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R R Schmidt

Publications and source records attributed to R R Schmidt.

At least 55 records · Page 3Linked to original sources
PubMed1994

Synthesis of 3-deoxy-2-octulosonic acid derivatives and characterisation of their 3-deoxyoctitols.

The diethyl dithioacetals of D-altrose, D-idose, and D-talose were used to synthesise the respective O-benzyl aldehydo-sugars as intermediates for the synthesis of 3-deoxy-D-glycero-D-gluco/manno-3-deoxy-D-glycero-L-gulo/ido -, and 3-deoxy-D-glycero-L-allo/altro-octonate derivatives, respectively. After reduction and deprotection, the respective 3-deoxyoctitols were obtained. For the synthesis of 3-deoxy-D-glycero-L-galacto/talo-octitol, 2,3:5,6-di-O-isopropylidene-D-gulono-1,4-lactone was transformed by reduction and selective oxidation at C-1 to the aldehydo-D-gulose, from which the 3-deoxy-D-glycero-L-galacto/talo-octonate was synthesised. Carboxyl- and carbonyl-reduction and deprotection gave the 3-deoxyoctitol. The 3-deoxyoctitols were characterised by GLC and GLC-MS in the acetylated and methylated form. The data presented here and the data published earlier [T. Krülle, O. Holst, H. Brade, and R.R. Schmidt, Carbohydr. Res., 247 (1993) 145-158] showed that methylated 3-deoxy-D-glycero-D-galacto/talo-octitol can be distinguished by GLC from the other 3-deoxy-D-octitols and thus allows the identification of the manno configuration of 3-deoxy-D-manno-octulosonic acid (Kdo) in natural products such as the lipopolysaccharides of different Gram-negative bacteria, where Kdo is a generally occurring constituent.

Carbohydrate Conformation↗
PubMed1994

A convenient synthesis of nucleoside monophosphate-N-acetylneuraminic acids (NMP-Neu5Ac).

Reaction of sialyl phosphites 2a,b with acetyl-protected ribonucleoside monophosphates 3C, 3U, 3A and 3G furnished without addition of a catalyst directly the corresponding beta-configurated sialyl ribonucleoside monophosphates 4C, 4U, 4A and 4G, respectively. Treatment of these compounds with sodium methanolate in methanol and sodium hydroxide afforded the disodium salts of CMP-Neu5Ac (1C), UMP-Neu5Ac (1U), AMP-Neu5Ac (1A), and GMP-Neu5Ac (1G).

Cytidine Monophosphate N-Acetylneuraminic Acid↗
PubMed1993

A convenient synthesis of N-acetyllactosamine derivatives from lactal.

In a thermal inverse-type hetero-Diels-Alder reaction of O-silyl-protected lactal 1 and bis(2,2,2-trichloroethyl) azodicarboxylate (2), the dihydrooxadiazine derivative 3 was obtained in a very high yield; transesterification with benzyl alcohol furnished the corresponding derivative 4. Treatment of 3 with methanol in the presence of BF3.OEt2 afforded the methyl lactoside derivative 5 which, after transesterification with benzyl alcohol, then hydrogenolytic debenzylation and concomitant NN-cleavage with Raney nickel, and N-acetylation, furnished methyl O-(2,4,6-tri-O-tert-butyldimethylsilyl-beta-D-galactopyranosyl)-(1-->4)- 2-acetamido-3,6-di-O-tert-butyldimethylsilyl-2-deoxy-beta-D-glucopyra nos ide (7) in high yield. Desilylation of 4, then O-acetylation, methyl glycoside formation with methanol-BF3.OEt2, hydrogenolytic debenzylation, and NN-cleavage with Raney nickel, and N-acylation afforded methyl O-(2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-(1-->4)-2-acetamido-3 ,6-di-O-acetyl-2-deoxy-beta-D-glucopyranoside (10).

Amino Sugars↗
PubMed1993

Synthesis of Kdo-alpha-glycosides of lipid A derivatives.

