Attempts to oxidize the primary amine resulting from initial Fmoc removal were fruitless (see SI). Inspired by the work of Beaucheman and co-workers, a number of oxidants were screened such as urea hydrogen peroxide complex/HFA, mCPBA, or BPO which either didn't react or gave overoxidized materials . A relentless screening of oxidants led to the finding that DMDO could cleanly oxidize the secondary amine to the corresponding PMB-protected hydroxylamine derivative (not shown). These mild conditions allowed for a sequential addition of reagents to remove the sulfinamide, Boc, and TBS groups along with guanidine installation to furnish 46 (not isolated); immediate treatment of the reaction mixture with DDQ afforded nitrone 47 in 45% yield over two steps. Unveiling this nitrone intermediate to the corresponding hydroxylamine proved to be challenging. Various logical conditions (phosphoric acid solution, diluted HCl solution, diethylamine, piperidine) were evaluated and failed (see SI).