Reaction of methyl [benzyl 2-[(benzyloxycarbonyl)-amino]-3-chloro-2,3,4-trideoxy-β-L-threo-hex-4-enopyrano-sid]uronate,3,4-trideoxy-β-L-threo-hex-4-enopyranosidjuronate (7) with silver fluoride gave the 5-fluoro, 3,4-unsaturated uronate derivative8, which, on treatment with methanolic ammonia, afforded the corresponding 5-meth-oxy, uronamide9. The structures of8and9were confirmed by spectral data and by x-ray crystallographic analysis of8.1H NMR spectroscopy parameters for 9 and its diastercomen11have been used to probe the conformational preferences in solution.