The criteria of ideal conjugation reaction
1) the use of 1:1 stoichiometry of the two reagents;
2) proceed rapidly under aqueous conditions;
3) tolerate all unprotected functional groups;
4) operate without toxic reagents or byproducts.
Potassium acyltrifluoroborates (KATs) and Ocarbamoylhydroxylamines tolerates all common unprotected functional groups and forms amide bonds under aqueous conditions with a second-order rate constant of 20 M−1 s−1.
KAT ligations are accelerated in aqueous solvents and are not affected by the nature or presence of organic cosolvents. The presence of water, however, is essential; under strictly anhydrous conditions the rate of the ligation slows dramatically.
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