A new synthesis of (-)-anisomycin and its demethoxy analogue from D-ribose

2,3-O-Isopropylidene-D-ribose (7) reacted with p-methoxybenzylmagnesium chloride in tetrahydrofuran to give the D-allotriol (6a) (77%). Periodate oxidation of compound (6a) followed by reaction with hydroxylamine hydrochloride in pyridine gave (E,Z)-5-deoxy-2,3-O-isopropylidene-5-(p-methoxy-phenyl)-L- ribose oxime (18a) which was converted into the nitrile methanesulphonate (19a) with methanesulphonyl chloride in pyridine. Reduction of the nitrile (19a) with lithium aluminium hydride gave (2R,3S,4R)-3,4-isopropylidenedioxy-2-(p- methoxybenzyl)pyrrolidine (2a) [45% from (6a)], which was converted into the epoxide (24a) (68%) via the bromo acetates (28a) and (29a). Regioselective opening of the epoxide ring in compound (24a) with acidic allyl alcohol gave the allyl ether (30a) (63%) which was converted into the N-benzyl 3-acetoxy compound (31a) (77%). Removal of the allyl and benzyl groups, by treatment with palladium-charcoal under acidic conditions followed by hydrogenolysis, gave (-)-anisomycin (1a) (86%). A similar series of reactions afforded demethoxyanisomycin (1b) which showed antibiotic activity against Trichomonas vaginalis [about one sixth the activity of anisomycin (1a)].