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.