sulfonium, and sulfide analogues of metoclopramide with the dopamine D2 receptor

A series of permanently charged ammonium and sulfonium analogues of metoclopramide as well as a permanently uncharged sulfide analogue were synthesized and evaluated for their ability to inhibit apomorphine-induced responses on mouse striatal slices. Three of the four permanently charged analogues were found to inhibit apomorphine's effects, although at higher concentrations than either metoclopramide or its dimethyl analogue. In contrast, the sulfide analogue was inactive at concentrations up to 100 microM. These findings are consistent with earlier studies of chlorpromazine and sulpiride analogues and provide further evidence that dopamine antagonists bind in their charged molecular forms to anionic sites on the D2 receptor. Further, the results of this study in conjunction with those of our earlier sulpiride study would seem to indicate that differences in the biological profiles of metoclopramide, a type 1 benzamide useful as a gastric prokinetic agent, and sulpiride, a type 2 benzamide useful for its antipsychotic effects, are not due to any appreciable differences in the binding of the basic nitrogen atom of these molecules.

New mechanism-based inactivators of trypsin-like proteinases. Selective inactivation of urokinase by functionalized cyclopeptides incorporating a sulfoniomethyl-substituted m-aminobenzoic acid residue

In order to obtain selective suicide substrates of trypsin-like proteases including plasminogen activators, plasmin, and thrombin, a series of cyclopeptides cyclo[Arg or Lys-aB(CH2X)-Gly4], in which a substituted o- or m-aminobenzoyl group constitutes a latent electrophile, have been prepared. Treatment of the corresponding phenyl ethers cyclo[P1-aB(CH2OC6H5)-Gly4] with HBr/HOAc or R1R2S/TFA gives the bromides (X = Br) or the sulfonium salts (X = +SR1R2 with R1 = R2 = Me or R1 = Me and R2 = C6H5), respectively. These water-soluble cyclopeptides behave as time-dependent inhibitors of bovine trypsin and human urokinase (u-PA) but have no effect on tissue plasminogen activator (t-PA) and no or poor effect on plasmin and thrombin. The compounds containing a m-aminobenzoic acid residue are more efficient inactivators than their anthranilic analogues. The kinetic criteria expected for a suicide inhibition are met. A mechanism of inhibition involving the formation of a quinonimmonium methide intermediate is proposed. The activity of the inhibitors is very sensitive to the nature of the X benzylic substituent. An increased efficiency for the inactivation of human urokinase is observed with the sulfonium salts. The selectivity of the inactivation of u-PA compared to t-PA could be of therapeutical significance in controlling cell proliferation and invasion.

Ion chromatographic analysis of the purity and synthesis of sulfonium and selenonium ions

The use of single-column ion chromatography with conductometric detection was shown to be useful for the analysis of sulfonium and selenonium ions. A Hamilton PRP X-200 cation column was eluted with either solvent A (5 mM nitric acid in 30% methanol) or solvent B (4 mM nitric acid). With solvent B, trimethylsulfonium ion was separated from trimethylselenonium ion. With solvent A, amounts of trimethylsulfonium ion from 2 to 250 nmol were detected with a linear response. The retention times and response factors for a series of sulfonium ions with various organic groups were determined. In general the ions with more hydrophobic groups eluted later, but all had similar response factors. The method was shown to be useful for optimizing conditions for the synthesis of methylsulfonium ions, specifically the reaction of methyl iodide with diallyl sulfide.

Chemical synthesis and physiological activity of sulfonium analogues of platelet activating factor

Phosphatidylsulfocholine (PSC), the sulfonium analogue of phosphatidylcholine (PC), occurs naturally in some diatoms. The replacement of the [formula; see text] group by a [formula; see text] results in an increase in the polar head group size in PSC relative to that of PC, consistent with the observed increase in permeability of PSC bilayers towards urea. It was of interest to see whether replacement of the [formula; see text] group in platelet activating factor (PAF) by an [formula; see text] group leads to any change in platelet aggregation or other physiological activity. Synthesis of the sulfonium analogue of PAF was carried out by suitable modifications of known procedures. The PAF-sulfonium analogue was found to have almost the same platelet aggregating activity as PAF itself, in the concentration range 1-20 microM, but a much lower activity in the range 0.01-1 microM. The analogue had little or no effect on the platelet aggregation activity of PAF when added in the concentration range 0.01-1 microM and had about half the hypotensive activity of PAF towards hypertensive CDF male rats. The sulfonium analogue, however, was much more cytotoxic to HL-60 cells than PAF itself, in the concentration range 0-15 microM; replacement of the acetate group by a benzyl group increased the cytotoxicity to the level of that of the methoxy analogue of PAF. Thus, replacement of the [formula; see text] group by a [formula; see text] group in the polar head group region of PAF results in a relatively small change in its platelet aggregation activity and a decrease in its hypotensive activity, but greatly increases its antitumor activity.

