Synthesis and conformational analysis of a simplified inositol-model of the Streptococcus pneumoniae 19F capsular polysaccharide repeating unit.

Carbohydrate mimics have been studied for a long time as useful sugar substitutes, both in the investigation of biological events and in the treatment of sugar-related diseases. Here we report further evaluation of the capabilities of inositols as carbohydrate substitutes. The conformational features of an inositol-model of a simplified repeating unit corresponding to the capsular polysaccharide of Streptococcus pneumoniae 19F has been evaluated by computational analysis, and compared to the native repeating unit. The inositol mimic was synthesized, and its experimental spectroscopic data allowed for verification of the theoretical results.

Useful access to enantiomerically pure protected inositols from carbohydrates: the aldohexos-5-uloses route.

The intramolecular aldol condensation of aldohexos-5-ulose derivatives of the D-xylo and L-ribo stereoseries has been studied. Only one of the four possible inososes was isolated from both stereoseries in reasonable yields (30-38%). The results obtained, together with the previous findings for the L-arabino and L-lyxo stereoseries, allowed for the rationalisation of a mechanism of the reaction based on open-transition-state models and electron-withdrawing inductive effects. Complementary reductions of the intermediate inososes were possible by changing the reaction conditions, and two isomeric inositol derivatives were obtained with complete stereoselection from each inosose. The presented approach permits us to control the configuration of three out of the six stereocentres of the inositol frame and gives access to seven of the nine inositols. Noteworthy, for the D-xylo derivative, the two-step sequence (condensation followed by reduction with NaBH(OAc)3) represents the biomimetic synthesis of myo-inositol. Furthermore, the sugar-based pathway leads directly to enantiomerically pure selectively protected inositols and does not require any desymmetrisation procedure which is needed when myo-inositol and other achiral precursors are employed as starting materials. As an example of application of the method, the indirect selective protection of secondary inositols' hydroxy functions, by placing specific protecting groups on the aldohexos-5-ulose precursor has been presented.

Stereoselective synthesis of ß-d-GlcNAc-(1→4)-D-Glc disaccharide starting from lactose.

The stereoselective preparation of the ß-d-GlcNAc-(1→4)-D-Glc disaccharide starting from known 4-O-[6-O-(1-methoxy-1-methylethyl)-3,4-O-isopropylidene-ß-d-talopyranosyl]-2,3:5,6-di-O-isopropylidene-aldehydo-D-glucose dimethyl acetal (2), in turn easily obtained from lactose, is reported. Key steps of this new procedure, that avoids the glycosylation reaction, are (a) a first epimerization at C-4' through an unusual procedure involving a completely stereospecific hydroboration-oxidation of the enol ether group of the hex-4-enopyranoside 4, obtained from 3 by base promoted acetone elimination, (b) an amination with inversion by S(N)2 reaction on an imidazylate intermediate, and, finally, (c) N-acetylation followed by complete deprotection.

Prevalence of oxetanose forms in the tautomeric equilibrium of ß-hydroxy-1,5-dicarbonyl monosaccharides.

The synthesis of 4-deoxy- and 4-deoxy-4-C-methylhexos-5-uloses, starting from 4-deoxyhex-4-enopyranosides, and a nuclear magnetic resonance (NMR) study of their isomeric composition are reported. The NMR spectra show that the two δ-dicarbonyl sugars exist as two anomeric α- and ß-oxetanosyl forms, derived from the hemiacetalization of the C-3 hydroxyl group with the aldehydic carbon. The observed tautomeric equilibria have been rationalized with computational calculations. Interestingly, this is the first time that dicarbonyl derivatives are mostly present in their oxetanose forms, offering a new entry into this very interesting type of scaffold.

Efficient double glycoconjugation to naturalize high molecular weight disperse dyes.

Commercially available Disperse Orange 29 (1a) and Disperse Red 1 (2a) were elaborated to glycoconjugated species, following a new version of a previously-described 'naturalisation' procedure. Glutamic acid was chosen to achieve a double glycoconjugation, which is essential to give to the original disperse dye a water solubility suitable for reaching optimal dyeing conditions. UV-vis plot of the 'naturalised' species showed negligible differences when compared to those of the commercial dyes.

Fusarium oxysporum degradation and detoxification of a new textile-glycoconjugate azo dye (GAD).

