Synthesis of analogs of methyl β-D-galactopyranoside modified at C-4

Chemical synthesis of the pentasaccharide repeating unit of the O-antigen from Escherichia coli strain SDLZB008 in the form of its 2-aminoethyl glycoside

Chemical synthesis of the pentasaccharide repeating unit of the O-antigen from E. coli strain SDLZB008 is accomplished through a linear strategy using rationally protected monosaccharide derivatives ensuring desired stereochemical outcome up on glycosylations. 2-Aminoethyl glycoside is incorporated at the reducing end of the target pentasaccharide. The terminal free amine may be used for further conjugation with suitable aglycon without hampering the reducing end stereochemistry. The rare D-Fucp3NAc moiety is incorporated through the corresponding 3-azido derivative derived from a known 3-azido quinovose derivative.

Hypoglycemic activity of extracts and compounds from the leaves of Hintonia standleyana and H. latiflora: potential alternatives to the use of the stem bark of these species

The CH(2)Cl(2)-MeOH (1:1) extract of the leaves of Hintonia standleyana and H. latiflora caused significant decrease in blood glucose levels in both normal and streptozotozin (STZ)-induced diabetic rats when compared with vehicle-treated groups (p < 0.05). These extracts were not toxic to mice according to the Lorke criteria. From the hypoglycemic extract of H. standleyana, two new 4-phenylcoumarins, namely, 6''-O-acetyl-5-O-beta-d-galactopyranosyl-7,4'-dihydroxy-4-phenylcoumarin (1) and 6''-O-acetyl-5-O-beta-d-galactopyranosyl-7,3',4'-trihydroxy-4-phenylcoumarin (2), were obtained. The analogous extract of H. latiflora yielded the new 5-O-[beta-d-xylopyranosyl-(1-->6)-beta-d-glucopyranosyl]-7,4'-dimethoxy-4-phenylcoumarin (3) along with several known compounds, including ursolic acid and desoxycordifolinic acid. Phenylcoumarins 1 and 2 showed hypoglycemic activity. HPLC profiles of the leaf extracts of both plants revealed the presence of known hypoglycemic phenylcoumarins as well as chlorogenic acid. The overall results have indicated that the leaves of H. standleyana and H. latiflora possess similar antidiabetic potential to their stem bark. Therefore, the leaves from these species could represent an alternative to the use of their stem bark, which, in turn, would contribute to the conservation of these Mexican medicinal plants.

Utilization of nosylepimines of 1,6-anhydro-β-d-hexopyranoses for the preparation of halogenated aminosaccharides

The aziridine ring cleavage of N-nosylepimines 3 and 7 having D-allo and D-manno configurations with halides led regioselectively to N-o-nitrobenzenesulfonylated 2-halo-3-amino- and 3-halo-2-amino-2,3-dideoxy derivatives of 1,6-anhydro-beta-D-glucopyranose 8-14 in 59-81% yields. Removal of o-nitrobenzenesulfonyl protecting group with benzenethiol afforded aminosaccharides, which were converted into more stable hydrochlorides 15-18.

Synthesis of specifically monofluorinated ligands related to the O-polysaccharide of Shigella dysenteriae type 1

The synthesis is reported of galactopyranose nucleophiles monofluorinated at positions 3, 4, or 6 and protected by 4,6-O-benzylidene, 3,6-di-O-benzyl, or 3,4-O-isopropylidene groups, respectively. The condensation of these nucleophiles with 2,3,4-tri-O-benzoyl-alpha-L-rhamnosyl bromide gave, after deprotection, the disaccharide analogues of methyl O-alpha-L-rhamnopyranosyl-(1-->2)-alpha-D-galactopyranoside, monofluorinated at position 3, 4, or 6 of the galactoside residue.

A convenient synthesis of 4-amino-4-deoxy-L-arabinose and its reduction product, 1,4-dideoxy-1,4-imino-L-arabinitol

Methyl beta-D-xylopyranoside in a mixture of N,N-dimethylformamide and 2-methoxypropene containing a little hydrogen chloride gave preponderantly the 2,3-O-isopropylidene derivative, which was readily converted into its 4-trifluoromethanesulfonate. The facile displacement of the triflate group gave a 4-azido-4-deoxy-alpha-L-arabinopyranoside derivative, and this, on mild acid treatment, was hydrolyzed to the 2,3-diol, or under more vigorous conditions to 4-azido-4-deoxy-L-arabinose. Methyl 2,3-di-O-acetyl-4-azido-4-deoxy-alpha-L-arabinopyranoside, from the diol, appears (1H-n.m.r. data) to exist as an equilibrating mixture of the 4C1 and 1C4 conformers in chloroform solution. The reduction of the azido sugar by hydrogen over Pd/C in .6M HCl yielded 4-amino-4-deoxy-L-arabinopyranose as its hydrochloride; in 0.1M HCl, further reactions occurred to give 1,4-dideoxy-1,4-imino-L-arabinitol as the final product. The aminodeoxypentose from lipid A precursor IIA, isolated from a Salmonella mutant by Raetz et al. in 1985, was shown to be identical with the synthetic aminoarabinose by t.l.c., 1H-n.m.r. spectroscopy, and g.l.c. of the acetylated reduction products.

Synthesis of 4-deoxy-D-xylo-hexose and 4-azido-4-deoxy-D-glucose and their effects on lactose synthase

Syntheses are reported of 4-deoxy-D-xylo-hexose and 4-azido-4-deoxy-D-glucose as potential inhibitors for lactose synthase [uridine 5'-(alpha-D-galactopyranosyl pyrophosphate):D-glucose 4-beta-D-galactopyranosyltransferase, EC 2.4.1.22]. These syntheses involved SN2 displacement of the 4-methylsulfonyloxy group of methyl 2,3,6-tri-O-benzoyl-4-O-methylsulfonyl-alpha-D-galactopyranoside by iodide and azide ions. In both cases, inversion in configuration was observed. The resulting intermediates, methyl 2,3,6-tri-O-benzoyl-4-deoxy-4-iodo-alpha-D-glucopyranoside and methyl 4-azido-2,3,6-tri-O-benzoyl-4-deoxy-alpha-D-glucopyranoside, were obtained in crystalline form. Both 4-deoxy-D-xylo-hexose and 4-azido-4-deoxy-D-glucose were found to be inhibitors for lactose synthase in the presence of alpha-lactalbumin, but had no effect in the absence of alpha-lactalbumin. Both D-glucose analogues bind to the enzyme system far more weakly than D-glucose, suggesting that the recognition of the 4-OH group of the acceptor substrate is an important factor in binding.