Enantioselective divergent approaches to both (−)-platensimycin and (−)-platencin

Catalyst-Controlled Regiodivergent Oxidation of Unsymmetrical Diols

In this work we use aminoxyl-peptide conjugates to catalyze the regiodivergent oxidation of unsymmetrical diols. Through structural tuning of both the aminoxyl catalytic core and the chiral peptide backbone, we achieved catalyst control that either reinforces or overrides the intrinsic steric bias, leading to oxidation of either the less hindered or the more hindered alcohol in high selectivity.

Asymmetric Synthesis and Biological Evaluation of Platensilin, Platensimycin, Platencin, and Their Analogs via a Bioinspired Skeletal Reconstruction Approach

Platensilin, platensimycin, and platencin are potent inhibitors of β-ketoacyl-acyl carrier protein synthase (FabF) in the bacterial and mammalian fatty acid synthesis system, presenting promising drug leads for both antibacterial and antidiabetic therapies. Herein, a bioinspired skeleton reconstruction approach is reported, which enables the unified synthesis of these three natural FabF inhibitors and their skeletally diverse analogs, all stemming from a common ent-pimarane core. The synthesis features a diastereoselective biocatalytic reduction and an intermolecular Diels-Alder reaction to prepare the common ent-pimarane core. From this intermediate, stereoselective Mn-catalyzed hydrogen atom-transfer hydrogenation and subsequent Cu-catalyzed carbenoid C-H insertion afford platensilin. Furthermore, the intramolecular Diels-Alder reaction succeeded by regioselective ring opening of the newly formed cyclopropane enables the construction of the bicyclo[3.2.1]-octane and bicyclo[2.2.2]-octane ring systems of platensimycin and platencin, respectively. This skeletal reconstruction approach of the ent-pimarane core facilitates the preparation of analogs bearing different polycyclic scaffolds. Among these analogs, the previously unexplored cyclopropyl analog 47 exhibits improved antibacterial activity (MIC80 = 0.0625 μg/mL) against S. aureus compared to platensimycin.

Navigating the Chiral Pool in the Total Synthesis of Complex Terpene Natural Products

The pool of abundant chiral terpene building blocks (i.e., "chiral pool terpenes") has long served as a starting point for the chemical synthesis of complex natural products, including many terpenes themselves. As inexpensive and versatile starting materials, such compounds continue to influence modern synthetic chemistry. This review highlights 21st century terpene total syntheses which themselves use small, terpene-derived materials as building blocks. An outlook to the future of research in this area is highlighted as well.

Highly stereoselective cyclopropanation of various olefins with diazosulfones catalyzed by Ru(ii)–Pheox complexes

A highly stereoselective cyclopropanation of various olefins with diazosulfones catalyzed by chiral Ru(ii)–Pheox complexes was developed to give chiral cyclopropyl sulfones in high yields (up to 99%) with excellent trans-selectivity and enantioselectivity (up to 98% ee).

Total synthesis of natural products using hypervalent iodine reagents

We present a review of natural product syntheses accomplished in our laboratory during the last 5 years. Each synthetic route features a phenol dearomatization promoted by an environmentally benign hypervalent iodine reagent. The dearomatizations demonstrate the "aromatic ring umpolung" concept, and involve stereoselective remodeling of the inert unsaturations of a phenol into a highly functionalized key intermediate that may contain a quaternary carbon center and a prochiral dienone system. Several new oxidative strategies were employed, including transpositions (1,3-alkyl shift and Prins-pinacol), a polycyclization, an ipso rearrangement, and direct nucleophilic additions at the phenol para position. Several alkaloids, heterocyclic compounds, and a polycyclic core have been achieved, including sceletenone (a serotonin reuptake inhibitor), acetylaspidoalbidine (an antitumor agent), fortucine (antiviral and antitumor), erysotramidine (curare-like effect), platensimycin (an antibiotic), and the main core of a kaurane diterpene (immunosuppressive agent and stimulator of apoptosis). These concise and in some cases enantioselective syntheses effectively demonstrate the importance of hypervalent iodine reagents in the total synthesis of bioactive natural products.

Formal synthesis of (−)-platensimycin

An efficient formal synthesis of (−)-platensimycin was completed by using a tandem C–H oxidation/C–C coupling (cyclization)/rearrangement as the key step.

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.

Catalytic desymmetrization of cyclohexadienes by asymmetric bromolactonization

Asymmetric bromolactonization of prochiral cyclohexadiene derivatives with N-bromosuccimide proceeded in the presence of (DHQD)(2)PHAL as a chiral catalyst to afford the corresponding bromolactones with up to 93% ee. This reaction was also applicable to the kinetic resolution of a racemic cyclic ene-carboxylic acid, where the starting material was recovered with high enantioselectivity.

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.

Stereoselective total synthesis of nemorosone

The highly stereoselective total synthesis of nemorosone via a new approach to the bicyclo[3.3.1]nonane-2,4,9-trione core which features intramolecular cyclopropanation of an α-diazo ketone, stereoselective alkylation at the C8 position, and regioselective ring-opening of cyclopropane is described. The total synthesis of nemorosone includes chemo- and stereoselective hydrogenation directed by the internal alkene.