Neuroprotective phenylpropanoid esters of rhamnose isolated from roots of Scrophularia buergeriana

Four phenylpropanoid esters of rhamnose, buergerisides A1, B1, B2 and C1 were isolated from roots of Scrophularia huergeriana MIQ. (Scrophulariaceae), and were characterized as 2-O-acetyl-3,4-di-O-(E)-p-methoxycinnamoyl-alpha-L-rhamnopyranosid e, 2-O-acetyl-3-O-(E)-p-methoxycinnamoyl-alpha-L-rhamnopyranoside, 2-O-acetvl-3-O-(Z)-p-methoxycinnamoyl-alpha-L-rhamnopyranosi de and 4-O-(E)-p-methoxycinnamoyl-alpha-L-rhamnopyranoside, respectively. In addition, six known phenylpropanoids were authenticated as: (E)-cinnamic acid, (E)-p-methoxycinnamic acid, (E)-p-methoxycinnamic acid methyl ester, (E)-p-coumaric acid, (E)-caffeic acid, (E)-ferulic acid and a phenylalcohol, 2-(3-hydroxy-4-methoxyphenyl)ethanol. These ten phenylpropanoids all attenuated glutamate-induced neurotoxicity when added to primary cultures of rat cortical cells in a dose-dependent manner. These results demonstrate that phenylpropanoids isolated from S. buergeriana may exert significant protective effects against glutamate-induced neurodegeneration in primary cultures of cortical neurons.

Thermodynamic binding studies of lectins from the diocleinae subtribe to deoxy analogs of the core trimannoside of asparagine-linked oligosaccharides

Lectins from seven different species of the Diocleinae subtribe have been recently isolated and characterized in terms of their carbohydrate binding specificities (Dam, T. K., Cavada, B. S., Grangeiro, T. B., Santos, C. F., de Sousa, F. A. M., Oscarson, S., and Brewer, C. F. (1998) J. Biol. Chem. 273, 12082-12088). The lectins included those from Canavalia brasiliensis, Cratylia floribunda, Dioclea rostrata, Dioclea virgata, Dioclea violacea, and Dioclea guianensis. All of the lectins exhibited specificity for Man and Glc residues, but much higher affinities for the branched chain trimannoside, 3,6-di-O-(alpha-d-mannopyranosyl)-d-mannose, which is found in the core region of all asparagine-linked carbohydrates. In the present study, isothermal titration microcalorimetry is used to determine the binding thermodynamics of the above lectins, including a new lectin from Canavalia grandiflora, to a complete series of monodeoxy analogs of the core trimannoside. From losses in the affinity constants and enthalpies of binding of certain deoxy analogs, assignments are made of the hydroxyl epitopes on the trimannoside that are involved in binding to the lectins. The pattern of binding of the deoxy analogs is similar for all seven lectins, and similar to that of concanavalin A which is also a member of the Diocleinae subtribe. However, differences in the magnitude of the thermodynamic binding parameters of the lectins are observed, even though the lectins possess conserved contact residues in many cases, and highly conserved primary sequences. The results indicate that non-contact residues in the lectins, even those distant from the binding sites, modulate their thermodynamic binding parameters.

Metabolites of 2'-fluoro-2'-deoxy-D-glucose detected by 19F magnetic resonance spectroscopy in vivo predict response of murine RIF-1 tumors to 5-fluorouracil

There is a clinical need for early detection of tumor response to therapy. This study aimed to determine whether metabolites of fluorodeoxyglucose (FDG) detected in solid mouse tumors in situ by I9F magnetic resonance spectroscopy (19F MRS) correlated with response to 5-fluorouracil chemotherapy. After injection of FDG (1.4 mmol/kg i.p.), uptake and metabolism was monitored for 2 h in RIF-1 tumors. FDG was detectable immediately, and after 10 min, a second broad peak was detected 5-6 ppm upfield. 19F MRS analysis of cell and tumor extracts in vitro showed that the upfield peak (> or =15% of the total detectable 19F signal) consisted of the epimer alpha-fluorodeoxymannose (FDM) and various conjugates. Mice treated with 5-fluorouracil (130 mg/kg) received, 48 h later, a repeat dose of FDG. The change in the rate of FDM formation, but not the FDG or total 19F signal, correlated significantly with the response to 5-fluorouracil (P = 0.032), suggesting that 19F MRS of FDM metabolism in vivo may be a novel means of predicting tumor response.

