Abstract
In Chapter 1 a brief outline of the range of naturally-occurring oxygen
heterocycles is presented. This is follow ed by a com prehensive review of
non-flavanoid naturally-occurring chromanones, including reference to any
im portant biosynthetic studies. This is follow ed by a review of the synthesis of
such compounds, concentrating on more recent developments
Chapter 2 concerns the biosynthesis of the chrom anone LL-D253a, a
metabolite of P. p ig m e ntivora . A review of previous studies is presented,
followed by a brief account of the existence of the phenonium ion, though t to
be an intermediate in the biosynthesis of LL-D253a. The incorporation of
sodium [2 - 2H3,13C]-acetate, and of diethyl [ 2 - 13C]-malonate, into LL-D253a give
an insight into the mechanism of its form ation. Chemical manipulation of
deuterium labelled LL-D253a derivatives has supported the existence of a
"phenonium'' intermediate. Chemical synthesis of some postulated prrecursors
to Ll-D253a was undertaken.
Chapter 3 concerns the biosynthesis of averufin, known to be a precursor
to aflatoxin B-|. An overview of aflatoxin biosynthesis is presented, and includes
a detailed review of relevant studies reported since 1980. The incorporation of
[ 2 - 2H2]-hexanoic acid, and of diethyl [ 2 - 13C]-malonate, into averufin is
reported. These results confirm that averufin is a decaketide, but during its
biosynthesis it is able to exchange with endogenous hexanoate. Attem pted
chemical manipulation of averufin, and incorporation of [7 - 2H2]-averufin into
aflatoxin B-, is discussed.
