New norclerodane diterpenoids from bulbils of Dioscorea bulbifera L.

Abstract

Investigation of extracts from bulbils of Dioscorea bulbifera L. yielded two new norclerodane diterpenoids, diosbulbin N acetate (1) and epi-diosbulbin B (3), together with eleven known compounds. Their structures were established based on spectroscopy. The absolute configurations of 1 and diosbulbin B (2) were determined by X-ray crystallographic analysis using Cu Kα radiation. The absolute configuration of 3 was determined by comparison of its ECD spectrum to that of 2. Isolated phenanthrenes 7, 9 and 10 exhibited moderate cytotoxicity against the HelaS3 cell line with IC₅₀ values of 9.03 ± 0.04, 27.13 ± 6.86 and 10.88 ± 2.75 µM, respectively. In addition, 7-9 and 11 showed potent inhibition of NO production by LPS-induced RAW 264.7 macrophages.

Graphical Abstract

Keywords:

• Dioscorea bulbifera
• norclerodane diterpenoid
• phenanthrene derivative
• cytotoxicity
• anti-inflammatory

Acknowledgements

This work is dedicated to our best friend, the late Dr. Pongpan Siripong, who worked on Thai medicinal plants for preventing and treating cancer for her whole life at the National Cancer Institute, Bangkok, Thailand. The authors acknowledge the Center of Excellence for Innovation in Chemistry (PERCH-CIC) and Natural Products Research Unit, Khon Kaen University for partial support.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Thailand Research Fund via Royal Golden Jubilee Ph.D. Program and Khon Kaen University [grant number PHD/0034/2559] for Apisara Somteds.