Mohammed A.E. Sallam

Characterization of the alginates from algae harvested at the Egyptian Red Sea coast

The alginates from five species of brown algae from the Egyptian Red Sea coast, namely: Cystoseira trinode, Cystoseira myrica, Sargassum dentifolium, Sargassum asperifolium, and Sargassum latifolium, were isolated and their compositions and structures studied by 1H NMR spectroscopy. All the alginates studied contain more guluronic acid (G) than mannuronic acid (M) and have a homopolymeric block-type structure (eta<1). The intrinsic viscosity of the alginate samples range from 8.6 to 15.2 and the gel strength ranges from 10.97 to 15.51. The constitutional G- and M-blocks of alginates from two different species (C. trinode and S. latifolium) were separated after partial acid hydrolysis. The 1H NMR spectral data of the blocks GG and MM obtained by chemical fractionation were compared with those of polymeric alginates. The monomeric uronic acids were separated by complete acid hydrolysis of S. asperifolium alginate and the G and M monomers were characterized by 1H, 13C NMR spectroscopy as well as by paper electrophoresis.

3-β-d-erythrofuranosyl-1-phenylpyrazolo[3,4-b]quinoxaline, a new C-nucleoside analog

Abstract Dehydration of the hydroxyalkyl chain of 1-phenyl-3-( d - arabino -tetritol-1-yl)pyrazolo[3,4- b ]quinoxaline gave the C -nucleoside 3-β- d -erythrofuranosyl-1-phenyl-pyrazolo[3,4- b ]quinoxaline ( 2 ) in 82% yield. The structure, and the configuration at the anomeric carbon atom, of 2 were elucidated by periodate oxidation, c.d. and n.m.r. spectroscopy, and mass spectrometry. N.m.r.-spectral and c.d. studies revealed that, due to the large size of the heterocyclic base, compound 2 is formed by inversion in the configuration or C-1 of the side chain. The mechanism of the dehydrative cyclization with inversion is discussed.

Studies on anhydro-osazones. Structure and anomeric configuration of the 3,6-anhydro-osazone derivatives obtained from D-galacto-2-heptulose phenylosazone

Abstract Dehydration of D - galacto -2-heptulose phenylosazone with methanolic sulfuric acid afforded two 3,6-anhydro-osazone derivatives ( 2 and 3 ). Compound 2 was obtained as the preponderant isomer, without inversion at C-1 (C-3 of the starting osazone), and 3 was obtained with inversion. The anomeric configurations of 2 and 3 were determined by n.m.r. spectroscopy. Refluxing of 2 and 3 with copper sulfate afforded two C -nucleoside analogs, namely, 4-β- and 4-α- D -lyxofuranosyl-2-phenyl-1,2,3-triazole, 4 and 5 , respectively. The anomeric configurations of 4 and 5 were determined by n.m.r and c.d. spectroscopy. Acetylation of 4 and 5 afforded the tri- O -acetyl derivatives. The mass spectra of these compounds were discussed.

Acid-catalyzed dehydrative cyclization of 4-(D-galacto -pentitol-1-yl)-2-phenyl-2H-1,2,3-triazole. synthesis and anomeric configuration of D-lyxo-C-nucleoside analogs.

Dehydration of 4-(D-galacto-pentitol-1-yl)-2-phenyl-2H-1,2,3-triazole with 20% methanolic sulfuric acid afforded the anomeric pairs of nucleosides, 4-(alpha-D-lyxopyranosyl)-2-phenyl-2H-1,2,3-triazole (major component) and its beta-anomer, as well as 4-(alpha-D-lyxofuranosyl)-2H-1,2,3-triazole and its beta-anomer. The four anomeric C-nucleosides were separated by chromatography, and their structure and anomeric configuration were determined by periodate oxidation, acylation, and NMR spectroscopy as well as mass spectrometry. The anomeric assignment from optical rotation was not in agreement with final structure assignment and represented a violation of the Hudson isorotation rules. NOE studies and X-ray diffraction measurements confirmed the anomeric configuration.

