Interrupted Corey-Chaykovsky Reaction of Tethered Bis-Enones to Access 2,3-Epoxy-hexahydrofluoren-9-ones

The Corey-Chaykovsky reaction is usually employed to synthesize cyclopropanes from activated olefins. We intercepted the intermediates prevailing during this transformation and diverted the process for the creation of intricate molecular motifs. We describe an unusual skeletal remodelling of tethered bis-enones to 2,3-epoxy-hexahydrofluoren-9-ones via an "interrupted Corey-Chaykovsky reaction". The strategy rationally merges the nucleophilic features of sulfur ylides with electronically biased olefins to achieve the regio- and stereoselective synthesis of several new classes of hydrofluorenones. We have demonstrated the synthetic utility of the products in accessing several highly functionalized molecules.

One-step route to tricyclic fused 1,2,3,4-tetrahydroisoquinoline systems via the Castagnoli-Cushman protocol

The Castagnoli-Cushman reaction of 3,4-dihydroisoquinolines with glutaric anhydride, its oxygen and sulfur analogues was investigated as a one-step approach to the benzo[a]quinolizidine system and its heterocyclic analogs. An extension towards the pyrrolo[2,1-a]isoquinoline system was achieved with the use of succinic anhydride. The results are evidence of an unexplored method for the access of the aforementioned tricyclic annelated systems incorporating a bridgehead nitrogen atom. The structures and relative configurations of the new compounds were established by means of 1D and 2D NMR techniques. The reactions between 1-methyldihydroisoquinoline and glutaric, diglycolic and succinic anhydrides yielded unexpected isoquinoline derivatives containing an exocyclic double bond. The compounds prepared bear the potential to become building blocks for future synthetic bioactive molecules.

Natural products as modulators of the cyclic-AMP pathway: evaluation and synthesis of lead compounds

It is now well recognized that the normal cellular response in mammalian cells is critically regulated by the cyclic-AMP (cAMP) pathway through the appropriate balance of adenylyl cyclase (AC) and phosphodiesterase-4 (PDE4) activities. Dysfunctions in the cAMP pathway have major implications in various diseases like CNS disorders, inflammation and cardiac syndromes and, hence, the modulation of cAMP signalling through appropriate intervention of AC/PDE4 activities has emerged as a promising new drug discovery strategy of current interest. In this context, synthetic small molecules have had limited success so far and therefore parallel efforts on natural product leads have been actively pursued. The early promise of using the diterpene forskolin and its semi-synthetic analogs as AC activators has given way to new leads in the last decade from novel natural products like the marine sesterterpenoids alotaketals and ansellones and the 9,9'-diarylfluorenone cored selaginpulvilins, etc. and their synthesis has drawn much attention. This review captures these contemporary developments, particularly total synthesis campaigns and structure-guided analog design in the context of AC and PDE-4 modulating attributes and the scope for future possibilities.

Synthesis of Cyclopropanoids via Substrate-Based Cyclization Pathways

A series of unexpected reactions triggered by the dimethyloxosulfonium methylide led to the discovery of unconventional approaches for the synthesis of cyclopropa-fused tetralones and indeno-spirocyclopropanes. These highly functionalized structures were further elaborated in one step to privileged scaffolds such as tetralones, indenones, and fluorenones. As a whole, the results presented herein establish new diversity-oriented folding pathways.

Divergent synthesis and identification of the cellular targets of deoxyelephantopins

Herbal extracts containing sesquiterpene lactones have been extensively used in traditional medicine and are known to be rich in α,β-unsaturated functionalities that can covalently engage target proteins. Here we report synthetic methodologies to access analogues of deoxyelephantopin, a sesquiterpene lactone with anticancer properties. Using alkyne-tagged cellular probes and quantitative proteomics analysis, we identified several cellular targets of deoxyelephantopin. We further demonstrate that deoxyelephantopin antagonizes PPARγ activity in situ via covalent engagement of a cysteine residue in the zinc-finger motif of this nuclear receptor.

Deoxyelephantopin is a naturally occurring sesquiterpene lactone with known anticancer properties. Here, the authors synthesize deoxyelephantopins and a range of analogues including alkyne-tagged probes, using them to identify its cellular targets.

