The systematic modification of natural products through diverted total synthesis is a powerful concept for the systematic modification of natural products with the aim of studying mechanistic aspects of their biological activity. This concept offers far-reaching opportunities for discovery at the interface of biology and chemistry. It is underpinned by the power of chemical synthesis, which manifests itself in the ability to modify structure at will. Its implementation, when combined with innovative design, enables the preparation of unique mechanistic probes that can be decisive in differentiating and validating biological hypotheses at the molecular level. This Review assembles a collection of classic and current cases that illustrate and underscore the scientific possibilities for practitioners of chemical synthesis.