Direct 18F-Labeling of Biomolecules via Spontaneous Site-Specific Nucleophilic Substitution by F- on Phosphonate Prostheses

We describe a high radiochemical yield late-stage direct ¹⁸F-labeling of bare biomolecules containing common active groups. Spontaneity and site-selectivity are attributed to the remarkably higher rates of nucleophilic substitution reactions on phosphonates than on other electrophiles by F^- at various hydrogen bond forms. Rapid access to many medicinally significant ¹⁸F-labeled biomolecules is achieved at 21-68% radiochemical yields and 35.9-55.1 GBq μmol^-1 molar activities both manually or automatically.

Late-Stage Conversion of Diphenylphosphonate to Fluorophosphonate Probes for the Investigation of Serine Hydrolases

Diphenylphosphonates (DPPs) have been used for 50 years to inactivate serine hydrolases, creating adducts representative of tetrahedral intermediates of this important class of enzymes. Failure to react at active site serine residues, however, can thwart their usefulness. Here, we describe a facile route and allied mechanistic studies to highly reactive, structurally complex organofluorophosphonates (FPs) by direct fluorinative hydrolysis of DPPs. Advantages over current preparations of FPs are exemplified by the synthesis of a β-lactam-containing peptide substrate analog capable of modifying the C-terminal, dual-function thioesterase involved in nocardicin A biosynthesis. Although this serine hydrolase was found to resist modification by classic DPP inhibitors, active site selective phosphonylation by the corresponding FP occurs rapidly to form a stable adduct. This simple, late-stage method enables the ready preparation of FP probes that retain important structural motifs of native substrates, thus promoting efforts in mechanistic enzymology by accessing biologically relevant enzyme-inhibitor co-structures.

Synthesis of Furan-Annelated BINOL Derivatives: Acid-Catalyzed Cyclization Induces Partial Racemization

In this account, we describe the synthesis of a series of BINOL-based bis- and trisphosphoric acids 11d/e/f, which commonly feature an unusual phosphoric acid monoester motif. This motif is generated by an acid-catalyzed 5- endo- dig cyclization of the 3-alkynyl-substituted BINOL precursors to give the corresponding Furan-annelated derivatives, followed by phosphorylation of the remaining phenolic alcohols. In the cyclization reaction, we observed an unexpected partial racemization in the bis- and tris-BINOL scaffolds, leading to mixtures of diastereomers that were separated and characterized spectroscopically and by X-ray crystal structure analyses. The cyclization and racemization processes were investigated both experimentally and by DFT-calculations, showing that although the cyclization proceeds faster, the barrier for the acid-catalyzed binaphthyl-racemization is only slightly higher.

Fluorinative hydrolysis of phosphorothioic acid esters with a binaphthyl group through axis-to-center chirality transfer leading to the formation of P-chiral phosphorothioic monofluoridic acid salts

Asymmetric synthesis of P-chiral phosphorothioic monofluoridic acid ammonium salts was achieved via axis-to-center chirality transfer reactions by using phosphorothioic acid O-esters with a binaphthyl group, and the absolute stereochemistry of the salts was determined by X-ray analyses and by comparison of their CD spectra.