Use of cerny epoxides for the accelerated synthesis of glycosaminoglycans

[reaction: see text]. 1,6:2,3-Dianhydrohexopyranoses (Cerny epoxides) are versatile intermediates for the synthesis of glycosaminoglycans. Complex heparan and chondroitin sulfate disaccharide synthons can be assembled from a single common precursor in a short sequence of steps.     

Synthesis of Disaccharides Containing 6-Deoxy-a-L-talose as Potential Heparan Sulfate Mimetics

A 6-deoxy-a-L-talopyranoside acceptor was readily prepared from methyl a-L-rhamnopyranoside and glycosylated with thiogalactoside donors using NIS/TfOH as the promoter to give good yields of the desired a-linked disaccharide (69-90%). Glycosylation with a 2-azido-2-deoxy-D-glucosyl trichloroacetimidate donor was not completely stereoselective (a:b = 6:1), but the desired a-linked disaccharide could be isolated in good overall yield (60%) following conversion into its corresponding tribenzoate derivative. The disaccharides were designed to mimic the heparan sulfate (HS) disaccharide GlcN(2S,6S)-IdoA(2S). However, the intermediates readily derived from these disaccharides were not stable to the sulfonation/deacylation conditions required for their conversion into the target HS mimetics.     

Pre-activation-based one-pot synthesis of an alpha-(2,3)-sialylated core-fucosylated complex type bi-antennary N-glycan dodecasaccharide

Synthesis of N-glycans is of high current interests due to their important biological properties. A highly efficient convergent strategy based on the pre-activation method for assembly of the complex type core fucosylated bi-antennary N-glycan dodecasaccharide has been developed. Retrosynthetically, this extremely challenging target is broken down to three modules: a sialyl disaccharide, a glucosamine building block and a hexasaccharide diol acceptor. The sialyl disaccharide was easily obtained by selective activation of a new 5-N-trichloroacetyl protected sialyl donor in the presence of a thiogalactoside acceptor. The hexasaccharide diol module was produced by double mannosylation of a fucosylated tetrasaccharide acceptor, which in turn was generated by glycosylation of a alpha-fucosylated disaccharide with a beta-mannose containing disaccharide donor. The union of the three modules was performed in one-pot giving the fully protected dodecasaccharide in high yield. This synthesis is characterized by minimum protective group and aglycon adjustment on oligosaccharide intermediates, thus greatly enhancing the overall synthetic efficiency. The modular feature of this strategy suggests that this method can be readily adapted to the synthesis of a wide variety of N-glycan structures.     

Synthesis and biological activities of lipid A analogs: modification of a glycosidically bound group with chemically stable polar acidic groups and lipophilic groups on the disaccharide backbone with tetradecanoyl or N-dodecanoylglycyl groups.

Six novel lipid A analogs were synthesized. The first two analogs, 4 and 5, have an alpha-glycosidically bound carboxymethyl or 1,3-dicarboxyisopropyl group on the disaccharide backbone with four tetradecanoyl groups. The next three analogs, 6, 7 and 8, have two or four N-dodecanoylglycyl groups on the 1-alpha-O-phosphonooxyethylated disaccharide backbone. Analog 6 bears N-dodecanoylglycyl groups on the hydroxyl functions at positions 3 and 3', and tetradecanoyl groups on the amino functions at positions 2 and 2'. Analog 7 is a 2, 3, 2' and 3'-tetrakis(N-dodecanoylglycyl) derivative, and analog 8 resembles compound 6, but the binding of the N-dodecanoylglycyl and tetradecanoyl groups at positions 2, 2' and 3, 3' are reversed. The third analog, 9, has the same acyl group configuration as compound 6, but has a 1,3-dicarboxyisopropyl group at position C-1. Compounds 4 and 5 exhibited definite antitumor activity against Meth A fibrosarcoma, indicating that the phosphate group at the C-1 position in lipid A could be replaced by the carboxylic acid without reducing the antitumor activity. In rabbits, compounds 6 and 9 exhibited potent antitumor activity, but their toxicity was extremely low. On the other hand, compounds 7 and 8 showed no antitumor activity. The levels of antitumor activity of 6 and 9 were similar to those of the natural-type lipid A. The antitumor activities of analogs with a N-dodecanoylglycyl group on the disaccharide backbone depended on the connecting sites of the acyl groups.     

One‐Pot Protection‐Glycosylation Reactions for Synthesis of Lipid II Analogues

(2,6‐Dichloro‐4‐methoxyphenyl)(2,4‐dichlorophenyl)methyl trichloroacetimidate ( 3 ) and its polymer‐supported reagent 4 can be successfully applied to a one‐pot protection‐glycosylation reaction to form the disaccharide derivative 7 d for the synthesis of lipid II analogues. The temporary protecting group or linker at the C‐6 position and N‐Troc protecting group of 7 d can be cleaved simultaneously through a reductive condition. Overall yields of syntheses of lipid II ( 1 ) and neryl‐lipid II N^ε‐dansylthiourea are significantly improved by using the described methods.     

