A Brief Overview of Two Major Strategies in Diversity-Oriented Synthesis: Build/Couple/Pair and Ring-Distortion

In the interdisciplinary research field of chemical biology and drug discovery, diversity-oriented synthesis (DOS) has become indispensable in the construction of novel small-molecule libraries rich in skeletal and stereochemical diversity. DOS aims to populate the unexplored chemical space with new potential bioactive molecules via forward synthetic analysis. Since the introduction of this concept by Schreiber, DOS has evolved along with many significant breakthroughs. It is therefore important to understand the key DOS strategies to build molecular diversity with maximized biological relevancy. Due to the length limitations of this mini review, we briefly discuss the recent DOS plans using build/couple/pair (B/C/P) and ring-distortion strategies for the synthesis of major biologically relevant target molecules like natural products and their related compounds, macrocycles, and privileged structures.

Combining the Petasis 3-component reaction with multiple modes of cyclization: a build/couple/pair strategy for the synthesis of densely functionalized small molecules

A build/couple/pair strategy for the synthesis of complex and densely functionalized small molecules is presented. The strategy relies on synthetically tractable building blocks (build), that is, diversely substituted hydrazides, α-hydroxy aldehydes, and boronic acids, which undergo Petasis 3-component reactions (couple) to afford densely functionalized anti-hydrazido alcohols. The resulting scaffolds can subsequently be converted via chemoselective cyclization reactions (pair), including intramolecular Diels-Alder or Ru-alkylidene catalyzed ring-closing metathesis, into sets of structurally diverse heterocycles in good yields in only 3-4 steps.

Towards the optimal screening collection: a synthesis strategy

The development of effective small-molecule probes and drugs entails at least three stages: 1) a discovery phase, often requiring the synthesis and screening of candidate compounds, 2) an optimization phase, requiring the synthesis and analysis of structural variants, 3) and a manufacturing phase, requiring the efficient, large-scale synthesis of the optimized probe or drug. Specialized project groups tend to undertake the individual activities without prior coordination; for example, contracted (outsourced) chemists may perform the first activity while in-house medicinal and process chemists perform the second and third development stages, respectively. The coordinated planning of these activities in advance of the first small-molecule screen tends not to be undertaken, and each project group can encounter a bottleneck that could, in principle, have been avoided with advance planning. Therefore, a challenge for synthetic chemistry is to develop a new kind of chemistry that yields a screening collection comprising small molecules that increase the probability of success in all three phases. Although this transformative chemistry remains elusive, progress is being made. Herein, we review a newly emerging strategy in diversity-oriented small-molecule synthesis that may have the potential to achieve these challenging goals.