Paul Boullanger

The use of N-alkoxycarbonyl derivatives of 2-amino-2-deoxy-d-glucose as donors in glycosylation reactions

1,3,4,6-Tetra-O-acetyl-2-alkoxycarbonylamino-2-deoxy-beta-D-glu copyranoses and 3,4,6-tri-O-acetyl-2-alkoxycarbonylamino-2-deoxy-alpha-D-glucopyra nosyl bromides have been used as donors in glycosylation reactions with model alcohols. beta-Glycosides were obtained in good yields and with a high degree of 1,2-trans stereoselectivity. An oxazolidinone was formed as the main product from the reaction of some of the glucopyranosyl bromides with alcohols of low reactivity, but the formation of all products could be interpreted by a strong participation of the alkoxycarbonylamino group.

Further biochemical characterization of human pancreatic lipase-related protein 2 expressed in yeast cells

Recombinant human pancreatic lipase-related protein 2 (rHPLRP2) was produced in the protease A-deficient yeast Pichia pastoris. A major protein with a molecular mass of 50 kDa was purified from the culture medium using SP-Sepharose and Mono Q chromatography. The protein was found to be highly sensitive to the proteolytic cleavage of a peptide bond in the lid domain. The proteolytic cleavage process occurring in the lid affected both the lipase and phospholipase activities of rHPLRP2. The substrate specificity of the nonproteolyzed rHPLRP2 was investigated using pH-stat and monomolecular film techniques and various substrates (glycerides, phospholipids, and galactolipids). All of the enzyme activities were maximum at alkaline pH values and decreased in the pH 5–7 range corresponding to the physiological conditions occurring in the duodenum. rHPLRP2 was found to act preferentially on substrates forming small aggregates in solution (monoglycerides, egg phosphatidylcholine, and galactolipids) rather than on emulsified substrates such as triolein and diolein. The activity of rHPLRP2 on monogalactosyldiglyceride and digalactosyldiglyceride monomolecular films was determined and compared with that of guinea pig pancreatic lipase-related protein 2, which shows a large deletion in the lid domain. The presence of a full-length lid domain in rHPLRP2 makes it possible for enzyme activity to occur at higher surface pressures. The finding that the inhibition of nonproteolyzed rHPLRP2 by tetrahydrolipstatin and diethyl-p-nitrophenyl phosphate does not involve any bile salt requirements suggests that the rHPLRP2 lid adopts an open conformation in aqueous media.

Synthesis of Biotinylated α-D-Mannoside or N-Acetyl β-D-Glucosaminoside Decorated Gold Nanoparticles: Study of Their Biomolecular Recognition with Con A and WGA Lectins

Gold nanoparticles (NPs) functionalized with a mixed shell of well-defined biotinylated glycopolymers and polyethylene glycol (PEG) provide an effective platform for the biomolecular recognition of proteins both in solution and on surfaces. Well-defined biotinylated glycopolymers were first synthesized by the reversible addition-fragmentation chain transfer (RAFT) process. They contain two types of carbohydrate residues either N-acetyl β-D-glucosaminopyranoside (GlcNAc) or α-D-mannopyranoside (Man) as pendent groups. The biotinylated glycopolymers and polyethylene glycol were subsequently used in the in situ formation of gold glyconanoparticles via an easy photochemical process. The obtained biotinylated glyconanoparticles were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The bioavailability of the biotin and specific carbohydrate residues at the periphery of the NPs were assessed using the diffraction optic technology (DOT) system. The studies showed the accessibility of the biotin ligands for conjugation to immobilized avidin on the DOTLab biosensor. Furthermore, these avidin conjugated glyconanoparticles were found to selectively immobilize lectins. The specificity of lectin binding was dependent on the type of carbohydrate residues. As such, N-acetyl β-D-glucosaminoside decorated gold nanoparticles were found to specifically interact with wheat germ agglutinin (WGA) lectin, whereas α-D-mannoside ones were found to specifically interact with Concanavalin A (Con A) lectin.

The lectin binding and targetable cellular uptake of lipid-coated polysaccharide microcapsules

In this study, a capsule/lipid composite system has been developed for targeted delivery of small molecular drugs (daunorubicin hydrochloride, DNR) to cancer cells. The lipid coating not only provides a sealed barrier to prevent the leakage of the encapsulated drugs, but also can be used as a means to attach biological functionality to capsule surfaces. A neoglycolipid incorporated into the supported lipid membrane has shown high affinity in lectin binding studies (concanavalin A), while a folate-linked lipid in the lipid membrane provides a functional capacity to target cancer cells (MCF-7). Folate-targeted capsules are much more efficient than the non-targeted capsules in delivering DNR to MCF-7 cells. The system provides a way to create a biomimetic delivery vehicle for the effective and selective targeting of drugs.

Syntheses of amphiphilic glycosylamides from glycosyl azides without transient reduction to glycosylamines.

