A Nine-Step Total Synthesis of (−)-Platencin

Stereochemical editing logic powered by the epimerization of unactivated tertiary stereocenters

The stereoselective synthesis of complex targets requires the precise orchestration of chemical transformations that simultaneously establish the connectivity and spatial orientation of desired bonds. In this work, we describe a complementary paradigm for the synthesis of chiral molecules and their isomers, which tunes the three-dimensional structure of a molecule at a late stage. Key to the success of this strategy is the development of a mild and highly general photocatalytic method composed of decatungstate polyanion and disulfide cocatalysts, which enable the interconversion of unactivated tertiary stereogenic centers that were previously configurationally fixed. We showcase the versatility of this method-and the implementation of stereoediting logic-by the rapid construction of chiral scaffolds that would be challenging to access using existing tools and by the late-stage stereoediting of complex targets.

Comparison the effect of fruits extract with fungal protease on waffle quality

The purpose of this study was investigated the effect of kiwifruit and fig extracts contain of protease enzyme as a natural additives in comparison with fungal protease enzyme on the sensory and quality properties of waffle. It was done by use of the one- way ANOVA design for three independent variables including: kiwifruit extract and fig extract (0.03 and 0.05%) and fungal protease enzyme (0.003 and 0.005%). These results suggest that pH, moisture, firmness, dough consistency, density, color and texture of waffles were improved by the addition of fungal protease enzyme and kiwifruit extract in comparison with fig extract. The dough Consistency (cm) was reduced by using protease enzyme from 8.95 ± 0.92 to 19.75 ± 1.03. The moisture content and dough density was reduced by using protease enzyme and the minim moisture and dough density was at waffle with 0.05% kiwifruit. The color index, SEM, hardness and extensibility were improved by using 0.005% protease enzyme and 0.05% kiwi fruit extract. The highest sensory properties were at sample with 0.05% kiwi fruit extract. The result demonstrated that the addition of 0.05% kiwifruit extract improved the quality of the waffle, and could replace by fungal protease enzyme for reduce cost in production.

An Experimental Toolbox for Structure-Based Hit Discovery for P. aeruginosa FabF, a Promising Target for Antibiotics

FabF (3-oxoacyl-[acyl-carrier-protein] synthase 2), which catalyses the rate limiting condensation reaction in the fatty acid synthesis II pathway, is an attractive target for new antibiotics. Here, we focus on FabF from P. aeruginosa (PaFabF) as antibiotics against this pathogen are urgently needed. To facilitate exploration of this target we have set up an experimental toolbox consisting of binding assays using bio-layer interferometry (BLI) as well as saturation transfer difference (STD) and WaterLOGSY NMR in addition to robust conditions for structure determination. The suitability of the toolbox to support structure-based design of FabF inhibitors was demonstrated through the validation of hits obtained from virtual screening. Screening a library of almost 5 million compounds resulted in 6 compounds for which binding into the malonyl-binding site of FabF was shown. For one of the hits, the crystal structure in complex with PaFabF was determined. Based on the obtained binding mode, analogues were designed and synthesised, but affinity could not be improved. This work has laid the foundation for structure-based exploration of PaFabF.

Short Enantioselective Formal Synthesis of (-)-Platencin

A short enantioselective formal synthesis of the antibiotic natural product platencin is reported. Key steps in the synthesis include enantioselective decarboxylation alkylation, aldehyde/olefin radical cyclization, and regioselective aldol cyclization.

Nutritional control of antibiotic production by Streptomyces platensis MA7327: importance of l-aspartic acid

Streptomyces platensis MA7327 is a bacterium producing interesting antibiotics, which act by the novel mechanism of inhibiting fatty acid biosynthesis. The antibiotics produced by this actinomycete are platensimycin and platencin plus some minor related antibiotics. Platensimycin and platencin have activity against antibiotic-resistant bacteria such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus; they also lack toxicity in animal models. Platensimycin also has activity against diabetes in a mouse model. We have been interested in studying the effects of primary metabolites on production of these antibiotics in our chemically defined production medium. In the present work, we tested 32 primary metabolites for their effect. They included 20 amino acids, 7 vitamins and 5 nucleic acid derivatives. Of these, only l-aspartic acid showed stimulation of antibiotic production. We conclude that the stimulatory effect of aspartic acid is due to its role as a precursor involved in the biosynthesis of aspartate-4-semialdehyde, which is the starting point for the biosynthesis of the 3-amino-2,4-dihydroxy benzoic acid portion of the platensimycin molecule.

Recent advances in the synthesis of natural multifunctionalized decalins

This review highlights recent innovative synthetic strategies developed for the stereoselective construction of natural complex decalin systems. It offers an insight into various synthetic targets and approaches and provides information for developments within the area of natural products as well as synthetic methodology.

