The structure of d-threo-2,5-hexodiulosonic acid and derivatives in solution

The structure of d-threo-2,5-hexodiulosonic acid (1) and various derivatives in solution was determined by ¹³C-n.m.r. spectroscopy to be a hydrated, pyranose form. The structures of the methyl ester of 1 and of its 5-(dimethyl acetal) were confirmed by chemical means and by X-ray structure analysis.     

Modified xanthan—its preparation and viscosity

Xanthan with various pyruvic acid and acetate contents has been prepared from a single commercial polysaccharide sample using optimised chemical conditions (acid and alkali hydrolysis, respectively) for removal of acetal and acyl groups. The only significant change found on analysis of the modified xanthans was loss of pyruvic acid and/or acetate; no low moleculur weight carbohydrate-containing material was released. Contrary to some previous reports, evidence is presented to show that the pyruvic acid acetal and o-acetyl contents of xanthan do not affect solution viscosity. The viscosities of native, pyruvate-free and pyruvate/acetate-free xanthan solutions (0·3% w/v) were similar at shear rates 8·8–88·3 s^?1 in both distilled water and 1% KCl. Over the concentration range 0·2-1·5%, the viscosities of native and pyruvate-free xanthan at 10 s^?1 were similar. The viscosity increase on addition of 1% KCl to salt-free xanthan solutions was independent of pyruvic acid acetal substitution. Our results suggest that xanthan samples with various pyruvic acid acetal and o-acetal contents, prepared under different fermentation conditions of Xanthomonas campestri should not normally be used for assessing the contribution of these groups to solution viscosity.     

Synthesis of 4,5-dideoxy-4-C-[(R,S)-phenylphosphinyl]-d-ribo- and l-lyxo-furanose and their 1,2,3-triacetates

2,3-O-Isopropylidene-d-ribose diethyl dithioacetal, prepared from d-ribose, was converted in three steps into the corresponding dimethyl acetal, which was monotosylated at O-5, and the ester oxidized at C-4 with pyridinium chlorochromate; addition of methyl phenylphosphinate to the resulting pentos-4-ulose derivative then provided (4R,S)-4,5-anhydro-2,3-O-isopropylidene-4-C-[(R,S)-(methoxy)phenylphosphinyl]-d-erythro-pentose dimethyl acetal. Hydrogenation of this compound in the presence of Raney Ni, followed by reduction with SDMA, hydrolysis, and acetylation, yielded the title compounds (seven kinds), the structures of which were established on the basis of their 400-MHz, ¹H-n.m.r. and mass spectra. A general dependence of the ²J_PH and ³J_PH values on the OPCH and PCCH dihedral angles provided an effective method for the assignment of the configurations and conformations of these 4-deoxy-4-phosphinyl-pentofuranoses.     

Properties of 3-hydroxypropionaldehyde 3-phosphate.

Several modifications to the synthesis of the diethyl acetal of 3-hydroxypropionaldehyde-3-P (HPAP) are described. HPAP is liberated from its acetal by treatment with Dowex 50-H⁺ at 40 °C for 4 min, and longer time or higher temperature lower yields. Breakdown of the dianion of HPAP (pK 6.7) is self-catalyzed, with the phosphate acting as a general base to remove a proton from carbon 2 and allow elimination of phosphate to give acrolein. Monoanion breakdown is at least 400-fold slower. At 25 °C the dianion breaks down with k = 0.025 min^?1, and the activation energy for the process is 24 kcal/mol. Buffers have little effect on breakdown of HPAP, except for those containing primary or secondary amines. Thus morpholine enhances breakdown by forming a Schiff's base with a positively charged nitrogen, and Tris inhibits breakdown by forming one with an uncharged nitrogen. The aldehyde group of HPAP is 60% hydrated in water.     

Structure of the K82 Capsular Polysaccharide from <Emphasis Type="Italic">Acinetobacter baumannii</Emphasis> LUH5534 Containing a <Emphasis Type="SmallCaps">d</Emphasis>-Galactose 4,6-Pyruvic Acid Acetal

Type K82 capsular polysaccharide (CPS) was isolated from Acinetobacter baumannii LUH5534. The structure of a linear tetrasaccharide repeating unit of the CPS was established by sugar analysis along with one- and two-dimensional ¹H and ¹³C NMR spectroscopy. Proteins encoded by the KL82 capsule gene cluster in the genome of LUH5534 were assigned to roles in the synthesis of the K82 CPS. In particular, functions were assigned to two new glycosyltransferases (Gtr152 and Gtr153) and a novel pyruvyltransferase, Ptr5, responsible for the synthesis of D-galactose 4,6-(R)-pyruvic acid acetal.     

