Asymmetric Allenylation of Alkynes mediated by Chiral Organoselenated Reagents under Oxidative Conditions.

The reactivity of novel chiral lactamide-substituted diselenide-based reagents under oxidative conditions was exploited to develop a metal-free method for the preparation of enantioenriched allenylamides from simple alkynes in good yields, and with enantiomeric excesses up to 99 %. The key of the success in this method is attributed to the hydrogen-bonded lactamide appendages that ensure configurational stability of chiral vinyl selenoxide intermediates for an optimal enantiotopic β-syn-elimination step.

Bispericyclic Diels-Alder Dimerization of ortho-Quinols in Natural Product (Bio)Synthesis: Bioinspired Chemical 6-Step Synthesis of (+)-Maytenone.

Many natural products of plant or microbial origins are derived from enzymatic dearomative oxygenation of 2-alkylphenolic precursors into 6-alkyl-6-hydroxycyclohexa-2,4-dienones. These so-called ortho-quinols cyclodimerize via a remarkably selective bispericyclic Diels-Alder reaction. Whether or not the intervention of catalytic or dirigent proteins is involved during this final step of the biosynthesis of these natural products, this cyclodimerization of ortho-quinols can be chemically reproduced in the laboratory with the same strict level of site-specific regioselectivity and stereoselectivity.

Real-Time Analysis of Polyphenol-Protein Interactions by Surface Plasmon Resonance Using Surface-Bound Polyphenols.

A selection of bioactive polyphenols of different structural classes, such as the ellagitannins vescalagin and vescalin, the flavanoids catechin, epicatechin, epigallocatechin gallate (EGCG), and procyanidin B2, and the stilbenoids resveratrol and piceatannol, were chemically modified to bear a biotin unit for enabling their immobilization on streptavidin-coated sensor chips. These sensor chips were used to evaluate in real time by surface plasmon resonance (SPR) the interactions of three different surface-bound polyphenolic ligands per sensor chip with various protein analytes, including human DNA topoisomerase IIα, flavonoid leucoanthocyanidin dioxygenase, B-cell lymphoma 2 apoptosis regulator protein, and bovine serum albumin. The types and levels of SPR responses unveiled major differences in the association, or lack thereof, and dissociation between a given protein analyte and different polyphenolic ligands.

Synthesis and leishmanicidal evaluation of sulfanyl- and sulfonyl-tethered functionalized benzoate derivatives featuring a nitroimidazole moiety.

A series of new nitroimidazole-containing derivatives was synthesized by coupling of 2-[2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethylthio]ethanol with diversely substituted benzoic acids. Upon treatment with m-CPBA, 12 of these sulfanyl compounds were further oxidized to their sulfonyl analogs. All the 26 synthetic compounds were examined for in vitro activity against Leishmania (V.

Blue LED Irradiation of Iodonium Ylides Gives Diradical Intermediates for Efficient Metal-free Cyclopropanation with Alkenes.

A facile and highly chemoselective synthesis of doubly activated cyclopropanes is reported where mixtures of alkenes and β-dicarbonyl-derived iodonium ylides are irradiated with light from blue LEDs. This metal-free synthesis gives cyclopropanes in yields up to 96 %, is operative with cyclic and acyclic ylides, and proceeds with a variety of electronically-diverse alkenes. Computational analysis explains the high selectivity observed, which derives from exclusive HOMO to LUMO excitation, instead of free carbene generation.

Bio-inspired Total Synthesis of Twelve Securinega Alkaloids: Structural Reassignments of (+)-Virosine B and (-)-Episecurinol A.

The so-called Securinega alkaloids constitute a class of tetracyclic biologically active specialised metabolites isolated principally from subtropical plants belonging to the Phyllanthaceae family. Following a strategy based on alternative hypotheses for their biosynthesis, an easy and time-efficient divergent synthesis enabled access to twelve of those alkaloids featuring (neo)(nor)securinane skeletons. Moreover, this work permitted to reassign the absolute configurations of (+)-virosine B and (-)-episecurinol A.

Synthesis of [7]Helicene Enantiomers and Exploratory Study of Their Conversion into Helically Chiral Iodoarenes and Iodanes.

The facile and convenient preparation of both enantiomers of a [7]helicene scaffold from inexpensive (l)-(+)-tartaric acid and 4-methylstyrene is described. These helical structures were transformed into bis-iodinated ether derivatives in order to explore their potential as precursors of novel chiral organoiodane reagents or as iodoarene pre-catalysts. Promising results were obtained in hydroxylative phenol dearomatization/[4+2] cycloaddition cascade and dearomative spirolactonization reactions with encouraging enantiomeric excesses.

Synthesis of Scyphostatin Analogues through Hypervalent Iodine-Mediated Phenol Dearomatization.

A concise synthesis of two scyphostatin analogues is achieved from readily available ortho-substituted phenols. Key features include an asymmetric and biomimetic hydroxylative phenol dearomatization (HPD) reaction promoted by a chiral salen-type bis(λ-iodane) reagent, followed by an in situ regio- and diastereocontrolled epoxidation.

Bioinspired Total Synthesis of (-)-Vescalin: A Nonahydroxytriphenoylated C-Glucosidic Ellagitannin.

The first total synthesis of the 2,3,5-O-(S,R)-nonahydroxytriphenoylated (NHTP) C-glucosidic ellagitannin (-)-vescalin was accomplished through a series of transformations mimicking the sequence of events leading to its biogenesis. The key steps of this synthesis encompass a Wittig-mediated ring opening of a glucopyranosic hemiacetal, a C-glucosidation event through a phenolic aldol-type reaction, and a Wynberg-Feringa-Yamada-type oxidative phenolic coupling, which forged the NHTP unit of (-)-vescalin.

