Neoverataline A and B, two antifungal alkaloids with a novel carbon skeleton from Veratrum taliense

Bioassay-guided fractionation of the ethanol extract of the roots and rhizomes of Veratrum taliense yielded two new and thirteen known steroidal alkaloids. The structures of the two new compounds, neoverataline A and B, were established by extensive spectroscopic analyses to be 3.4-secocevane-4,9-olid-14,15,16,20-tetra-ol-3-oic acid and 3,4-secocevane-4,9-olid-7,14,15,16,20-penta-ol-3-oic acid, respectively, and are a novel carbon skelton. All of the fifteen alkaloids were subjected to in vitro antifungal assays, which showed that the verazine- (veramitaline. stenophylline B, stenophylline B-3-O-beta-D-glucopyranoside, veramiline-3-O-beta-D-glucopyranoside) and jerveratrum-type (jervine, jervine-3-O-beta-D-glucopyranoside) alkaloids exhibited strong antifungal activities against the phytopathogenic fungus Phytophthora capisis with MICs of 160, 120, 160, 80, 80 and 120 mug(.)L(-1), respectively. Furthermore, the verazine-type alkaloids stenophylline B. stenophylline B 3-O-beta-D-glucopyranoside and veramiline 3-O-beta-D-glucopyranoside were shown to also inhibit the growth of another fungal phytopathogen Rhizoctonia cerealis with MICs of 160, 120 and 120 mug mL(-1). The MICs of triadimefon (an antifungal agrochemical used herein as a positive control) against P. capisis and R. cerealis were 120 and 80 mug mL(-1), respectively. A preliminary structure-activity relationship regarding these alkaloids has been formulated. (C) 2003 Elsevier Ltd. All rights reserved.