Rhodium-catalysed connective synthesis of diverse reactive probes bearing S(VI) electrophilic warheads.

The value of small molecules that chemically modify proteins is increasingly being recognised and utilised in both chemical biology and drug discovery. The discovery of such chemical tools may be enabled by screening diverse sets of reactive probes. Most existing sets of reactive probes are armed with cysteine-directed warheads, a limitation that we sought to address. A connective synthesis was developed in which α-diazoamide substrates, armed with a S(VI) warhead, were reacted with diverse co-substrates. A high-throughput approach was used to identify promising substrate/co-substrate/catalyst combinations which were then prioritised for purification by mass-directed HPLC to yield a total of thirty reactive probes. The structural diversity of the probe set was increased by the multiplicity of reaction types between rhodium carbenoids and the many different co-substrate classes, and the catalyst-driven selectivity between these pathways. The probes were screened for activity against Trypanosma brucei, and four probes with promising anti-trypanosomal activity were identified. Remarkably, the synthetic approach was compatible with building blocks bearing three different S(VI) warheads, enabling the direct connective synthesis of diverse reactive probes armed with non-cysteine-directed warheads. Reactive probes that are synthetically accessible using our approach may be of value in the discovery of small molecule modifiers for investigating and engineering proteins.