Adamantaplatensimycin: a bioactive analogue of platensimycin

7-Phenylplatensimycin and 11-methyl-7-phenylplatensimycin: more potent analogs of platensimycin

Carbonyl ylide cycloaddition strategy was employed in the synthesis of platensimycin analogs. 7-Phenylplatensimycin and 11-methyl-7-phenylplatensimycin are more potent analogs of platensimycin.

Total synthesis of platensimycin and related natural products

Platensimycin is the flagship member of a new and growing class of antibiotics with promising antibacterial properties against drug-resistant bacteria. The total syntheses of platensimycin and its congeners, platensimycins B(1) and B(3), platensic acid, methyl platensinoate, platensimide A, homoplatensimide A, and homoplatensimide A methyl ester, are described. The convergent strategy developed toward these target molecules involved construction of their cage-like core followed by attachment of the various side chains through amide bond formation. In addition to a racemic synthesis, two asymmetric routes to the core structure are described: one exploiting a rhodium-catalyzed asymmetric cycloisomerization, and another employing a hypervalent iodine-mediated de-aromatizing cyclization of an enantiopure substrate. The final two bonds of the core structure were forged through a samarium diiodide-mediated ketyl radical cyclization and an acid-catalyzed etherification. The rhodium-catalyzed asymmetric reaction involving a terminal acetylene was developed as a general method for the asymmetric cycloisomerization of terminal enynes.

Total syntheses of (+/-)-platencin and (-)-platencin

The secondary metabolites platensimycin and platencin, isolated from the bacterial strain Streptomyces platensis, represent a novel class of natural products exhibiting unique and potent antibacterial activity. Platencin, though structurally similar to platensimycin, has been found to operate through a slightly different mechanism of action involving the dual inhibition of lipid elongation enzymes FabF and FabH. Both natural products exhibit strong, broad-spectrum, gram-positive antibacterial activity to key antibiotic resistant strains, including methicillin-resistant Staphylococcus aureus, vancomycin-intermediate S. aureus, and vancomycin-resistant Enterococcus faecium. Described herein are our synthetic efforts toward platencin, culminating in both racemic and asymmetric preparation of the natural product. The syntheses demonstrate the power of the cobalt-catalyzed asymmetric Diels-Alder reaction and the one-pot reductive rearrangement of [3.2.1] bicyclic ketones to [2.2.2] bicyclic olefins.

Isoplatensimycin: Synthesis and biological evaluation

Isoplatensimycin, a novel analog of platensimycin, was synthesized via intramolecular dipolar cycloaddition of a carbonyl ylide. Isoplatensimycin showed little activities against strains of Staphylococcus aureus, but exhibited activities against some vancomycin-resistant enteroccoci.

Synthesis and biological evaluation of platensimycin analogs

Platensimycin (1) displays antibacterial activity due to its inhibition of the elongation condensing enzyme (FabF), a novel mode of action that could potentially lead to a breakthrough in developing a new generation of antibiotics. The medicinal chemistry efforts were focused on the modification of the enone moiety of platensimycin and several analogs showed significant activity against FabF and possess antibacterial activity.

Total synthesis of (-)-platensimycin, a novel antibacterial agent

An enantioselective synthesis of platensimycin, a novel antibiotic natural product that inhibits bacterial beta-ketoacyl-(acyl-carrier-protein) synthase (FabF), is described. Our synthetic strategy for the construction of the oxatetracyclic core involved an intramolecular Diels-Alder reaction. Our preliminary studies provided a complex tetracyclic product by first undergoing an interesting 1,5-hydride shift followed by a Diels-Alder reaction. Further optimization of the diene's electronic properties, by incorporation of a methoxy group, led to the oxatetracyclic core of platensimycin. The three required chiral centers, including two all-carbon quaternary chiral centers, were built in the intramolecular Diels-Alder step. The synthesis utilized natural (+)-carvone as the key chiral starting material, which determined the stereochemistry of the final product. The synthesis also featured an efficient Petasis olefination, a hydroboration sequence, a Gais's asymmetric Horner-Wadsworth-Emmons reaction, and a mercury salt catalyzed enol ether isomerization.

Engineered Streptomyces platensis strains that overproduce antibiotics platensimycin and platencin

Platensimycin, which is isolated from Streptomyces platensis MA7327, and platencin, which is isolated from S. platensis MA7339, are two recently discovered natural products that serve as important antibiotic leads. Here we report on the identification of S. platensis MA7327 as a dual producer of both platensimycin and platencin. A PCR-based approach was used to locate and clone the locus involved in platensimycin and platencin production, including ptmR1, which encodes a putative GntR-like transcriptional regulator. Deletion of this gene from the producing organism allowed us to isolate strains that overproduce platensimycin and platencin with yields of 323 +/- 29 mg/liter and 255 +/- 30 mg/liter, respectively. These results illustrate the effectiveness of genetic manipulation for the rational engineering of improvements in titers.

A symmetry-based concise formal synthesis of platencin, a novel lead against "superbugs"

Quick access: A concise and efficient formal synthesis of platencin has been accomplished in nine steps from a commercially available starting material. The synthesis utilized only one protecting group. The base-catalyzed Michael cyclization of precursor 1 afforded the key diketone 2, which was converted into the desired core structure 4 via the radical intermediate 3.

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.

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)].

Design, synthesis, and biological evaluation of platensimycin analogues with varying degrees of molecular complexity

The molecular design, chemical synthesis, and biological evaluation of two distinct series of platensimycin analogues with varying degrees of complexity are described. The first series of compounds probes the biological importance of the benzoic acid subunit of the molecule, while the second series explores the tetracyclic cage domain. The biological data obtained reveal that, while the substituted benzoic acid domain of platensimycin is a highly conserved structural motif within the active compounds with strict functional group requirements, the cage domain of the molecule can tolerate considerable structural modifications without losing biological action. These findings refine our present understanding of the platensimycin pharmacophore and establish certain structure-activity relationships from which the next generation of designed analogues of this new antibiotic may emerge.

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.

Total synthesis and antibacterial properties of carbaplatensimycin

The chemical synthesis and biological evaluation of carbaplatensimycin, the carbon analogue of the recently reported antibiotic platensimycin has been accomplished. Carbaplatensimycin exhibited similar potency to the natural product as an antibacterial agent against a variety of strains, including methicilin- and vancomycin-resistant bacteria.

Enantioselective Synthesis of (−)-Platensimycin Oxatetracyclic Core by Using an Intramolecular Diels−Alder Reaction

An enantioselective route to the oxatetracyclic core of (-)-platensimycin (1) has been investigated by using an intramolecular Diels-Alder reaction as the key step. The thermal reaction of E/Z mixture (1:1) provided oxatetracyclic core 2 from the E-diene and the Z-diene was recovered unchanged. The Diels-Alder substrate was conveniently assembled in optically active form with use of (S)-carvone as the starting material.