title: Antifungal saponins from bulbs of white onion, Allium cepa L.
abstract: Three saponins, named ceposide A, ceposide B, and ceposide C were isolated from the bulbs of white onion, Allium cepa L. Elucidation of their structure was carried out by comprehensive spectroscopic analyses, including 2D NMR spectroscopy and mass spectrometry, and chemical evidences. The structures of the compounds were identified as (25R)-furost-5(6)-en-1β,3β,22α,26-tetraol 1-O-β-D-xylopyranosyl 26-O-α-D-rhamnoyranosyl-(1→2)-O-β-D-galactopyranoside (ceposide A), (25R)-furost-5(6)-en-1β,3β,22α,26-tetraol 1-O-β-D-xylopyranosyl 26-O-α-D-rhamnoyranosyl-(1→2)-O-β-D-glucopyranoside (ceposide B), and (25R)-furost-5(6)-en-1β,3β,22α,26-tetraol 1-O-β-D-galactopyranosyl 26-O-α-D-rhamnoyranosyl-(1→2)-O-β-D-galactopyranoside (ceposide C). The isolated compounds, alone and in combinations, were evaluated for their antimicrobial activity on ten fungal species. Antifungal activity of all three saponins increased with their concentration and varied with the following rank: ceposide B>ceposide A-ceposide C. We found a significant synergism in the antifungal activity of the three ceposides against Botrytis cinerea and Trichoderma atroviride, because growth of these fungi was strongly inhibited when the three saponins were applied in combination. In contrast, Fusarium oxysporum f. sp. lycopersici, Sclerotium cepivorum and Rhizoctonia solani were very little affected by saponins.
authors.affiliation: Dipartimento di Scienza degli Alimenti Università degli Studi di Napoli Federico II, via Università 100, 80055 Portici, Napoli, Italy. lanzotti@unina.it
authors.forename: Virginia
authors.initials: V
authors.lastname: Lanzotti
authors.forename: Adriana
authors.initials: A
authors.lastname: Romano
authors.forename: Stefania
authors.initials: S
authors.lastname: Lanzuise
authors.forename: Giuliano
authors.initials: G
authors.lastname: Bonanomi
authors.forename: Felice
authors.initials: F
authors.lastname: Scala
mesh_terms: D000935:Antifungal Agents / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D004357:Drug Synergism; D005658:Fungi / Q000187:drug effects* / Q000254:growth & development; D008826:Microbial Sensitivity Tests; D015394:Molecular Structure; D019697:Onions / Q000737:chemistry*; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology*; D018517:Plant Roots / Q000737:chemistry*; D012503:Saponins / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*
chemical_list: D000935:Antifungal Agents; D010936:Plant Extracts; D012503:Saponins; C572832:ceposide A; C572833:ceposide B; C572834:ceposide C