Synthesis of the macrolide antibiotic A26771B methyl ester

Divergent Synthesis of Six Recent Berkeleylactones

The six recently isolated berkeleylactones E, J, K, M, N, and O were synthesized for the first time by a divergent strategy starting from a common intermediate in our synthesis of berkeleylactone A. Key features were the stereoselective formation of the γ,δ-dihydroxy-α,β-unsaturated ester moiety and the development of a general protection group strategy. Along the way we also established a short high-yielding formal synthesis of the often-synthesized antibiotic A26771B.

Berkeleylactones and a Citreohybriddione Analogue from Penicillium turbatum

In 2017 we reported the isolation and characterization of berkeleylactones A-H and A26771B from a coculture of two extremophilic Penicillium sp. isolated from an acid mine waste lake. Berkeleylactone A exhibited potent activity against several strains of multi-drug-resistant Staphylococcus aureus and Bacillus anthracis. A26771B, which is related to the berkeleylactones, also exhibited antibiotic activity. Although the berkeleylactones were novel compounds, A26771B was originally isolated by scientists at Eli Lilly Company from P. turbatum and reported in1977. We recently obtained P. turbatum and grew it in axenic culture. We isolated five new berkeleylactones (2 and 4-7), two berkeley-γ-lactones (8 and 9), and citreohybriddional (10), as well as the known compounds A26771B (1), berkeleylactone E (3), and gliovictin. The structures of the novel compounds were deduced from analysis of spectral data. Compounds 2 and 4 -7 are 16-membered macrolides, while 8 and 9 are γ-lactones that share the hexadecanoic acid skeleton. A26771B (1) and berkeleylactone I (2) were active against several strains of Staphylococcus aureus, including four multi-drug-resistant strains. Berkeleylactone N (8) was active only against Streptococcus pyogenes.

A Concise Asymmetric Synthesis of the Macrolide Antibiotic (-)-A26771B and Evaluation of its Antibacterial Activity and Some of its Precursors

An asymmetric synthesis of the macrolide antibiotic (-)-A26771B (1) has been developed wherein the stereochemistries at its C-5 and C-15 centres were installed using an ( R)-BINOL-catalyzed allylation and a lipase-catalyzed acylation respectively. Acrylation at the C-15 centre under Mitsunobu conditions followed by a ring closing metathesis provided the macrocylic skeleton, which was suitably functionalized to obtain (-)-1. The biological assay of the antibiotic and two of its precursors suggested that presence of the γ-oxo moiety and the succinate function in (-)-1 were detrimental to its antibacterial activity.

The Berkeleylactones, Antibiotic Macrolides from Fungal Coculture

A carefully timed coculture fermentation of Penicillium fuscum and P. camembertii/clavigerum yielded eight new 16-membered-ring macrolides, berkeleylactones A-H (1, 4, 6-9, 12, 13), as well as the known antibiotic macrolide A26771B (5), patulin, and citrinin. There was no evidence of the production of the berkeleylactones or A26771B (5) by either fungus when grown as axenic cultures. The structures were deduced from analyses of spectral data, and the absolute configurations of compounds 1 and 9 were determined by single-crystal X-ray crystallography. Berkeleylactone A (1) exhibited the most potent antimicrobial activity of the macrolide series, with low micromolar activity (MIC = 1-2 μg/mL) against four MRSA strains, as well as Bacillus anthracis, Streptococcus pyogenes, Candida albicans, and Candida glabrata. Mode of action studies have shown that, unlike other macrolide antibiotics, berkeleylactone A (1) does not inhibit protein synthesis nor target the ribosome, which suggests a novel mode of action for its antibiotic activity.

Chemoenzymatic synthesis of the macrolide antibiotic (−)-A26771B

The macrolide antibiotic (−)-A26771B is synthesized using lipase catalyzed reactions as the key steps.

Synthesis and biological properties of macrolactam analogs of the natural product macrolide (-)-A26771B

Promising synthetic derivatives of macrolactone natural product (-)-A26771B have been designed and synthesized both from semisynthesis and total synthesis. Further optimization led to the first synthesis of macrolactam analogs of (-)-A26771B with improved antibacterial activity and metabolic stability.