LC-MS-Guided Isolation of Triterpene Glycosides from Holothuria atra: Structural Features Governing TRPA1 Inhibition

The LC-MS-guided separation of the extract from the sea cucumber Holothuria atra led to the isolation of 16 triterpene glycosides (1-16), including seven previously unreported derivatives consisting of three sulfated (1, 3, 5) and four nonsulfated congeners (12, 13, 15, and 16). Notably, compounds 15 and 16 feature a new aglycone structure bearing an 8(9),11(12)-diene scaffold. All isolates were evaluated for their inhibitory activity toward transient receptor potential ankyrin 1 (TRPA1). In addition, to investigate the structural features governing the activity based on wider chemical diversity, desulfated derivatives (17-19) and sapogenins (20-22) were obtained through the chemical modifications of natural saponins and evaluated for their activity. The tetracyclic aglycone scaffold and the structure of the side branch attached to C-20 were critical for activity, with sulfated glycoside 6, containing a 9(11)-holostene-3β, 12α, 17α-triol with a side branch bearing a 22-hydroxy group, being the most potent (IC₅₀ 1.4 μM). The findings of this study may provide valuable insights into designing TRPA1 antagonists based on saponins.