Electrochemistry at Krakowian research institutions

The electrochemistry research team activity from Poland is marked by significant increase in the last 20 years. The joining of European Community in 2004 gives an impulse for the development of Polish science. The development of electrochemistry has been stimulated by cooperation with industry and the establishment of technology transfer centers, technology parks, business incubators, etc. and the mostly by simplified international collaborations. Five research institutions from Krakow reports work in the field of electrochemistry. The achievements of all teams are briefly described.

Nucleophilic substitution at the anomeric position of furanose carbohydrates. The case of the C-allylations

Taking advantage of the locked conformation of cyclic furanose form, carbohydrate derivatives have been transformed into relevant tetrahydrofuran moieties through a chemical operation commonly known as C-glycosylation reaction. Consequently, a large number of total synthesis of naturally occurring products containing this heterocycle have been accomplished by applying this reaction. In this regard, the C-allylation reaction of furanose carbohydrates provides flexible routes for stereoselective anomeric functionalization by incorporating an allyl group, which is eventually re-functionalized into advanced natural product intermediates. Therefore, this mini review deals with the description of the origin of the stereoselectivity and synthetic applications of this type of glycosylation reaction, which can be also called as: "Nucleophilic Substitution at the Anomeric Position", conducted by various research groups including our own group.

Drug Leads Derived from Japanese Marine Organisms

Many natural products with extraordinary chemical structures and brilliant biological activities have been obtained from marine organisms. We have investigated such fascinating bioactive molecules, exemplified by the potent marine toxin palytoxin and the antitumor molecule halichondrin B, which has been developed as the anticancer drug Halaven®, to explore novel frontiers in organic chemistry and bioscience. Working within the traditional discipline, we have sought to acquire a deeper understanding of biological phenomena. We introduce here our major work along with up-todate topics. We isolated yoshinone A from marine cyanobacteria and completed a gram-scale synthesis. Yoshinone A is a novel polyketide that inhibited the differentiation of 3T3-L1 cells into adipocytes without significant cytotoxicity. The detailed mechanisms of action will be elucidated via further experiments in vitro and in vivo. In this study, we explore the true producers of okadaic acid and halichondrin B by immunostaining of Halichondria okadai with an antibody that was prepared using these natural products as an antigen. We will analyze isolated symbionts and reveal biosynthetic pathways.

Synthesis of Pyranopyrans Related to Diplopyrone and Evaluation as Antibacterials and Herbicides

Stereoselective syntheses of new pyranopyrans that are related to the natural product diplopyrone, which is a phytotoxin implicated in cork oak decline, have been achieved from carbohydrate starting materials in two approaches that are based on C-glycosides as key intermediates. A C-alkynyl glycoside prepared by Ferrier rearrangement was used as the precursor to a new pyranopyran alkyne that showed potent antibacterial activity against the common bacterial pathogen Edwardsiella ictaluri that causes enteric septicemia in catfish. The C-alkynyl glycoside also showed herbicidal activity. New bioassay data for the pyranopyran nitrile (4aR,6S,8aR)-6-cyano-6,8a-dihydropyrano-[3,2-b]pyran-2(4aH)-one, the most potent of the pyranopyrans synthesized to date, were obtained in greenhouse studies that revealed additional herbicidal activity. Other new analogues that were synthesized included desmethylpyranopyrans that were prepared by Isobe C-alkynylation-rearrangement/reduction and RCM-based pyranopyran construction. The antibiotic and phytotoxic activities of the new pyranopyrans synthesized in this study highlight the importance of substituents on the nonlactone ring and demonstrate the potential of such compounds as antibiotics and herbicides.

