of fortimicin B , the synthesis of 2-amino-3-O-demethyl-2-deoxy- and 3-amino-3-demethoxy fortimicin A , and a number of fortimicin analogs modified in the sugar ring, including 4'-hydroxyfortimicin D , 7'-C-propylfortimicin A , 7'-(3-hydroxypropyl)fortimicin A and its 6'-epimer , 7'-phenylfortimicin A and its 6'-epimer , and 3'-enofortimicin D . Of these analogs, only 2-amino-3-O-demethyl-2-deoxy- and 3-amino-3-demethoxyfortimicin A showed activity comparable to that of fortimicin A; the others were either inactive or less active than the parent compounds.
Several synthetic methodologies have been employed to convert the 1,6-an-hydromaltose derivative 396 to the 1,4-diaminocyclitol aminoglycoside 397 a fortim-icin analog. However, this compound was approximately 25% as potent as fortimicin A . The same precursor was also used to prepare fortimicin A analogue 398 via regio- and stereoselective introduction of azido and methylamino groups and transformation of the 1,6-anhydrohexopyranose moiety into a cyclitol ring  (compounds 396-398 ).
3',4'-Dideoxyneamine has been used to prepare demethylated analogs of istamycin A (399). Antibacterial activity screening of these compounds revealed that the 4-N-methyl group is essential for antibacterial activity, since 4-N-demethylated derivatives exhibited weak activity, whereas 6'-N-3-O-didemethylistamycin A still showed activity .
The compounds 2"-N-formimidoylistamycin (403) and 2'-N-formimidoylsta-mycin B (404) have been prepared by treatment of appropriately protected istamycin A0 and B0 derivatives with N-ferf-butoxycarbonylglycine (compounds 399-404 ). De-
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