Driven by the ever-increasing pace
of drug discovery and the need
to push the boundaries of unexplored chemical space, medicinal chemists
are routinely turning to unusual strained bioisosteres such
as bicyclo[1.1.1]pentane, azetidine, and cyclobutane to modify their
lead compounds. Too often, however, the difficulty of installing these
fragments surpasses the challenges posed even by the construction
of the parent drug scaffold. This full account describes the development
and application of a general strategy where spring-loaded, strained
C–C and C–N bonds react with amines to allow for the
“any-stage” installation of small, strained ring systems.
In addition to the functionalization of small building blocks and
late-stage intermediates, the methodology has been applied to bioconjugation
and peptide labeling. For the first time, the stereospecific strain-release
“cyclopentylation” of amines, alcohols, thiols,
carboxylic acids, and other heteroatoms is introduced. This report
describes the development, synthesis, scope of reaction, bioconjugation,
and synthetic comparisons of four new chiral “cyclopentylation”
reagents.