The excesses of reagents used in protein chemistry are often incompatible with the reduced or even inverse stoichiometries used for efficient radiolabeling. Analysis and screening of aqueous Pd(0) ligand systems has revealed the importance of a guanidine core and the discovery of 1,1-dimethylguanidine as an enhanced ligand for aqueous Suzuki–Miyaura cross-coupling. This novel Pd catalyst system has now allowed the labeling of small molecules, peptides, and proteins with the fluorine-18 prosthetic [18F]4-fluorophenylboronic acid. These findings now enable site-specific protein 18F-labeling under biologically compatible conditions using a metal-triggered reaction.

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The radiochemical synthesis of [18F]4‐fluorophenols is based on phenol umpolung under oxidative conditions and direct nucleophilic fluorination with [18F]fluoride (see scheme, TBAF=tetra‐n‐butylammonium fluoride, TFA=trifluoroacetic acid). Readily available O‐unprotected 4‐tert‐butyl phenols are used as precursors in this one‐pot protocol. The reaction is completed in less than 30 minutes at room temperature and can be performed using standard or microfluidic technology.

Caught in the middle: The ionomycin calcium complex (see structure; O red, Ca green) was the target of an approach featuring the efficient asymmetric synthesis of an allene by a copper(I)-mediated anti-selective S(N)2' reaction, a highly stereoselective gold(III)-catalyzed cycloisomerization of an alpha-hydroxyallene, and a Rh-catalyzed rearrangement of an alpha-diazo-beta-hydroxyketone.