Properties of C-N.M.R. spectra of O-(1-carboxyethylidene) derivatives of methyl β-d-galactopyranoside: models for determination of pyruvic acid acetal structures in polysaccharides

¹³C-N.m.r. spectra were recorded of compounds containing O-(1-carboxyethylidene) groups linked to galactopyranose and fucopyranose derivatives. These compounds are useful as aids in determination of the positions and configurations of pyruvic acid acetal substituents in polysaccharides. Chemical shifts of non-protonated acetal carbons depend on whether the acetal ring is 5-membered (δ_c 107–109.5) or 6-membered (δ_c 100.5–102.4). The C-3 signals of 3,4-(1-carboxyethylidene) acetals are typical, being at δ_c 81 and in the case of the barium salt of the methyl β-d-galactopyranoside derivative. The exact value depends on the configuration, whether it is as in 6 (δ_c 81.1) or 5 (δ_c 80.4). The CH₃ signals of proton-n.m.r. spectra are also diagnostically useful, falling at δ 1.97 and 2.07 respectively. (The foregoing shift-values are pH-dependent). The pyruvylated galactan from the snail, Pomacea lineata, was shown to contain some residues that could be assigned a structure corresponding, in the positions of acetal substitution and acetal configuration, to structure 6. Compound 6 (barium salt) is of interest as its ¹³C-n.m.r. spectrum lacks non-protonated carbonyl and acetal carbon resonances, when obtained by the usual procedures. While this is principally because of long T₁ values, the non-protonated acetal carbon signals are comparatively broad, possibly through slow conformational interchange. In the case of the carbonyl resonance, the lack of sensitivity is because of a low n.O.e. value of 1.4, approximately one half that of other carbon atoms in the molecule.     

Preparation of 1-thioglycosides having ω-aldehydo aglycons useful for attachment to proteins by reductive amination

A series of 1-thioglycosides containing an ω-aldehydo group (as the dimethyl acetal) on the aglycon were prepared by reaction of O-acetyl-1-thioaldoses with N-(chloroacetyl)aminoacetaldehyde dimethyl acetal, a compound readily prepared by the action of chloroacetyl chloride or chloroacetic anhydride on 2-aminoacetaldehyde dimethyl acetal. O-Deacetylation of the 1-thioglycosides, followed by deacetalation, yielded the desired products. An analogous 1-thioglycoside having a longer aglycon was prepared by reaction of 1-thio-D-galactose with (6-aminohexanoyl)-aminoacetaldehyde dimethyl acetal, obtained by condensing 6-bromohexanoic acid and aminoacetaldehyde with 3-(3-dimethylaminopropyl)-1-ethylcarbodiimide. These glycosides were found to be useful for modification of proteins to yield neoglyco-proteins.     

Hydrogenolysis of the isomeric 1,2:4,6-di-O-benzylidene-α-d-glucopyranose derivatives with the LiAlH4AlCl3 reagent

Both isomers of 1,2:4,6-di-O-benzylidene-α-d-glucopyranose (and their 3-O-acetyl and 3-O-benzyl derivatives) have been prepared and their ¹H- and ¹³C-n.m.r. spectra assigned. The mode of hydrogenolysis of the dioxolane ring in these isomers by the LiAlH₄AlCl₃ reagent is determined by the configuration at the acetal carbon and is independent of the electronic character of the two oxygen atoms.     

A new method of acetonation. Synthesis of 4,6-O-isopropylidene-D-glucopyranose

Ethyl isopropenyl ether reacts with D-glucose in N,N-dimethylformamide containing a trace of p-toluenesulfonic acid to give crystalline 4,6-O-isopropylidene-α,β-D-glucopyranose (2) in near-quantitative yield. The structure of 2 was established by n.m.r. spectroscopy of it and of its β-triacetate 3, and by conversion of 3 through deacetonation and subsequent acetylation into β-D-glucopyranose pentaacetate (5). The acetonation reagent operates under kinetic control, with favored attack at primary hydroxyl groups, instead of by the thermodynamic control associated with conventional acetonation methods. The reagents converts methyl α-D-glucopyranoside (7) into the 4,6-isopropylidene acetal 8, and D-mannitol (9) into a 2:1 mixture of the 1,2:5,6-di-isopropylidene acetal 10 and the 1,2:3,4:5,6-tri-isopropylidene acetal 11.     

