Total Synthesis of Abyssomicin C and atrop-Abyssomicin C

The evolving role of chemical synthesis in antibacterial drug discovery

The discovery and implementation of antibiotics in the early twentieth century transformed human health and wellbeing. Chemical synthesis enabled the development of the first antibacterial substances, organoarsenicals and sulfa drugs, but these were soon outshone by a host of more powerful and vastly more complex antibiotics from nature: penicillin, streptomycin, tetracycline, and erythromycin, among others. These primary defences are now significantly less effective as an unavoidable consequence of rapid evolution of resistance within pathogenic bacteria, made worse by widespread misuse of antibiotics. For decades medicinal chemists replenished the arsenal of antibiotics by semisynthetic and to a lesser degree fully synthetic routes, but economic factors have led to a subsidence of this effort, which places society on the precipice of a disaster. We believe that the strategic application of modern chemical synthesis to antibacterial drug discovery must play a critical role if a crisis of global proportions is to be averted.

Strategic innovation in the total synthesis of complex natural products using gold catalysis

This review has been organized from the perspective of synthetic target families, with emphasis on the use of gold-catalyzed transformations and cascade reactions that significantly increase molecular complexity.

Constructing molecular complexity and diversity: total synthesis of natural products of biological and medicinal importance

The advent of organic synthesis and the understanding of the molecule as they occurred in the nineteenth century and were refined in the twentieth century constitute two of the most profound scientific developments of all time. These discoveries set in motion a revolution that shaped the landscape of the molecular sciences and changed the world. Organic synthesis played a major role in this revolution through its ability to construct the molecules of the living world and others like them whose primary element is carbon. Although the early beginnings of organic synthesis came about serendipitously, organic chemists quickly recognized its potential and moved decisively to advance and exploit it in myriad ways for the benefit of mankind. Indeed, from the early days of the synthesis of urea and the construction of the first carbon-carbon bond, the art of organic synthesis improved to impressively high levels of sophistication. Through its practice, today chemists can synthesize organic molecules--natural and designed--of all types of structural motifs and for all intents and purposes. The endeavor of constructing natural products--the organic molecules of nature--is justly called both a creative art and an exact science. Often called simply total synthesis, the replication of nature's molecules in the laboratory reflects and symbolizes the state of the art of synthesis in general. In the last few decades a surge in total synthesis endeavors around the world led to a remarkable collection of achievements that covers a wide ranging landscape of molecular complexity and diversity. In this article, we present highlights of some of our contributions in the field of total synthesis of natural products of biological and medicinal importance. For perspective, we also provide a listing of selected examples of additional natural products synthesized in other laboratories around the world over the last few years.

Gene sequence based clustering assists in dereplication of Pseudoalteromonas luteoviolacea strains with identical inhibitory activity and antibiotic production

Some microbial species are chemically homogenous, and the same secondary metabolites are found in all strains. In contrast, we previously found that five strains of P. luteoviolacea were closely related by 16S rRNA gene sequence but produced two different antibiotic profiles. The purpose of the present study was to determine whether such bioactivity differences could be linked to genotypes allowing methods from phylogenetic analysis to aid in selection of strains for biodiscovery. Thirteen P. luteoviolacea strains divided into three chemotypes based on production of known antibiotics and four antibacterial profiles based on inhibition assays against Vibrio anguillarum and Staphylococcus aureus. To determine whether chemotype and inhibition profile are reflected by phylogenetic clustering we sequenced 16S rRNA, gyrB and recA genes. Clustering based on 16S rRNA gene sequences alone showed little correlation to chemotypes and inhibition profiles, while clustering based on concatenated 16S rRNA, gyrB, and recA gene sequences resulted in three clusters, two of which uniformly consisted of strains of identical chemotype and inhibition profile. A major time sink in natural products discovery is the effort spent rediscovering known compounds, and this study indicates that phylogeny clustering of bioactive species has the potential to be a useful dereplication tool in biodiscovery efforts.

Organoiodine(V) reagents in organic synthesis

Organohypervalent iodine reagents have attracted significant recent interest as versatile and environmentally benign oxidants with numerous applications in organic synthesis. This Perspective summarizes synthetic applications of hypervalent iodine(V) reagents: 2-iodoxybenzoic acid (IBX), Dess-Martin periodinane (DMP), pseudocyclic iodylarenes, and their recyclable polymer-supported analogues. Recent advances in the development of new catalytic systems based on the generation of hypervalent iodine species in situ are also overviewed.