The synthesis of the lipopolysaccharide fragment O-(4,5,7,8-tetra-O-acetyl-3-deoxy-N-methyl-alpha-D-manno-2- octulopyranosylonamide)-(2-->6)-O-(2-deoxy-2-[(3R)-3- dodecanoyloxytetradecanamido]-4-O- phosphono-3-O-tetradecanoyl-beta-D-glucopyranosyl)-(1-->6)-1-O-acetyl-2- deoxy-2 - [(3R)-3-dodecanoyloxytetradecanamido]-3-O-tetradecanoyl-alpha-D- glucopyranose (35 alpha) is performed via anomeric O-alkylation. With this objective, the 2-azido-3-O-benzyl-2-deoxy-6-O-trifluoromethanesulfonyl-beta-D-glu copyranosides 5, 7, and 19 alpha, beta were synthesized from D-glucal and employed as alkylating agents. Reaction of 5 with the O-cyclohexylidene-protected Kdo-derivative 10 afforded the desired alpha-linked disaccharide, tert-butyldimethylsilyl 4-O-allyl-2-azido-3-O-benzyl-2-deoxy-6- O-(4,5:7,8-di-O-cyclohexylidene-3-deoxy-N-methyl-alpha-D-manno-2- octulopyranosylonamide)-beta-D-glucopyranoside (11); even better yields of the structurally related disaccharide 12 were obtained with the 4-O-unprotected 7 as alkylating agent. 1-O-Desilylation of 12 furnished the lactol 20, which could be alkylated at the anomeric position with 1-O-allyl protected alkylating agents 19 alpha and 19 beta, both of which furnished exclusively the desired beta-(1-->6)-linked trisaccharides allyl O-(4,5:7,8-di-O-cyclohexylidene-3- deoxy-N-methyl-alpha-D-manno-2-octulopyranosylonamide)-(2-->6)-O-( 2-azido-3- O-benzyl-2-deoxy-beta-D-glucopyranosyl)-(1-->6)-2-azido-3, 4-di-O-benzyl-2-deoxy-alpha- (21 alpha) and -beta-D-glucopyranoside (21 beta), respectively. Phosphorylation with diphenyl phosphorochloridate, replacement of the O-cyclohexylidene protective group by O-triethylsilyl (TES) protective groups, removal of the 1-O-allyl group, azido group reduction, subsequent N-acylation, and then O-acetylation provided the key 1-O-acetyl protected intermediate 30 alpha. Removal of the O-TES groups, subsequent O-acetylation, and hydrogenolytic O-debenzylation furnished O-[4,5:7,8-tetra-O-acetyl-3-deoxy-N-methyl-alpha-D-manno-2- octulopyranosylonamide]-(2-->6)-O-(2-deoxy-4-O-diphenoxyphospho ryl-2-[(3R)- 3-dodecanoyloxytetradecanamido]-beta-D-glucopyranosyl)-(1-->6)-1-O -acetyl-2- deoxy-2[(3R)-dodecanoyloxytetradecanamido]-alpha-D-glucopyranose (33 alpha), which underwent the required selective O-tetradecanoylation at the 3-O- and 3'-O-position, thus furnishing, after hydrogenolytic O-dephenylation of the diphenoxyphosphoryl group, the target molecule 35 alpha.

Glycosides↗
PubMed1993

Synthesis of phosphites and phosphates of neuraminic acid and their glycosyl donor properties--convenient synthesis of GM3.

The importance and requirements for catalytic activation of sialyl donors are discussed, leading to the acid sensitive phosphite and phosphate moiety, respectively, as leaving group and nitriles as solvent. Therefore, from readily available N-acetylneuraminic acid, derivative 1 with phosphochloridites 2a-f and Huenigs' base sialyl phosphites 3a-f were prepared and isolated in high yields. Oxidation of 3a,c with tert-butyl-hydroperoxide afforded the corresponding phosphates 4a,c. As expected, phosphites 3 could be activated in acetonitrile by catalytic amounts of TMSOTf; thus, from 3a-e as donors and lactose derivatives 8A,B as acceptors the ganglioside building blocks 9A and 9B, respectively, were obtained in good yields. The best results were obtained with diethyl phosphite derivative 3a as sialyl donor, which exceeded by far the results obtained with the corresponding phosphate derivative 4a. Trisaccharide 9B was transformed into known 9A and into the fully O-acetylated GM3-trisaccharide 10.

Carbohydrate Sequence↗
PubMed1992

Differential eicosanoid synthesis by murine fetal thymic non-lymphoid cells.