Degradation and detoxification of textile dyes are of interest due to the huge environmental impact of such chemicals. An isolate of Fusarium oxysporum was used to degrade and to detoxify a new chemical class of textile dyes called Glycoconjugate Azo Dye (GAD). After 6 d of growth in a liquid batch culture, the fungus degraded the dye and the culture medium at the end of incubation period showed a ˜100% detoxification compared to the initial dye solution. Increasing the initial fungal inoculum, the dye was totally decolourized after 24 h of incubation. The degradation ability was found to be common among various isolates of F. oxysporum suggesting this as a specific trait of this species. Degrading rate was enhanced in concomitancy to the glucose depletion and the beginning of the stationary phase of growth, suggesting that the shift from the primary to the secondary metabolism may be the trigger of the degradation pathway. The Daphnia magna acute toxicity test demonstrated a strong detoxification of GAD-4 by F. oxysporum, resulting in non-toxic metabolite production. Fusarium oxysporum could, therefore, be taken into consideration to develop new remediation strategies of textile effluents.

Deoxynojirimycin and its hexosaminyl derivatives bind to natural killer cell receptors rNKR-P1A and hCD69.

Deoxynojirimycin (1) and two new related 4-O-hexosaminyl-containing disaccharide mimics, beta-d-TalNAc-(1-->4)-DNJ (4) and beta-d-ManNAc-(1-->4)-DNJ (5), have been studied as agonists of natural killer (NK) cell receptors. As a positive and unexpected result, DNJ (1) displayed a remarkable activation effect towards both NKR-P1A (rat) and CD69 (human) receptors, and a quite similar activity was found for 4 and 5. The synthesis of the two disaccharide mimics is based on an approach that avoids the glycosylation step using known intermediates arising from lactose. The key stage of the synthesis involves the construction of the DNJ unit through an initial C-5 oxidation of the reducing d-glucopyranosyl unit followed by a stereoselective double-reductive aminocyclization of the 1,5-dicarbonyl disaccharide intermediates.

Lactose as an inexpensive starting material for the preparation of aldohexos-5-uloses: synthesis of L-ribo and D-lyxo derivatives.

Partially protected derivatives of L-ribo- and D-lyxo-aldohexos-5-ulose have been prepared starting from triacetonlactose dimethyl acetal derivatives. Key steps of the synthetic sequences are (a) the synthesis of 4'-deoxy-4'-eno- and 6'-deoxy-5'-eno lactose derivatives, and (b) the epoxidation-methanolysis of the above-mentioned enol ethers to give 1,5-bis-glycopyranosides, masked form of the target 1,5-dicarbonyl hexoses.

A new route for the synthesis of Streptococcus pneumoniae 19F and 19A capsular polysaccharide fragments avoiding the beta-mannosamine glycosylation step.

The recently described [Attolino, E.; Bonaccorsi, F.; Catelani, G.; D'Andrea, F. Carbohydr. Res. 2008, 343, 2545-2556.] beta-D-MaNAcp-(1-->4)-beta-D-Glcp thiophenyl glycosyl donor 3 was used in alpha-glycosylation reactions of OH-2 and OH-3 of the suitably protected p-MeO-benzyl alpha-l-rhamnopyranoside acceptors 7 and 8. Glycosylation of the axial OH-2 of 7 took place in high yield (76%) and with acceptable stereoselectivity (alpha/beta=3.4) leading to the protected trisaccharide alpha-11, corresponding to the repeating unit of Streptococcus pneumoniae 19F. The same reaction on equatorial OH-3 of acceptor 8 gave the trisaccharide alpha-15, a constituent of the repeating unit of S. pneumoniae 19A, but in lower yield (41%) and without stereoselection (alpha/beta=1:1.3). Utilizing the introduced orthogonal protection of OH-1 and OH-4'', the trisaccharide alpha-11 was transformed into a trisaccharide building block suitable for the synthesis of its phosphorylated oligomers.

Toward the synthesis of fine chemicals from lactose: preparation of D-xylo and L-lyxo-aldohexos-5-ulose derivatives.

The transformation of (5R)-2,6-di-O-benzyl-5-C-methoxy-beta-D-galactopyranosyl-(1-->4)-2,3:5,6-di-O-isopropylidene-aldehydo-D-glucose dimethyl acetal (8) into partially protected derivatives of D-xylo- and L-lyxo-aldohexos-5-ulose has been reported, applying appropriate epimerisation methods to its 3'-O- and 4'-O-protected alcoholic derivatives.

Stereoselective entry into the D-GalNAc series starting from the D-Gal one: a new access to N-acetyl-D-galactosamine and derivatives thereof.

