Synthesis and Biological Evaluation of Aurachin D Analogues as Inhibitors of Mycobacterium tuberculosis Cytochrome bd Oxidase

Aggie Lawer; Chelsea Tyler; Kiel Hards; Laura M Keighley; Chen-Yi Cheung; Fabian Kierek; Simon Su; Siddharth S Matikonda; Tyler McInnes; Joel D A Tyndall; Kurt L Krause; Gregory M Cook; Allan B Gamble

doi:10.1021/acsmedchemlett.2c00401

Synthesis and Biological Evaluation of Aurachin D Analogues as Inhibitors of Mycobacterium tuberculosis Cytochrome bd Oxidase

ACS Med Chem Lett. 2022 Sep 26;13(10):1663-1669. doi: 10.1021/acsmedchemlett.2c00401. eCollection 2022 Oct 13.

Authors

Affiliations

¹ School of Pharmacy, University of Otago, Dunedin 9054, New Zealand.
² Department of Microbiology and Immunology, University of Otago, Dunedin 9054, New Zealand.
³ Department of Biochemistry, University of Otago, Dunedin 9054, New Zealand.
⁴ Maurice Wilkins Centre for Molecular Biodiscovery, University of Otago, Dunedin 9054, New Zealand.

Abstract

A revised total synthesis of aurachin D (1a), an isoprenoid quinolone alkaloid that targets Mycobacterium tuberculosis (Mtb) cytochrome bd (cyt-bd) oxidase, was accomplished using an oxazoline ring-opening reaction. The ring opening enabled access to a range of electron-poor analogues, while electron-rich analogues could be prepared using the Conrad-Limpach reaction. The aryl-substituted and side-chain-modified aurachin D analogues were screened for inhibition of Mtb cyt-bd oxidase and growth inhibition of Mtb. Nanomolar inhibition of Mtb cyt-bd oxidase was observed for the shorter-chain analogue 1d (citronellyl side chain) and the aryl-substituted analogues 1g/1k (fluoro substituent at C6/C7), 1t/1v (hydroxy substituent at C5/C6) and 1u/1w/1x (methoxy substituent at C5/C6/C7). Aurachin D and the analogues did not inhibit growth of nonpathogenic Mycobacterium smegmatis, but the citronellyl (1d) and 6-fluoro-substituted (1g) inhibitors from the Mtb cyt-bd oxidase assay displayed moderate growth inhibition against pathogenic Mtb (MIC = 4-8 μM).