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 degrees C, which spread over a close range (delta 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).

Synthesis of dibekacin analogs containing 3-oxa- and 3-aza-2,3,4-trideoxy-D-glycero-hexopyranose

6-O-(3-Oxa-2,3,4-trideoxy-alpha-D-glycero-hexopyranosyl) derivatives (10 and 17) of both 3',4'-dideoxyneamine and 5-epifluoro-5,3',4'-trideoxyneamine have been prepared by coupling ethyl 6-O-benzyl-3-oxa-2,3,4-trideoxy-1-thio-D-glycero-hexopyranoside (5) with suitable aglycons. The corresponding 3"-aza derivative (19) of dibekacin (6) was prepared by oxidation of 1,3,2',6'-tetra-N-tosyldibekacin (7) with Pb(OAc)4 followed by treatment with NH4OAc and reduction with NaBH3CN. Related ring-opening compounds (11 and 25) were also prepared.

Syntheses of 3',4',5,6-tetradioxyneamine and 5,6-dideoxyneamine

3',4',5,6-Tetradoxyneamine (7) was synthesized from neamine by the reaction sequence N-acetylation, O-mesylation, treatment with sodium iodide-zinc dust, hydrogenation, and base hyrolysis, Alternatively, 7 was obtained by treatment of tetra-(N-methoxycarbonyl)neamine with sulphuryl chloride, followed by hydrogenation in the presence of palladium-on-charcoal and triethylamine, and removal of the N-protecting groups. 5,6-Dideoxyneamine (11) was synthesized from known 5,6-O-cyclohexylidene-tetra-(N-methoxycarbonyl)neamine by the reaction sequence 3',4'-O-acetylation, removal of the 5,6-O-cyclohexylidene group, 5,6-di-O-mesylation, treatment with sodium iodide-zinc dust, hydrogenation, and base hydrolysis. An alternative route involved treatment of 3',4'-di-O-acetyl-tetra-(N-methoxycarbonyl)-neamine (8) with sulphuryl chloride, hydrogenation of the product, and removal of the protecting groups to give 11.

Chemical modification of aminocyclitol antibiotics

The aminocyclitol antibiotic neamine has been chemically modified at the hydroxyl group on C-6 of the 2-deoxystrepatamine moiety. The partially acetylated neamine derivatives, 6,3,4-tri-O-acetyl- (3) and 5,3-57,4-tri-O-acetyl-1,3,2,6-tetra-N-(ethoxycarbonyl)neamine (4), were prepared by random hydrolysis of the 5,6-O-ethoxyethylidene derivative (2), followed by chromatographic purification. Condensation of 4 and 2,3,5-tri-O-benzoyl-D-ribofuranosyl chloride led to 6-O-(beta-D-ribonfuranosyl)neamine (7). Analogous condensation of 4 with 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl bromide or 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide afforded the corresponding 6-O-(D-hexopyranosyl)neamines.

A synthesis of 3',4'-dideoxykanamycin B

3',4',-Dideoxykanamycin B, the kanamycin B derivative that is active against resistant bacteria, was prepared from kanamycin B via N-tosylation, 3',4'-O-sulphonylation, 3',4'-unsaturation, and hydrogenation. The unsaturated intermediate was obtained from the 3',4'-di-O-sulphonyl derivatives by the action of sodium iodide in N,N-dimethylformamide; if zinc dust was added in this reaction, aziridine derivatives were formed. Removal of the tosyl group was successfully performed by using sodium in ammonia-ethylamine.