Production of polyhydroxyalkanoic acids by Ralstonia eutropha and Pseudomonas oleovorans from an oil remaining from biotechnological rhamnose production

Screening experiments identified several bacteria which were able to use residual oil from biotechnological rhamnose production as a carbon source for growth. Ralstonia eutropha H16 and Pseudomonas oleovorans were able to use this waste material as the sole carbon source for growth and for the accumulation of polyhydroxyalkanoic acids (PHA). R. eutropha and P. oleovorans accumulated PHA amounting to 41.3% and 38.9%, respectively, of the cell dry mass, when these strains were cultivated in mineral salt medium with the oil from the rhamnose production as the sole carbon source. The accumulated PHA isolated from R. eutropha consisted of only 3-hydroxybutyric acid, whereas the PHA isolated from P. oleovorans consisted of 3-hydroxyhexanoic acid, 3-hydroxyoctanoic acid, 3-hydroxydecanoic acid, and 3-hydroxydodecanoic acid. The composition was confirmed by gas chromatography of the isolated polyesters. Batch and fed-batch cultivations in stirred-tank reactors were done.

Syntheses of methyl (4,6-dideoxy-alpha-L-lyxo-hexopyranosyl)-(1-->3)- and (4-deoxy-4-fluoro-alpha-L-rhamnopyranosyl)-(1-->3)- 2-acetamido-2-deoxy-alpha-D-glucopyranosides, analogs of the mycobacterial arabinogalactan linkage disaccharide

We have made thioglycoside donors for the 4,6-dideoxy-L-lyxo-hexopyranosyl ('4-deoxy-L-rhamnosyl') and 4-deoxy-4-fluoro-L-rhamnosyl monosaccharide residues. The preparation of the deoxyfluororhamnose was not straightforward, and revealed some unexpected behavior of the diethylaminosulfur trifluoride (DAST) reagent. The new glycosyl donors were used to synthesize two analogs of the mycobacterial arabinogalactan linkage disaccharide -->4)-alpha-L-Rha-(1-->3)-alpha-D-GlcNAc. These analogs are prototypes for a family of potential inhibitors of the enzymes involved in the early stages of cell-wall construction in mycobacteria.

Synthesis and biological evaluation of coumarincarboxylic acids as inhibitors of gyrase B. L-rhamnose as an effective substitute for L-noviose

A series of novobiocin-like coumarincarboxylic acids has been prepared bearing the L-rhamnosyl moiety as the sugar portion of the molecule. The similar DNA gyrase inhibitory activity of the novel class of coumarins to that of novobiocin demonstrates that L-rhamnose can effectively replace L-noviose. Introduction of alkyl side-chains at C-5 of coumarin leads to improved in vitro antibacterial properties in the novel series.

Recombination between gtfB and gtfC is required for survival of a dTDP-rhamnose synthesis-deficient mutant of Streptococcus mutans in the presence of sucrose

The rml genes are involved in dTDP-rhamnose synthesis in Streptococcus mutans. A gene fusion between gtfB and gtfC, which both encode extracellular water-insoluble glucan-synthesizing enzymes, accompanied by inactivation of the rml genes was observed for cells grown in the presence of sucrose. The survival rates of rml mutants isolated in the absence of sucrose were drastically reduced in the presence of sucrose. The rates were consistent with the frequency of spontaneous gene fusions between gtfB and gtfC, suggesting that the spontaneous recombinant organisms were selected in the presence of sucrose. The rml mutants with a gtfB-gtfC fusion gene had markedly reduced water-insoluble glucan synthetic activity and lost the ability to colonize glass surfaces in the presence of sucrose. These results suggest that the rml mutants of S. mutans, which are defective in dTDP-rhamnose synthesis, can survive only in the absence of water-insoluble glucan synthesis.

