Syntheses of N-Acyl and N-Alkoxycarbonyl Derivatives of 2-Alkoxycarbonylamino-2-deoxy-D-glucose

Abstract

N-Acyl and N-alkoxycarbonyl derivatives of l, 3, 4, 6-tetra-O-acetyl-2-alkoxy-carbonylamino-2-deoxy-β-D-glucopyranose have been synthesized using mixed anhydrides and symmetrical or disymetrical pyrocarbonates. These derivatives have been used as donors in 1, 2-trans-glycosylation reactions promoted by Lewis acids. Besides the expected (β-D-glycosides, cyclisation and rearrangement side-products were often encountered in such glycosylations.     

Algebra and Geometry of Rewriting

We present various results of the last 20 years converging towards a homotopical theory of computation. This new theory is based on two crucial notions: polygraphs (introduced by Albert Burroni) and polygraphic resolutions (introduced by François Métayer). There are two motivations for such a theory:

• Providing invariants of computational systems to study those systems and prove properties about them;
• Finding new methods to make computations in algebraic structures coming from geometry or topology.

This means that this theory should be relevant for mathematicians as well as for theoretical computer scientists, since both may find useful tools or concepts for their own domain coming from the other one.

     

Establishment of mass spectrometric fingerprints of novel synthetic cholesteryl neoglycolipids: The presence of a unique <Emphasis Type="Italic">C</Emphasis>-glycoside species during electrospray ionization and during collision-induced dissociation tandem mass spectrometry

In this study we evaluated the fragmentation pattern of 16 novel amphiphilic neoglycolipid cholesteryl derivatives that can be efficiently used to increase cationic liposomal stability and to enhance gene transfer ability. These neoglycolipids bear different sugar moieties, such as D-glucosamine, N-acetyl-D-glucosamine, N-trideuterioacetyl-D-glucosamine, N-acetyllactosamine, L-fucose, N-allyloxycarbonyl-D-glucosamine, and some of their per-O-acetylated derivatives. Regardless of the structure of the tested neoglycolipid, QqToF-MS analysis using electrospray ionization (ESI) source showed abundant protonated [M+H]+ species. We also identified by both QqToF-MS and low-energy collision tandem mass spectrometry (CID-MS/MS) of the [M+H]+ ion, the presence of specific common fingerprint fragment ions: [Cholestene]+, sugar [oxonium]+, [(Sugar-spacer-OH)+H]+, [oxonium-H2O]+, and [(Cholesterol-spacer-OH)+H]+. In addition, we observed a unique ion that could not be rationally explained by the expected fragmentation of these amphiphilic molecules. The structure of this ion was tentatively proposed with that of a C-glycoside species formed by a chemical reaction between the sugar portion and the cholesterol. MS/MS analysis of this unique [C-glycoside]+ confirmed the validity of the proposed structure of this ion. The presence of an amino group at position C-2 and free hydroxyl groups of the sugar motif is crucial for the formation of a "reactive" sugar oxonium ion that can form the [C-glycoside]+ species. In summary, we precisely established the fragmentation patterns of the tested series of neoglycolipid cholesteryl derivatives and authenticated their structure as well; moreover, we speculated on the formation of a C-glycoside with the ESI source under atmospheric pressure and in the collision cell during MS/MS analysis.     

Synthesis and liquid crystalline properties of mono-, di- and tri-O-alkyl pentaerythritol derivatives bearing tri-, di- or monogalactosyl heads: the effects of curvature of molecular packing on mesophase formation