Antibacterials from the sea

The ocean contains a host of macroscopic life in a great microbial soup. Unlike the terrestrial environment, an aqueous environment provides perpetual propinquity and blurs spatial distinctions. Marine organisms are under a persistent threat of infection by resident pathogenic microbes including bacteria, and in response they have engineered complex organic compounds with antibacterial activity from a diverse set of biological precursors. The diluting effect of the ocean drives the construction of potent molecules that are stable to harsh salty conditions. Members of each class of metabolite-ribosomal and non-ribosomal peptides, alkaloids, polyketides, and terpenes-have been shown to exhibit antibacterial activity. The sophistication and diversity of these metabolites points to the ingenuity and flexibility of biosynthetic processes in Nature. Compared with their terrestrial counterparts, antibacterial marine natural products have received much less attention. Thus, a concerted effort to discover new antibacterials from marine sources has the potential to contribute significantly to the treatment of the ever increasing drug-resistant infectious diseases.

The abyssomicin C family as in vitro inhibitors of Mycobacterium tuberculosis

The antimycobacterial efficacy of the abyssomicin C family of natural products, in addition to a key synthetic intermediate, has been investigated given their reported inhibition of Bacillus subtilis p-aminobenzoate biosynthesis. The naturally occurring (-)-abyssomicin C and its atropisomer were found to exhibit low micromolar growth inhibition against the relatively fast-growing and non-virulent Mycobacterium smegmatis and the vaccine strain Mycobacterium bovis BCG, while their antipodes were slightly less active. (-)-abyssomicin C and its atropisomer were particularly efficacious against Mycobacterium tuberculosis H37Rv, exhibiting MIC values of 3.6 and 7.2 μM, respectively. More specifically, (-)-abyssomicin C was bactericidal. This complex natural product and its analogs, thus, hold promise as chemical tools in the study of M. tuberculosis metabolism.

Novel anti-infective compounds from marine bacteria

As a result of the continuous evolution of microbial pathogens towards antibiotic-resistance, there have been demands for the development of new and effective antimicrobial compounds. Since the 1960s, the scientific literature has accumulated many publications about novel pharmaceutical compounds produced by a diverse range of marine bacteria. Indeed, marine micro-organisms continue to be a productive and successful focus for natural products research, with many newly isolated compounds possessing potentially valuable pharmacological activities. In this regard, the marine environment will undoubtedly prove to be an increasingly important source of novel antimicrobial metabolites, and selective or targeted approaches are already enabling the recovery of a significant number of antibiotic-producing micro-organisms. The aim of this review is to consider advances made in the discovery of new secondary metabolites derived from marine bacteria, and in particular those effective against the so called "superbugs", including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin resistant enterococci (VRE), which are largely responsible for the increase in numbers of hospital acquired, i.e., nosocomial, infections.

Expanding the range of 'druggable' targets with natural product-based libraries: an academic perspective

Existing drugs address a relatively narrow range of biological targets. As a result, libraries of drug-like molecules have proven ineffective against a variety of challenging targets, such as protein-protein interactions, nucleic acid complexes, and antibacterial modalities. In contrast, natural products are known to be effective at modulating such targets, and new libraries are being developed based on underrepresented scaffolds and regions of chemical space associated with natural products. This has led to several recent successes in identifying new chemical probes that address these challenging targets.

Scalable total synthesis and biological evaluation of haouamine A and its atropisomer

A total synthesis of the complex, bent aromatic ring-containing marine alkaloid haouamine A is achieved through a route in which every step (with the exception of the final deprotection) is performed on a gram-scale. This is accomplished through the development of a method for the dehydrogenation of cyclohexenones that allows for point-to-planar chirality transfer. This strategy makes it possible to program the desired atropisomeric outcome from a simple chiral cyclohexenone. By synthesizing atrop-haouamine A, this work has firmly established that natural haouamine exists as a single, nonequilibrating atropisomer. Finally, biological investigations demonstrate that the bent aromatic ring of this natural product is critical for anticancer activity against PC3 cells.

Marine natural products

This review covers the literature published in 2007 for marine natural products, with 948 citations(627 for the period January to December 2007) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, cnidarians,bryozoans, molluscs, tunicates, echinoderms and true mangrove plants. The emphasis is on new compounds (961 for 2007), together with the relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.1 Introduction, 2 Reviews, 3 Marine microorganisms and phytoplankton, 4 Green algae, 5 Brown algae, 6 Red algae, 7 Sponges, 8 Cnidarians, 9 Bryozoans, 10 Molluscs, 11 Tunicates (ascidians),12 Echinoderms, 13 Miscellaneous, 14 Conclusion, 15 References.