Sex Differences in Human and Animal Toxicology

Sex, the states of being female or male, potentially interacts with all xenobiotic exposures, both inadvertent and deliberate, and influences their toxicokinetics (TK), toxicodynamics, and outcomes. Sex differences occur in behavior, exposure, anatomy, physiology, biochemistry, and genetics, accounting for female-male differences in responses to environmental chemicals, diet, and pharmaceuticals, including adverse drug reactions (ADRs). Often viewed as an annoying confounder, researchers have studied only one sex, adjusted for sex, or ignored it. Occupational epidemiology, the basis for understanding many toxic effects in humans, usually excluded women. Likewise, Food and Drug Administration rules excluded women of childbearing age from drug studies for many years. Aside from sex-specific organs, sex differences and sex × age interactions occur for a wide range of disease states as well as hormone-influenced conditions and drug distribution. Women have more ADRs than men; the classic sex hormone paradigm (gonadectomy and replacement) reveals significant interaction of sex and TK including absorption, distribution, metabolisms, and elimination. Studies should be designed to detect sex differences, describe the mechanisms, and interpret these in a broad social, clinical, and evolutionary context with phenomena that do not differ. Sex matters, but how much of a difference is needed to matter remains challenging.

Strategies for the Optimization of Natural Leads to Anticancer Drugs or Drug Candidates

Natural products have made significant contribution to cancer chemotherapy over the past decades and remain an indispensable source of molecular and mechanistic diversity for anticancer drug discovery. More often than not, natural products may serve as leads for further drug development rather than as effective anticancer drugs by themselves. Generally, optimization of natural leads into anticancer drugs or drug candidates should not only address drug efficacy, but also improve absorption, distribution, metabolism, excretion, and toxicity (ADMET) profiles and chemical accessibility associated with the natural leads. Optimization strategies involve direct chemical manipulation of functional groups, structure-activity relationship directed optimization and pharmacophore-oriented molecular design based on the natural templates. Both fundamental medicinal chemistry principles (e.g., bioisosterism) and state-of-the-art computer-aided drug design techniques (e.g., structure-based design) can be applied to facilitate optimization efforts. In this review, the strategies to optimize natural leads to anticancer drugs or drug candidates are illustrated with examples and described according to their purposes. Furthermore, successful case studies on lead optimization of bioactive compounds performed in the Natural Products Research Laboratories at UNC are highlighted.

Enantioselective Synthesis of α-exo-Methylene γ-Butyrolactones via Chromium Catalysis

Enantioenriched α-exo-methylene γ-butyrolactones have been obtained via a two-step sequence consisting of a highly enantioselective chromium-catalyzed carbonyl 2-(alkoxycarbonyl)allylation and lactonization. A variety of functional groups are compatible under the mild reaction conditions. The synthetic utility of this methodology was demonstrated by two short derivatization transformations and the enantioselective synthesis of (+)-methylenolactocin.

Selected hybrid natural products as tubulin modulators

Modulators of microtubule dynamics have received increasing attention because of their potential to stop cancer growth. Although it belongs to the category of complex protein-protein interactions (PPIs), which are generally considered difficult to modulate through small molecules, the use of microtubule is considered a well-validated target. There are a number of bioactive natural products and related compounds that are currently in use as drugs or in clinical trials as next generation anti-cancer agents. The present review article is focused on two such bioactive natural products, epothilone and halichondrin B, and covers some of the key papers published after 2005 that outline various synthetic approaches to obtain next generation structural analogs as well as the synthesis of hybrid compounds.

Total synthesis of (+)-spirastrellolide A methyl ester: Challenges and discoveries

This review focuses on recent synthetic efforts by our group towards spirastrellolide A methyl ester, a complex marine macrolide containing two spiroacetal ring systems that shows promising anticancer properties. The evolution of a flexible, modular strategy leading to the first total synthesis of (+)-spirastrellolide A methyl ester, and the associated challenges overcome, are highlighted, particularly in dealing with the initial structural ambiguities. This work enabled the development of an improved second-generation synthesis, which revealed a critical dependence of the key macrolactonization step on the nature of the protecting groups in the linker region between the spiroacetal motifs.

