Jeffrey A. Pfefferkorn

Selenium-Based Solid-Phase Synthesis of Benzopyrans I: Applications to Combinatorial Synthesis of Natural Products.

Combinatorial chemistry is becoming an increasingly important tool in both chemical biology and drug discovery, and its continued expansion is, to a large extent, contingent upon advances in solid-phase organic synthesis (SPOS) as well as in automation and high-throughput screening (HTS) technologies.[1] Since the demand for libraries of small organic molecules continues to grow, particularly as a result of recent advances in the fields of chemical genetics, genomics, and proteomics, there is an urgent need to develop more efficient strategies for the high-fidelity solid-phase construction of libraries of natural-product-like and drug-like compounds.[2] Toward this end our research group has been engaged in the development of novel resins as well as improved linking and release strategies.[3] Recently, we disclosed[4] the construction of a polystyrene-based selenenyl bromide resin which encompasses the essential features of both a solid-phase reagent[5a] and a traceless linker.[5b±k] We envisaged that such a resin should ideally act as a linker that facilitates bond constructions during the loading operation (that is, acts as a reagent) and then serve as a robust tether through subsequent operations until it is ultimately cleaved in a traceless or functionalizing fashion to effect release of the target. The versatility and efficiency of such a method is readily evident since it reduces the extraneous (noncomplexity building) operations typically associated with the loading of a scaffold and also eliminates the problem of residual functionality in the target structure resulting from the linker.[6] In this and the following communication[7] we describe our preliminary efforts toward the application of such a linking strategy for the construction of several polycyclic natural products and other medicinally relevant small organic molecules. As a forum for demonstrating the utility and efficiency of the proposed seamless linking strategy, we chose to target the 2,2-dimethylbenzopyran moiety which is embedded in numerous natural products including flavanoids, coumarins, rotenoids, stilbenoids, chromene glycosides, and othersÐseveral of which have potential applications in medicine.[8] For example, 1 (Scheme 1),[9] 2,[9] and 3[10] exhibit anticancer activities, whereas 4 and 5 are non-nucleoside, HIV-1-specific, reverse transcriptase inhibitors currently in clinical development.[11] The cube resin derived agents 6, 8, 9, and related structures

Discovery of (S)-6-(3-Cyclopentyl-2-(4-(trifluoromethyl)-1H-imidazol-1-yl)propanamido)nicotinic Acid as a Hepatoselective Glucokinase Activator Clinical Candidate for Treating Type 2 Diabetes Mellitus

Glucokinase is a key regulator of glucose homeostasis, and small molecule allosteric activators of this enzyme represent a promising opportunity for the treatment of type 2 diabetes. Systemically acting glucokinase activators (liver and pancreas) have been reported to be efficacious but in many cases present hypoglycaemia risk due to activation of the enzyme at low glucose levels in the pancreas, leading to inappropriately excessive insulin secretion. It was therefore postulated that a liver selective activator may offer effective glycemic control with reduced hypoglycemia risk. Herein, we report structure-activity studies on a carboxylic acid containing series of glucokinase activators with preferential activity in hepatocytes versus pancreatic β-cells. These activators were designed to have low passive permeability thereby minimizing distribution into extrahepatic tissues; concurrently, they were also optimized as substrates for active liver uptake via members of the organic anion transporting polypeptide (OATP) family. These studies lead to the identification of 19 as a potent glucokinase activator with a greater than 50-fold liver-to-pancreas ratio of tissue distribution in rodent and non-rodent species. In preclinical diabetic animals, 19 was found to robustly lower fasting and postprandial glucose with no hypoglycemia, leading to its selection as a clinical development candidate for treating type 2 diabetes.

Combinatorial synthesis through disulfide exchange: discovery of potent psammaplin A type antibacterial agents active against methicillin-resistant Staphylococcus aureus (MRSA).

Psammaplin A is a symmetrical bromotyrosine-derived disulfide natural product isolated from the Psammaplysilla sponge, which exhibits in vitro antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). Inspired by the structure of this marine natural product, a combinatorial scrambling strategy for the construction of heterodimeric disulfide analogues was developed and applied to the construction of a 3828-membered library starting from 88 homodimeric disulfides. These psammaplin A analogues were screened directly against various gram positive bacterial strains leading to the discovery of a series of potent antibacterial agents active against methicillin-resistant Staphylococcus aureus (MRSA). Among the most active leads derived from these studies are compounds 104, 105, 113, 115, 123, and 128. The present, catalytically-induced, disulfide exchange strategy may be extendable to other types of building blocks bearing thiol groups facilitating the construction of diverse discovery-oriented combinatorial libraries.

Combinatorial synthesis of novel and potent inhibitors of NADH:ubiquinone oxidoreductase

BACKGROUND NADH:ubiquinone oxidoreductase (complex I) is the first of three large enzyme complexes located in the cells inner mitochondrial membrane which form the electron transport chain that carries electrons from NADH to molecular oxygen during oxidative phosphorylation. There is significant interest in developing small molecule inhibitors of this enzyme for use as biological probes, insecticides and potential chemopreventive/chemotherapeutic agents. Herein we describe the application of novel natural product-like libraries to the discovery of a family of potent benzopyran-based inhibitors. RESULTS Initially a combinatorial library of benzopyrans, modeled after natural products, was synthesized using a solid phase cycloloading strategy. Screening of this diversity oriented library for inhibitory potency against NADH:ubiquinone oxidoreductase activity in vitro using bovine heart electron transport particles provided several lead compounds which were further refined through a series of focused libraries. CONCLUSIONS Using this combinatorial library approach, a family of potent 2,2-dimethylbenzopyran-based inhibitors was developed with IC(50) values in the range of 18-55 nM. Cell-based assays revealed that these inhibitors were rather non-cytotoxic in the MCF-7 cell line; however, they were quite cytostatic in a panel of cancer cell lines suggesting their potential as chemotherapeutic/chemopreventive candidates.