A new stereoselective preparation of N-aceyl-D-galactosamine (1b) starting from the known p-methoxyphenyl 3,4-O-isopropylidene-6-O-(1-methoxy-1-methylethyl)-beta-D-galactopyranoside (10) is described using a simple strategy based on (a) epimerization at C-2 of 10 via oxidation-reduction to give the talo derivative 11, (b) amination with configurational inversion at C-2 of 11 via a S(N)2-type reaction on its 2-imidazylate, (c) anomeric deprotection of the p-methoxyphenyl beta-D-galactosamine glycoside 14, (d) complete deprotection. Applying the same protocol to 2,3:5,6:3',4'-tri-O-isopropylidene-6'-O-(1-methoxy-1-methylethyl)-lactose dimethyl acetal (4), directly obtained through acetonation of lactose, the disaccharide beta-D-GalNAcp-(1-->4)-D-Glcp (1a) was obtained with complete stereoselectivity in good (40%) overall yield from lactose.

Synthesis of glycose carbamides and evaluation of the induction of erythroid differentiation of human erythroleukemic K562 cells.

A series of carbamides derived from 1,2:5,6-di-O-isopropylidene-D-gluco- and D-allofuranose as well as their 5,6-O-deprotected analogues (2 and 4) and methyl 3,4-O-isopropylidene-alpha- and beta-D-galactopyranosides (5 and 6) have been prepared in order to evaluate their ability to induce erythroid differentiation of human erythroleukemic K562 cells. Twenty out of 51 carbamides tested exhibit an appreciable activity as inducers of erythroid differentiation and have been fully characterized and described.

Stereoselective synthesis of a model alpha-glycoside of the beta-D-ManNAcp-(1-->4)-d-Glc disaccharide starting from lactose, avoiding the beta-mannosaminylation step.

A model isopropyl alpha-glycoside of the beta-d-ManNAc-(1-->4)-d-Glc disaccharide has been prepared from lactose, avoiding the beta-mannosaminylation step. Three complementary approaches involving first the preparation and then the glycosidation of beta-thiophenyl donors of the protected disaccharides, (a) beta-d-ManNAc-(1-->4)-d-Glc, (b) beta-d-TalNAc-(1-->4)-d-Glc and (c) lactose, were compared. The best results were obtained employing a suitably protected lactose donor, and submitting its alpha-isopropyl glycoside to an amination with inversion in position 2' followed by an epimerization at C-4'.

'Naturalization' of textile disperse dyes through glycoconjugation: the case of a bis(2-hydroxyethyl) group containing azo dye.

A family of five strictly related glycoconjugated azo dyes (GADs), characterized by the presence of the same chromophore and a variable number (1-4) of deprotected hexose units, has been prepared by employing succinate bridges for connecting the azo dye and the sugar portions. The modulation of the hydrophilic portion determines the appreciable changes in the water solubility of GADs. In all the cases, however, hydrophobic fibres (polyester) were homogeneously dyed with GADs at temperatures lower than that used for original azo dyes, at atmospheric pressure, and avoiding the use of surfactants. Furthermore, GADs show an interesting multipurpose character leading to dyeing well also the natural fibres as, for instance, wool. The presence of a variable number of hexose units in the different GADs determines some changes in the colour intensity of dyed fabrics, but in all the cases an appreciable rubbing and water fastness were maintained.

A new and efficient entry to D-xylo-hexos-4-ulose and some derivatives thereof through epoxidation of the 3,4-hexeno derivative of diacetone-D-glucose.

A new preparation of D-xylo-hexos-4-ulose (1) and of its 3-m-chlorobenzoate (2) has been devised using the epoxidation of 3-deoxy-1,2:5,6-di-O-isopropylidene-D-erythro-hex-3-enofuranose (6) as the key step. The epoxidation of 6 in CH2Cl2 furnished with high yield 1,2:5,6-di-O-isopropylidene-3-O-m-chlorobenzoyl-4-C-hydroxy-D-xylo-hexos-4-ulo-1,4-furanose as a mixture of C-4 hemiacetal anomers (7a,b), which, on acid hydrolysis, gave a tautomeric mixture of 3-O-m-chlorobenzoyl-D-xylo-hexos-4-ulose (2) with an overall 60% yield from 6. The formation of 4-C-methoxy-diacetone-D-glucose derivatives (11a,b) through epoxidation-methanolysis of 6, took place with reduced yield because of the competition between m-chlorobenzoic acid (MCBA) and methanol to the opening by attack at C-4 of the intermediate epoxide and the formation of acyclic products arising from the alternative nucleophilic attack at C-1. Acid hydrolysis of derivatives 11 gave D-xylo-hexos-4-ulose (1) with a 35% overall yield from 6. NMR analysis showed that 2 is composed, in CD3CN, mainly by a 7:3 mixture of 4-keto-alpha- and beta-pyranose forms, while 1, in D2O, is present as a more complex mixture constituted mainly by 4-keto-alpha- and beta-pyranoses and their respective hydrates in a 17:15:34:34 ratio.

