Retrosynthesis examples
The concepts of retrosynthesis are applied here to four drugs of simple structure and to a complex natural product. In each case the strategic bonds are sought, the possible disconnections compared and the analysis checked against the synthesis actually used.
Strategic bonds are, in general, the polar bonds that can be built from smaller molecules: the C–O bond of an ester, the C–N bond of an amide or amine, the C–C bond next to a carbonyl or an aromatic ring. In simple drugs there is almost always a cheap aromatic precursor (benzene, phenol, anilines) and the problem comes down to introducing the substituents in the right order, bearing in mind the directing effects of electrophilic aromatic substitution.