Production of rhamnolipid biosurfactant by fed-batch culture of Pseudomonas aeruginosa using glucose as a sole carbon source

The pH-stat fed-batch culture of Pseudomonas aeruginosa YPJ-80 was done to produce a rhamnolipid biosurfactant. With glucose as the sole carbon source, the final concentrations of cells and rhamnolipid biosurfactant obtained in 25 h were 25 g cell dry weight/l and 4.4 g/l, respectively.

Structure of the O-specific polysaccharide of a serologically separate strain Proteus penneri 2 from a new proposed serogroup O66

O-specific polysaccharide chain of Proteus penneri strain 2 lipopolysaccharide was studied by full and partial acid hydrolysis, Smith degradation, methylation analysis, and NMR spectroscopy, including two-dimensional rotating-frame NOE spectroscopy (ROESY) and 1H,13C heteronuclear multiple-quantum coherence (HMQC) experiments. Together with D-glucose and 2-acetamido-2-deoxy-D-glucose, the polysaccharide was found to contain two rarely occurring sugars, 6-deoxy-L-talose (L-6dTal) and 2,3-diacetamido-2,3,6-trideoxy-L-mannose (L-RhaNAc3NAc), and the following structure of a non-stoichiometrically O-acetylated tetrasaccharide repeating unit was established: [equation: see text] The O-specific polysaccharide studied has a unique composition and structure and, accordingly, P. penneri 2 is serologically separate among Proteus strains. Therefore, we propose for P. penneri 2 a new Proteus O-serogroup O66 where this strain is at present the single representative.

Conversion of dTDP-4-keto-6-deoxyglucose to free dTDP-4-keto-rhamnose by the rmIC gene products of Escherichia coli and Mycobacterium tuberculosis

dTDP-rhamnose is made from glucose-1-phosphate and dTTP by four enzymes encoded by rmIA-D. An Escherichia coli rmIC mutant was constructed and a crude enzyme extract prepared from it did not produce dTDP-4-keto-rhamnose, in contrast to a crude enzyme extract prepared from a wild-type E. coli strain where small amounts of this intermediate were found after incubation with dTDP-glucose in the absence of NADPH. These results showed that dTDP-4-keto-rhamnose, the product of RmIC, exists as a free intermediate. Further, the Mycobacterium tuberculosis rmIC gene was expressed and incubation of the resulting purified M. tuberculosis RmIC enzyme with dTDP-4-keto-6-deoxyglucose resulted in the conversion of approximately 7% of dTDP-4-keto-6-deoxyglucose to dTDP-4-keto-rhamnose. The enzyme also allowed for the incorporation of two deuterium atoms from deuterium oxide solvent into dTDP-4-keto-glucose. Thus the rmIC gene encodes dTDP-4-keto-6-deoxyglucose epimerase capable of epimerizing at both C-3' and C-5'; this enzyme produces free dTDP-4-keto-rhamnose but the equilibrium of the 4-keto sugar nucleotides lies strongly on the side of the gluco configuration.

Purification, crystallization and preliminary structural studies of dTDP-6-deoxy-D-xylo-4-hexulose 3,5-epimerase (RmlC), the third enzyme of the dTDP-L-rhamnose synthesis pathway, from Salmonella enterica serovar typhimurium

L-Rhamnose is an essential component of the cell wall of many pathogenic bacteria. Its precusor, dTDP-L-rhamnose, is synthesized from alpha-D-glucose-1-phosphate and dTTP via a pathway requiring four distinct enzymes: RmlA, RmlB, RmlC and RmlD. RmlC was overexpressed in Escherichia coli. The recombinant protein was purified by a two-step protocol involving anion-exchange and hydrophobic chromatography. Dynamic light-scattering experiments indicated that the recombinant protein is monodisperse. Crystals were obtained using the sitting-drop vapour-diffusion method with ammonium sulfate as precipitant. Diffraction data were collected on a frozen crystal to a resolution of 2.17 A. The crystal belongs to either space group P3121 or P3221, with unit-cell parameters a = b = 71.56, c = 183.53 A and alpha = beta = 90, gamma = 120 degrees.