The temporal patterns of synthesis of prostaglandin (PG)E2 and PGI2 by organ-cultured fetal thymic lobes and the cell population(s) responsible for synthesis of such products within the murine fetal thymus have been investigated. Embryonic day 14 thymic lobes were organ-cultured in defined media for 14 days and the media were collected every 24 h and replaced with fresh media. Collected media were processed for quantitation of either PGE2 or PGI2. Lobes were also cultured in 2'-deoxyguanosine (1.35 mmol/L) to produce an enriched non-lymphoid population. The per cent cyclooxygenase-positive cells within non-lymphoid cell-enriched lobes as well as the capacity of such lobes to synthesize either PGE2 or PGI2 were determined and compared with that of intact thymic lobes. Results demonstrate that fetal thymic lobes, in vitro, differentially synthesize PGI2 and synthesize PGE2 at a constant rate. Moreover, lobes enriched for non-lymphoid cells contain a greater percentage of cyclooxygenase-positive cells and synthesize increased amounts of eicosanoids per 10(4) cells compared with controls.

Animals↗
PubMed1991

Expression of prostaglandin G/H synthase (cyclooxygenase) during murine fetal thymic development.

Fetal thymic lobes in organ culture have been shown to have the capacity to metabolize [14C]arachidonic acid (AA) to prostaglandins (PGs), including 6-ketoPGF1 alpha, PGF2 alpha, PGE2, and PGA2. Inhibition of AA metabolism results in inhibition of growth and Thy 1 expression during thymic organ culture. We report herein that freshly-isolated fetal thymic lobes also have the capacity to metabolize [14C]AA to PGs and HETEs at Days 14 and 16 of prenatal murine development. RNA encoding phospholipase A2, which liberates arachidonic acid from membrane phospholipids, and cyclooxygenase (prostaglandin G/H synthase), the first enzyme involved in the conversion of AA to PGs, are expressed during thymic development. We have localized the cyclooxygenase protein to stromal cells in the fetal and adult thymus. Exogenous AA or an analogue of PGI2 (iloprost) stimulated growth of fetal thymocytes in organ culture. These findings, together with our studies of the morphology of thymic lobes cultured with inhibitors of arachidonate metabolism, support the hypothesis that PGs are required for thymocyte proliferation during thymic development.

Animals↗
PubMed1991

Sphingolipid biosynthesis in cultured neurons. Down-regulation of serine palmitoyltransferase by sphingoid bases.

Addition of exogenous sphingosine homologues (D-erythro configuration) with different alkyl chain lengths (12 and 18 carbon atoms) to the medium of primary cultured cerebellar cells resulted in a decrease of serine palmitoyltransferase activity in a time- and concentration-dependent manner. This enzyme catalyzes the first committed step in sphingolipid biosynthesis. Half-maximal reduction of enzyme activity occurred after a 4-h treatment with 25 microM sphingoid bases. Maximal decrease (approx. 80%) was obtained after treating the cells for 4-8 h with 50 microM long-chain bases. When a biosynthetically inert sphingoid, azidosphingosine (10-50 microM), was fed to the cells, decrease of 3-ketosphinganine formation was much slower, reaching its maximum (approx. 80%) after 24 h. In contrast to D-erythro-sphingosine, L-threo-C18-sphingosine did not yield any decrease of serine palmitoyltransferase activity when added to the cells under identical experimental conditions. Decrease of serine palmitoyltransferase activity was fully reversible after removal of the long-chain bases from the culture medium. Activities of other enzymes of lipid metabolism, ceramide synthase, long-chain acyl-CoA synthase and choline phosphotransferase, were not affected by the addition of sphingoid bases, indicating that the down regulation of serine palmitoyltransferase is quite specific.

Acyltransferases↗
PubMed1991

The structure of bergenin.

X-ray analysis of the 3,4,8,10,11-penta-acetate (3) of bergenin has confirmed the earlier structural assignments.

Benzopyrans↗
PubMed1991

A nuclear gene with many introns encoding ammonium-inducible chloroplastic NADP-specific glutamate dehydrogenase(s) in Chlorella sorokiniana.

Chlorella sorokiniana possesses ammonium-inducible, chloroplastic, NADP-specific glutamate dehydrogenase (NADP-GDH) homo- or heterohexamers composed of alpha- and/or beta-subunits which were previously shown to derive from precursor protein(s) of identical size. From the present studies, data are consistent with these two subunits being encoded by a single nuclear gene. The NADP-GDH gene is greater than 7 kb in length due to the presence of at least 21 introns, an unusually large number for a eukaryotic microorganism. The exons, identified by comparison with sequences of NADP-GDH cDNA clones, include a region which is highly conserved among NADP-GDH genes. This region in the C. sorokiniana gene is 77% and 73% identical to the corresponding regions in the Escherichia coli and Neurospora crassa NADP-GDH genes, respectively. Seventeen independent NADP-GDH cDNA clones were analyzed by restriction mapping and partial sequencing, and no differences were detected among them. The longest cDNA was fused in frame with lacZ in a Bluescript vector and was expressed in E. coli as NADP-GDH antigen. During a 240 min induction period, under conditions in which both types of subunits were synthesized, only a single (2.2 kb) NADP-GDH mRNA band was detected on northern blots using cDNA probes from the highly conserved and 3'-untranslated regions. Collectively, these results are consistent with a single mRNA encoding a precursor-protein which is differentially processed to yield either an alpha- or beta-subunit.

