Total synthesis of depsilairdin.
The total synthesis of depsilairdin, a host-selective phytotoxin isolated from Leptosphaeria maculans (the causal agent of blackleg disease of oilseed Brassicas), has been achieved by N-terminal extension of a suitably protected derivative of the hitherto unknown amino acid (2S,3S,4R)-3,4-dihydroxy-3-methyl-proline (Dhmp) followed by esterification with lairdinol A. The latter esterification, complicated by the sterically hindered nature of the carboxyl group, was accomplished by a novel method involving reaction of the 1-hydroxybenzotriazole (HOBt) derived active ester with the bromomagnesium alkoxide of lairdinol A. Three depsilairdin analogues were also prepared by replacing the Dhmp residue with L-proline and cis- and trans-4-hydroxy-L-proline. Phytotoxicity assays showed that the analogues were nontoxic to both blackleg-susceptible (brown mustard) and -resistant (canola) plants, suggesting that the presence of the Dhmp residue in depsilairdin is important for its host-selective toxicity toward brown mustard.
Ward
Dale E
DE
Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, SK S7N 5C9, Canada. dale.ward@usask.ca
Pardeshi
Sandip G
SG
D004951:Esterification; D009682:Magnetic Resonance Spectroscopy; D012717:Sesquiterpenes / Q000138:chemical synthesis* / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization
D012717:Sesquiterpenes; C507168:depsilairdin