Bioactive natural products from Papua New Guinea marine sponges

The discovery of novel natural products for drug development relies heavily upon a rich biodiversity, of which the marine environment is an obvious example. Marine natural product research has spawned several drugs and many other candidates, some of which are the focus of current clinical trials. The sponge megadiversity of Papua New Guinea is a rich but underexplored source of bioactive natural products. Here, we review some of the many natural products derived from PNG sponges with an emphasis on those with interesting biological activity and, therefore, drug potential. Many bioactive natural products discussed here appear to be derived from non-ribosomal peptide and polyketide biosynthesis pathways, strongly suggesting a microbial origin of these compounds. With this in mind, we also explore the notion of sponge-symbiont biosynthesis of these bioactive compounds and present examples to support the working hypothesis.

Synthesis of the C1-C26 hexacyclic subunit of pectenotoxin 2

Synthesis of the C1-C26 hexacyclic subunit of pectenotoxin-2 (PTX-2) is described that features a stereoselective annulation to generate the C-ring by triple asymmetric Nozaki-Hiyama-Kishi coupling followed by oxidative cyclization. Preparation of the C1-C14 AB spriroketal-containing subunit employs a recently developed metallacycle-mediated reductive cross-coupling between a TMS-alkyne and a terminal alkene.

Concise and highly stereoselective synthesis of the C20-C26 building block of halichondrins and Eribulin

A concise, stereoselective, and scalable synthesis of the C20-C26 building block of halichondrins and Eribulin is reported. The synthesis relies on three key transformations: regiospecific Ru-catalyzed intramolecular hydrosilylation, highly stereoselective S(N)2' substitution, and selective conversion of a C-Si to C-I bond. It is carried out in a 5-pot/4-workup operation without chromatographic purification, except for filtration through a silica-gel plug, to give the C20-C26 building block (dr > 200:1; ee > 99%) in ca. 60% overall yield from epoxide 1.

Total synthesis of halichondrin C

The first total synthesis of halichondrin C has been completed, highlighted by development of the synthetic method to construct the C8-C14 polycycle. Cr-mediated coupling reactions are used seven times to form a new C-C bond. The acid stability of halichondrin C is studied, demonstrating that the macrolactone stabilizes the C8-C14 polycycle, relative to the one present in the C1-C16 model.

Interactions of halichondrin B and eribulin with tubulin

Compounds that modulate microtubule dynamics include highly effective anticancer drugs, leading to continuing efforts to identify new agents and improve the activity of established ones. Here, we demonstrate that [(3)H]-labeled halichondrin B (HB), a complex, sponge-derived natural product, is bound to and dissociated from tubulin rapidly at one binding site per αβ-heterodimer, with an apparent K(d) of 0.31 μM. We found no HB-induced aggregation of tubulin by high-performance liquid chromatography, even following column equilibration with HB. Binding of [(3)H]HB was competitively inhibited by a newly approved clinical agent, the truncated HB analogue eribulin (apparent K(i), 0.80 μM) and noncompetitively by dolastatin 10 and vincristine (apparent K(i)'s, 0.35 and 5.4 μM, respectively). Our earlier studies demonstrated that HB inhibits nucleotide exchange on β-tubulin, and this, together with the results presented here, indicated the HB site is located on β-tubulin. Using molecular dynamics simulations, we determined complementary conformations of HB and β-tubulin that delineated in atomic detail binding interactions of HB with only β-tubulin, with no involvement of the α-subunit in the binding interaction. Moreover, the HB model served as a template for an eribulin binding model that furthered our understanding of the properties of eribulin as a drug. Overall, these results established a mechanistic basis for the antimitotic activity of the halichondrin class of compounds.

Second generation synthesis of C27-C35 building block of E7389, a synthetic halichondrin analogue

A practical method is reported to synthesize E7389 C27-C35 building block 13 from 1,2-O-isopropylidene-alpha-D-5-deoxyglucurono-6,3-lactone (3). This synthesis relies on two key processes: (1) C34/C35-diol is introduced via asymmetric dihydroxylation with dr = 3:1, with the undesired C34-diastereomer effectively removed by crystallization of 11, and (2) the C30 PhSO2CH2 group is introduced stereoselectively (>100:1) via hydrogenation of 12 in the presence of the Crabtree catalyst. The reported synthesis is practically free from chromatographic separation.

