Structural Elucidation of Three Novel Kaempferol O-tri-Glycosides that Are Involved in the Defense Response of Hybrid Ornithogalum to Pectobacterium carotovorum

摘要

Ornithogalum is an ornamental flowering species that grows from a bulb and is highly susceptible to soft-rot disease caused by Pectobacterium carotovorum (Pc). Interspecific hybridization between O. thyrsoides and O. dubium yielded hybrids with enhanced resistance to that pathogen. The hybrids displayed distinct phenolic-compound profiles with several peaks that were specifically heightened following Pc infection. Three of these compounds were isolated and identified as novel kaempferol O-tri-glycosides. The structures of these compounds were elucidated using reversed phase high-performance liquid chromatography (RP-LC), RP-LC coupled to high-resolution mass spectrometry (RP-LC-MS), and nuclear magnetic resonance (NMR) (1D ¹H and ¹³C, DEPT, HMQC, HMBC, COSY, and NOE), in order to achieve pure and defined compounds data. The new compounds were finally identified as kaempferol 3-O-[4-O-α-l-(3-O-acetic)-rhamnopyranosyl-6-O-β-d-xylopyranosyl]-β-d-glucopyranoside, kaempferol 3-O-[4-O-α-l-(2-O-acetic)-rhamnopyranosyl-6-O-β-d-xylopyranosyl]-β-d-glucopyranoside and kaempferol 3-O-[4-O-α-l-(2,3-O-diacetic)-rhamnopyranosyl-6-O-β-d-xylopyranosyl]-β-d-glucopyranoside.