4-N-acylfortimicins B and the preparation of fortimicin A from fortimicin B.

Selective 4-N-acylation of fortimicin B (2) has been accomplished by 4-N-acylation of 1,2',6'-tri-N-benzyloxycarbonylfortimicin B (4) followed by hydrogenolysis of the N-protecting benzyloxycarbonyl groups. In this manner, fortimicin B was converted into fortimicin A (1), and a series of 4-N-acylfortimicins B (3) was prepared for antibacterial assay. The key intermediate, 1,2',6'-tri-N-benzyloxycarbonylfortimicin B, was prepared either directly from fortimicin B or by converting fortimicin A into 1,2',6',2''-tetra-N-benzyloxycarbonylfortimicin A (6a), followed by selective hydrolysis of the 4-N-(N-benzyloxycarbonyl)glycyl group of the latter.