Alison Thompson

Synthesis of natural products containing the pyrrolic ring

Covering: up to the end of January 2010 This review provides an overview of the synthetic chemistry that has been utilised to prepare natural products containing a pyrrolic ring.

Chiral molecules containing the pyrrole framework

This review summarizes strategies by which chiral pyrroles, both simple and complex, have been prepared: strategies include formation of the pyrrolic ring using starting materials appended with chirality, as well as the attachment of chirality to a pre-formed pyrrolic ring.

Use of F-BODIPYs as a Protection Strategy for Dipyrrins: Optimization of BF2 Removal

We recently reported the first general method for the deprotection of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes (F-BODIPYs) involving a microwave-assisted procedure for the removal of the BF(2) moiety, and liberation of the corresponding free-base dipyrrin. Further optimization of the reaction has resulted in a more convenient and accessible protocol. The availability of this new methodology enables BF(2)-complexation to be used as a dipyrrin protection strategy. Herein lies a detailed examination of the deprotection reaction, with a view to optimization and gaining mechanistic insight, and its application in facilitating a multistep synthesis of pyrrolyldipyrrins.

Synthesis and Characterization of Fluorescent Pyrrolyldipyrrinato Sn(IV) Complexes

A series of neutral, 5-coordinate pyrrolyldipyrrinato Sn(IV) complexes have been synthesized via reaction of a pyrrolyldipyrrin, or its corresponding hydrochloride salt, with dibutyltin or diphenyltin oxide. The complexes are structurally unique in that all three nitrogen atoms of the pyrrolyldipyrrinato ligand bind to the tin center, making these complexes the first examples of pyrrolyldipyrrins behaving as LX(2) ligands. The complexes are highly fluorescent, exhibiting fluorescence quantum yields between 0.28 and 0.61, and display interesting preliminary biological activity.

Conversion of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes (F-BODIPYs) to dipyrrins with a microwave-promoted deprotection strategy.

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacenes (F-BODIPYs) have been deprotected to give the corresponding free-base dipyrrins by heating a solution of the F-BODIPY in tert-butanol under 600 W of microwave irradiation in the presence of 6 equiv of potassium tert-butoxide for 40 min at 92 degrees C. Investigations of BODIPY modification at the meso position have also been undertaken and a meso-butyl product has been isolated.

Synthetic prodigiosenes and the influence of C-ring substitution on DNA cleavage, transmembrane chloride transport and basicity.

Analogues of the tripyrrolic natural product prodigiosin bearing an additional methyl and a carbonyl group at the C-ring were synthesised and evaluated. In vitro anticancer activity screening (NCI) and the study of modes of action (copper-mediated cleavage of double-stranded DNA and transmembrane transport of chloride anions) showed that the presence of the methyl group is not detrimental to activity. Furthermore, although the presence of an ester conjugated to the prodigiosene C-ring seems to decrease both pK(a) and chloride transport efficiency compared to the natural product, these analogues still exhibit a high rate of chloride transport. All analogues exhibit good in vitro anticancer activity and reduced toxicity compared to the natural product: compare an acute systemic toxicity of 100 mg kg(-1) in mice vs. 4 mg kg(-1) for prodigiosin, pointing towards a larger therapeutic window than for the natural product.

The use of chiral sulfides in catalytic asymmetric epoxidation

Abstract Non racemic epoxides with ees of 23–41 % have been prepared from aldehydes and phenyl diazomethane using catalytic amounts of sulfides derived from camphor.

Eight-membered ring-containing jadomycins: implications for non-enzymatic natural products biosynthesis.

Jadomycin Oct (1) was isolated from Streptomyces venezuelae ISP5230 and characterized as a structurally unique eight-membered l-ornithine ring-containing jadomycin. The structure was elucidated through the semisynthetic derivatization of starting material via chemoselective acylation of the l-ornithine α-amino group using activated succinimidyl esters. Incorporation of 5-aminovaleric acid led to jadomycin AVA, a second eight-membered ring-containing jadomycin. These natural products illustrate the structural diversity permissible from a non-enzymatic step within a biosynthetic pathway and exemplifies the potential for discovery of novel scaffolds.

Conversion of F-BODIPYs to Cl-BODIPYs: enhancing the reactivity of F-BODIPYs.

A new method for the synthesis of Cl-BODIPYs from F-BODIPYs is reported, merely requiring treatment of the F-BODIPY with boron trichloride. Cl-BODIPYs are exploited as synthetic intermediates generated in situ for the overall conversion of F-BODIPYs to O- and C-BODIPYs in high overall yields using a mild one-pot procedure. This route enables F-BODIPYs to be transformed into derivatives that are not accessible via the direct route, as demonstrated via the use of 1,3-propanediol.

Activation and deprotection of F-BODIPYs using boron trihalides

The activation of F-BODIPYs with boron trihalides, followed by treatment with a nucleophile, effects facile substitution at boron; using water as the nucleophile promotes deprotective removal of the -BF2 moiety and thereby production of the corresponding parent dipyrrin salt in quantitative yield under extremely mild conditions.