Preparation and biological evaluation of some 1,2-O-isopropylidene-D-hexofuranose esters.

The synthesis and biological evaluation of some new glycose esters bearing the 1,2-O-isopropylidene-d-hexofuranose functionality and belonging to the 3-O-acyl-d-allose and 6-O-acyl-d-glucose series are reported. When the results concerning cell growth inhibition are compared, it appears that the 6-O-acyl-d-glucose derivatives are more active than the 3-O-acyl-d-allose compounds. Within both 6-O-acyl-d-glucose and 3-O-acyl-d-allose derivatives, butyric esters displayed the highest inhibitory effects. Inhibition of cell growth is not associated with high induction levels of erythroid differentiation, despite the fact that pivaloates induce erythroid differentiation to an extent similar to that exhibited by previously reported molecules [Bioorg. Med. Chem. Lett.1999, 9, 3153-3158].

Convenient preparation of L-arabino-hexos-5-ulose derivatives from lactose.

2,6-di-O-benzyl- (9), 2-O-benzyl-3,4-O-isopropylidene- (19), and 2-O-benzyl-6-O-m-chlorobenzoyl-L-arabino-hexos-5-ulose (20) have been prepared using 4'-deoxy-4'-eno- and 6'-deoxy-5'-eno lactose dimethyl acetal derivatives 7 and 14 as key intermediates. The synthesis of enol ethers 7 and 14 has been performed with good yields by base-promoted elimination of acetone or p-toluenesulfonic acid from 2',6'-di-O-benzyl-, and 6'-O-p-toluenesulfonyl-2,3:5,6:3',4'-tri-O-isopropylidenelactose dimethyl acetal, respectively. The epoxidation with MCPBA of 7 and 14 in methanol or dichloromethane furnishes C-5'-methoxy and C-5'-m-chlorobenzoyloxy derivatives, easily transformed with good yields into L-arabino 5-ketoaldohexoses 9, 19 and 20.

A new route for the chemical valorisation of lactose.

A totally protected di-O-benzyl derivative of triacetonlactose dimethyl acetal was transformed into a 4'-hexeno disaccharide by elimination of acetone with t-BuOK in DMF and subsequently in 5'-C-methoxy derivative by oxidation with MCPBA in methanol as a solvent. The hydrolysis of this latter compound affords 2,6-di-O-benzyl-L-arabino-aldohexosos-5-ulose, which by intramolecular aldol condensation with DBU gives an inosose that was stereoselectively reduced to epi-inositol. Therefore our synthetic strategy offers a new and simple method to transform lactose into carbocyclic monosaccharide analogues.

Conformational evaluation of some 4-deoxyhex-4-enopyranose derivatives and their use in the preparation of a previously undescribed class of 3-thio-L-sorbopyranosides and their 6-C-methoxy analogues.

A new series of thio-substituted sugars were synthesised relying on the totally regio- and stereoselective cycloaddition of 4-deoxyhex-4-enopyranose derivatives to 'in situ' generated oxothiones. Conformational studies of the above unsaturated sugars showed a marked prevalence of the all-axial conformer.

Intramolecular aldol cyclization of L-lyxo-hexos-5-ulose derivatives: a new diastereoselective synthesis of D-chiro-inositol.

The DBU-promoted intramolecular aldol condensation of two partially protected L-lyxo-hexos-5-ulose derivatives (8 and 9), in turn obtained starting from methyl beta-D-galactopyranoside, takes place with fairly good yield and complete diastereoselectivity to give 2L-(2,3,6/4,5)-pentahydroxycyclohexanone derivatives, 10 and 11. The stereoselective reduction of inosose 10 with sodium triacetoxyborohydride leads, after catalytic debenzylation, to D-chiro-inositol (1), while the sodium borohydride reduction furnishes, with opposite stereoselectivity, a derivative of allo-inositol.