The effect of immersion cleansers on gloss,colour and sorption of acetal denture base material

doi: 10.1111/j.1741‐2358.2012.00657.x The effect of immersion cleansers on gloss, colour and sorption of acetal denture base material Objective: To study the effect of peroxide and hypochlorite cleansers on gloss, colour and sorption of acetal denture resins. Materials and methods: Pink acetal and thermoplastic acrylic resins were evaluated. Thirty‐five specimens 39 × 39 × 1.8 mm of each resin were prepared. Each group of specimens (n = 7) was then immersed into cleansers for 100 days. Group I immersed in tap water, Group II in Corega Extradent for 5 min, Group III in Corega Extradent for 8 h, Group IV in NitrAdine? Seniors for 15 min and Group V in NaOCl 5.25%. Gloss, colour and weight measurements were taken initially and after 100 days. Data subjected to two‐way anova and Tukey’s test at α = 0.05. Results: Acrylic resin showed reductions of glossiness from ?5 to ?15 and acetal from ?0.2 to ?6. Colour changes (ΔΕ*) ranged from 2.64 to 7.64 for acrylic and 2.77 to 26.54 for acetal resin. Sorption for acrylic ranged from 11.64 to 17.06 μg/mm³ and 9.18 to 24.79 μg/mm³ for acetal resin. The results of (ΔΕ*) and sorption showed an interaction between denture resins and cleansers. Conclusions: The gloss of acetal resin was less affected by water, peroxides and NaOCl 5.25% compared with acrylic resin. Acetal resin showed clinically acceptable (ΔΕ*) whereas acrylic resin unacceptable ones for water and peroxide solutions. The immersion of acetal resin in NaOCl 5.25% showed clinically unacceptable (ΔΕ*) and higher sorption and should be avoided or should be managed with care.     

The structure of the carbohydrate backbone of the core–lipid A region of the lipopolysaccharide from Proteus penneri strain 40: new Proteus strains containing open-chain acetal-linked N-acetylgalactosamine in the core part of the LPS

Analysis of the core part of the LPS from several strains of Proteus revealed that P. penneri strains 2, 11, 19, 107, and P. vulgaris serotypes O4 and O8 have the same structure with a new type of linkage between monosaccharides–an open-chain acetal — that was previously determined for P. vulgaris OX2 and P. penneri 17. The LPS from P. penneri strain 40 contains the same structure substituted with one additional monosaccharide:

Full-size image (5K)

where (1S)-GalaNAc¹ is a residue of N-acetyl- -galactosamine in the open-chain form. It is connected as a cyclic acetal to positions 4 and 6 of the galactosamine residue having a free amino group. All other sugars are in the pyranose form.     

Structural investigation of the capsular polysaccharide of Klebsiella serotype K80

The use of methylation, periodate oxidation, β-elimination, and selective hydrolysis enabled the structure of the K80 polysaccharide to be determined. The nature of the anomeric linkages was established by ¹H-n.m.r. spectroscopy, and confirmed by the results of oxidation of the fully acetylated polysaccharide with chromic acid. The K80 polysaccharide is comprised of repeating units of the pentasaccharide shown, and contains a pyruvic acetal on each repeating unit. This pattern constitutes the first instance, in this series of polysaccharides, of a pyruvic acetal attached to a side-chain rhamnosyl group.

     

Triterpenoid prosaponins from leaves of Maesa chisia var. angustifolia

Acid hydrolysis of the saponin fraction of the leaves ofMaesa chisia var.angustifolia yielded a monoglucoside fraction besides camelliagenin A as a minor constituent. The glucose moiety of the former could be removed by hydrolysis by Smith degradation to yield two new acylated triterpenoids characterised as 16α-O-acetyl-22α-O-angeloyl-camelliagen A and 16α-O-acetyl-22α-O-(2′-methylbutyroyl)-camelliagenin A as well as camelliagenin A and its 22α,28-glycolaldehyde acetal. The possibility of the later acetal derivative being an artefact could not, however, be ruled out.     

Configuration of the acetal carbon atom of pyruvic acid acetals in some bacterial polysaccharides

The configuration at the acetal carbon atom of pyruvic acid acetals present in some extracellular bacterial polysaccharides has been investigated. Assignment of the absolute configuration was made by comparing signals in the ¹³C- and ¹H-n.m.r. spectra of the polysaccharides with those of model substances. The S-configuration was demonstrated in eight polysaccharides in which pyruvic acid is linked to O-4 and O-6 of D-glucopyranosyl or D-mannopyranosyl residues. The R-configuration was demonstrated in four polysaccharides in which pyruvic acid is linked to O-4 and O-6 of D-galactopyranosyl residues. Consequently, in each of these acetals, which form 1,3-dioxane rings, the methyl group is equatorial and the carboxyl group axial. The S-form was further demonstrated in four polysaccharides in which the pyruvic acid is linked to O-3 and O-4 of D-galactopyranosyl groups.     

