Silver-leaf disease

The utility of the electrohydrocyclization reaction to assemble natural products remains essentially untapped. It has, however, been used in the synthesis of the tricyclic sesquiterpene 1-sterpurene (3), the presumed causative agent of the so-called silver leaf disease that effects certain species of scrubs and trees in Western North America [15]. As is illustrated in Scheme 1 and in Table 2, the electrohydrocyclization reaction of bisenoate (5) was used to create the five-membered ring of the natural product. 

A relatively recent application to natural product synthesis stems from efforts to synthesize a sesquiterpene called 1-sterpurene 7 [17]. This substance is thought to be the causative agent of the so-called silver leaf disease that affects certain species of shrubs and trees. The strategy focuses on three key steps (a) electrochemical cyclization of the bis unsaturated ester 11 to produce the five-membered ring of 10, (b) a Ruhlman-modified acyloin condensation to... 

The silver-leaf disease of fruit trees is caused by the fungus Stereum pur-pureum. The phytotoxic metabolites such as sterpuric acid (5.82) possess the sterpurane skeleton which may also be derived from a protoilludane by a series of rearrangements. 

Aucuparin has been found to be a fungicidic phytoalexin of the loquat (Eriobotry japonica, Rosaceae) (119) and the compound also occurs in the sap-wood of the apple tree (Malus pumila, Rosaceae) when infected with the fungus that causes silver leaf disease (Chondrostereum purpureum) (70). The infected wood of the closely related pear tree (Pyrus communis, Rosaceae) (69) and the infected wood of Cotoneaster lactea (Rosaceae) (20) contain phytoalexins of the biogenetically related dibenzofuran type (a-, P-, and y-pyrufuran, and cotone-furan, 23 a-d). 

---