Total synthesis of preaurovertin, putative biogenetic precursor of aurovertin. Biosynthetic interrelationships between the aurovertins, citreoviridinols and asteltoxin

Abstract

A number of complementary biomimetic approaches to the tetrahydrofuranyl portion of the dienal 13, which was used in a synthesis of preaurovertin, are described. Epoxidation of the trienoate 31 produces largely the β-epoxide 32, which on treatment with aqueous trifluoroacetic acid undergoes deacetalisation and concomitant cyclisation leading to compound 34. After conversion of 34 into dienal 13, a Wittig reaction with the ylide derived from the phosphonium salt 37 produces preaurovertin.

Preaurovertin is a putative biogenetic precursor of aurovertin found in Calcarisporium arbuscula. Citreoviridin produced by Penicillium citreoviride relates to preaurovertin, and the citreoviridinols are related structurally to aurovertin. In addition, aurovertin is related biogenetically to asteltoxin found in Aspergillus stellatus. These structural and biosynthetic interrelationships are considered alongside the synthetic work.