Gregory S. Bisacchi

BMS-200475, a novel carbocyclic 2′-deoxyguanosine analog with potent and selective anti-hepatitis B virus activity in vitro

BMS-200475, a novel carbocyclic analog of 2′-deoxyguanosine, is a potent inhibitor of hepatitis B virus in vitro (ED50 = 3 nM) with relatively low cytotoxicity (CC50 = 21–120 μM). A practical 10-step asymmetric synthesis was developed affording BMS-200475 in 18% overall chemical yield and >99% optical purity. The enantiomer of BMS-200475 as well as the adenine, thymine, and iodouracil analogs are much less active.

Origins of the Quinolone Class of Antibacterials: An Expanded “Discovery Story”

Published descriptions of the specific lines of research leading to the discovery of therapeutically important medicines, especially major new class medicines, have long provided value to the biopharmaceutical community as models of success, often influencing the strategies and methods of subsequent drug research. Quinolone antibacterials represent one of medicines most important classes of anti-infective agents; yet in contrast to many other classes of anti-infectives, astonishingly few details concerning the origin of the class or the rationale leading to the selection of the first clinical agent, nalidixic acid, were ever published by the discoverers. Moreover, earlier disclosures of an independent discovery of the quinolone class of antibacterials have been almost entirely overlooked by the scientific literature. This review brings together all the available information from primary literature sources relating to both discoveries and provides for the first time a much fuller, if still partially speculative, story of the earliest years of this important class of drugs.

Synthesis and SAR of 4-carboxy-2-azetidinone mechanism-based tryptase inhibitors

A series of N1-activated C4-carboxy azetidinones was prepared and tested as inhibitors of human tryptase. The key stereochemical and functional features required for potency, serine protease specificity and aqueous stability were determined. From these studies compound 2, BMS-262084, was identified as a potent and selective tryptase inhibitor which, when dosed intratracheally in ovalbumin-sensitized guinea pigs, reduced allergen-induced bronchoconstriction and inflammatory cell infiltration into the lung.

Synthesis of potent and highly selective inhibitors of human tryptase

The serine protease tryptase has been implicated in allergic and inflammatory diseases and associated with asthma. The synthesis and SAR of a series of N1-activated-4-carboxy azetidinones are described, resulting in identification of BMS-363131 (2) as a potent inhibitor of human tryptase (IC(50)<1.7 nM) with high selectivity (>3000-fold) for tryptase versus related serine proteases including trypsin.

A New-Class Antibacterial—Almost. Lessons in Drug Discovery and Development: A Critical Analysis of More than 50 Years of Effort toward ATPase Inhibitors of DNA Gyrase and Topoisomerase IV

The introduction into clinical practice of an ATPase inhibitor of bacterial DNA gyrase and topoisomerase IV (topo IV) would represent a new-class agent for the treatment of resistant bacterial infections. Novobiocin, the only historical member of this class, established the clinical proof of concept for this novel mechanism during the late 1950s, but its use declined rapidly and it was eventually withdrawn from the market. Despite significant and prolonged effort across the biopharmaceutical industry to develop other agents of this class, novobiocin remains the only ATPase inhibitor of gyrase and topo IV ever to progress beyond Phase I. In this review, we analyze the historical attempts to discover and develop agents within this class and highlight factors that might have hindered those efforts. Within the last 15 years, however, our technical understanding of the molecular details of the inhibition of the gyrase and topo IV ATPases, the factors governing resistance development to such inhibitors, and our knowledge of the physical properties required for robust clinical drug candidates have all matured to the point wherein the industry may now address this mechanism of action with greater confidence. The antibacterial spectrum within this class has recently been extended to begin to include serious Gram negative pathogens such as Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae. In spite of this recent technical progress, adverse economics associated with antibacterial R&D over the last 20 years has diminished industrys ability to commit the resources and perseverance needed to bring new-class agents to launch. Consequently, a number of recent efforts in the ATPase class have been derailed by organizational rather than scientific factors. Nevertheless, within this context we discuss the unique opportunity for the development of ATPase inhibitors of gyrase and topo IV as new-class antibacterial agents with broad spectrum potential.

Molecular Determinants of AcrB-Mediated Bacterial Efflux Implications for Drug Discovery

