Some amino sugars structurally related to 6-deoxymannojirimycin precursors prepared from methyl 6-deoxy-2,3-O-isopropylidene-alpha-D-lyxo-hexofuranosid-5-ulose and methyl 2,3-O-isopropylidene-alpha-D-lyxo-pentodialdo-1,4-furanoside

Reaction of selected carbohydrate aldehydes with benzylmagnesium halides: benzyl versus o-tolyl rearrangement

The Grignard reaction of 2,3-O-isopropylidene-α-D-lyxo-pentodialdo-1,4-furanoside and benzylmagnesium chloride (or bromide) afforded a non-separable mixture of diastereomeric benzyl carbinols and diastereomeric o-tolyl carbinols. The latter resulted from an unexpected benzyl to o-tolyl rearrangement. The proportion of benzyl versus o-tolyl derivatives depended on the reaction conditions. Benzylmagnesium chloride afforded predominantly o-tolyl carbinols while the application of benzylmagnesium bromide led preferably to the o-tolyl carbinols only when used in excess or at higher temperatures. The structures of the benzyl and o-tolyl derivatives were confirmed unambiguously by NMR spectral data and X-ray crystallographic analysis of their 5-ketone analogues obtained by oxidation of the corresponding mixture of diastereomeric carbinols. A possible mechanism for the Grignard reaction leading to the benzyl→o-tolyl rearrangement is also proposed.

Highly Diastereoselective Cyanation of Methyl Ketimines Obtained from (R)-Glyceraldehyde

[reaction: see text] Addition of trimethylsilyl cyanide to ketimines derived from (R)-2,2-dimethyl-1,3-dioxolan-4-yl methyl ketone to generate a quaternary stereocenter has been achieved with high yields and excellent diastereoselectivity. The stereoselectivity was found to be temperature and solvent dependent. The beta-hydroxy-alpha-amino nitrile of syn configuration was the major compound in kinetically controlled reactions, whereas the anti stereoisomer was obtained in excess in thermodynamically controlled reactions. Double stereodifferentiation under kinetic control conditions was successful, and the cyanation reaction occurred with complete syn diastereoselectivity using the matched pair. The versatility of the resulting amino nitrile as a synthetic intermediate was tested by performing the synthesis of orthogonally protected (R)-(2-aminomethyl)alanine.

Characterisation and X-ray crystallography of products from the Bucherer-Bergs reaction of methyl 2,3-O-isopropylidene-alpha-D-lyxo-pentodialdo-1,4-furanoside

Methyl 2,3-O-isopropylidene-alpha-D-mannofuranosidurononitrile [alternative name: methyl (5R)-5-C-cyano-2,3-O-isopropylidene-alpha-D-lyxofuranoside] (2), methyl 2,3-O-isopropylidene-alpha-D-mannofuranosiduronamide [methyl (5S)-5-C-carbamoyl-2,3-O-isopropylidene-alpha-D-lyxofuranoside; methyl (5S)-2,3-O-isopropylidene-alpha-D-lyxo-hexofuranosiduronamide] (3), methyl 2,3-O-isopropylidene-alpha-D-mannofuranosiduronic acid [methyl (5S)-2,3-O-isopropylidene-alpha-D-lyxo-hexofuranosiduronic acid] (4), methyl 5-deoxy-2,3-O-isopropylidene-5-ureido-beta-L-gulofuranosiduronamide [methyl (5R)-5-deoxy-2,3-O-isopropylidene-5-ureido-alpha-D-lyxo-hexofuranosiduronamide (5), and (4S,5S,6R)-5,6-dihydro-6-hydroxy-4,5-isopropylidenedioxy-4H-pyrido[2,1-e]imidazolidine-2',4'-dione [IUPAC name: (3aS,4R,8aS)-4-hydroxy-2,2-dimethyl-3a,8a-dihydro-4H-1,3-dioxa-4a,6-diaza-s-indacene-5,7-dione] (6), instead of the expected hydantoin derivative, were obtained from the Bucherer-Bergs reaction of methyl 2,3-O-isopropylidene-alpha-D-lyxo-pentodialdo-1,4-furanoside (1). The structure of 6 was deduced from NMR and mass spectral data and confirmed by X-ray crystallography. The configuration at C-5 in 2-5 was confirmed by establishing the 5S configuration of 3 by X-ray crystallography. Conformations of the six- and five-membered rings in 3 and 6 are also discussed.