The syntheses of new C8-carbasugars and -aminocyclitols related to miglitol and voglibose are described. The key step involves the ring closing metathesis of 1,9-dienes derived from D-mannitol. Chemical transformations of the newly created double bond of the resulting cyclooctenes involved notably hydroboration and reductive amination. The inhibitory activity of the glycomimetics so-obtained has been evaluated towards 24 commercially available glycosidases. (c) 2005 Elsevier Ltd. All rights reserved.