Slava Ziegler

Highly enantioselective synthesis and cellular evaluation of spirooxindoles inspired by natural products

In biology-oriented synthesis the underlying scaffold classes of natural products selected in evolution are used to define biologically relevant starting points in chemical structure space for the synthesis of compound collections with focused structural diversity. Here we describe a highly enantioselective synthesis of natural-product-inspired 3,3′-pyrrolidinyl spirooxindoles—which contain an all-carbon quaternary centre and three tertiary stereocentres. This synthesis takes place by means of an asymmetric Lewis acid-catalysed 1,3-dipolar cycloaddition of an azomethine ylide to a substituted 3-methylene-2-oxindole using 1–3 mol% of a chiral catalyst formed from a N,P-ferrocenyl ligand and CuPF6(CH3CN)4. Cellular evaluation has identified a molecule that arrests mitosis, induces multiple microtubule organizing centres and multipolar spindles, causes chromosome congression defects during mitosis and inhibits tubulin regrowth in cells. Our findings support the concept that compound collections based on natural-product-inspired scaffolds constructed with complex stereochemistry will be a rich source of compounds with diverse bioactivity. A Lewis-acid-catalysed 1,3-dipolar cycloaddition provides rapid access to a variety of substituted spirooxindoles. Initial cellular evaluations supports the view that compound collections based on natural-product-inspired scaffolds constructed with complex stereochemistry, and decorated with assorted substituents, will be a rich source of compounds with diverse bioactivity.

Target Identification for Small Bioactive Molecules: Finding the Needle in the Haystack

Identification and confirmation of bioactive small-molecule targets is a crucial, often decisive step both in academic and pharmaceutical research. Through the development and availability of several new experimental techniques, target identification is, in principle, feasible, and the number of successful examples steadily grows. However, a generic methodology that can successfully be applied in the majority of the cases has not yet been established. Herein we summarize current methods for target identification of small molecules, primarily for a chemistry audience but also the biological community, for example, the chemist or biologist attempting to identify the target of a given bioactive compound. We describe the most frequently employed experimental approaches for target identification and provide several representative examples illustrating the state-of-the-art. Among the techniques currently available, protein affinity isolation using suitable small-molecule probes (pulldown) and subsequent mass spectrometric analysis of the isolated proteins appears to be most powerful and most frequently applied. To provide guidance for rapid entry into the field and based on our own experience we propose a typical workflow for target identification, which centers on the application of chemical proteomics as the key step to generate hypotheses for potential target proteins.

De novo branching cascades for structural and functional diversity in small molecules

The limited structural diversity that a compound library represents severely restrains the discovery of bioactive small molecules for medicinal chemistry and chemical biology research, and thus calls for developing new divergent synthetic approaches to structurally diverse and complex scaffolds. Here we present a de novo branching cascades approach wherein simple primary substrates follow different cascade reactions to create various distinct molecular frameworks in a scaffold diversity phase. Later, the scaffold elaboration phase introduces further complexity to the scaffolds by creating a number of chiral centres and incorporating new hetero- or carbocyclic rings. Thus, employing N-phenyl hydroxylamine, dimethyl acetylenedicarboxylate and allene ester as primary substrates, a compound collection of sixty one molecules representing seventeen different scaffolds is built up that delivers a potent tubulin inhibitor, as well as inhibitors of the Hedgehog signalling pathway. This work highlights the immense potential of cascade reactions to deliver compound libraries enriched in structural and functional diversity.

Natural product–inspired cascade synthesis yields modulators of centrosome integrity

In biology-oriented synthesis, the scaffolds of biologically relevant compound classes inspire the synthesis of focused compound collections enriched in bioactivity. This criterion is, in particular, met by the scaffolds of natural products selected in evolution. The synthesis of natural product-inspired compound collections calls for efficient reaction sequences that preferably combine multiple individual transformations in one operation. Here we report the development of a one-pot, twelve-step cascade reaction sequence that includes nine different reactions and two opposing kinds of organocatalysis. The cascade sequence proceeds within 10-30 min and transforms readily available substrates into complex indoloquinolizines that resemble the core tetracyclic scaffold of numerous polycyclic indole alkaloids. Biological investigation of a corresponding focused compound collection revealed modulators of centrosome integrity, termed centrocountins, which caused fragmented and supernumerary centrosomes, chromosome congression defects, multipolar mitotic spindles, acentrosomal spindle poles and multipolar cell division by targeting the centrosome-associated proteins nucleophosmin and Crm1.

