Synthesis of a phosphonate-linked aminoglycoside-coenzyme a bisubstrate and use in mechanistic studies of an enzyme involved in aminoglycoside resistance.

Just five steps! The synthesis of a phosphonate-linked aminoglycoside-coenzyme A derivative (see scheme) that includes a Michael addition in water has been realized in just five steps. Aminoglycoside N-6'-acetyltransferases (AAC(6')s) are important determinants of antibiotic resistance. A good mechanistic understanding of these enzymes is essential to overcome aminoglycoside resistance. We have previously reported the synthesis of amide- and sulfonamide-linked aminoglycoside-coenzyme A conjugates, which were useful mechanistic and structural probes of AAC(6')s. We report here the synthesis of a phosphonate-linked aminoglycoside-coenzyme A variant, which is expected to be a superior mimic of the tetrahedral intermediate proposed for catalysis by AAC(6')s. This synthetic target is especially challenging for a number of reasons, including the presence of multiple functional groups, the water solubility of both starting materials, and incompatibility of P(III) chemistry with water. We have overcome these challenges by adding the expensive coenzyme A in the last step by means of an elegant Michael-type addition onto a vinylphosphonate in water. Overall, a single protection step was needed. The decreased inhibitory potency of this bisubstrate compared to that of the amide-linked analogue suggests that Enterococcus faecium AAC(6')-Ii may not stabilize the proposed tetrahedral intermediate, and may act mainly through proximity catalysis.