So now there's "natural" chemistry and "plain" chemistry? I thought molecules are molecules, and don't care how they came to be. What if humans were to artificially select some bacteria over a few generations to synthesize a certain molecule. Would that molecule now be "natural" or synthetic? In fact, it can be argued that many "natural" molecules are a result of that exact process, because their synthesizing organism has evolved to survive human effects.
EDIT: as pointed out by localhost, natural products chemistry is actually a well defined -- and widely accepted -- term.