Scott D. Taylor

An efficient new protocol for the formation of unsymmetrical tri- and tetrasubstituted ureas

Abstract A new method for producing unsymmetrical, tetrasubstituted ureas from N, N′-carbonyldiimidazole (CDI) is presented. Carbamoyl imidazolium salts are prepared from the reaction of CDI with a secondary amine, followed by alkylation with MeI. Secondary amines add with ease to imidazolium salts at room temperature to give unsymmetrical, tetrasubstituted ureas in excellent yields.

Recent advances in protein tyrosine phosphatase 1B inhibitors

Type 2 diabetes and obesity are characterised by insulin and leptin resistance. Studies suggest that these may be due to defects in the insulin and leptin signalling pathways. Over the last decade, a considerable body of evidence has been amassed indicating that protein tyrosine phosphatase 1B (PTP1B) is involved in the downregulation of insulin and leptin signalling. Consequently, compounds that inhibit PTP1B have potential as therapeutics for treating Type 2 diabetes and obesity. This review covers recent advances in PTP1B inhibitors with an emphasis on recent attempts to create potent, selective and cell-permeable small-molecule inhibitors.

Potent non-peptidyl inhibitors of protein tyrosine phosphatase 1B.

The development of inhibitors of protein tyrosine phosphatases (PTPs) has recently been the subject of intensive investigation due to their potential as chemotherapeutics and as tools for studying signal transduction pathways. Here we report the evaluation of a variety of small molecule, non-peptidyl inhibitors of protein tyrosine phosphatase 1B (PTP1B), bearing the alpha, alpha-difluoromethylenephosphonic acid (DFMP) group, a non-hydrolyzable phosphate mimetic. A series of phenyl derivatives bearing a single DFMP group were initially surveyed. In general, these were not significantly more potent inhibitors than the parent compound, alpha, alpha-difluorobenzylphosphonic acid, with the exception being the meta-phenyl substituted species which decreased the IC50 by approximately 17-fold relative to alpha, alpha-difluorobenzylphosphonic acid. However, certain compounds bearing two DFMP moieties were very potent inhibitors. Some of these are among the most potent small molecule inhibitors of any PTP reported to date with the best one exhibiting a Ki of 1.5 microM. The structural basis for these results are discussed. One of the bis-DFMP inhibitors was examined in detail and it was found that the fluorines were essential for potent inhibition. Inhibition was independent of pH between pH 5.5-7.2 suggesting that both the mono and dianionic forms of the individual DFMP groups bind equally well. The trends observed in the inhibitory potency of these compounds with PTP1B were very similar to the trends observed by other workers on the K(m)s of the analogous phenylphosphate substrates with rat PTP1. This indicates that studies of non-peptidyl substrates with rat PTP1 can be used as a guide for the development of human PTP1B inhibitors.

Cardiolipin Prevents Membrane Translocation and Permeabilization by Daptomycin

Background: Daptomycin forms oligomeric pores in bacterial cell membranes. Cardiolipin is a membrane lipid associated with bacterial resistance to the antibiotic. Results: Cardiolipin makes liposomes impervious to daptomycin permeabilization, and it confines daptomycin to the outer membrane leaflet. Conclusion: Preventing daptomycin from reaching the inner membrane leaflet inhibits pore formation. Significance: Bacteria may become resistant to daptomycin by changing their membrane lipid composition. Daptomycin is an acidic lipopeptide antibiotic that, in the presence of calcium, forms oligomeric pores on membranes containing phosphatidylglycerol. It is clinically used against various Gram-positive bacteria such as Staphylococcus aureus and Enterococcus species. Genetic studies have indicated that an increased content of cardiolipin in the bacterial membrane may contribute to bacterial resistance against the drug. Here, we used a liposome model to demonstrate that cardiolipin directly inhibits membrane permeabilization by daptomycin. When cardiolipin is added at molar fractions of 10 or 20% to membranes containing phosphatidylglycerol, daptomycin no longer forms pores or translocates to the inner membrane leaflet. Under the same conditions, daptomycin continues to form oligomers; however, these oligomers contain only close to four subunits, which is approximately half as many as observed on membranes without cardiolipin. The collective findings lead us to propose that a daptomycin pore consists of two aligned tetramers in opposite leaflets and that cardiolipin prevents the translocation of tetramers to the inner leaflet, thereby forestalling the formation of complete, octameric pores. Our findings suggest a possible mechanism by which cardiolipin may mediate resistance to daptomycin, and they provide new insights into the action mode of this important antibiotic.