Recent advances in the chemistry and biology of naturally occurring antibiotics

Ever since the world-shaping discovery of penicillin, nature's molecular diversity has been extensively screened for new medications and lead compounds in drug discovery. The search for agents intended to combat infectious diseases has been of particular interest and has enjoyed a high degree of success. Indeed, the history of antibiotics is marked with impressive discoveries and drug-development stories, the overwhelming majority of which have their origin in natural products. Chemistry, and in particular chemical synthesis, has played a major role in bringing naturally occurring antibiotics and their derivatives to the clinic, and no doubt these disciplines will continue to be key enabling technologies. In this review article, we highlight a number of recent discoveries and advances in the chemistry, biology, and medicine of naturally occurring antibiotics, with particular emphasis on total synthesis, analogue design, and biological evaluation of molecules with novel mechanisms of action.

Discoveries from the Abyss: The Abyssomicins and Their Total Synthesis

Abyssomicin C is a recently discovered antibiotic with promising antibacterial activity, high structural complexity, and a novel mechanism of action. We give an account of our abyssomicin campaign and some of the discoveries that were borne of our total synthesis efforts, including a new Lewis acid-templated Diels-Alder reaction, the previously undescribed atrop-abyssomicin C, a facile Brønsted acid-catalyzed isomerization of abyssomicin C, and clarification of the likely biosynthetic origin of abyssomicin D.

Panning for chemical gold: marine bacteria as a source of new therapeutics

Marine bacteria are emerging as an exciting resource for the discovery of new classes of therapeutics. The promising anticancer clinical candidates salinosporamide A and bryostatin only hint at the incredible wealth of drug leads hidden just beneath the ocean surface. For example, if properly developed, marine bacteria could provide the drugs needed to sustain us for the next 100 years in our battle against drug-resistant infectious diseases. This review will focus on several recently discovered compounds, primarily from cyanobacteria and actinobacteria, that illustrate the tremendous potential of marine bacteria as a source of new therapeutics within the areas of oncology and infectious diseases.

From nature to the laboratory and into the clinic

Natural products possess a broad diversity of structure and function, and they provide inspiration for chemistry, biology, and medicine. In this review article, we highlight and place in context our laboratory's total syntheses of, and related studies on, complex secondary metabolites that were clinically important drugs, or have since been developed into useful medicines, namely amphotericin B (1), calicheamicin gamma(1)(I) (2), rapamycin (3), Taxol (4), the epothilones [e.g., epothilones A (5) and B (6)], and vancomycin (7). We also briefly highlight our research with other selected inspirational natural products possessing interesting biological activities [i.e., dynemicin A (8), uncialamycin (9), eleutherobin (10), sarcodictyin A (11), azaspiracid-1 (12), thiostrepton (13), abyssomicin C (14), platensimycin (15), platencin (16), and palmerolide A (17)].

Nickel-Catalyzed Cycloisomerization of Enynes: Catalyst Generation via C-H Activation of Carbene Ligands

The combination of Ni(0) and an N-heterocyclic carbene act as a precatalyst for the cycloisomerization of enynes to afford 1,3-dienes. During the course of the reaction, a nickel hydride is formed from oxidative addition of the ortho C-H on the carbene ligand. Deuteriumn labeling studies are presented.

Total synthesis of complex heterocyclic natural products

Total synthesis campaigns toward complex heterocyclic natural products are a prime source of inspiration for the design and execution of complex cascade sequences, powerful reactions, and efficient synthetic strategies. We highlight selected examples of such innovations in the course of our total syntheses of diazonamide A, azaspiracid-1, thiostrepton, 2,2'-epi-cytoskyrin A and rugulosin, abyssomycin C, platensimycin, and uncialamycin.

Progress Towards the Total Synthesis of Trichodermamides A and B: Construction of the Oxazine Ring Moiety

Trichodermamides are modified heterocyclic dipeptides that possess a unique 4H-5,6-dihydro-1,2-oxazine ring. Starting from affordable, easily available (-)-quinic acid, the enantioselective synthesis of this oxazine moiety was achieved by an intramolecular epoxide ring-opening reaction by an oxime. [structure: see text]