Synthesis of Enantioenriched 3,4-Disubstituted Chromans through Lewis Base Catalyzed Carbosulfenylation.

A method for the catalytic, enantioselective, carbosulfenylation of alkenes to construct 3,4-disubstituted chromans is described. Alkene activation proceeds through the intermediacy of enantioenriched, configurationally stable thiiranium ions generated from catalytic, Lewis base activation of an electrophilic sulfenylating agent. The transformation affords difficult-to-generate, enantioenriched, 3,4-disubstituted chromans in moderate to high yields and excellent enantioselectivities. A variety of substituents are compatible including electronically diverse functional groups as well as several functional handles such as aryl halides, esters, anilines, and phenols. The resulting thioether moiety is amenable to a number of functional group manipulations and transformations. Notably, the pendant sulfide was successfully cleaved to furnish a free thiol which readily provides access to most sulfur-containing functional groups which are present in natural products and pharmaceuticals.

Design, Synthesis, and Characterization of Novel Small Molecules as Broad Range Antischistosomal Agents.

Schistosomiasis is a major human parasitic disease afflicting more than 250 million people, historically treated with chemotherapies praziquantel or oxamniquine. Since oxamniquine is species-specific, killing Schistosoma mansoni but not other schistosome species (S. haematobium or S. japonicum) and evidence for drug resistant strains is growing, research efforts have focused on identifying novel approaches. Guided by data from X-ray crystallographic studies and Schistosoma worm killing assays on oxamniquine, our structure-based drug design approach produced a robust structure-activity relationship (SAR) program that identified several new lead compounds with effective worm killing. These studies culminated in the discovery of compound 12a, which demonstrated broad-species activity in killing S. mansoni (75%), S. haematobium (40%), and S. japonicum (83%).

Synthesis and Characterization of Pyridine Compounds for Amperometric Measurements of Leukocyte Esterase.

We introduce a new class of substrates (compounds I-III) for leukocyte esterase (LE) that react with LE yielding anodic current in direct proportion to LE activity. The kinetic constants Km and kcat for the enzymatic reactions were determined by amperometry at a glassy carbon electrode. The binding affinity of I-III for LE was two orders of magnitude better than that of existing optical LE substrates. The specificity constant kcat /Km was equal to 2.7, 3.8, and 5.8×105 m-1 s-1 for compounds containing the pyridine (I), methoxypyridine (II), and (methoxycarbonyl)pyridine (III), respectively, thus showing an increase in catalytic efficiency in this order. Compound III had the lowest octanol/water partition coefficient (log p=0.33) along with the highest topological surface area (tPSA=222 Å2 ) and the best aqueous solubility (4.0 mg mL-1 ). The average enzymatic activity of LE released from a single leukocyte was equal to 4.5 nU when measured with compound III.

Electrochemical Substrate and Assay for Esterolytic Activity of Human White Blood Cells.

The ester 4-((tosyl-l-alanyl)oxy)phenyl tosyl-l-alaninate (TAPTA) was synthesized and tested as a substrate for leukocyte esterase (LE), an enzyme produced by leukocytes (white blood cells). In the presence of LE, TAPTA released a redox-active fragment whose oxidation at an electrode provided a direct numerical measure of LE activity. The assays showed that LE recognized TAPTA as its substrate with the Michaelis constant Km and Imax equal to 0.24 mM and 0.13 mA cm-1, respectively. The esterolytic activity of leukocyte suspensions was determined by using the internally calibrated electrochemical continuous enzyme assay (ICECEA). One activity unit (U) of LE catalyzed the hydrolysis of 1.0 µmol of TAPTA per minute in a pH 7.40 phosphate buffer saline solution containing 10% dimethyl sulfoxide (DMSO) at 21 °C. The measured units were directly proportional to the number of leukocytes in the range of 0.028-4.2 U L-1 (9-690 µg L-1 LE protein). One white blood cell displayed the average esterolytic activity of 0.86 and 1.4 nU when the ultrasonic and chemical cytolysis were used, respectively. The ICECEA is an electrochemical alternative to optical assays for the determination of LE activity as an inflammatory biomarker and proxy for the presence of leukocytes.