Rhamnose lipids--biosynthesis, microbial production and application potential

Biosurfactants containing rhamnose and beta-hydroxydecanoic acid and called rhamnolipids are reviewed with respect to microbial producers, their physiological role, biosynthesis and genetics, and especially their microbial overproduction, physicochemical properties and potential applications. With Pseudomonas species, more than 100 g l-1 rhamnolipids were produced from 160 g l-1 soybean oil at a volumetric productivity of 0.4 g l-1 h-1. The individual rhamnolipids are able to lower the surface tension of water from 72 mN m-1 to 25-30 mN m-1 at concentrations of 10-200 mg l-1. After initial testing, rhamnolipids seem to have potential applications in combating marine oil pollution, removing oil from sand and in combating zoosporic phytopathogens. Rhamnolipids are also a source of L-rhamnose, which is already used for the industrial production of high-quality flavor components.

Catalytic mechanism and specificity for hydrolysis and transglycosylation reactions of cytosolic beta-glucosidase from guinea pig liver

Cytosolic beta-glucosidase (CBG) from mammalian liver is known for its broad substrate specificity and has been implicated in the transformation of xenobiotic glycosides. CBG also catalyzes a variety of transglycosylation reactions, which have been been shown with other glycosylhydrolases to function in synthetic and genetic regulatory pathways. We investigated the catalytic mechanism, substrate specificity, and transglycosylation acceptor specificity of guinea pig liver CBG by several methods. These studies indicate that CBG employs a two-step catalytic mechanism with the formation of a covalent enzyme-sugar intermediate and that CBG will transfer sugar residues to primary hydroxyls and equatorial but not axial C-4 hydroxyls of aldopyranosyl sugars. Kinetic studies revealed that correction for transglycosylation reactions is necessary to derive correct kinetic parameters for CBG. Further analyses revealed that for aldopyranosyl substrates, the activation energy barrier is affected most by the presence of a C-6 carbon and by the configuration of the C-2 hydroxyl, whereas the binding energy is affected modestly by the configuration and substituents at C-2, C-4, and C-5. These data indicate that the transglycosylation activity of CBG derives from the formation of a covalently linked enzyme-sugar intermediate and that the specificity of CBG for transglycosylation reactions is different from its specificity for hydrolysis reactions.

Stereochemical course of hydrolysis catalysed by alpha-L-rhamnosyl and alpha-D-galacturonosyl hydrolases from Aspergillus aculeatus

The stereochemical course of hydrolysis catalysed by four Aspergillus aculeatus enzymes acting on alpha-L-rhamnosyl and alpha-D-galacturonosyl linkages in the hairy regions of pectins has been determined using 1H-NMR. Exogalacturonase acts with inversion of anomeric configuration (e-->a), shown by the initial release of beta-D-GalpA from the non-reducing end of polygalacturonic acid. Similarly, rhamnogalacturonan (RG) hydrolase also acts with inversion of anomeric configuration (e-->a) during hydrolysis of alpha-D-GalpA-(1-->2)-alpha-L-Rhap linkages in RG, initially releasing oligosaccharides with beta-D-GalpA at the reducing end. This result is consistent with the recently solved crystal structure of this enzyme, as well as its classification based on amino acid sequence similarity into glycosyl hydrolase family 28. alpha-L-Rhamnosidase and RG-rhamnohydrolase also act with inversion of configuration (a-->e), initially releasing beta-L-Rhap from p-nitrophenyl alpha-L-rhamnopyranoside and RG oligosaccharides, respectively. Thus, all four enzymes examined are inverting hydrolases which probably catalyse hydrolysis via single displacement mechanisms.