Bromotyrosine-Derived Natural and Synthetic Products as Inhibitors of Mycothiol-S-Conjugate Amidase

A series of bromotyrosine-derived compounds, including marine natural products and members of a psammaplin A-inspired combinatorial synthetic library, were screened for their ability to inhibit the Mycobacterium tuberculosis detoxification enzyme mycothiol-S-conjugate amidase (MCA). Correlations between the structures and their respective IC(50) values (which range from 3 microM to 2.7 mM) should prove valuable when optimizing more potent inhibitors of MCA.

Glycomimetic Ligands for the Human Asialoglycoprotein Receptor

The asialoglycoprotein receptor (ASGPR) is a high-capacity galactose-binding receptor expressed on hepatocytes that binds its native substrates with low affinity. More potent ligands are of interest for hepatic delivery of therapeutic agents. We report several classes of galactosyl analogues with varied substitution at the anomeric, C2-, C5-, and C6-positions. Significant increases in binding affinity were noted for several trifluoromethylacetamide derivatives without covalent attachment to the protein. A variety of new ligands were obtained with affinity for ASGPR as good as or better than that of the parent N-acetylgalactosamine, showing that modification on either side of the key C3,C4-diol moiety is well tolerated, consistent with previous models of a shallow binding pocket. The galactosyl pyranose motif therefore offers many opportunities for the attachment of other functional units or payloads while retaining low-micromolar or better affinity for the ASGPR.

Synthesis and Biological Activity of Sarcodictyins

A new class of potential antitumor agents with a taxol-like mechanism of action is presented by the sarcodictyins 1. Modification of the reported syntheses of sarcodictyins permitted the preparation of additional derivatives, the biological properties of which are highly dependent upon the structure.

Designing glucokinase activators with reduced hypoglycemia risk: discovery of N,N-dimethyl-5-(2-methyl-6-((5-methylpyrazin-2-yl)-carbamoyl)benzofuran-4-yloxy)pyrimidine-2-carboxamide as a clinical candidate for the treatment of type 2 diabetes mellitus

Glucokinase is a key regulator of glucose homeostasis and small molecule activators of this enzyme represent a promising opportunity for the treatment of Type 2 diabetes. Several glucokinase activators have advanced to clinical studies and demonstrated promising efficacy; however, many of these early candidates also revealed hypoglycemia as a key risk. In an effort to mitigate this hypoglycemia risk while maintaining the promising efficacy of this mechanism, we have investigated a series of substituted 2-methylbenzofurans as “partial activators” of the glucokinase enzyme leading to the identification of N,N-dimethyl-5-(2-methyl-6-((5-methylpyrazin-2-yl)-carbamoyl)benzofuran-4-yloxy)pyrimidine-2-carboxamide as an early development candidate.

Strategies for the design of hepatoselective glucokinase activators to treat type 2 diabetes

Introduction: Type 2 diabetes mellitus (T2DM) represents a rapidly expanding healthcare challenge. There is a significant need for novel therapies to help patients achieve and maintain glycemic control in order to avoid the long-term microvascular and macrovascular complications associated with the disease. Small molecule allosteric activators of the glucokinase enzyme, an important regulator of glucose homeostasis, have emerged as a potential new class of therapeutics. Glucokinase activators have been shown to effectively lower fasting and postprandial glucose in T2DM patients; however, hypoglycemia emerged as a potential risk limiting their therapeutic potential. To mitigate this risk, recent efforts have focused on the design of liver-specific activators that seek to normalize hepatic glucose uptake and production without potentiating glucose-stimulated insulin secretion. Areas covered: The article reviews the various drug discovery strategies that have emerged for the development of candidates that selectively activate glucokinase in the liver. Literature from 2000 to 2012 is surveyed including scientific publications, patent applications, conferences and clinical trials. Expert opinion: Liver selective agents have proven to be an effective strategy for mitigating the hypoglycemia risk that has been historically associated with this mechanism. The ultimate therapeutic potential of this approach will depend on the results of longer patient studies which are currently being conducted with several clinical candidates. The discovery of these liver-specific activators has highlighted several challenges in the design of tissue-selective therapeutics, which will need to be overcome in the future.

P2Y1 receptor antagonists as novel antithrombotic agents.

The P2Y(1) and P2Y(12) purinergic receptors are responsible for mediating adenosine diphosphate (ADP) dependent platelet aggregation. Evidence from P2Y(1) knockout studies as well as from nucleotide-based small molecule P2Y(1) antagonists has suggested that the antagonism of this receptor may offer a novel and effective method for the treatment of thrombotic disorders. Herein, we report the identification and optimization of a series of non-nucleotide P2Y(1) antagonists that are potent and orally bioavailable.