Attempts to improve the overall stereoselectivity of the Ireland-Claisen rearrangement

With focus on the steric effects present in the transition states for the [3,3]-sigmatropic rearrangement, the substrate 5 has been designed to improve the overall stereoselectivity of the Ireland-Claisen rearrangement. Experimentally, it has been found that (1) only Z-6 rearranges to 7 at 80 degrees C and (2) E-6 isomerizes to Z-6 at 80 degrees C, thereby allowing the transformation of 5 into 7 in an almost quantitative yield. To illustrate the usefulness of this approach, two additional examples are given.

Effective Procedure for Selective Ammonolysis of Monosubstituted Oxiranes: Application to E7389 Synthesis

A highly effective procedure is reported to synthesize 1,2-aminoalcohols by regio- and chemo-selective ammonolysis of monosubstituted epoxides. Additive- and concentration-effects were studied, revealing that: (1) methanesulfonic acid is most effective among the additives tested and (2) formation of bis-adducts is practically eliminated at [C] Collapse

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Grants

• R01 CA022215 NCI NIH HHS
• R01 CA022215-28 NCI NIH HHS
• R37 CA022215 NCI NIH HHS

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Affiliation(s)

Yosuke Kaburagi Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, USA
Yoshito Kishi Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, USA

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Sponge-associated microorganisms: evolution, ecology, and biotechnological potential

Marine sponges often contain diverse and abundant microbial communities, including bacteria, archaea, microalgae, and fungi. In some cases, these microbial associates comprise as much as 40% of the sponge volume and can contribute significantly to host metabolism (e.g., via photosynthesis or nitrogen fixation). We review in detail the diversity of microbes associated with sponges, including extensive 16S rRNA-based phylogenetic analyses which support the previously suggested existence of a sponge-specific microbiota. These analyses provide a suitable vantage point from which to consider the potential evolutionary and ecological ramifications of these widespread, sponge-specific microorganisms. Subsequently, we examine the ecology of sponge-microbe associations, including the establishment and maintenance of these sometimes intimate partnerships, the varied nature of the interactions (ranging from mutualism to host-pathogen relationships), and the broad-scale patterns of symbiont distribution. The ecological and evolutionary importance of sponge-microbe associations is mirrored by their enormous biotechnological potential: marine sponges are among the animal kingdom's most prolific producers of bioactive metabolites, and in at least some cases, the compounds are of microbial rather than sponge origin. We review the status of this important field, outlining the various approaches (e.g., cultivation, cell separation, and metagenomics) which have been employed to access the chemical wealth of sponge-microbe associations.

Small molecule natural products in the discovery of therapeutic agents: the synthesis connection

Natural products have been a rich source of agents of value in medicine. They have also inspired, at various levels, the fashioning of nonnatural agents of pharmaceutical import. Hitherto, these nonnatural derivatives have been primarily synthesized by manipulating the natural product. As a consequence of major innovations in the subscience of synthetic methodology, the capacity of synthesis to deal with molecules of considerable complexity has increased dramatically. In this paper, we show by example some total syntheses which draw from strategy-enabling advances in methodology. Moreover, we show how these capabilities can be used to discover and develop new agents of potential pharmaceutical value without recourse to the natural product itself.

A New Method for Translating the Asymmetric Ni/Cr-Mediated Coupling Reactions from Stoichiometric to Catalytic

[reaction: see text] A new method has been developed for effectively translating the degree of asymmetric induction and the chemical yield achieved in the stoichiometric asymmetric Ni/Cr-mediated coupling to a catalytic asymmetric process via a chiral sulfonamide ligand. It has also been shown that the Ni catalyst plays a central role. Among a number of the Ni catalysts, the 2,9-dimethylphenanthroline/NiCl(2) complex (7) has been found to be the most effective.