Page 56 - Visions of the Future Chemistry and Life Science

World champion chemists 45

added will act on the whole molecule. This is not a problem for the struc-
tures illustrated in Figure 3.1, because there is only one alcohol group in
the starting material and so all of the alcohols are transformed into
ketones. It is a problem if the same transformation is used to make a more
complicated molecule, such as PM-toxin (Figure 3.2). In this molecule,

Figure 3.2. PM-toxin A. This molecule, which is produced by the fungal pathogen
Phyllosticta maydis, has been the cause of major epidemics of leaf blight disease
in the United States. The molecule is toxic only to specific plants. As in Figure 3.1
both a line drawing and a ball and stick representation of the same molecule are
shown. The top representation is much more concise, but does not give
information about the shape of the molecule. The lower illustration shows how
the atoms are arranged in space as well as how they are connected to each other. A
low energy conformation of the molecule is illustrated. This molecule has four
alcohol groups (an oxygen joined to a carbon atom and a hydrogen atom by single
bonds). Changing one of these to a ketone (an oxygen joined to a carbon by a
double bond) without affecting the others will be difficult, as all the reagents
which can do this are likely to act on the whole molecule, not just on a specific
part of it.