Synthesis and antiviral properties of spirocyclic [1,2,3]-triazolooxazine nucleosides.

An efficient synthesis of spirocyclic triazolooxazine nucleosides is described. This was achieved by the conversion of ß-D-psicofuranose to the corresponding azido-derivative, followed by alkylation of the primary alcohol with a range of propargyl bromides, obtained by Sonogashira chemistry. The products of these reactions underwent 1,3-dipolar addition smoothly to generate the protected spirocyclic adducts. These were easily deprotected to give the corresponding ribose nucleosides. The library of compounds obtained was investigated for its antiviral activity using MHV (mouse hepatitis virus) as a model wherein derivative 3 f showed the most promising activity and tolerability.

A marine viral halogenase that iodinates diverse substrates.

Oceanic cyanobacteria are the most abundant oxygen-generating phototrophs on our planet and are therefore important to life. These organisms are infected by viruses called cyanophages, which have recently shown to encode metabolic genes that modulate host photosynthesis, phosphorus cycling and nucleotide metabolism. Herein we report the characterization of a wild-type flavin-dependent viral halogenase (VirX1) from a cyanophage. Notably, halogenases have been previously associated with secondary metabolism, tailoring natural products. Exploration of this viral halogenase reveals it capable of regioselective halogenation of a diverse range of substrates with a preference for forming aryl iodide species; this has potential implications for the metabolism of the infected host. Until recently, a flavin-dependent halogenase that is capable of iodination in vitro had not been reported. VirX1 is interesting from a biocatalytic perspective as it shows strikingly broad substrate flexibility and a clear preference for iodination, as illustrated by kinetic analysis. These factors together render it an attractive tool for synthesis.

Scalable total synthesis and comprehensive structure-activity relationship studies of the phytotoxin coronatine.

Natural phytotoxins are valuable starting points for agrochemical design. Acting as a jasmonate agonist, coronatine represents an attractive herbicidal lead with novel mode of action, and has been an important synthetic target for agrochemical development. However, both restricted access to quantities of coronatine and a lack of a suitably scalable and flexible synthetic approach to its constituent natural product components, coronafacic and coronamic acids, has frustrated development of this target. Here, we report gram-scale production of coronafacic acid that allows a comprehensive structure-activity relationship study of this target. Biological assessment of a >120 member library combined with computational studies have revealed the key determinants of potency, rationalising hypotheses held for decades, and allowing future rational design of new herbicidal leads based on this template.

Synthesis of the himandrine skeleton.

The hexacyclic himandrine skeleton 5, which is present in the most complex alkaloids of the tropical rain forest tree Galbulimima belgraveana, has been prepared for the first time. The synthesis begins from the known [3.2.1]benzobicyclooctene intermediate 10. Key steps include a Diels-Alder cycloaddition, Curtius rearrangement, Birch reduction, an intramolecular nucleophilic amination, and a palladium-mediated alkene amination. [reaction: see text]

The total synthesis of the Galbulimima alkaloid GB 13.

This contribution describes a synthetic approach to alkaloid GB 13, previously isolated from the North Australian and Papua New Guinean rain forest tree Galbulimima belgraveana. A Birch reductive alkylation of 2,5-dimethoxybenzoic acid by 3-methoxybenzyl bromide, followed by an acid-catalyzed cyclization was used to synthesize the [3.3.1]bicyclononane 8. A ring contraction performed on the diazo derivative 9 of the [3.3.1]bicyclononane led to [3.2.1]bicyclooctane 10. This [3.2.1]bicyclooctane was converted into a dienophile and subjected to a Diels-Alder reaction to generate a pentacyclic intermediate 13 with a carbon skeleton closely resembling the target alkaloid. The surplus substituent, required for activation and regioselectivity in the Diels-Alder reaction, was removed using Birch reductive conditions to effect a decyanation. It was discovered that a Birch reduction of the aromatic ring also present in the molecule could be performed at the same time to give the enone 15, which was cleaved by means of an Eschenmoser fragmentation. The piperidine ring found in the natural product was formed by reductive cyclization of the bis-oxime 18 derived from the alkynyl ketone 17 and the resulting material further elaborated to GB 13 (1) via ketone 20.