Page 58 - Visions of the Future Chemistry and Life Science

World champion chemists 47

foolish response to any situation that is presented, but the details of the
response are not predictable. The same is true of organic synthesis, con-
tending with the properties of molecules. Organic reactions are well under-
stood, but if a reaction is performed in a completely new context, then the
molecule’s response may not be exactly as expected from the experience
gained through earlier studies of related systems. The variety of possible
responses makes chess a demanding game, and organic synthesis a chal-
lenging subject.
Chess is, however, succumbing to computers. Only the very best
human chess players can compete on a level with the best chess-playing
computers, and every year the computers become more powerful. It is
unlikely that the chess champion of the world will be human for any of the
third millennium. At the end of the second millennium, the best design-
ers of organic syntheses were unquestionably human. For how much
longer will this pre-eminence continue?
A molecule-building computer would need to understand chemistry.
This is possible. Quantum mechanics provides a method for calculating
how molecules behave with a high level of precision, using Schrödinger’s
equation. In 1929, Dirac wrote ‘The underlying physical laws necessary for
the mathematical theory of a large part of physics and the whole of chem-
istry are thus completely known, and the difficulty is only that the exact
application of these laws leads to equations much too complicated to be
soluble’ (Dirac 1929). Since that time, advances in computers have made
some of these complicated equations not only soluble, but routinely used.
However, the equations become more complicated very rapidly as larger
systems are considered, and so the exact application of these laws remains
out of reach, except for the smallest molecules. Many useful approxima-
tions have been developed in order to extend the range of possible calcula-
tions, and the effects of these simplifications are now well known. The
1998 Nobel prize in chemistry was awarded to Pople and Kohn for the
development of methods for calculating chemistry.
Solving quantum mechanical problems is a conceptually straightfor-
ward way of solving organic chemistry. The problem is simply one of com-
puter power. In order to calculate the energy of a molecule the size of
PM-toxin (Figure 3.2) or bryostatin (Figure 3.3), an extremely complex cal-
culation must be done. It is now possible to do this, using advanced
quantum chemistry programs. If lower accuracy is acceptable, then the cal-
culation may even be made easy using the much greater approximations of