One-pot azidochlorination of glycals

A simple one-pot azidochlorination for the preparation of nitrogen-containing Koenigs-Knorr glycosyl donors proceeds upon reaction of protected glycals with sodium azide, ferric chloride, and hydrogen peroxide. Different mono- and disaccharide galactals and glucals are converted in a highly α-selective manner to the 2-azido glycosyl chlorides. Starting from disaccharide galactals, building blocks for the synthesis of the T-antigen are obtained in a straightforward manner. The simplicity of the reaction conditions allows for an efficient and scalable α-selective synthesis of 2-azido substituted glycosyl chlorides.     

Synthesis of the carboline disaccharide domain of shishijimicin A

A synthetic route to the carboline disaccharide domain (2) of shishijimicin A (1) has been developed. The convergent synthesis relies on a novel application of the Reetz-Mu?ller-Starke reaction to form the central, sulfur-bearing quaternary carbon center and addition of the carboline structural motif as a dianion to a disaccharide aldehyde fragment.     

1 H and 13C NMR Assignments of 2.3-Diacetylamido-2,3-Dideoxy-D-Glucopyranose

Abstract

Lipid A exhibits thp most important biological attributes of lipopolysaccharide (LPS) of gram-negative bacteria including endotoxicity, adjuvanticity and antitu-mor activity.′ The lipid A backbone, in general, is found to consist of a pyranosidic β 1,6-linked D-glucosamine disaccharide [β-D-Glc_pN-(1→6)-α-D-Glc_pN] phospho-rylated at 1 and 4′ positions and bearing two amide bound and two ester linked hydroxy and/or acyloxy fatty acids.² However, the lipid A moiety of LPS from var-ious strains of the two gram-negative, photosynthetic bacteria, Rhodopseudomonas virtdia and Rhodopseudomonas palustrts, possesses 2,3-diamino-2,3-dideoxy-D-glucose as a constituent sugar. 3 This diamino sugar has been also reported to occur in LPS from several other bacterial specie^4.5 Recently we found that the lipid X of Brucella abortus contains p(1→6)-linked 2,3-diamino-2,3-dideoxy-D- glucopyranose disaccharide moiety with a phosphate group at the 4′ position and amide bound acyloxy and hydroxy fatty acids.⁶     

Analysis of carbohydrates by fast atom bombardment mass spectrometry: 2—Influence of the matrix and the nature of the alkaline cations in the attachment process of an alkaline cation to a disaccharide molecule

The fast atom bombardment (FAB) ionization process of a non-reducing disaccharide by an attachment reaction with an alkaline cation has been investigated according to the nature of both the matrix (glycerol, diethanolamine, triethanolamine) and the alkaline cation (lithium, sodium, potassium, rubidium, caesium). We have established that one way of forming the cationized disaccharide molecular ions, [disaccharide-cat]⁺, is by a desolvation reaction from the cationized solvated disaccharide molecular ions, [disaccharide-cat-matrix]⁺. This process, which has been established by mass-analysed ion kinetic energy (MIKE) spectral analysis of the solvated species, is shown to be drastically affected by the nature of the involved matrix but only slightly by the alkaline cation. The variations in the relative abundances of the disaccharide cationized molecular ions compared to their solvated clusters in the FAB mass spectra, due to the matrix employed, have been explained according to the unimolecular dissociation of the solvated clusters examined by MIKE analysis. However, the variations in the abundance of the disaccharide cationized molecular ions in relation to the alkaline cation used—a higher sensitivity has been observed for lithium, sodium and potassium alkaline cations—have been explained in terms of the cations available at the target surface for the attachment process to the sugar molecule, and by a ligand exchange reaction between the matrix and the disaccharide.     

Tyrosine-selective protein alkylation using pi-allylpalladium complexes

A new protein modification reaction has been developed based on a palladium-catalyzed allylic alkylation of tyrosine residues. This technique employs electrophilic pi-allyl intermediates derived from allylic acetate and carbamate precursors and can be used to modify proteins in aqueous solution at room temperature. To facilitate the detection of modified proteins using SDS-PAGE analysis, a fluorescent allyl acetate was synthesized and coupled to chymotrypsinogen A and bacteriophage MS2. The tyrosine selectivity of the reaction was confirmed through trypsin digest analysis. The utility of the reaction was demonstrated by using taurine-derived carbamates as water solubilizing groups that are cleaved upon protein functionalization. This solubility switching technique was used to install hydrophobic farnesyl and C(17) chains on chymotrypsinogen A in water using little or no cosolvent. Following this, the C(17) alkylated proteins were found to associate with lipid vesicles. In addition to providing a new protein modification strategy targeting an under-utilized amino acid side chain, this method provides convenient access to synthetic lipoproteins.     