Protected glycosyl azides react with acyl chlorides in the presence of triphenylphosphine to afford glycosylamides in high yields, at room temperature. Starting from the beta-glycosyl azides, the reaction is highly stereoselective and occurs with retention of configuration, whereas the alpha-azido anomers display a lower stereoselectivity giving rise to alpha/beta mixtures of glycosylamides. The reaction was applied to several monosaccharidic azides and to lactosyl azide with various acyl chlorides; it was shown to be of general use for preparing 1,2-trans beta-glycosylamides.

Synthesis and interfacial behavior of three homologous glycero neoglycolipids with various chain lengths

Abstract Three neoglycolipids 1a – c derived from glycerol were synthezised and their molecular arrangements were studied at the air/water interface through Langmuir–Blodgett technique. The common structural features of these neoglycolipids are: a triethyleneglycol spacer at C-2 of glycerol, a GlcNAc hydrophilic head group at the end of the spacer, two saturated aliphatic chains at C-1 and C-3 of glycerol, linked by ether bonds. Compounds 1a – c differ only by the length of their lipid moieties. By increasing the hydrocarbon chain length from C 11 to C 16 , a densely packed state was reached in the monolayer. The compression isotherms displayed an expanded state during the whole compression for compounds 1a and 1c bearing two C 11 or one C 11 and one C 16 chains. Compound 1b bearing two C 16 chains displayed a quite different interfacial behavior. The transfer of these monolayers onto a solid substrate can be obtained only with a trigger molecule, a phosphatidic acid.

Synthesis and surface-active properties of amphiphilic 6-aminocarbonyl derivatives of d-glucose

Abstract Several 6-amido-6-deoxy derivatives of methyl α- d -glucopyranoside and d -glucopyranose were prepared via peracetylated 6-azido-6-deoxy or 6-deoxy-6-isocyanato intermediates. These compounds displayed high Krafft temperatures which could result from hydrogen bonding between NH and O-5. Their tensio-active properties above the Krafft temperature were compared with Hecameg (methyl 6-O-(N-heptylcarbamoyl)-α- d -glucopyranoside).

A One-Pot Synthesis of Glycosyl Amides from Glycosyl Azides Using a Modified Staudinger Reaction

In a continuation of our research devoted to the synthesis and supramolecular assemblies of amphiphilic carbohydrates,1–3 we report a new preparation of glycosyl amides β-3a. Interest in such compounds lies in their ability to escape glycosidases in vivo and in their use as potent nonionic biosurfactants. Several methods have already been reported in the literature for the preparation of such derivatives (Scheme 1).

Continuous measurement of galactolipid hydrolysis by pancreatic lipolytic enzymes using the pH-stat technique and a medium chain monogalactosyl diglyceride as substrate

Galactolipids are the main lipids from plants and galactolipases play a major role in their metabolism. These enzymes were however poorly studied so far and only few assays have been developed. A specific and continuous galactolipase assay using synthetic medium chain monogalactosyl diacylglycerol (MGDG) as substrate was developed using the pH-stat technique and recombinant human (rHPLRP2) and guinea pig (rGPLRP2) pancreatic lipase-related protein 2 as model enzymes. PLRP2s are the main enzymes involved in the digestion of galactolipids in the gastrointestinal tract. Monogalactosyl di-octanoylglycerol was mixed with bile salt solutions by sonication to form a micellar substrate before launching the assay. The nature of the bile salt and the bile salt to MGDG ratio were found to significantly affect the rate of MGDG hydrolysis by rHPLRP2 and rGPLRP2. The maximum galactolipase activity of both enzymes was recorded with sodium deoxycholate (NaDC) and at a NaDC to MGDG ratio of 1.33 and at basic pH values (8.0-9.0). The maximum rates of hydrolysis were obtained using a MGDG concentration of 10(-2) M and calcium chloride was found to be not necessary to obtain the maximum of activity. Under these conditions, the maximum turnovers of rGPLRP2 and rHPLRP2 on mixed NaDC/MGDG micelles were found to be 8000+/-500 and 2800+/-60 micromol/min/mg (U/mg), respectively. These activities are in the same order of magnitude as the activities on triglycerides of lipases and they are the highest specific activities ever reported for galactolipases. For the sake of comparison, the hydrolysis of mixed bile salt/MGDG micelles was also tested using other pancreatic lipolytic enzymes and only native and recombinant human carboxyl ester hydrolase were found to display significant but lower activities (240+/-17 and 432+/-62 U/mg, respectively) on MGDG.

The relative stability of allyl ether, allyloxycarbonyl ester and prop-2 enylidene acetal, protective groups toward iridium, rhodium and palladium catalysts

Abstract The deprotection of allyloxycarbonyl derivatives of sugars was realized in the presence of allylether or prop-2-enylidene acetal with Pd(PPh 3 ) 4 or RhCl (PPh 3 ) 3 as catalyst while [Ir (COD) [PMePh 2 ) 2 ]PF 6 isomerized selectively the allyl ethers.