Amino Acid Sequence↗
PubMed1990

The rate of bulk flow from the Golgi to the plasma membrane.

A truncated analog of the backbone of sphingomyelin and glycolipids was synthesized. This truncated C8C8 ceramide was soluble in water (but was still able to cross cell membranes) and was utilized by the Golgi apparatus of living cells to produce water-soluble truncated phospholipids and glycolipids that were then secreted into the medium. Sphingomyelin is synthesized in a proximal (likely the cis) Golgi compartment. At 37 degrees C in CHO cells, the sphingomyelin analog is secreted with a half time of about 10 min. With this rate of bulk flow, no special signal is needed to pass through the Golgi to the plasma membrane. At 30 degrees C the half time of secretion of a lumenal ER marker is about 18 min, and that of the truncated sphingomyelin is about 14 min. Comparison of these rates sets an upper limit of about 4 min for half of the ER to be drained into the proximal Golgi at 30 degrees C.

Animals↗
PubMed1990

Muramic acid derivatives as glycosyl donors for the synthesis of muramyl-containing glycosphingolipids and fatty acids.

2-Azido-2-deoxy-4,6-O-isopropylidene-3-O-[(1R)-(methoxycarbonyl)ethyl]- alpha-D-glucopyranosyl trichloroacetimidate (3 alpha) has been used as the glycosyl donor in the synthesis of glycosphingolipids 14 and 27. Reaction of 3 alpha with (2S, 3R, 4E)-2-azido-3-benzoyloxy-4-octadecen-1-ol (6) gave (2S, 3R, 4E)-2-azido-1-(2-azido-2-deoxy-4,6-O-isopropylidene-3-O-[(1R)-1-(m ethoxycarbonyl)ethyl]-beta-D-glucopyranosyloxyl)-3-benzoyloxy-4- octadecene (7), which was converted into (2S, 3R, 4E)-1-(2-deoxy-2-hexadecanoylamino-3-O-[(2R)-propanoyl-(L-alanyl-D -isoglutamine benzyl ester)-2-yl]-beta-D-glucopyranosyloxy)-2-hexadecanoylamino-4-oc tadecen-ol (14). Reaction of 3 alpha with tert-butyldimethylsilyl 2-azido-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranoside (15) gave tert-butyldimethylsilyl 2-azido-4-O-(2-azido-2-deoxy-4,6-O-isopropylidene-3-O-[(1R)-1-(methox ycarbonyl)ethyl]-beta-D-glucopyranosyl)-3,6-di-O-benzyl-2-deoxy-be ta- D-gluc opyranoside (16 beta), which was converted into 1,3,6-tri-O-acetyl-2-deoxy-4-O-(4,6-di-O-acetyl-2-deoxy-2-hexadecanoy lam ino-3-O-[2R)-propanoyl-(L-alanyl-D-isoglutamine methyl ester)-2-yl]-beta-D-glucopyranosyl)-2-hexadecanoylamino-D-glucopyranose (27).

Carbohydrate Sequence↗
PubMed1990

Modulation of sphingolipid biosynthesis in primary cultured neurons by long chain bases.

Sphingolipid biosynthesis was studied in cultured murine cerebellar cells in the absence and presence of exogenous sphingosine homologues with different alkyl chain lengths (12, 18, and 24 carbon atoms). Labeling of cells with [14C]serine for 24 h indicated that endogenous sphingosine biosynthesis with incorporation of radiolabeled serine was inhibited by these long chain bases (0.5-50 microM) in a concentration-dependent manner; the inhibition was fully reversible after removal of the long chain bases from the culture medium. Metabolic labeling of neurons with [14C]galactose provided strong evidence that the cells were able to use the exogenous sphingosine homologues, irrespective of their alkyl chain length, as substrates for the biosynthesis of glycosphingolipids. When the biosynthetically inert sphingoid, azidosphingosine (5-50 microM), was fed to the cells, de novo sphingosine and glycosphingolipid biosynthesis were both strongly inhibited.

