Synthesis, Antibacterial Activity, and Nephrotoxicity of Polymyxin B Analogues Modified at Leu-7, d-Phe-6, and the N-Terminus Enabled by S-Lipidation.

With the post-antibiotic era rapidly approaching, many have turned their attention to developing new treatments, often by structural modification of existing antibiotics. Polymyxins, a family of lipopeptide antibiotics that are used as a last line of defense in the clinic, have recently developed resistance and exhibit significant nephrotoxicity issues. Using thiol-ene chemistry, the facile preparation of six unique S-lipidated building blocks was demonstrated and used to generate lipopeptide mimetics upon incorporation into solid-phase peptide synthesis (SPPS). We then designed and synthesized 38 polymyxin analogues, incorporating these unique building blocks at the N-terminus, or to replace hydrophobic residues at positions 6 and 7 of the native lipopeptides. Several polymyxin analogues bearing one or more S-linked lipids were found to be equipotent to polymyxin, showed minimal kidney nephrotoxicity, and demonstrated activity against several World Health Organisation (WHO) priority pathogens. The S-lipidation strategy has demonstrated potential as a novel approach to prepare innovative new lipopeptide antibiotics.

A review of the synthesis of α-carbolines.

Since the first reported synthesis of an α-carboline almost a century ago, there has been a steady interest in the development of strategies towards this unique heterocyclic motif. This interest can mainly be attributed to a range of biological activity displayed by the α-carboline natural products including cytotoxicity, anticancer properties or CNS activity. Numerous studies have led to the development of a number of alternative methods to prepare simple α-carbolines as well as a range of synthetic α-carboline derived compounds.

Total synthesis of the macrocyclic N-Methyl enamides palmyrolide A and 2S-sanctolide A.

Full details of the total syntheses of the initially reported and revised structures of the neuroprotective agent palmyrolide A are reported. The key macrocyclization step was achieved using a sequential ring-closing metathesis/olefin isomerization reaction. Furthermore, the total synthesis of the related macrolide (2S)-sanctolide A is reported. The synthesis used key elements from the synthesis of palmyrolide A, including the RCM/olefin isomerization sequence. The synthetic work described herein serves to facilitate the assignment of stereochemistry of the natural product sanctolide A and demonstrates the utility of this approach for the synthesis of macrocyclic tertiary enamide natural products.

Total synthesis of the initially reported and revised structures of the neuroprotective agent palmyrolide A.

The total syntheses of the initially reported and revised structures of the neuroprotective agent palmyrolide A are reported. The key macrocyclization step was achieved using a sequential ring closing metathesis/olefin isomerization reaction. The synthetic work described herein serves to confirm the recent structural revision of this unusual natural product.