Pattern recognition in retrosynthetic analysis: snapshots in total synthesis.

In this Perspective, the value of small molecule natural products (SMNPs) in the discovery of active biological agents is discussed. The usefulness of the natural products-based method of potential pharma discovery is much augmented by the capacities of chemical synthesis. The great advances in synthetic methodology allow for major editing of the natural product in the hopes of optimizing potency and therapeutic index. As a consequence of the enormous increase in the power of multistep chemical synthesis, one can now approach structures of previously impractical complexity. In constructing a plan for a multistep synthesis, two complementary thought styles are often encountered. One is the traditional and extremely powerful concept of prioritized strategic bond disconnections. The other, which we term "pattern recognition," involves the identification of moieties within the target, which are associated with reliable chemistry, and can serve to facilitate progress to the target. Recognition of such targets may require substantial recasting of the target structure to connect it to well-established types of transformations. Some of our older ventures, where ideas about pattern recognition were first being fashioned and used productively, are revisited. In addition, we provide snapshots of recently achieved total syntheses of SMNPs of novel biological potential. These vignettes serve to harmonize insights occasioned by pattern recognition, in concert with transformations enabled by the enormous growth in the power of synthesis.