Animals↗
PubMed1990

O-alkylation at the anomeric centre for the stereoselective synthesis of Kdo-alpha-glycosides.

O-Alkylation at the anomeric centre of the dianion of 4,5:7,8-di-O-cyclohexylidene-3-deoxy-N-methyl-alpha-D-manno- octulopyranosonamide (1) with several triflates led diastereoselectively to the alpha-glycosides. In this way, lipopolysaccharide building-blocks containing alpha-Kdo-(2----6)-GlcN and alpha-Kdo-(2----6)-beta-GlcN-(1----6)-GlcN moieties were obtained and deployed in the synthesis of decyl 4,5,7,8-tetra-O-acetyl-3-deoxy-N-methyl-alpha-D-manno-2-octulopyranos idonamide (18), 2,3-di-O-tetradecanoyl-D-glycer-1-yl 4,5,7,8-tetra-O-acetyl-3-deoxy-N-methyl- alpha-D-manno-2-octulopyranosid-onamide (22), methyl 2,3,4-tri-O-acetyl-6-O-(methyl 4,5,7,8-tetra-O-acetyl-3-deoxy-alpha-D- manno-2-octulopyranosylonate)-alpha-D-glucopyranoside (28), 1-O-acetyl-2-deoxy-6-O-(methyl 4,5,7,8-tetra-O-acetyl-3-deoxy-alpha-D-manno-2- octulopyranosylonate)-2-tetradecanoylamino-alpha-D-glucopyra nose (33), tert-butyldimethylsilyl O-(methyl 4,5:7,8-di-O-cyclohexylidene-3-deoxy-alpha-D- manno-2-octulopyranosylonate)-(2----6)-O-(3,4-di-O-benzyl-2-deoxy- 2- tetradecanoylamino-beta-D-glucopyranosyl)-(1----6)-3,4-di-O-benzyl -2-deoxy-2- tetradecanoylamino-alpha-D-glucopyranoside (36).

Alkylation↗
PubMed1990

Sphingomyelin is synthesized in the cis Golgi.

We have employed in vitro a truncated ceramide analogue with 8 carbon atoms in the sphingosine and the fatty acyl residue, each, to investigate the activity of various membrane fractions to synthesize truncated sphingomyelin. This shortened ceramide readily diffuses through membranes and therefore can easily find access to the lumina of intact organelles. Sphingomyelin synthase activity resides in the Golgi apparatus, and after sucrose density gradient centrifugation of Golgi-enriched fractions sphingomyelin synthesis follows a cis Golgi marker enzyme.

Animals↗
PubMed1990

Biosynthesis of digalactosyldiacylglycerol in plastids from 16:3 and 18:3 plants.

Intact chloroplasts isolated from leaves of eight species of 16:3 and 18:3 plants and chromoplasts isolated from Narcissus pseudonarcissus L. flowers synthesize galactose-labeled mono-, di-, and trigalactosyldiacylglycerol (MGDG, DGDG, and TGDG) when incubated with UDP-[6-(3)H]galactose. In all plastids, galactolipid synthesis, and especially synthesis of DGDG and TGDG, is reduced by treatment of the organelles with the nonpenetrating protease thermolysin. Envelope membranes isolated from thermolysin-treated chloroplasts of Spinacia oleracea L. (16:3 plant) and Pisum sativum L. (18:3 plant) or membranes isolated from thermolysin-treated chromoplasts are strongly reduced in galactolipid:galactolipid galactosyltransferase activity, but not with regard to UDP-Gal:diacylglycerol galactosyltransferase. For the intact plastids, this indicates that thermolysin treatment specifically blocks DGDG (and TGDG) synthesis, whereas MGDG synthesis is not affected. Neither in chloroplast nor in chromoplast membranes is DGDG synthesis stimulated by UDP-Gal. DGDG synthesis in S. oleracea chloroplasts is not stimulated by nucleoside 5'-diphospho digalactosides. Therefore, galactolipid:galactolipid galactosyltransferase is so far the only detectable enzyme synthesizing DGDG. These results conclusively suggest that the latter enzyme is located in the outer envelope membrane of different types of plastids and has a general function in DGDG synthesis, both in 16:3 and 18:3 plants.

Journal Article↗