The biosynthetic pathway of crucifer phytoalexins and phytoanticipins: de novo incorporation of deuterated tryptophans and quasi-natural compounds.
Although several biosynthetic intermediates in pathways to cruciferous phytoalexins and phytoanticipins are common, questions regarding the introduction of substituents at N-1 of the indole moiety remain unanswered. Toward this end, we investigated the potential incorporations of several perdeuterated d- and l-1'-methoxytryptophans, d- and l-tryptophans and other indol-3-yl derivatives into pertinent phytoalexins and phytoanticipins (indolyl glucosinolates) produced in rutabaga (Brassica napus L. ssp. rapifera) roots. In addition, we probed the potential transformations of quasi-natural compounds, these being analogues of biosynthetic intermediates that might lead to "quasi-natural" products (products similar to natural products but not produced under natural conditions). No detectable incorporations of deuterium labeled 1'-methoxytryptophans into phytoalexins or glucobrassicin were detected. l-tryptophan was incorporated in a higher percentage than d-tryptophan into both phytoalexins and phytoanticipins. However, in the case of the phytoalexin rapalexin A, both d- and l-tryptophan were incorporated to the same extent. Furthermore, the transformations of both 1'-methylindolyl-3'-acetaldoxime and 1'-methylindolyl-3'-acetothiohydroxamic acid (quasi-natural products) into 1'-methylglucobrassicin but not into phytoalexins suggested that post-aldoxime enzymes in the biosynthetic pathway of indolyl glucosinolates are not substrate-specific. Hence, it would appear that the 1-methoxy substituent of the indole moiety is introduced downstream from tryptophan and that the post-aldoxime enzymes of the glucosinolate pathway are different from the enzymes of the phytoalexin pathway. A higher substrate specificity of some enzymes of the phytoalexin pathway might explain the relatively lower structural diversity among phytoalexins than among glucosinolates.
Pedras
M Soledade C
MSC
Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, SK, Canada S7N 5C9. Electronic address: s.pedras@usask.ca.
Okinyo-Owiti
Denis P
DP
Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, SK, Canada S7N 5C9.
Thoms
Ken
K
Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, SK, Canada S7N 5C9.
Adio
Adewale M
AM
Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, SK, Canada S7N 5C9.
D001688:Biological Products / Q000378:metabolism*; D029688:Brassica napus / Q000737:chemistry / Q000378:metabolism*; D003903:Deuterium; D005960:Glucosides / Q000737:chemistry / Q000378:metabolism; D007211:Indoles / Q000737:chemistry / Q000378:metabolism*; D015394:Molecular Structure; D018517:Plant Roots / Q000378:metabolism; D035281:Plant Tubers / Q000737:chemistry / Q000378:metabolism; D012717:Sesquiterpenes; D013729:Terpenes / Q000737:chemistry / Q000378:metabolism*; D014364:Tryptophan / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism*; D000094162:Phytoalexins
D001688:Biological Products; D005960:Glucosides; D007211:Indoles; D012717:Sesquiterpenes; D013729:Terpenes; D014364:Tryptophan; D003903:Deuterium; D000094162:Phytoalexins