Facile construction of structurally diverse thiazolidinedione-derived compounds via divergent stereoselective cascade organocatalysis and their biological exploratory studies

In this article, we present a new approach by merging two powerful synthetic tactics, divergent synthesis and cascade organocatalysis, to create a divergent cascade organocatalysis strategy for the facile construction of new "privileged" substructure-based DOS (pDOS) library. As demonstrated, notably 5 distinct molecular architectures are produced facilely from readily available simple synthons thiazolidinedione and its analogues and α,β-unsaturated aldehydes in 1-3 steps with the powerful strategy. The beauty of the chemistry is highlighted by the efficient formation of structurally new and diverse products from structurally close reactants under the similar reaction conditions. Notably, structurally diverse spiro-thiazolidinediones and -rhodanines are produced from organocatalytic enantioselective 3-component Michael-Michael-aldol cascade reactions of respective thiazolidinediones and rhodanines with enals. Nevertheless, under the similar reaction conditions, reactions of isorhodanine via a Michael-cyclization cascade lead to structurally different fused thiopyranoid scaffolds. This strategy significantly minimizes time- and cost-consuming synthetic works. Furthermore, these molecules possess high structural complexity and functional, stereochemical, and skeletal diversity with similarity to natural scaffolds. In the preliminary biological studies of these molecules, compounds 4f, 8a, and 10a exhibit inhibitory activity against the human breast cancer cells, while compounds 8a, 9a, and 9b display good antifungal activities against Candida albicans and Cryptococcus neoformans. Notably, their structures are different from clinically used triazole antifungal drugs. Therefore, they could serve as good lead compounds for the development of new generation of antifungal agents.

Design of chemical libraries for screening

IMPORTANCE OF THE FIELD

The ultimate goal of discovery screening is to have a fast and cost-effective strategy to meet the demands of producing high-content lead series with improved prospects for clinical success. While high-throughput screening (HTS) dominates the drug discovery landscape, other processes and technologies have emerged, including high-content screening and fragment-based design to provide alternatives that may be more suitable for certain targets. There has been a growing interest in reducing the number of compounds to be screened to prevent the escalation in the costs, time and resources associated with HTS campaigns. Library design plays a central role in these efforts.

AREAS COVERED IN THIS REVIEW

This opinion provides a survey of some recent developments in the diversity based library design process, but within a historical context. In particular, the importance of chemotyping and substructure analysis and the challenges presented by novel lead discovery technologies that require the design of libraries for screening are discussed.

WHAT THE READER WILL GAIN

Readers will gain an appreciation of some developments in the field of library design and the factors that are driving the development of new library design technologies; specifically, challenges presented for chemoinformatics with the novel screening technologies in diversity based screening and compound filtering.

TAKE HOME MESSAGE

Chemotyping and substrutural analysis are techniques that have been underutilized in the process of library design. However, they offer a direct way to evaluate libraries and have been successfully used to develop predictive methodologies. Tools are available to this end, but the full power of the approach has not been realized yet.

Automated three-component synthesis of a library of γ-lactams

A three-component method for the synthesis of γ-lactams from commercially available maleimides, aldehydes, and amines was adapted to parallel library synthesis. Improvements to the chemistry over previous efforts include the optimization of the method to a one-pot process, the management of by-products and excess reagents, the development of an automated parallel sequence, and the adaption of the method to permit the preparation of enantiomerically enriched products. These efforts culminated in the preparation of a library of 169 γ-lactams.

Synthesis of an Isoindoline-Annulated, Tricyclic Sultam Library via Microwave-Assisted, Continuous-Flow Organic Synthesis (MACOS)

A microwave-assisted, continuous-flow organic synthesis (MACOS) protocol for the synthesis of an isoindoline-annulat-ed, tricyclic sultam library, utilizing a Heck-aza-Michael (HaM) strategy, is reported. This sequence involves a Heck reaction on vi-nylsulfonamides with batch microwave heating followed by a one-pot, sequential intramolecular aza-Michael cyclization/Boc-deprot-ection using MACOS. Subsequent cyclization with either 1,1'-carbonyldiimidazole or chloromethyl pivalate using MACOS provided an array of tricyclic sultams. This efficient three-step protocol requires only a few hours to produce the target sultams starting from simple starting materials. Using this strategy, a 38-member library of isoindoline-annulated sultams was generated in good to excellent overall yields (53-87%).

Automated synthesis of a 184-member library of thiadiazepan-1,1-dioxide-4-ones

The construction of a 225-member (3 × 5 × 15) library of thiadiazepan-1,1-dioxide-4-ones was performed on a Chemspeed Accelerator (SLT-100) automated parallel synthesis platform, culminating in the successful preparation of 184/225 sultams. Three sultam core scaffolds were prepared based upon the utilization of an aza-Michael reaction on a multifunctional vinyl sulfonamide linchpin. The library exploits peripheral diversity in the form of a sequential, two-step [3 + 2] Huisgen cycloaddition/Pd-catalyzed Suzuki-Miyaura coupling sequence.