Asymmetric Alkynylation of β-Ketoesters and Naphthols Promoted by New Chiral Biphenylic Iodanes.

The preparation of new chiral biphenylic λ -iodane reagents bearing transferable alkynyl ligands is described. These reagents transfer their carbon-based ligands onto β-ketoesters with an enantiomeric excess (ee) up to 68 %, and most remarkably, enable the dearomative alkynylation of naphthols in good to high yields up to 84 % ee.

ortho-Quinol Acetate Chemistry: Reactivity toward Aryl-Based Nucleophiles and Applications to the Synthesis of Natural Products.

Two model ortho-quinol acetates were easily prepared by iodane-mediated acetoxylative phenol dearomatization and evaluated for their reactivity toward various aryl-based nucleophiles, i.e., aryl metallic reagents and phenolic derivatives.

Epicocconone-Hemicyanine Hybrids: Near Infrared Fluorophores for Protein Staining and Cell Imaging.

The development of new near infrared (NIR) dyes is crucial for diverse applications and especially bioimaging, as they absorb and emit light in the "therapeutic window" (650-950 nm). We report here a new family of NIR fluorophores that has been obtained by hybridising hemicyanines with epicocconone. Emission wavelengths of these hybrid dyes is in the range 715-795 nm and is combined with large Stokes' shifts (75-95 nm).

Flexible Total Synthesis of (±)-Aureothin, a Potent Antiproliferative Agent.

Amenable to late-stage preparation of analogues, a flexible and convergent total synthesis of (±)-aureothin is presented. The strategy was based on a desymmetrization of α,α'-dimethoxy-γ-pyrone by a process combining 1,4-addition and alkylation of vinylogous enolate to stereoselectively reach the backbone of the target. Palladium-catalyzed cyanation of an elaborated and isomerizable E,Z dienyl motif followed by Pinner cyclization enabled the construction of the tetrahydrofuran motif while a first approach based on a late-stage oxidation was unsuccessful.

Total Synthesis of (-)-Bacchopetiolone via an Asymmetric Hydroxylative Phenol Dearomatization/[4+2]-Dimerization Cascade Promoted by a Novel Salen-Type Chiral Iodane.

The first total and biomimetic synthesis of the natural bis(sesquiterpene) (-)-bacchopetiolone (revised structure) was completed through a highly diastereoselective hydroxylative phenol dearomatization/[4+2]-dimerization cascade conversion of (+)-curcuphenol using a novel C2-symmetrical chiral Salen-type bis(λ(5)-iodane).

Phenol Dearomatization with Hypervalent Iodine Reagents.

This chapter highlights recent developments in phenol dearomatization using organoiodane reagents and a selection of applications in natural product synthesis.

Design and synthesis of epicocconone analogues with improved fluorescence properties.

Epicocconone is a natural latent fluorophore that is widely used in biotechnology because of its large Stokes shift and lack of fluorescence in its unconjugated state. However, the low photostability and quantum yields of epicocconone have limited its wider use, and in the absence of a total synthesis, this limitation has been a long-standing problem. Here we report a general strategy for the synthesis of epicocconone analogues that relies on a 2-iodoxybenzoic acid-mediated dearomatization and on the replacement of the triene tail of the natural product by an aromatic ring.

Asymmetric hydroxylative phenol dearomatization promoted by chiral binaphthylic and biphenylic iodanes.

The long-standing quest for chiral hypervalent organoiodine compounds (i.e., iodanes) as metal-free reagents for asymmetric synthesis continues.

A theoretical study on diastereoselective oxidative dearomatization by iodoxybenzoic acid.

The reaction mechanism of diastereoselective oxidative dearomatization by iodoxybenzoic acid of key compounds involved in the total synthesis of epicocconone analogs, which are efficient fluorophores with a wide range of applications in protein staining and separation, was studied using density functional theory. In particular, the conformational space was investigated, as was the role of the so-called hypervalent twist move, which is thought to be the rate-determining step. Both kinetic and thermodynamical aspects of the mechanism were considered from static and dynamic viewpoints, including solvent effects.

The role of different structural motifs in the ultrafast dynamics of second generation protein stains.

Engineering the properties of fluorescent probes through modifications of the fluorophore structure has become a subject of interest in recent times. By doing this, the photophysical and photochemical properties of the modified fluorophore can be understood and this can guide the design and synthesis of better fluorophores for use in biotechnology. In this work, the electronic spectra and fluorescence decay kinetics of four analogues of the fluorescent natural product epicocconone were investigated.

Electronic excitations in epicocconone analogues: TDDFT methodological assessment guided by experiment.

In this work we present a combined theoretical and experimental study of UV/vis absorption spectra of novel organic chromophores derived from epicocconone. A computational protocol, consistent with experimental findings, is proposed in the framework of time-dependent density functional theory. More precisely, the influence of density functional, basis set, and solvation effects is assessed through theory-experiment matching.

Total synthesis of echinopines A and B: exploiting a bioinspired late-stage intramolecular cyclopropanation.

Total synthesis of echinopine A and B have been accomplished, based on a strategy that involved two transition-metal-mediated ene-yne cycloisomerizations. A modified Pd-catalyzed enyne cycloisomerization/intramolecular Diels-Alder cascade rendered a more streamlined synthesis of tricyclic ketone 15, and a Ru-catalyzed ene-yne cycloisomerization/cyclopropanation resembled the late-stage [5/7] → [3/5/5/7] ring-forming sequence in the proposed biosynthetic pathway.