Chemical structure of escherichia coli lipid A

The chemical structure of E. coli lipid A was elucidated to be $\text{2}$ by determination of the nature of the individual acyl groups bound to the two hydroxyl groups in positions 3,3′ and the two amino groups of the D-glucosamine disaccharide phosphate backbone.     

Modulating membrane properties: the effect of trehalose and cholesterol on a phospholipid bilayer

The protective properties of trehalose on cholesterol-containing lipid dipalmitoylphosphatidylcholine (DPPC) bilayers are studied through molecular simulations. The ability of the disaccharide to interact with the phospholipid headgroups and stabilize the membrane persists even at high cholesterol concentrations and restricts some of the changes to the structure that would otherwise be imposed by cholesterol molecules. Predictions of bilayer properties such as area per lipid, tail ordering, and chain conformation support the notion that the disaccharide decreases the main melting transition in these multicomponent model membranes, which correspond more closely to common biological systems than pure bilayers. Molecular simulations indicate that the membrane dynamics are slowed considerably by the presence of trehalose, indicating that high sugar concentrations would serve to avert possible phase separations that could arise in mixed phospholipid systems. Various time correlation functions suggest that the character of the modifications in lipid dynamics induced by trehalose and cholesterol is different in the hydrophilic and hydrophobic regions of the membrane.     

Switchable Chemoselectivity of Reactive Intermediates Formation and Their Direct Use in A Flow Microreactor

A chemoselectivity switchable microflow reaction was developed to generate reactive and unstable intermediates. The switchable chemoselectivity of this reaction enables a selection for one of two different intermediates, an aryllithium or a benzyl lithium, at will from the same starting material. Starting from bromo-substituted styrenes, the aryllithium intermediates were converted to the substituted styrenes, whereas the benzyl lithium intermediates were engaged in an anionic polymerization. These chemoselectivity-switchable reactions can be integrated to produce polymers that cannot be formed during typical polymerization reactions.     

A convenient route to conjugates of 1,2-diglycerides with functionalized oligoethylene glycol spacer arms

A controlled reaction of a mixture of structural isomers of diacylglycerol (DAG) with N,N-disuccinimidyl carbonate and then with b-alanine provided intermediates of 1,2-diacylglycerol (1,2-DAG) which were further modified with carboxy- and amino-terminated oligoethylene glycol spacer arms of different length. As an example of bioactive molecules intended for the incorporation in lipid bilayer of artificial or cell membranes, 1,2-DAGs bearing tetrasaccharide Sialyl Lewis X or triglycine at the terminus of polar spacer were synthesized. The synthetic scheme can be readily scaled-up by the use of DAGs from food industry.     

Elucidation of the molecular structure of lipid A isolated from both a rough mutant and a wild strain of Aeromonas salmonicida lipopolysaccharides using electrospray ionization quadrupole time-of-flight tandem mass spectrometry

The chemical structure of lipid A, isolated by mild acid hydrolysis from a rough mutant and a wild strain of Aeromonas salmonicida lipopolysaccharide, was investigated using electrospray ionization quadrupole time-of-flight (QqToF) hybrid tandem mass spectrometry and showed a great degree of microheterogeneity. The chemical structure of the main constituent of this heterogeneous mixture was identified as a beta-D-(1 --> 6) linked D-glucosamine disaccharide substituted by two phosphate groups, one being bound to the non-reducing end at position O-4' and the other to the position O-1 of the reducing end of the D-glucosamine disaccharide. The location of the fatty acids linked to the disaccharide backbone was established by identifying diagnostic ions in the conventional QqToF-MS scan. Low-energy collision tandem mass spectrometry analysis of the selected precursor diagnostic ions confirmed, unambiguously, their proposed molecular structures. We have established that myristyloxylauric (C14:0(3-O(12:0))) acid residues were both N-2' and O-3' linked to the non-reducing end of the D-GlcN residue, and that two 3-hydroxymyristic (C14:0(3-OH)) acid chains acylated the remaining positions of the reducing end. The MS and MS/MS data obtained allowed us to determine the complex molecular structure of lipid A. The QqToF-MS/MS instrument has shown excellent superiority over a conventional quadrupole-hexapole-quadrupole tandem instrument which failed to fragment the selected precursor ion.     

Mechanistic studies on the nucleophilic reaction of porphyrins with organolithium reagents.