Chromatography of phosphorylases on N-acylchitosan gels

Depolymerization of bacterial, capsular polysaccharides by phage enzymes is a convenient method of preparing oligosaccharides that correspond to one, or several, repeating unit(s). Thus, the capsular polysaccharide from Klebsiella K21 yields a linear pentasaccharide, and that from Klebsiella K32, a linear tetrasaccharide. Both oligosaccharides contain acetal substituents, but, whereas the 4,6-O-(1-carboxyethylidene)-D-galactosyl residue in the K21 structure is relatively acid-stable, the corresponding 3,4-O-(1-carboxyethylidene)-l-rhamnosyl residue in K32 is extremely acid-labile. Phage degradation may, therefore, be the only way by which an oligosaccharide corresponding to an intact repeating-unit may be obtained in such circumstances.     

Synthèse des l-fucose et l-(3-2H)fucose à partir du d-mannose

Oxidation with the dimethyl sulfoxide-acetic anhydride reagent of methyl 2-O-acetyl-4,6-O-benzylidene-α-d-mannopyranoside, obtained in quantitative yield from the corresponding 4,6-benzylidene acetal by stereoselective opening of a 2,3-orthoester, led in good yield to methyl 2-O-acetyl-4,6-O-benzylidene-α-d-arabino-hexopyranosid-3-ulose, which was reduced with either sodium borohydride or sodium borodeuteride into a methyl 4,6-O-benzylidene-α-d-altropyranoside or its 3-²H derivative. A sequence involving a C-6 halogenation-dehydrohalogenation followed by catalytic hydrogenation of the resulting methyl 6-deoxy-α-d-arabino-hex-5-enopyranoside gave methyl 6-deoxy-β-l-galactopyranoside (methyl β-l-fucopyranoside) and then α-l-fucose, with an overall yield of 24% with respect to the starting methyl α-d-mannopyranoside.     

Synthesis and structure–activity relationship of pyripyropene A derivatives as potent and selective acyl-CoA:cholesterol acyltransferase 2 (ACAT2) inhibitors: Part 2

Synthesis and structure–activity relationships of 7-O-p-cyanobenzoyl pyripyropene A derivatives with modification at C1 and 11 are described. Regioselective mono-deprotection of di-tert-butylsilylene acetal was critical in their synthesis.     

Synthesis and properties of some O-[2,2-bis(alkylthio)ethyl]-glycolaldehydes

O-[2,2-Bis(alkylthio)ethyl]glycoaldehydes (1a–e; alkyl = Et, Pr, Prⁱ, Bu^t, and -CH₂-, respectively) have been prepared from the corresponding O-[2,2-bis(alkylthio)ethyl]glycolaldehyde dimethyl acetals (2a–e) by acid hydrolysis. In anhydrous 1,4-dioxane in the presence of BF₃ · (Et₂O)₂,1a–c were partially transformed into glycolaldehyde bis(dialkyl dithioacetals),1d afforded trans-2,6-bis(tert-butylthio)-1,4-dioxane and 3,5-bis(tert-butylthio)-1,4-oxathiane, and1e did not react. The acetals2a–e) were prepared from the appropriate glycolaldehyde dialkyl dithioacetal by O-alkylation with bromoacetaldehyde dimethyl acetal.     

Immunochemical studies on shigella dysenteriae type 9 bacterial polysaccharide

On graded hydrolysis and Smith degradation, the O-somatic polysaccharide isolated from Shigella dysenteriae type 9 bacteria, strain NCTC 7919, yielded five oligosaccharides which were characterized. The positions of the O-acetyl and pyruvic acetal groups in the repeating unit were identified. Immunochemical studies indicated that d-galactose is the immunodominant sugar in the polysaccharide, and one of the oligomers, having the structure Gal-(1→3)-GlcNAc-(1→3)-Gal-(1→4)-Man, showed maximum inhibition of the homologous precipitation.     

Structure–activity-relationship studies on dihydrofuran-fused perhydrophenanthrenes as an anti-Alzheimer’s disease agent

As an extended study on development of anti-Alzheimer’s disease agent, we newly synthesized various dihydrofuran-fused perhydrophenanthrenes via o-quinodimethane chemistry. This study revealed that the introduction of carbon side-chain on 8-position or removal of the acetal moiety on 3-position arose a cytotoxicity on rat cortical neurons. On the other hand, the ethereal or thio-ethereal substituent on 8-position enhanced the elongation effect on Aβ-damaged neurons. The necessity of the cyano group on 10b position was also proved in this structure–activity-relationship study.