Short and Efficient Synthesis of Alkyl- and Aryl-Ortho-Hydroxy-Anilides and their Antibiotic Activity

Ortho-hydroxy-anilides are part of natural products like the new antibiotics platencin (A) and platensimycin (B). An important step in the total synthesis of these antibiotics or their derivatives is the preparation of the o-hydroxy-anilide partial structure. The presented method allows the preparation of o-hydroxy-anilides and o-dihydroxy-anilides from 2-nitrophenol esters in a one-step synthesis without protecting the hydroxy group. Aryl- and alkyl-anilides were prepared following this method as simple analogues of platensimycin (A). The resulting compounds were tested in an agar diffusion assay for their antibiotic potency.

A concise formal synthesis of platencin

A formal synthesis of platencin features an organocatalytic approach to the [2.2.2] bicycle, a radical reductive elimination, a Au-catalyzed rearrangement and a Rh-catalyzed hydrosilylation.

Enantioselective synthesis of bicyclo[2.2.2]octane-1-carboxylates under metal free conditions

A new tandem reaction permits rapid access to bicyclo[2.2.2]octane-1-carboxylates with excellent enantioselectivities under metal free, mild, and operationally simple conditions.

A new route to platencin via decarboxylative radical cyclization

A new approach to platencin, a potent antibiotic isolated from Streptomyces platensis, has been established. The highly congested tricyclic core of the natural product was successfully constructed by decarboxylative radical cyclization of an alkynyl silyl ester with Pb(OAc)4 in the presence of pyridine in refluxing 1,4-dioxane. The key decarboxylation, which likely takes place via lead(IV) esterification followed by carbon-centered radical generation and subsequent capture of the radical with a triple bond, allows the rapid construction of the twisted polycyclic system.

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.

Platensimycin and platencin: promising antibiotics for future application in human medicine

Platensimycin and platencin are novel antibiotics produced by Streptomyces platensis. They are potent and non-toxic natural products active against Gram-positive pathogens, including antibiotic-resistant strains and Mycobacterium tuberculosis. They were isolated using an intriguing target-based whole-cell antisense differential sensitivity assay as inhibitors of fatty acid biosynthesis of type II. This type of biosynthesis is not present in humans. Platensimycin inhibits the elongation-condensing enzyme FabF, whereas platencin inhibits both FabF and FabH. For these antibiotics to become successful drugs, their pharmacokinetics must be improved. They have too high a rate of clearance in the body, yielding a low degree of systematic exposure. They work well when administered by continuous infusion, but this is not a useful method of delivery to patients. The two antibiotics and many analogs have been prepared by chemical synthesis. Natural congeners have also been obtained from the producing actinomycete. However, none of these molecules are as active as platensimycin and platencin. Using tools of rational metabolic engineering, superior strains have been produced making hundreds of times more antibiotic than the natural strains.

Syntheses and antibacterial properties of iso-platencin, Cl-iso-platencin and Cl-platencin: identification of a new lead structure

Platencin is a novel antibiotic which is active against multiresistant pathogens. We describe efficient syntheses of three platencin analogues of varying activities which allow further conclusions about the pharmacophoric part of the molecule. The unnatural antibiotic iso-platencin, which is about as active as natural platencin, but much more selective, was identified as a new lead structure.

Discovery and syntheses of "superbug challengers"-platensimycin and platencin

Bacteria have developed resistance to almost all existing antibiotics known today and this has been a major issue over the last few decades. The search for a new class of antibiotics with a new mode of action to fight these multiply-drug-resistant strains, or "superbugs", allowed a team of scientists at Merck to discover two novel antibiotics, platensimycin and platencin using advanced screening strategies, as inhibitors of bacterial fatty acid biosynthesis, which is essential for the survival of bacteria. Though both these antibiotics are structurally related, they work by slightly different mechanisms and target different enzymes conserved in the bacterial fatty acid biosynthesis. This Focus Review summarizes the synthetic and biological aspects of these natural products and their analogues and congeners.

Synthesis and antibacterial properties of (-)-nor-platencin

An asymmetric Diels-Alder reaction between acrolein and 1-benzyloxymethyl-1,3-cyclohexadiene affords a bicyclic aldehyde that was elaborated in 11 steps to nor-platencin. nor-Platencin is 4-16 times less active than platencin against several resistant strains of Staphylococcus aureus, macrolide-resistant Enterococcus faecalis, and vancomycin-resistant Enterococcus faecium.

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.

The economies of synthesis

In this tutorial review the economies of synthesis are analysed from both detailed and macroscopic perspectives, using case-studies from complex molecule synthesis. Atom, step, and redox economy are more than philosophical constructs, but rather guidelines, which enable the synthetic chemist to design and execute an efficient synthesis. Students entering the field of synthesis might find this tutorial helpful for understanding the subtle differences between these economic principles and also see real-world situations where such principles are put into practice.

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.