[Synthesis of triterpene 2,6-dideoxy-alpha-L-arabino-hexopyranosides from L-rhamnal. Their pharmacological properties]

Triterpene 2,6-dideoxy-alpha-L-arabino-hexopyranosides were synthesized by the glycosylation of oleanane triterpene alcohols with L-rhamnal acetate in the presence of cationite KU-2-8 and lithium bromide. 2,6-Dideoxy-alpha-L-arabino-hexopyranosides of allobetulin and methyl glycyrrhetinate showed pronounced antiulcerous activity; the latter also stimulated reparative skin regeneration in rats and was effective as a hepatoprotectant.

Selection and partial characterization of a Pseudomonas aeruginosa mono-rhamnolipid deficient mutant

Pseudomonas aeruginosa produces rhamnolipids which are tenso-active compounds with potential industrial and environmental applications. There are two main types of rhamnolipids produced in liquid cultures, rhamnosyl-beta-hydroxydecanoyl-beta-hydroxydecanoate (mono-rhamnolipid) and rhamnosyl-rhamnosyl-beta-hydroxydecanoyl-beta-hydroxyd ecanoate (di-rhamnolipid). In this work we report the selective isolation of a rhamnolipid deficient mutant (IBT8), which does not accumulate mono-rhamnolipid while still producing di-rhamnolipid. IBT8 was selected after random mutagenesis with Tn501; yet, its mono-rhamnolipid deficiency was found associated neither with its Tn501 insertion nor with a possible alteration in the rhlABRI genes for rhamnosyl-transferase 1 synthesis. Different possibilities to explain IBT8 phenotype are discussed.

Extracellular particles of polymeric material formed in n-hexadecane fermentation by Pseudomonas aeruginosa

In n-hexadecane fermentation by Pseudomonas aeruginosa, the production of rhamnolipids (biosurfactants) caused by nitrogen source limitation was observed during the stationary phase. The rhamnolipids caused severe foaming in the process, particularly at higher pH (ca. > 6.8). To reduce the foaming, several runs were made at a lower pH, i.e. 6.5 +/- 0.1. Some, however, behaved anomalously different. The rhamnolipid synthesis was very low. Instead, a large quantity of waxy particles with sizes up to 3-5 mm were formed. The waxy material was practically insoluble in all of the organic solvents tested, suggesting the cross-linked polymeric structure. A white, brittle solid was obtained after the material was thoroughly washed (with 0.05 M sodium bicarbonate, distilled water, and hexane) and vacuum-dried. Characterization of the washed material was made by Fourier-transformed infrared (FTIR) spectroscopy, thin-layer chromatography (TLC), and wet chemical analyses. It was found to contain less than 2.5% (w/w) proteins and less than 9% carbohydrates, of which only one sugar component was observed and tentatively identified as glucose by the TLC analysis. The material was, therefore, predominantly hydrocarbon-based, with oxidized functional groups such as esters, alcohols, and carboxylic acids being identified by FTIR. The lipase-catalyzed esterification of fatty acids and alcohols, within the oil droplets or at the oil/water interface of low local water activity, is postulated to play an important role in the waxy particle formation.

19F NMR of 2-deoxy-2-fluoro-D-glucose for tumor diagnosis in mice. An NDP-bound hexose analog as a new NMR target for imaging

A well-known radiopharmaceutical 2-deoxy-2-fluoro-D-glucose widely used for positron emission tomography diagnosis in terms of glucose utilization, was re-evaluated here as a nuclear magnetic resonance pharmaceutical for cancer detection. The uptake and metabolism of FDG in the experimental tumor, MH134, transplanted to the peritoneum of C3H mice as an ascitic tumor was studied extensively by ex vivo 19F NMR. Prolonged retention of FDG and its metabolites over 2 days was confirmed in the tumor cells as well as in the heart. In these tissues, the 6-phosphate of the injected compound was converted reversibly to its epimer 2-deoxy-2-fluoro-D-mannose and further to their NDP bound forms. The metabolites were almost cleared within a day from the other healthy organs where the formation of NDP-2-deoxy-2-fluoro-D-mannose was low. Thus, the 19F NMR signal of NDP-FDM detected 1 day after the FDG injection could be used as a target signal for tumor detection. Through the use of in vivo 19F NMR spectra and 19F chemical shift images, the feasibility of this proposal was demonstrated. It was concluded that FDG-NMR has a potential for tumor diagnosis in animals.

