This thesis is divided into five chapters, the
first two of which are introductory. In Chapter 1 the
secondary metabolism of fungi is briefly discussed with
special reference to the polyketide pathway. Chapter 2
comprises a short r e v i e w of the isotopic tracer methods
important in biosynthetic studies, concentrating on the
use of nuclear magnetic resonance techniques.
Chapter 3 concerns LL-D253α, a 4-chromanonemetabolite
of Phoma pigmentivora. Spectroscopic evidence has led to
a revision of the original structure; both this and the
new structure have been synthesised. [2-¹⁴C]-, [1-¹³ C]-,
[2-¹³C]-, [1,2-¹³C₂], [1-¹³C, ²H₃]-, [1-¹³C, 18O₂-, and
[²H₃] acetates, [ 1-¹⁴C] glycollate, [U-¹⁴C]oxalate, [5-¹⁴C] -
mevalonate and ¹⁸O2 gas have all been administered to
P. pigmentivora. The results indicate a polyketide
biogenesis for LL-D253α and a two-chain pathway has been
proposed to account for the structure. A spiro-cyclopropyl
intermediate formed by aryl participation is postulated to
explain the unusual scrambling of carbon and hydrogen
label observed in the 2-hydroxyethyl side-chain.
Possible mechanisms for formation of the pyranone ring are
discussed.
Chapter 4 concerns meroterpenoid metabolites of
Aspergillus species. The incorporations of ¹⁸0₂ gas and
[1-¹³c, ¹⁸0₂]acetate into andibenin B and andilesin A, both
known triprenyl-phenols of A.variecolor , suggest possible
pathways for the formation of the spiro-lactone moiety
of the andibenins. Incorporation of acetate oxygen into
andilesin A was too low to distinguish between possible
orsellinate and deoxyorsellinate intermediates.
The biosynthesis of terretonin by A. terveus has
been investigated. Assignment of the ¹³C n.m.r. spectrum is
13 described in detail. Incorporations of [1,2-¹³C₂]acetate
and [carboxyl, 2-¹⁴C]- and [3-methyl, ²H₃]-3,5-dimethyl-
orsellinates indicate a triprenyl-phenol biogenesis,
contrary to previous suggestions.
In Chapter 5 the incorporations of gas into
tajixanthone and shamixanthone, metabolites of A. variecolor,
are discussed. The results are consistent with earlier
observations indicating the occurrence of free rotation
of the symmetrical elem e n t of a b e n z o p h e n o n e intermediate.
The principal mode of xanthone ring closure is demonstrated.
Evidence that all the atmospherically-derived oxygen
atoms are independently introduced is presented and a
pathway via an anthraquinone intermediate is suggested.
