Multi-bond forming and iodo-selective base-promoted homolytic aromatic substitution

Base-promoted homolytic aromatic substitution (BHAS) has been applied as a means to effect multi-bond forming reactions.</p

Xanthones from fungi, lichens, and bacteria : the natural products and their synthesis

Many fungi, lichens, and bacteria produce xanthones (derivatives of 9H-xanthen-9-one, “xanthone” from the Greek “xanthos”, for “yellow”) as secondary metabolites. Xanthones are typically polysubstituted and occur as either fully aromatized, dihydro-, tetrahydro-, or, more rarely, hexahydro-derivatives. This family of compounds appeals to medicinal chemists because of their pronounced biological activity within a notably broad spectrum of disease states, a result of their interaction with a correspondingly diverse range of target biomolecules. This has led to the description of xanthones as “privileged structures”.(1) Historically, the total synthesis of the natural products has mostly been limited to fully aromatized targets. Syntheses of the more challenging partially saturated xanthones have less frequently been reported, although the development in recent times of novel and reliable methods for the construction of the (polysubstituted) unsaturated xanthone core holds promise for future endeavors. In particular, the fascinating structural and biological properties of xanthone dimers and heterodimers may excite the synthetic or natural product chemist

Xanthones are privileged scaffolds in medicinal chemistry - but are they over-privileged?

The xanthone core underpins a staggering diversity of bioactive molecules. Xanthones, of either natural or of synthetic origin, have been found to be active in virtually every class of major disease state known. This plethora of activities includes anti-algal, anti-allergic, anti-bacterial, anti-cancer, anti-fungal, anti-HIV, anti-inflammatory, anti-mutagenic, anti-leukemia, anti-malarial, anti-nociception, anti-oxidant, anti-Parkinson's, anti-protozoal, anti-tubercular, anti-viral, anthelmintic, enzyme inhibition, hepatoprotection, nerve-growth factor inducing activity, neurogenic inflammation and vasorelaxant activity, neuroprotective and novel cytotoxicity, amongst many others. The structural characteristics which allow these compounds to bind to target biomolecules are multiple and include: (1) a planar, or predominantly planar (unsaturated xanthones) tricyclic core; (2) the ubiquitous feature of a carbonyl functionality on the central ring; (3) the presence of a biaryl-ether, further modifying the electronics of this system; (4) the frequent presence of phenolic hydroxyl group(s); (5) the further annulation of the core tricyclic system, or (6) its elaboration with a vast variety of substituents

ortho-Bromo(propa-1,2-dien-1-yl)arenes : substrates for domino reactions

o-Bromo(propa-1,2-dien-1-yl)arenes exhibit novel and orthogonal reactivity under Pd catalysis in the presence of secondary amines to form enamines (concerted Pd insertion, intramolecular carbopalladation, and terminative Buchwald–Hartwig coupling) and of amides to form indoles (addition, Buchwald–Hartwig cyclization, and loss of the acetyl group). The substrates for these reactions can be accessed in a reliable and highly selective two-step process from 2-bromoaryl bromides

Xanthone dimers: a compound family which is both common and privileged

Covering: up to 2014 Xanthone dimers are a widespread, structurally-diverse family of natural products frequently found in plants, fungi and lichens. They feature an intriguing variety of linkages between the component xanthones (benzannulated chromanones). These synthetically elusive secondary metabolites are of great interest due to their broad array of bioactivities, which has led to the xanthones being designated as `privileged structures`. We seek herein to give an overview of all reliably-described xanthone dimers, their structures, occurrence, and the bioactivities established to date. The possible biosynthetic pathways leading to members of this family are also discussed in light of our current knowledge

An efficient synthesis of (±)-frondosin B using a Stille–Heck reaction sequence

A concise, convergent synthesis of (±)-frondosin B has been developed based on the application of a Stille–Heck reaction sequence of 2-chloro-5-methoxybenzo[b]furan-3-yl triflate and 2-(3-butenyl)-3-(trimethylstannyl)cyclohex-2-enone giving the racemic natural product in a 34% overall yield

Solid-state structure of some substituted hexahydro-1,4:5,8-diepoxy­naphthalenes

The structure of several carboxy-substituted hexahydro-1,4:5,8-diepoxynaphthalenes have been solved with X-ray crystallography, in some cases confirming previously contentious structures. The compounds of interest are constructed in efficient one-step 2 × [4+2] cycloaddition reactions from furan and acetylene carboxylate derivatives

Double trouble - The art of synthesis of chiral dimeric natural products

Double or nothing! Recently the total ynthesis of secalonic acids A and D was reported. This work and other natural product syntheses with a dimerization step as a common feature are featured in this highlight. The significant biological activity of the secalonic acids and the fact that their synthesis has fascinated synthetic chemists for the past forty years make this work a milestone in natural product synthesis

A reduction of diffusion in PVA Fricke hydrogels

A modification to the PVA-FX hydrogel whereby the chelating agent, xylenol orange, was partially bonded to the gelling agent, poly-vinyl alcohol, resulted in an 8% reduction in the post irradiation Fe3+ diffusion, adding approximately 1 hour to the useful timespan between irradiation and readout. This xylenol orange functionalised poly-vinyl alcohol hydrogel had an OD dose sensitivity of 0.014 Gy−1 and a diffusion rate of 0.133 mm2 h−1. As this partial bond yields only incremental improvement, it is proposed that more efficient methods of bonding xylenol orange to poly-vinyl alcohol be investigated to further reduce the diffusion in Fricke gels