Englerin A is a Potent and Selective Activator of TRPC4 and TRPC5 Calcium Channels

Current therapies for common types of cancer such as renal cell cancer are often ineffective and unspecific, and novel pharmacological targets and approaches are in high demand. Here we show the unexpected possibility for the rapid and selective killing of renal cancer cells through activation of calcium-permeable nonselective transient receptor potential canonical (TRPC) calcium channels by the sesquiterpene (-)-englerin A. This compound was found to be a highly efficient, fast-acting, potent, selective, and direct stimulator of TRPC4 and TRPC5 channels. TRPC4/5 activation through a high-affinity extracellular (-)-englerin A binding site may open up novel opportunities for drug discovery aimed at renal cancer.

Total Synthesis and Biological Evaluation of (-)Englerin A and B: Synthesis of Analogues with Improved Activity Profile

Currently approved therapies targetthe downstream signaling that leads to an over-expression ofangiogenic factors such as VEGF and PDGF and includetyrosine kinase inhibitors (sorafenib, sutinib) as well asmTOR inhibitors (temsirolimus, everolimus). Owing tosevere side effects and other drawbacks of the above-mentioned treatments, the identification of novel inhibitorsof kidney cancer signaling pathways remains highly desirable.Toward this end, a collection of plant extracts was screenedagainst an NCI 60-cell panel containing renal cancer cell linesalong with eight other organ panels. Selecting for specificinhibitors of renal cancer cell lines led to the identification ofenglerin A and B, metabolites of Phyllanthus engleri, which isa plant indigenous to the East African countries of Tanzaniaand Zimbabwe. Englerin A (1) is a densely functionalizedguaiane sesquiterpenoid with an oxatricyclic core flanked bytwo opposing ester side chains (Scheme 1). Following Beu-tlers initial report

A Natural Product Inspired Tetrahydropyran Collection Yields Mitosis Modulators that Synergistically Target CSE1L and Tubulin

A Prins cyclization between a polymer-bound aldehyde and a homoallylic alcohol served as the key step in the synthesis of tetrahydropyran derivatives. A phenotypic screen led to the identification of compounds that inhibit mitosis (as seen by the accumulation of round cells with condensed DNA and membrane blebs). These compounds were termed tubulexins as they target the CSE1L protein and the vinca alkaloid binding site of tubulin.

An Enantioselective Inverse-Electron-Demand Imino Diels–Alder Reaction

The imino Diels-Alder reaction is an efficient method for the synthesis of aza-heterocycles. While different stereo- and enantioselective inverse-electron-demand imino Diels-Alder (IEDIDA) reactions have been reported before, IEDIDA reactions including electron-deficient dienes are unprecedented. The first enantioselective IEDIDA reaction between electron-poor chromone dienes and cyclic imines, catalyzed by zinc/binol complexes is described. The novel reaction provides a facile entry to a natural product inspired collection of ring-fused quinolizines including a potent modulator of mitosis.

Discovery of Inhibitors of the Wnt and Hedgehog Signaling Pathways through the Catalytic Enantioselective Synthesis of an Iridoid-Inspired Compound Collection†

Cousins you can count on: An iridoid-inspired compound collection was synthesized efficiently by the resolution of cyclic enones in an asymmetric cycloaddition with azomethine ylides. The collection contained novel potent inhibitors of the Wnt and Hedgehog signaling pathways.

Biology‐Oriented Synthesis of a Withanolide‐Inspired Compound Collection Reveals Novel Modulators of Hedgehog Signaling

Biology-oriented synthesis employs the structural information encoded in complex natural products to guide the synthesis of compound collections enriched in bioactivity. The trans-hydrindane dehydro-δ-lactone motif defines the characteristic scaffold of the steroid-like withanolides, a plant-derived natural product class with a diverse pattern of bioactivity. A withanolide-inspired compound collection was synthesized by making use of three key intermediates that contain this characteristic framework derivatized with different reactive functional groups. Biological evaluation of the compound collection in cell-based assays that monitored biological signal-transduction processes revealed a novel class of Hedgehog signaling inhibitors that target the protein Smoothened.