Efficient, convergent syntheses of oligosaccharide allyl glycosides corresponding to the Streptococcus group A cell-wall polysaccharide

Convergent syntheses of di-, tri, tetra-, penta-, and hexa-saccharide allyl glycosides corresponding to the beta-hemolytic Streptococcus Group A cell-wall polysaccharide are described. The strategy relies on the preparation of related di- and tri-saccharide building blocks: beta-D-Glc pNAc-(1-3)-alpha-L-Rhap and alpha-L-Rhap-(1-2)-[(beta-D-Glc p NAc-(1-3)]-alpha-L-Rhap, which could be used either as glycosyl donors or acceptors in subsequent glycosylation reactions. The protecting groups were chosen to allow the selective removal of the allyl aglycon to access the intermediate glycosyl donors but also to allow their own removal without affecting the allyl group. The allyl group was intended for use in conjugation of the oligosaccharides to soluble protein carriers or solid supports for the preparation of antigens and immunoadsorbents, respectively.

Synthesis of four glycosides of a disaccharide fragment representing the terminus of the O-polysaccharide of Vibrio cholerae O:1, serotype Inaba, bearing aglycons suitable for linking to proteins

Methyl 4-azido-3-O-benzyl-4,6-dideoxy-alpha-D-mannopyranoside was converted into the crystalline 2-(trimethylsilyl)ethyl 4-azido-2-O-benzoyl-3-O-benzyl-4,6-dideoxy-alpha-D-mannopyranoside. Debenzoylation of the latter, followed by glycosylation of the resulting 2-hydroxy derivative with 2-O-acetyl-4-azido-4,6-dideoxy-alpha-D-mannopyranosyl chloride, gave the 2-(trimethylsilyl)ethyl glycoside of the corresponding disaccharide (8). Deacetylation of 8, followed by reduction of the resulting 4-azido-2-hydroxy derivative with H2S, gave the corresponding amine 10. The latter was treated with 4-O-benzyl-3-deoxy-L-glycero-tetronic acid to give, after debenzylation and acetylation, the fully protected 2-(trimethylsilyl)ethyl alpha-glycoside of the disaccharide fragment of the O-PS of Vibrio cholerae O:1, serotype Inaba (13). Compound 13 was transformed into the corresponding 1-trichloroacetimidate which was treated, separately, with methyl 6-hydroxy-hexanoate and 2-(2-methoxycarbonylethylthio)ethanol, to give two analogs of 13 possessing a differing linkage arm, namely the methyl esters 16 and 17. Each of 16 and 17 was treated with aqueous sodium hydroxide, followed by a cation-exchange resin, to give the two corresponding carboxylic acids (19 and 22). Alternately, treatment of 16 and 17 with hydrazine hydrate gave the acid hydrazides 20 and 23.

Substrate specificity of native dTDP-D-glucose-4,6-dehydratase: chemo-enzymatic syntheses of artificial and naturally occurring deoxy sugars