Porphyrins react readily with organolithium reagents under substitution of free meso positions. As this method has proven to be very versatile for the preparation of a wide range of meso substituted porphyrins, a mechanistic study of the reaction was undertaken using 5,15-diaryl- and dialkyl substituted porphyrins, 2,3,7,8,12,13,17,18-octaethylporphyrin, and the respective nickel(II) complexes. A combination of deuteration experiments, electronic absorption spectroscopy of the reactive intermediates, trapping of intermediates with organic electrophiles, and reaction at different pH values showed significant differences in the reaction pathways of free base porphyrins and metalloporphyrins. In both cases the reaction proceeds initially under formation of phlorin like intermediates which are stable in water. For the Ni(II)phlorins a mesomeric carbanionic form with a highly distorted structure exists that can react as a nucleophile with electrophiles such as RI, H+, or D+. In the latter case a protonation-deprotonation equilibrium involving porphodimethen intermediates has to be assumed. Free base phlorins do not react as nucleophiles but can undergo H/D exchange reactions in strongly acidic media.     

Stable σH-adducts in the reactions of the acridinium cation with heterocyclic N-nucleophiles

A reaction of NH-heterocycles with the 10-methylacridinium cation in the presence of a base led to 9,10-dihydro-10-methyl-9-substituted acridines, which can be considered as stable intermediates in the aromatic nucleophilic substitution reaction of hydrogen. The structure of the intermediates was studied and their oxidation potentials were determined. Generally, the oxidation potential was found to symbatically change with the changes in the energy of HOMO.     

Synthetic Studies Towards the O-Specific Polysaccharide of Shigella Sonnei

ABSTRACT

Synthetic routes are described to zwitter-ionic disaccharides that are diastereoisomerically related to frame-shifted repeating units of the title polysaccharide that contains 2-acetamido-4-amino-2,4,6-trideoxy-D-galactose and 2-acetamido-2-deoxy-L-altruronic acid. The intermediates corresponding to the trideoxygalactose residue feature acylamino functions at C-2 and an azido group at C-4. Best results were obtained with N-phthaloyl- and N-trichloroacetyl-protected derivatives. The intermediates corresponding to the uronic acid residue were either a D-altruronic acid-derived acceptor or a D-altrose-derived donor in which C-6 was oxidized after disaccharide formation.     

Synthesis and antitumor activity of lipid A analogs having a phosphonooxyethyl group with alpha- or beta-configuration at position 1

Three novel lipid A analogs, which have an alpha- or beta-glycosidically bound phosphonooxyethyl group instead of the alpha-glycosyl phosphate group of natural lipid A, were synthesized. The first analog (2) had an alpha-phosphonooxyethyl group on the identical acylated disaccharide 4'-phosphate structure found in natural lipid A (from Escherichia coli) and hence differed from the latter only in the nature of the acidic group at position 1. The second one (3) had tetradecanoyl groups in place of the two (R)-3-hydroxytetradecanoyl groups bound to the 2- and 3-hydroxyl function of 2, retaining the alpha-phosphonooxyethyl group. The structure of the third analog (4) was the same as that of 3 except that the phosphonooxyethyl group of the former was beta-oriented. Compounds 2 and 3 exhibited potent activity against Meth A at the same level as natural lipid A, whereas 4 showed less activity. This fact revealed that the glycosidic phosphate is not a prerequisite for the antitumor activity of lipopolysaccharide. It can be replaced with a phosphonooxyethyl group without any loss of activity provided that the alpha-anomeric configuration at C-1 is retained. The replacement of the hydroxytetradecanoyl groups with tetradecanoyl groups does not change the activity either.     

POCl3 chlorination of 4-quinazolones

The reaction of quinazolones with POCl(3) to form the corresponding chloroquinazolines occurs in two distinct stages, which can be separated through appropriate temperature control. An initial phosphorylation reaction occurs readily under basic conditions (R(3)N, aq pK(a) > 9) at t < 25 °C to give a variety of phosphorylated intermediates. Pseudodimer formation, arising from reaction between phosphorylated intermediates and unreacted quinazolone, is completely suppressed at these temperatures, provided the system remains basic throughout the POCl(3)addition. Clean turnover of phosphorylated quinazolones to the corresponding chloroquinazoline is then achieved by heating to 70-90 °C. (N)- and (O)-phosphorylated intermediates, involving multiple substitution at phosphorus, have been identified and their reactions monitored using a combination of (1)H, (31)P, and (19)F NMR. Kinetic analysis of the reaction profiles suggest that the various intermediates react with both Cl(-) and Cl(2)P(O)O(-), but product formation arises exclusively from reaction of (O)-phosphorylated intermediates with Cl(-). (O)- and (N)-phosphorylated intermediates equilibrate rapidly on the time scale of the reaction. A minimum of 1 molar equiv of POCl(3) is required for efficient conversion of the intermediates to product.