Trypethelone and phenalenone derivatives isolated from the mycobiont culture of Trypethelium eluteriae Spreng. and their anti-mycobacterial properties

Abstract

The metabolites of the mycobiont culture of the lichen Trypethelium eluteriae were isolated by column chromatography and preparative TLC. Nine compounds (1–9) including two new trypethelones, 8-methoxytrypethelone (6) and 5′-hydroxy-8-ethoxytrypethelone (9), together with four known trypethelones (3–4, 7–8), and two known phenalenones (1–2) were characterized. It is the first report of 8-methoxytrypethelone methyl ether (5) purification as a racemic mixture in T. eluteriae. Earlier, 7-hydroxyl-8-methoxyltrypethelone (10) was reported as new compound with erroneous spectroscopic data. This compound was identified later as 8-hydroxytrypethelone methyl ether (4). X-ray crystallographic structures of compounds 5–7 were elucidated for the first time. Phenalenones (1–2) and trypethelones (5–6 and 9) were the additional compounds discovered in the cultured mycobiont of T. eluteriae. Six compounds (1–2, 5–8) were screened against Mycobacterium tuberculosis H37Rv and two compounds (7–8) against non-tuberculosis mycobacteria and other human pathogenic bacteria. Compound (7) inhibited M. tuberculosis H37Rv strain with an MIC of 12.5 µg/mL.

Graphical Abstract

Keywords:

• Trypethelium eluteriae
• Trypetheliaceae
• mycobiont culture
• trypethelone
• phenalenone
• Mycobacterium tuberculosis H37Rv

Acknowledgements

The authors thank Prof. M.S. Swaminathan, Founder Chairman, M.S. Swaminathan Research Foundation, Chennai, India, and its Executive Director, for their support and encouragement; Dr. P.K. Sudhadevi Antharjanam for X-ray crystallography studies and NMR facility at Sophisticated Analytical Instrument Facility, Indian Institute of Technology Madras; Dr. J.D. Connolly, the University of Glasgow, Scotland for helpful discussions on structure elucidation; We thank Dr. Alan Orange, National Museum Wales, United Kingdom for correcting the language. Mr. G.K. Dayanandham for his help in checking the final version of the manuscript and Mr. E. Siva for laboratory assistance. This research work was carried out in the project entitled ‘National Network Program on Lichens’ funded by the Department of Biotechnology, Government of India [Grant number: BT/PR1457/NDB/39/204/2011] is also acknowledged.

Disclosure statement

No conflict of interest.