Recently considerable effort has been devoted to synthesize amino-monocarba-disaccharides [1], since numerous pseudodisaccharide-type aminocyclitol antibiotics (e.g., fortimycins, sporaricins, sannamycins, etc.), carrying one or more amino groups in either the cyclitol or the sugar portion, have been shown [2] to possess significant antibacterial activity. In addition, structurally similar compounds act as glycosidase enzyme inhibitors [1] and certain aminoglycosyl-inositol phosphates are considered [3] as insulin mimetics. The present communication reports the preparation of novel pseudodisaccharide-type aminocyclitol antibiotics from natural sugars, including o-arabinose, o-glucosamine, and 3-amino-2,3,6-trideoxy-L-hexoses [4], by the direct glycosylation of a functionalized cyclitol, or by means of the Ferrier carbocyclic ring-transformation [5] of a reducing disaccharide.
The aglycons (2S,3R,5R)-2,3-dibenzoyloxy-5-hydroxycyclohexanone (1) and the corresponding 3-azido analogue 2, employed for the glycosylations, were prepared by means of the mercury salt-mediated Ferrier carbocyclization of the respective methyl hex-5-enopyranosides [6,7]. Since glycosylation of inososes 1 and 2 with different donors and under various conditions led to extensive fl-elimination of the C-5 hydroxyl group, their carbonyl function was protected by treatment with 1,2-ethanedithiol (CH 2 C12-BF3 "Et 2 O) to afford the dithiolane derivatives 3 (82%; mp 131-132°C, [ ot ]o -43.3 °) and 4 (86%; [ or] o + 21.6°). From the azidocyclohexanone 2, the O-benzyloxime 5 (mp 89-90°C, [ oL ]o -81°) was also prepared in 76% yield.