Incubation of dTDP-glucose with the enzyme dTDP-glucose-4,6-dehydratase [EC 4.2.1.46] from wild type E. coli B yielded a mixture of 3- and 4-keto-6-deoxy sugars after work-up. Model experiments with chemically synthesized methyl 6-deoxy-4-keto-glucoside (9) revealed that dTDP-6-deoxy-alpha-D-ribo-hexopyran-3-ulose (3) is formed by keto-enol tautomerization during the isolation procedure from initially formed dTDP-6-deoxy-alpha-D-xylo-hexopyran-4-ulose (2). dTDP-3-deoxyglucose (4) and dTDP-3-azido-3-deoxyglucose (6) were substrates and showed Michaelis-Menten kinetics (4: KM = 200 microM and V(max) = 130 mumol/h mg; 6: KM = 300 microM and V(max) = 90 mumol/h mg). In 100-mg-scale experiments, both non-natural substrates gave the respective 6-deoxy-4-keto compounds, dTDP-3,6-dideoxy-alpha-D-erythro-hexopyran-4-ulose (5) and dTDP-3-azido-3,6-dideoxy-alpha-D-xylo-hexopyran-4-ulose++ + (7), in yields ranging from 24 to 40%.

Rhamnolipid biosurfactant enhancement of hexadecane biodegradation by Pseudomonas aeruginosa

Mutants of Pseudomonas aeruginosa that produce and do not produce rhamnolipid biosurfactant are used to investigate the influence of cell-associated biosurfactant on cellular association with the hydrocarbon-water interface and on hydrocarbon uptake. Rhamnolipid-nonproducing mutant 65E12 of P. aeruginosa is unable to grow in minimal media containing hexadecane as a carbon source in the absence of exogenously added surfactant. Mutant PG201::rhlR grows very slowly in the absence of exogenously added surfactants. Both mutants are deficient in the positive regulatory gene controlling the activation of rhamnolipid synthesis. 65E12 is a double mutant that is also deficient in lipopolysaccharide synthesis. However, growth on hexadecane may be restored to varying degrees when small amounts of purified rhamnolipids or the synthetic anionic surfactant alkyl benzene sulfonate (ABS) is added to the cultures. Rhamnolipid biosurfactant is shown to be approximately 9 times more effective than the structurally similar synthetic anionic surfactant ABS in solubilizing hydrocarbon into the aqueous phase. Physical characteristics of the rhamnolipid and ABS micelles as determined by laser light scattering are described to explain the greater effectiveness of the rhamnolipid in solubilizing hexadecane. The cellular attachment to hydrocarbon-water interfaces and cellular aggregation of the wild-type and mutant strains are examined in the presence and absence of rhamnolipid or synthetic ABS surfactants. Differences in observed hexadecane degradation rates are explained on the basis of emulsified hexadecane concentration, cell surface hydrophobicity, and cellular localization in the culture.

Synthesis and crystal structure of methyl 4-6-dideoxy-4-(3-deoxy-L- glycero-tetronamido)-2-O-methyl-alpha-D-mannopyranoside, the methyl alpha-glycoside of the terminal unit, and presumed antigenic determinant, of the O-specific polysaccharide of Vibrio cholerae O:1, serotype Ogawa

Methyl 4-azido-4,6-dideoxy-3-O-benzyl-alpha-D-mannopyranoside and its analogous 3-O-(4-methoxybenzyl) derivative were methylated and the 2-O-methyl derivatives formed were converted into methyl 4-amino-4,6-dideoxy-2-O-methyl-alpha-D- mannopyranoside [sequence: see text]. Reaction of the latter with 3-deoxy-L-glycero-tetronolactone gave the methyl glycoside of 4,6-dideoxy-4-(3-deoxy-L-glycero- tetronamido)-2-methyl-alpha-D-mannopyranose [sequence: see text], the monosaccharide that is reported to be the terminal moiety of the O-specific polysaccharide of Vibrio cholerae O:1, serotype Ogawa. The unit cell packing of the compound, which crystallized as a monohydrate, differs from that of the previously described crystalline compound lacking the 2-O-methyl group. The unmethylated sugar is the terminal moiety of the O-specific polysaccharide of Vibrio cholerae O:1, serotype Inaba. The crystal structure of methyl 4,6-dideoxy-2-O- methyl-4-trifluoroacetamido-alpha-D-mannopyranoside [sequence: see text] is also described.