Ptaquiloside

A toxic component of braken fern, perhaps either quercetin (105) or ptaquiloside, a glucoside (106), has a mixed history of carcinogenicity. It is sometimes impHcated in an increased incidence of bladder cancer in animals and esophageal cancer in humans. Multiple other dietary components seem to either promote or interfere with its action, and the significance of braken fern in human carcinogenesis remains unproven. 

Ojika, M., Wakamatsu, K., Niwa, H. and Yamada, K. 1987. Ptaquiloside, a potent carciogen isolated from bracken fern, Pteridium aquilinum var. latiusculum. structure elucidation based on chemical and spectral evidence, and reactions with aminoacids, nucleotides and nucleosides. Tetrahedron 43 5261-5274. 

In fact, the cyclopropyl group of 26 is strongly electrophilic and reacts readily with amino acids, nucleosides and nucleotides under mild conditions [25 d]. Thus dienone 26 forms covalent adducts with DNA and causes DNA strand breaks DNA is the principal biological target of ptaquiloside 25 [26]. 

CC 1065 108 is a highly toxic antibiotic isolated from Streptomyces zelensis containing a reactive spirocyclopropane ring. It cleaves DNA through a mechanism similar to the cleavage which occurs upon treatment of DNA with the carcinogenic ptaquiloside 25 (vide supra. Sect. 2.6), namely by depurination of alkyladenine adducts, Eq. (43) [142]. 

This reaction has recently been applied for the preparation of aza-analogs with the basic skeleton and functional groups of the extremely cytotoxic sesquiterpenes illudin (208) and ptaquiloside (209) [139]. Compounds 212-215 were successfully prepared by heating bicyclopropylidene (1) with the enantiomeri-cally pure nitrones 210,211 (Scheme 47) [138]. Some of these simple aza-analogs have indeed been found to exhibit DNA-cleaving abilities [138b,c]. 

Scheme47. Preparation of aza-analogs 212-215 with the basic skeleton and functional groups of the sesquiterpenes illudin (208) and ptaquiloside (209) [138]...

Ptaquiloside (see also Bracken fern) Pulp and paper manufaeture... 

A review on the isolation, chemistry, and biochemistry of the bracken fern (Pte-ridium aquilinum) carcinogen ptaquiloside (P) has been published (527). This fem and others contain the pterosins that were summarized previously (7). No new examples were reported in the interim. 

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