ABSTRACT
Potassium acyltrifluoroborates (KATs) undergo chemoselective amide-forming ligations with hydroxylamines. Under aqueous, acidic conditions these ligations can proceed rapidly, with rate constants of â¼20 M-1 s-1. The requirement for lower pH to obtain the fastest rates, however, limits their use with certain biomolecules and precludes in vivo applications. By mechanistic investigations into the KAT ligation, including kinetic studies, X-ray crystallography, and DFT calculations, we have identified a key role for a proton in accelerating the ligation. We applied this knowledge to the design and synthesis of 8-quinolyl acyltrifluoroborates, a new class of KATs that ligates with hydroxylamines at pH 7.4 with rate constants >4 M-1 s-1. We trace the enhanced rate at physiological pH to unexpectedly high basicity of the 8-quinoline-KATs, which leads to their protonation even under neutral conditions. This proton assists the formation of the key tetrahedral intermediate and activates the leaving groups on the hydroxylamine toward a concerted 1,2-BF3 shift that leads to the amide product. We demonstrate that the fast ligations at pH 7.4 can be carried out with a protein substrate at micromolar concentrations.
Subject(s)
Amides/chemical synthesis , Borates/chemistry , Quinolines/chemistry , Borates/chemical synthesis , Green Fluorescent Proteins/chemistry , Green Fluorescent Proteins/genetics , Hydroxylamines/chemistry , Kinetics , Models, Chemical , Mutation , Quinolines/chemical synthesisABSTRACT
A new prosthetic group is reported for 18F-labelling of peptides and proteins based on the chemoselective ligation of potassium acyltrifluoroborates (KATs) and hydroxylamines without any detectable 18F/19F isotope exchange at the acyltrifluoroborate moiety. The new building block is appended via a common amide bond at room temperature with no need for protecting groups which enables an effective orthogonal 18F-radiolabelling.
Subject(s)
Borates/chemistry , Fluorine Radioisotopes/chemistry , Isotope Labeling/methods , Peptides/chemistry , Proteins/chemistry , Pyridines/chemistry , Animals , Indicators and Reagents/chemistry , Male , Mice, Inbred C57BL , Peptides/metabolism , Positron-Emission Tomography/methods , Proteins/metabolism , Radiopharmaceuticals/chemistry , TemperatureABSTRACT
NOD2 (nucleotide-binding oligomerization domain-containing protein 2) is an internal pattern recognition receptor that recognizes bacterial peptidoglycan and stimulates host immune responses. Dysfunction of NOD2 pathway has been associated with a number of autoinflammatory disorders. To date, direct inhibitors of NOD2 have not been described due to technical challenges of targeting the oligomeric protein complex. Receptor interacting protein kinase 2 (RIPK2) is an intracellular serine/threonine/tyrosine kinase, a key signaling partner, and an obligate kinase for NOD2. As such, RIPK2 represents an attractive target to probe the pathological roles of NOD2 pathway. To search for selective RIPK2 inhibitors, we employed virtual library screening (VLS) and structure based design that eventually led to a potent and selective RIPK2 inhibitor 8 with excellent oral bioavailability, which was used to evaluate the effects of inhibition of RIPK2 in various in vitro assays and ex vivo and in vivo pharmacodynamic models.