Few chemical methods exist for the
covalent conjugation of two
proteins. We report the preparation of site-specific protein–protein
conjugates that arise from the sequential cross-coupling of cysteine
residues on two different proteins. The method involves the synthesis
of stable palladium–protein oxidative addition complexes (Pd-protein
OACs), a process that converts nucleophilic cysteine residues
into an electrophilic S-aryl-Pd-X unit by taking advantage of
an intramolecular oxidative addition strategy. This process
is demonstrated on proteins up to 83 kDa in size and can be conveniently
carried out in water and open to air. The resulting Pd-protein OACs
can cross-couple with other thiol-containing proteins to arrive at
homogeneous protein–protein bioconjugates.
Organometallic reagents enable practical strategies for bioconjugation. Innovations in the design of water‐soluble ligands and the enhancement of reaction rates have allowed for chemoselective cross‐coupling reactions of peptides and proteins to be carried out in water. There are currently no organometallic‐based methods for oligonucleotide bioconjugation to other biomolecules. Here we report bifunctional palladium(II)‐oxidative addition complexes (OACs) as reagents for high‐yielding oligonucleotide bioconjugation reactions. These bifunctional OACs react chemoselectively with amine‐modified oligonucleotides to generate the first isolable, bench stable oligonucleotide‐palladium(II) OACs. These complexes undergo site‐selective C‐S arylation with a broad range of native thiol‐containing biomolecules at low micromolar concentrations in under one hour. This approach provided oligonucleotide‐peptide, oligonucleotide‐protein, oligonucleotide‐small molecule, and oligonucleotide‐oligonucleotide conjugates in >80 % yield and afforded conjugation of multiple copies of oligonucleotides onto a monoclonal antibody.
Palladium oxidative addition complexes (OACs) are traditionally accessed by treating an aryl halide-containing substrate with a palladium(0) source. Here, a new strategy to selectively prepare stable OACs from amino groups on native proteins is presented. The approach relies on an amine-selective acylation reaction that occurs without modification of a preformed palladium(II)-aryl group. Once transferred onto a protein substrate, the palladium(II)-aryl group facilitates conjugation by undergoing reaction with a second, cysteine-containing protein. This operationally simple method is applicable to native, nonengineered enzymes as well as antibodies and is carried out in an aqueous setting and open to air. The resulting Pd−protein OACs are stable, storable reagents that retain biological activity and can be used to achieve protein−protein cross-coupling at nanomolar concentrations within hours.
Described herein are syntheses of the naturally occurring polyketides (-)-tetrapetalones A and C and their respective enantiomers. The employed strategy involves initial assembly of a masked N-aryl tetramic acid which is advanced via a highly selective conjugate addition/intramolecular Friedel-Crafts acylation sequence to deliver a key azepine intermediate. Application of recently developed C-H activation chemistry and subsequent Heck cyclization delivers the aglycone framework in an overall 12 steps. Resolution of the aglycone via stereospecific glycosylation with an enantiopure glycosyl donor followed by separation of the derived diastereomers enables further advancement to either (+)- or (-)-tetrapetalones A and C.
Amphiphilic ligands are valued for their ability to facilitate organometallic reactions in the presence of water. The regioselective sulfonation of a series of commercially available biaryl monophosphines to generate amphiphilic ligands is presented. In this one-step protocol, the temperature and addition of fuming sulfuric acid were carefully controlled to arrive at sulfonated biaryl monophosphine ligands in high yields with >95% regioselectivity without the need for chromatographic purification.
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