Synthesis of 2″-oxidized derivatives of 5-deoxy-5-epi-5-fluoro-dibekacin and -arbekacin, and study on structure-chemical shift relationships of urethane(or amide)-type NH protons in synthetic intermediates

Three 2″-modified dibekacin-analogs have been prepared as potential compounds active against resistant bacteria producing 2″-O-phosphotransferases; one is 5-deoxy-5,2″-diepi-5-fluorodibekacin (9) prepared from a suitably protected 2″-O-triflyl derivative through the 2″,3″-cyclic carbamate, and the others are 2″-oxo derivatives (12 and 22, both as the hydrate) of 5-deoxy-5-epi-5-fluoro-dibekacin and -arbekacin prepared through oxidation at C-2″ of suitably protected derivatives. Relationships between the t-butoxycarbonyl(= Boc)-NH-shifts of per-N-Boc synthetic intermediates and their structures were studied. It was found that the shifts, measured in pyridine-d5 at 80 °C, which spread over a close range (δ 6–7 ppm), are sensitively influenced by nearby and surrounding groups around the BocNH group in respect of electron-withdrawing character, hydrogen bonding (BocNH … acceptor), and also solvent effects (BocNH … NC5H5).