The synthesis and properties of peptidylmethylsulphonium salts with two cationic residues as potential inhibitors of prohormone processing

Peptidylmethylsulphonium salts incorporating consecutive basic residues at the C-terminus of the peptidyl portion such as -Arg-Arg-, -Arg-Lys-, -Lys-Lys- and -Lys-Arg- were synthesized and examined as proteinase inhibitors. Serine proteinases with a specificity directed towards hydrolysis at cationic residues were found to be unaffected by these derivatives. On the other hand, cysteine proteinases, cathepsin B and, in particular, clostripain were readily inactivated by affinity labelling. The reagents thus are of promise for the study of prohormone processing promoted by cysteine proteinases.

Dimethylsulfonium and thiolanium analogues of the muscarinic agent oxotremorine

Dimethylsulfonium (6a and 6b) and thiolanium analogues (7a and 7b) of oxotremorine were synthesized and found to be potent muscarinic agents in vivo and vitro. Compound 6a exceeded oxotremorine in potency. Their affinities for muscarinic receptors in the guinea pig ileum and urinary bladder, estimated pharmacologically, were higher than those of the corresponding trimethylammonium (8a and 8b) and N-methylpyrrolidinium compounds (9a and 9b). However, the new compounds had lower intrinsic efficacies than their quaternary ammonium analogues. The compounds also had high affinity for central muscarinic receptors as measured by displacement of specifically bound (-)-[3H]-N-methylscopolamine from homogenates of the rat cerebral cortex. Half-maximal occupation of cortical muscarinic receptors by 6a, 6b, 7a, and 7b was achieved at concentrations of 0.8, 5.4, 0.3, and 3.3 microM, respectively. The competition curves of 6a, 6b, and 7a were adequately described by a two-site binding equation. The ratio of low- and high-affinity dissociation constants agreed with relative efficacy estimated on the ileum. The thiolanium salt 7a was a fairly potent nicotinic agent on the frog rectus abdominis.

Dopamine agonists: effects of charged and uncharged analogues of dopamine

Dopamine, at physiological pH, may exist as either an uncharged amine or a charged ammonium species. In order to gain insight as to which species is better suited for interaction with the dopamine receptor, we have synthesized dopamine analogues in which the nitrogen atom is replaced with a neutral methyl sulfide, a neutral methyl selenide, a charged dimethylsulfonium iodide, and a charged dimethylselenonium iodide. These analogues were tested for their ability to inhibit the K+-stimulated release of [3H]acetylcholine from striatal slices. At 30 microM concentration, the charged sulfonium and selenonium salts possessed significant agonist activity while the corresponding neutral species were inactive, suggesting that a charged species is optimal for dopamine agonist activity. In addition, the methyl sulfide was converted into the corresponding sulfoxide and sulfone; however, neither of these oxidation products possessed significant activity as dopaminergic agonists.

Dopaminergic agonists: comparative actions of amine and sulfonium analogues of dopamine

We have investigated the possibility that structural modifications of the sulfonium analogue of dopamine (4) would produce the same pattern of biological activity as structural modifications of dopamine. A series of methyl- tetralinyl -, and naphthalenylsulfonium analogues 5-7 were prepared and tested for their ability to inhibit the potassium-evoked release of [3H]acetylcholine from striatal slices. All compounds were tested under normal conditions and after depletion of dopamine stores with reserpine and alpha-methyl-p-tyrosine. The amine and sulfonium analogues 2-6 all showed direct agonist activity. The sulfonium analogue 7 produced, predominantly, indirect activity. In contrast to the amine analogues, chemical modifications of the sulfonium compounds produced little change in their dopamine agonist activity.

Synthesis and evaluation of some stable multisubstrate adducts as inhibitors of catechol O-methyltransferase

A new series of methylase inhibitors has been designed in which the nucleophilic methyl acceptor is attached to the adenosine and/or homocysteine fragments of the methyl donor, S-adenosylmethionine, to form a "multisubstrate adduct". In the present case, catecholamine analogues attached through a phenethyl sulfide linkage to 5'-thioadenosine or homocysteine have been synthesized, together with the corresponding methylsulfonium salts. These compounds were assayed as inhibitors of catechol O-methyltransferase, and the adenosylsulfonium salts (4) were found to be inhibitors of the enzyme.

Inhibitors of tRNA methyltransferases. S-Adenosylsulfonium salts

Three new compounds have been synthesized and tested as in vitro inhibitors of normal and tumor tRNA methyltransferases. These compounds are 5'-methylethyl(5'adenosyl) sulfonium chloride (MEAS), 5'-methylpropyl-(5'adenosyl)sulfonium chloride (MPAS), and 5'-ethylpropyl(5'-adenosyl)sulfonium chloride (EPAS) They were prepared by reacting an alkyl iodide with the appropriate alkyladenosyl thioether. Inhibition assays revealed all three compounds to be inhibitors of normal and tumor tRNA methyltransferases. The propyl compounds were slightly better inhibitors of the tumor tRNA methyl transferases. MPAS, EPAS, and MEAS had KI's of 58.5, 61.7, and 24.5, respectively, for the normal tRNA methyltransferases and 15.3, 13.8, and 44.3, respectively, for the tumor tRNA methyltransferases.