Challenges and perspectives of chemical biology, a successful multidisciplinary field of natural sciences

Objects, goals, and main methods as well as perspectives of chemical biology are discussed. This review is focused on the fundamental aspects of this emerging field of life sciences: chemical space, the small molecule library and chemical sensibilization (small molecule microassays).

Improving drug discovery with contextual assays and cellular systems analysis

Despite rapid growth in our knowledge of potential disease targets following completion of the first drafts of the human genome over 10 years ago, the success rate of new therapeutic discovery has been frustratingly low. In addition to the widely reported costs and single-digit success rate of the entire drug discovery and development process, it has recently been estimated that even the preliminary process of transitioning new targets to preclinical development succeeds in less than 3% of attempts [Vogel (ed.) Drug Discovery and Evaluation: Pharmacological Assays. 3rd ed. Springer, Berlin (2007)]. At these early stages of development, poor understanding of therapeutic mechanisms and lack of compound selectivity are often to blame for failed compounds. It is worth noting than the emerging class of nucleic acid-based therapeutics, including miRNA and RNAi, are likely to be even more prone to unexpected system-wide and off-target activities. For all therapeutic approaches, it is clear that discovery strategies permitting the assessment of drug targets in their native context are required. At the same time, these strategies need to retain the high throughput of current reductionist approaches to enable broad assessment of chemical space for small molecule and genetic therapeutics. We describe here an integrated system based on high-content cellular analysis combined with system-wide pathway interrogation. The platform can be applied to novel therapeutic target and drug candidate identification, and for providing detailed mechanistic and selectivity information at an early stage of development.

Skeletal diversity via cationic rearrangements of substituted dihydropyrans

Substituted dihydropyrans, easily accessed from a commercially available glycal, undergo acid-catalyzed rearrangement to provide highly functionalized isochroman and dioxabicyclooctane scaffolds.

Enhancements of screening collections to address areas of unmet medical need: an industry perspective

The past 20 years have witnessed an impressive expansion of the 'drug space'; defined as the intersection of the Medicinal Chemistry space and the Biologically Active space relevant in the quest for new treatments for disease. Despite the success of known lead discovery tactics, areas of unmet medical need are often linked to challenging or novel targets and are poorly served by current screening collections. A successful strategy to fill the gaps is to diversify the approaches taken in the enhancement of screening collections. Possible strategies include investments through proven methods, exploring areas of chemical space previously neglected (e.g. hydrophilic compounds, natural product mimics), and applying tactics to the lead discovery process that are complementary to HTS (e.g. fragment based screening or multidisciplinary team efforts to tackle new target classes).

Regioselective intramolecular dipolar cycloaddition of azides and unsymmetrical alkynes

Enantioenriched allenylsilanes are used in three-component propargylation reactions with aldehydes and silyl ethers to form syn-homopropargylic ethers that contain an imbedded azide. These materials then undergo thermally induced intramolecular 1,3-dipolar cycloaddition reactions, resulting in unique fused ring systems containing 1,2,3-triazoles. The ability to modify all three components of the reaction allows for expedient access to compounds containing significant structural and stereochemical variation.

Terpenyl-purines from the sea

Agelasines, asmarines and related compounds are natural products with a hybrid terpene-purine structure isolated from numerous genera of sponges (Agela sp., Raspailia sp.). Some agelasine analogs and related structures have displayed high general toxicity towards protozoa, and have exhibited broad-spectrum antimicrobial activity against a variety of species, including Mycobacterium tuberculosis, and also an important cytotoxic activity against several cancer cell lines, including multidrug-resistant ones. Of particular interest in this context are the asmarines (tetrahydro[1,4]diazepino[1,2,3-g,h]purines), which have shown potent antiproliferative activity against several types of human cancer cell lines. This review summarizes the sources of isolation, chemistry and bioactivity of marine alkylpurines and their bioactive derivatives.

Synthesis of Diverse Heterocyclic Scaffolds via Tandem Additions to Imine Derivatives and Ring-Forming Reactions

A novel strategy has been developed for the efficient syntheses of diverse arrays of heterocyclic compounds. The key elements of the approach comprise a Mannich-type, multicomponent coupling reaction in which functionalized amines, aromatic aldehydes, acylating agents, and π- and organometallic nucleophiles are combined to generate intermediates that are then further transformed into diverse heterocyclic scaffolds via a variety of cyclization manifolds. Significantly, many of these scaffolds bear functionality that may be exploited by further manipulation to create diverse collections of compounds having substructures found in biologically active natural products and clinically useful drugs. The practical utility of this strategy was exemplified by its application to the first, and extraordinarily concise synthesis of the isopavine alkaloid roelactamine.