Convergent Synthesis of a Complex Oxime Library Using Chemical Domain Shuffling

Regioselective access to polycyclic N-heterocycles via homogeneous copper-catalyzed cascade cyclization of allenynes

Polycyclic N-heterocycles are important structural motifs commonly found in bioactive compounds, however, their selective construction via the cyclization of allenynes remains challenging yet highly desirable. Here we show a homogeneous copper-catalyzed hetero Diels-Alder (HDA) reaction of allenynes with cis-diazenes (PTAD, 4-phenyl-1,2,4-triazoline-3,5-dione), allowing the practical and efficient synthesis of a diverse array of valuable polycyclic N-heterocycles. A temperature-controlled and stereocontrolled chemoselectivity of the reaction was observed, leading to the chemodivergent synthesis of tetracyclic pyrrolidines, pentacyclic triazepanes and tricyclic pyrrolidines. Compared with related Au-catalyzed cyclization of allenynes, this copper catalysis achieves cyclization of allenynes terminating in C-N bond formation via the HDA reaction.

Design and synthesis of analogues of natural products

In this article strategies for the design and synthesis of natural product analogues are summarized and illustrated with some selected examples.

Large-scale synthesis of all stereoisomers of a 2,3-unsaturated C-glycoside scaffold

All stereoisomers of a highly functionalized 2,3-unsaturated C-glycoside can be accessed in 10-100 g quantities from readily available starting materials and reagents in 3-7 steps. These chiral scaffolds contain three stereogenic centers along with orthogonally protected functional groups for downstream reactivity.

Fragment-based domain shuffling approach for the synthesis of pyran-based macrocycles

Complexity and the presence of stereogenic centers have been correlated with success as compounds transition from discovery through the clinic. Here we describe the synthesis of a library of pyran-containing macrocycles with a high degree of structural complexity and up to five stereogenic centers. A key feature of the design strategy was to use a modular synthetic route with three fragments that can be readily interchanged or "shuffled" to produce subtly different variants with distinct molecular shapes. A total of 352 macrocycles were synthesized ranging in size from 14- to 16-membered rings. In order to facilitate the generation of stereostructure-activity relationships, the complete matrix of stereoisomers was prepared for each macrocycle. Solid-phase assisted parallel solution-phase techniques were employed to allow for rapid analogue generation. An intramolecular nitrile-activated nucleophilic aromatic substitution reaction was used for the key macrocyclization step.

Synthesis of unusual oxime ethers by reaction of tetranitromethane with B-alkylcatecholboranes

The reaction of tetranitromethane with B-alkylcatecholboranes leads to the formation of unusual dinitrooxime ethers. A tentative mechanism is provided, which suggests the involvement of extremely fast addition of alkyl radicals to tetranitromethane. The substitution of one of the nitro groups in the oxime ethers by nucleophiles (such as secondary amines, halogens and styrene) and by radicals generated from B-alkylcatecholboranes is reported.

A time-resolved fluorescence-resonance energy transfer assay for identifying inhibitors of hepatitis C virus core dimerization

Binding of hepatitis C virus (HCV) RNA to core, the capsid protein, results in the formation of the nucleocapsid, the first step in the assembly of the viral particle. A novel assay was developed to discover small molecule inhibitors of core dimerization. This assay is based on time-resolved fluorescence resonance energy transfer (TR-FRET) between anti-tag antibodies labeled with either europium cryptate (Eu) or allophycocyanin (XL-665). The N-terminal 106-residue portion of core protein (core106) was tagged with either glutathione-S-transferase (GST) or a Flag peptide. Tag-free core106 was selected as the reference inhibitor. The assay was used to screen the library of pharmacologically active compounds (LOPAC) consisting of 1,280 compounds and a 2,240-compound library from the Center for Chemical Methodology and Library Development at Boston University (CMLD-BU). Ten of the 28 hits from the primary TR-FRET run were confirmed in a secondary amplified luminescent proximity homogeneous assay (ALPHA screen). One hit was further characterized by dose-response analysis yielding an IC(50) of 9.3 microM. This 513 Da compound was shown to inhibit HCV production in cultured hepatoma cells.

Stereoselective synthesis of spirocyclic oxindoles via Prins cyclizations

The synthesis of spirocyclic oxindole pyran and oxepene frameworks using highly stereoselective Prins cyclizations of homoallylic and bis-homoallylic alcohols and isatin ketals is described.

Metathesis Cascade Strategies (ROM-RCM-CM): A DOS approach to Skeletally Diverse Sultams

The development of a ring-opening metathesis/ring-closing metathesis/cross metathesis (ROM-RCM-CM) cascade strategy to the synthesis of a diverse collection of bi- and tricyclic sultams is reported. In this study, functionalized sultam scaffolds derived from intramolecular Diels-Alder (IMDA) reactions undergo metathesis cascades to yield a collection tricyclic sultams. Additional appendage based diversity was achieved by utilizing a variety of CM partners.

Application of natural product-inspired diversity-oriented synthesis to drug discovery

Natural products have played a critical role in the identification of numerous medicines. Synthetic organic chemistry and combinatorial chemistry strategies such as diversity-oriented synthesis (DOS) have enabled the synthesis of natural product-like compounds. The combination of these approaches has both improved the desired biological properties of natural products as well as the identification of novel compounds. Diversity concepts and strategies to access novel compounds inspired by natural products will be reviewed.

Protected aminooxyprolines for expedited library synthesis: application to Tsg101-directed proline-oxime containing peptides

The stereoselective synthesis of aminooxy-containing proline analogues bearing Fmoc/Boc or Fmoc/Mtt protection that renders them suitable for incorporation into peptides using Fmoc protocols is reported. Acid-catalyzed unmasking at the completion of peptide synthesis yields free aminooxy-functionalities for oxime formation through reaction with libraries of aldehydes. This allows post solid-phase diversification strategies that may facilitate structure-activity relationship studies.

Identification of novel epoxide inhibitors of hepatitis C virus replication using a high-throughput screen

Using our high-throughput hepatitis C replicon assay to screen a library of over 8,000 novel diversity-oriented synthesis (DOS) compounds, we identified several novel compounds that regulate hepatitis C virus (HCV) replication, including two libraries of epoxides that inhibit HCV replication (best 50% effective concentration, < 0.5 microM). We then synthesized an analog of these compounds with optimized activity.

Exploring Skeletal Diversity via Ring Contraction of Glycal-Derived Scaffolds

Aryl ether C-glycoside scaffolds have been prepared from tri-O-acetyl-D-glucal by C-glycosylation followed by allylic substitution with phenols mediated by Pd(0). The aryl ethers were subjected to either [3,3]-sigmatropic rearrangement to produce 3-pyranyl-phenols or Au(III)-mediated ring contraction to create highly substituted tetrahydrofurans. [structure: see text]

Enantioselective Synthesis of Linear Polypropionate Arrays Using Anthracene-Tagged Organosilanes

[reaction: see text] Preparation and use of anthracene-tagged organosilanes in an iterative, resin-capture-release protocol for the stereocontrolled synthesis of polypropionate arrays are described.