Bacterial resistance to antibiotics is a serious threat to public health, with ”superbugs” such as MRSA (methicillin-resistant Staphylococcus aureus) responsible for nearly as many deaths in the U.S. as AIDS, viral hepatitis, and tuberculosis combined. More than half of bacterial strains isolated from patients in American intensive care units are resistant to at least one antibiotic, and globally >80% of isolates are resistant. In 2004, the Infectious Disease Society of America (IDSA) issued its oft-cited “Bad Bugs, No Drugs” report, highlighting an emerging public health crisis stemming from a decline in the development of new antibiotics while resistance increasingly renders existing antibiotics ineffective. In 2009 IDSA published an update, observing that the situation had grown still worse. Of particular concern is the increased occurrence of resistant infections due to the Gram-negative pathogens Acinetobacter baumanii, Pseudomonas aeruginosa, and Enterobacteriaceae, both in the U.S. and globally. Like MRSA, resistant Gram-negative infections result in longer hospital stays, greater morbidity, and significantly higher mortality rates. Strains resistant to more than one class of antibiotics are now emerging, culminating in pan-resistant Gram-negative strains causing serious and complicated infections for which no treatment is available. Tragically, Acinetobacter and Pseudomonas infections have emerged particularly among immunocompromised patient populations, where they threaten the hard-fought gains made in areas such as HIV and cancer chemotherapy. Resistance mechanisms specific to each class of antibiotics, for example, deactivating enzymes such as β-lactamases and aminoglycoside-modifying enzymes, have been described, but a mechanism common to all is that of reduced cell entry, by either reduced diffusion into the cell or efflux from it. Increased expression of efflux pumps is also often involved in multidrug resistance, and in some cases strains have acquired resistance via new efflux pumps obtained through horizontal gene transfer. Unlike Gram-positive bacteria, Gramnegative species have highly promiscuous efflux systems and pump a broad range of xenobiotics. Gram-negative pathogens are further protected by an outer cell membrane, which significantly limits the influx of solutes. This second membrane is asymmetric, with a phospholipid inner leaflet and a lipopolysaccharide outer leaflet punctuated by water-filled porin channels that allow small hydrophilic substrates required for bacterial growth to reach specific uptake systems in the inner membrane. Even in the absence of increased efflux pump expression, basal levels of pump activity are major contributors to primary resistance and largely responsible for the reduced antibiotic susceptibility observed, for instance, in P. aeruginosa relative to Hemophilis inf luenzae. Thus, primary resistance due to efflux plagues early stage drug discovery. AcrB is part of the most prevalent efflux transporter among Gram-negative species. It resides in the cytoplasmic membrane and complexes with AcrA and the TolC outer-membrane channel to pump substrates from the periplasmic space to the exterior of the cell (Figure 1). Substrates bind in the AcrB subunit and are extruded through conformational changes driven by a proton gradient maintained across the cytoplasmic membrane. AcrB has been implicated in the clinical resistance of Escherichia coli, P. aeruginosa, and Klebsiella pneumoniae to antibiotics representing numerous classes, including tetracyclines, aminoglycosides, (fluoro)quinolones, cephalosporins, and carbapenems. It is a ubiquitous and extremely promiscuous transporter and is, in our experience, possibly the single most significant hurdle to achieving therapeutic levels of antibacterials within Gram-negative cells. Numerous investigators have noted differences in physicochemical characteristics between antibiotics and other drugs. However, the exact set of properties that make small molecules effective against Gram-negative cells remains poorly understood. Among the handful of studies seeking systematic trends between Gram-negative activity and molecular properties, a common theme is that bacteria (and Gram-negatives in particular) tend to be more susceptible to hydrophilic compounds. O’Shea and Moser come closest to a set of guidelines for distinguishing compounds with probable Gramnegative activity based on simple physicochemical properties amenable to change through medicinal chemistry. They compared a set of 147 marketed and late-stage compounds with antibacterial activity to a background of drugs and druglike compounds and found that those with Gram-negative activity are profoundly more polar than other classes of drugs (as much as 4 orders of magnitude in terms of water/octanol partitioning) and that they possess a skewed distribution of molecular weight tending toward but not exceeding 600 Da, consistent with the limits imposed by porins. It followed that antibacterial discovery programs should focus their efforts on relatively small and polar compounds. Interestingly, these recommendations were somewhat inconsistent with our individual experiences within various lead optimization efforts, in which polarity seemed detrimental to Gram-negative activity, particularly by increasing the apparent susceptibility of compounds to efflux. To better understand this

Phenylimidazoles as Potent and Selective Inhibitors of Coagulation Factor XIa with in Vivo Antithrombotic Activity

Novel inhibitors of FXIa containing an (S)-2-phenyl-1-(4-phenyl-1H-imidazol-2-yl)ethanamine core have been optimized to provide compound 16b, a potent, reversible inhibitor of FXIa (Ki = 0.3 nM) having in vivo antithrombotic efficacy in the rabbit AV-shunt thrombosis model (ID50 = 0.6 mg/kg + 1 mg kg(-1) h(-1)). Initial analog selection was informed by molecular modeling using compounds 11a and 11h overlaid onto the X-ray crystal structure of tetrahydroquinoline 3 complexed to FXIa. Further optimization was achieved by specific modifications derived from careful analysis of the X-ray crystal structure of the FXIa/11h complex. Compound 16b was well tolerated and enabled extensive pharmacologic evaluation of the FXIa mechanism up to the ID90 for thrombus inhibition.

α-hydroxyamide derived aminodiols as potent inhibitors of hiv protease

Abstract A novel series of HIV protease inhibitors has been prepared. Replacement of the P2 carbamate of compound 1 [IC50 = 125 nM] with an α-hydroxy amide moiety results in a significant increase in anti-HIV protease activity [e. g., compound 25a; IC50 = 15 nM]. Furthermore, isomers with (R) absolute configuration at the P2 site show greater inhibitory activity than the corresponding (S)-isomers. A proposed binding mode based on molecular modeling is used to rationalize the structure-activity relationships.

Optically active fluorinated cyclobutane nucleoside analogs with potent anti-herpes activity

Abstract The synthesis and antiherpes activity of several optically active 4′-fluoro-2′,3′-dihydroxymethylcyclobutyl nucleoside analogs are described. A key synthetic step is the diastereoselective [2+2] cycloaddition of a novel fluoroketene acetal with (−)-dimethyl fumarate.

(2R, 4S, 5S)-1-(tetrahydro-4-hydroxy-5-methoxy-2-furanyl)thymine: a potent selective inhibitor of herpes simplex thymidine kinase

Abstract A series of thymidine analogues substituted with alkoxy groups of the C-4 position of the furan ring were synthesized. Among these compounds, the methoxy analogue 9 was the most potent inhibitor of herpes simplex virus type 1 thymidine kinase.