Chemistry and Phytotoxicity of Thaxtomin A Alkyl Ethers

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• 作者：Stuart B. Krasnoff ; Emil B. Lobkovsky ; Michael J. Wach ; Rosemary Loria ; and Donna M. Gibson
• 刊名：Journal of Agricultural and Food Chemistry
• 出版年：2005
• 出版时间：November 30, 2005
• 年：2005
• 卷：53
• 期：24
• 页码：9446 - 9451
• 全文大小：148K
• 年卷期：v.53,no.24(November 30, 2005)
• ISSN：1520-5118

文摘

The thaxtomin phytotoxins (1 and 2) from scab-producing Streptomyces pathogens of the potato are2,5-dioxopiperazines consisting of modified L-tryptophanyl and L-phenylalanyl units. Thaxtomin A (1)is hydroxylated at C-14, the mages/gifchars/alpha.gif" BORDER=0> carbon of the modified L-phenylalanyl moiety. Refluxing thaxtomin Ain acidified MeOH, EtOH, and i-PrOH afforded C-14 thaxtomin A methyl- (3a and 3b), ethyl- (4a and4b), and isopropyl- (5a and 5b) ethers, respectively, in both the 11S,14R (3a, 4a, and 5a) and 11S,14S(3b, 4b, and 5b) configurations. Crystal structures were determined for 3a and 4a. Extensive NMRas well as other spectroscopic data supported structural assignments for all of the derivatives. The11S,14R-configured derivatives were slightly less potent than the natural products (1 and 2) asinhibitors of lettuce seedling root growth, whereas the activity of the 11S,14S epimers was muchreduced, indicating that the configuration at C-14 found in the naturally occurring thaxtomins is essentialfor biological activity. Among the 11S,14R-configured compounds, potency decreased with anincreasing size of the substituted alkoxy group.Keywords: Thaxtomins; crystal structure; phytotoxin; Streptomyces