Self-organisation and self-assembly are critical to the stability of synthetic and biological membranes. Of particular importance is consideration of the packing arrangements of the various molecular species. Both phospho- and glycolipids can pack in ways in which curvature can be introduced into self-organised or self-assembled systems. For instance, it is known that the degree of curvature can affect the structures of any condensed phases that are formed. In this article we report on a systematic study in which we have varied the shapes of glycolipids and examined the condensed phases that they form. In doing so, we have also unified the shape dependency of lyotropic liquid crystals with those of thermotropic liquid crystals. In order to undertake this systematic study a range of different pentaerythritol derivatives was synthesized, which covers combinations of one to three alkyl chains of different lengths (6,7,9,10,11,12,14,16 carbon atoms) and three to one galactosyl heads. Mono- and di-O-galactosyl derivatives were prepared directly by glycosylation of the corresponding alcohols using 2,3,4,6-tetra-O-benzoyl or acetyl-alpha-D-galactopyranosyl trichloroacetimidate or bromide as the donors; the tri-O-galactosyl derivatives were synthesized from O-alkyl-O-benzyl di-O-galactosyl pentaerythritol intermediates, followed by de-O-benzylation and glycosylation steps. All of the fully deprotected products were obtained by standard methods, and their self-organising and self-assembling properties examined.     

Regio‐ and Stereospecificity in the Oxygenation of Arachidonic Acid Catalyzed by Leu597 Mutants of Rabbit 15‐Lipoxygenase: A QM/MM Study

We combined quantum mechanics/molecular mechanics calculations with molecular dynamics simulations to study the addition of O₂ to the pentadienyl radical of arachidonic acid (AA) catalyzed by the Leu597Val and Leu597Ala mutants of rabbit 15‐lipoxygenase (15‐rLO). In the Leu597Val mutant, the addition of O₂ to C15 of AA is the predominant path, although it reduces the C15/C11 product ratio by almost ten times with respect to the wildtype enzyme. The S stereochemistry is kept. Mutation to Ala causes just the opposite effect: regiospecificity favoring addition to C15 is somewhat sharper than that in the wildtype, but the stereochemistry is R. This is because the extra space created by the mutation to Ala is big enough for AA to move so that it can adopt an alternative binding mode, and this opens new feasible paths for the attack of O₂. So, we showed that the Leu597Ala mutant of 15r‐LO works as an aspirin‐acetylated cyclooxygenase‐2, which makes 15‐(R)‐ hydroperoxyeicosatetraenoic acid.     

Roundness Properties of Groups

Roundness of metric spaces was introduced by Per Enflo as a tool to study uniform structures of linear topological spaces. The present paper investigates geometric and topological properties detected by the roundness of general metric spaces. In particular, we show that geodesic spaces of roundness 2 are contractible, and that a compact Riemannian manifold with roundness >1 must be simply connected. We then focus our investigation on Cayley graphs of finitely generated groups. One of our main results is that every Cayley graph of a free Abelian group on ⩾ 2 generators has roundness =1. We show that if a group has no Cayley graph of roundness =1, then it must be a torsion group with every element of order 2,3,5, or 7 Partially supported by a Canisius College Summer Research Grant     

Simplical volume of closed locally symmetric spaces of non-compact type

We show that closed, locally symmetric spaces of non-compact type have positive simplicial volume. This gives a positive answer to a question that was first raised by (Gromov in Inst Hautes études Sci Publ Math 56:5, 1982).     

Polygraphic resolutions and homology of monoids

We prove that for any monoid M, the homology defined by the second author by means of polygraphic resolutions coincides with the homology classically defined by means of resolutions by free ZM-modules.     

Improvement of a biomimetic porphyrin catalytic system by addition of acids

The conditions of the use of the manganese/porphyrin/imidazole system needed to be improved in order to obtain larger amounts of models of metabolites. An increase of the oxidation yields and a better preservation of this catalytic system have been obtained on the examples of various alkanes, by an acid addition in the reaction mixture. Three manganoporphyrins were checked for evaluation of the reaction. These results were extended to molecules of therapeutical interest such as ibuprofen and phenylbutazone.     

Self-organizing properties of natural and related synthetic glycolipids

In this article we report on the syntheses, self-organizing properties, and structures of a variety of cerebrosides and related synthetic glycolipids. The thermotropic and lyotropic liquid crystalline properties of the materials were evaluated in detail. All of the families of materials studied exhibited columnar mesophases. In the dry state the aliphatic chains were found to be located on the exterior of the columns, whereas in the wet state the reverse was the case with the polar headgroups on the exterior. Thus, the aliphatic chains act almost like hydrocarbon solvents in the dry state.