Sulfonyl imidazolium salts as reagents for the rapid and efficient synthesis of nucleoside polyphosphates and their conjugates.

A procedure for the synthesis of nucleoside polyphosphates and their conjugates using sulfonylimidazolium salts as key reagents is described. The procedure is rapid and high yielding, does not require prior protection and subsequent deprotection of the donors or acceptors, and can be used to activate nucleoside mono-, di- and triphosphates, and a wide variety of acceptors and donors can be used.

Synthesis of aryl(difluoromethylenephosphonates) via electrophilic fluorination of α-carbanions of benzylic phosphonates with N-fluorobenzenesulfonimide

The electrophilic fluorination of a wide variety of benzylic phosphonates with N-fluorobenzenesulfonimide has been examined. The fluorination reaction proceeds well in the presence of an array of functional groups such as nitro, bromo, ketone, ester, phenyl and ether groups. Phenyl and biphenyl derivatives containing two α,α-difluoromethylenephosphonate groups can also be prepared. This procedure is compatible with methyl or ethyl phosphonate esters but not with t-butyl esters or with benzylic phosphonates containing an additional benzylic moiety at the para-position.

Characterization of daptomycin oligomerization with perylene excimer fluorescence: stoichiometric binding of phosphatidylglycerol triggers oligomer formation.

Daptomycin is a lipopeptide antibiotic that binds to and depolarizes bacterial cell membranes. Its antibacterial activity requires calcium and correlates with the content of phosphatidylglycerol in the target membrane. Daptomycin has been shown to form oligomers on liposome membranes. We here use perylene excimer fluorescence to further characterize the membrane-associated oligomer. To this end, the N-terminal fatty acyl chain was replaced with perylene-butanoic acid. The perylene derivative retains one third of the antibacterial activity of native daptomycin. On liposomes containing phosphatidylcholine and phosphatidylglycerol, as well as on Bacillus subtilis cells, the perylene-labeled daptomycin forms excimers, which shows that the N-terminal acyl chains of neighboring oligomer subunits are in immediate contact with one another. In a lipid bicelle system, oligomer formation can be titrated with stoichiometric amounts of phosphatidylglycerol. Therefore, the interaction of daptomycin with a single molecule of phosphatidylglycerol is sufficient to trigger daptomycin oligomerization.

Novel phosphate mimetics for the design of non-peptidyl inhibitors of protein tyrosine phosphatases

Benzylic alpha,alpha-difluorosulfonates, alpha,alpha-difluorotetrazoles, and alpha,alpha-difluorocarboxylates of type 5 and 6 were synthesized and examined as potential phosphate biosteres for PTP1B inhibition. The alpha,alpha-difluorosulfonates and alpha,alpha-difluorotetrazoles were found to be more effective inhibitors than the analogous compounds bearing the fluoromalonyl group, a phosphate biostere currently being used for PTP inhibition.

A new protocol for the formation of carbamates and thiocarbamates using carbamoyl imidazolium salts

Abstract Carbamoyl imidazolium salts are demonstrated to act as useful carbamoylation reagents, in reactions with alcohols, phenols, thiols and thiophenols to form carbamates and thiocarbamates under relatively mild conditions. The salts are stable and easily prepared from the corresponding amines using CDI.

O- and N-Sulfations of Carbohydrates Using Sulfuryl Imidazolium Salts

A series of sulfuryl imidazolium salts (SISs) were prepared and examined as reagents for incorporating trichloroethyl-protected sulfate esters into carbohydrates. The SIS that contained a 1,2-dimethylimidazolium moiety (SIS 9) proved to be a superior sulfating compared to SISs bearing no alkyl groups or bulkier alkyl groups on the imidazolium ring. Difficult O-sulfations that required prolonged reaction times and a large excess of the SIS bearing a 1-methylimidazolium group (SIS 5) were achieved in high yield using less than half the amount of SIS 9 in less time. Certain N-sulfated compounds that were practically inaccessible using SIS 5 were obtained in excellent yield using SIS 9.