The Total Synthesis of Antibiotic Fortimicin B

The total synthesis of antibiotic fortimicin B (1b) is described. The sugar component of 1b: 6-epi-purpurosamine B was converted to the sugar chloride: 2,6-bis(2,4-dinitrophenylamino)-2,3,4,6,7-pentadeoxy-β-l-lyxo-heptopyranosyl chloride (5). The aminocyclitol component of 1b: fortamine B was also converted to the partially protected aglycone (9). The condensation of aglycone 9 with the sugar chloride 5 gave the desired condensation product in 37% yield. The analogous condensation of the Dl-form of the aglycone with 5 afforded the same condensation product in 19% yield, it was then converted to 1b by step-by-step hydrolysis.