The carbohydrate component of the doum-palm kernel: characterization and identification of a mannan

Abstract A mannan composed of 95% of D -mannose residues and 5% of D -galactose residues has been isolated from the kernels of the doum palm ( Hyphaene thebaica ). It consists of 14–23 D -mannopyranose residues linked by β- D -(1→4)-linkages.

Synthesis and anomeric configuration of 2-(erythrofuranosyl)benzimidazole C-nucleoside analogues

Abstract Anomeric 2-(α- and β- d -erythrofuranosyl)benzimidazole C-nucleoside analogues 2 and 3 , were prepared from the corresponding epimeric 2-( d - arabino , and d - ribo -tetritol-1-yl)benzimidazole analogues 1 and 4 , respectively. Similarly, 2-(β- l -erythrofuranosyl)benzimidazole 13 was obtained from the precursor 2-( l - arabino -tetritol-1-yl)benzimidazole 12 . The structure and anomeric configuration of the C-nucleoside analogues 2 , 3 , and 13 were determined by acylation, 1 H and 13 C NMR spectroscopy, and mass spectrometry.

Synthetic and spectroscopic studies of 2-C-methyl-erythritol and 2-C-methyl-threito

Abstract The synthesis of 2- C -methyl- d,l -threitol and two isopropylidene derivatives of 2- C -methyl- d -erythritol is described. 1 H and 13 C NMR spectra of these and several related compounds are discussed.

6-chloro-3-β-d-erythrofuranosyl-l-phenyl- and -l-p-tolylpyrazolo-[3,4-b]quinoxaline

Abstract The C -nucleoside analogs 6-chloro-3-β- d -erythrofuranosyl-l-phenylpyrazolo-[3,4- b ]quinoxaline ( 5 ) and 3-β- d -erythrofuranosy]-l- p -tolylpyrazolo[3,4- b ]quinoxaline ( 10 ) were prepared by dehydration of the polyhydroxyalkyl chain of 6(7)-chlorolo-phenyl-3-( d - arabino -tetritol-l-yl)-pyrazolo(3,4- b ]quinoxaline and 3-( d - arbino -tetritol-l-yl)-l- p -tolylpyrazolo[3,4- b ]quinoxaline, respectively. The structure and anomeric configuration of 5 and 10 were determined by high-resolution, n.m.r. spectroscopy. The mass spectra and biological activities of some of these compounds are discussed.

3-β-D-erythrofuranosyl-6,7-dimethyl-1-p-tolyl- and -1-(p-chlorophenyl)-pyrazolo[3,4-b]quinoxaline C-nucleoside analogs

Abstract The C -nucleoside analogs 3-β- d -erythrofuranosyl-6,7-dimethyl-1- p -tolylpyrazolo[3,4- b ]quinoxaline ( 5 ) and 1-( p -chlorophenyl)-3-β- d -erythrofuranosyl- 6,7-dimethylpyrazolo[3,4- b ]quinoxaline ( 7 ) were prepared by the dehydrative cyclization of the polyhydroxyalkyl chain of 6,7-dimethyl-3-( d - arabino -tetritol-1- yl)-1- p -tolylpyrazolo[3,4- b ]quinoxaline and 1-( p -chlorophenyl)-6,7-dimethyl-3-( d - arabino -tetriol-1-yl)-1- p -tolylpyrazolo[3,4- b ]quinoxaline, respectively. The structure and anomeric configuration of compounds 5 and 7 , as well as of their 2′,3′-isopropylidene acetals were determined by n.m.r. spectroscopy. The mass spectra and biological activity are discussed.

6,7-Dimethyl-3-β-D-Erythrofuranosyl-1-Phenyl- and 1-p-Fluorophenyl-Pyrazolo[3,4-b]QUINOXALINE∗

Abstract The C-nucleoside analogs 6,7-dimethyl-3-β-D-erythrofuranosyl-1-phenylpyrazolo[3,4-b]quinoxaline 4 and 3-β- D -erythrofuranosyl-1-p-fluorophenylpyrazolo[3,4-b]quinoxaline 8 were prepared by dehydration of the polyhydroxyalkyl chain of 6,7-dimethyl-1-phenyl-3-( D -arabino-tetritol-1-yl)-pyrazolo[3,4-b]quinoxaline 3 and 1-p-fluorophenyl-3-( D -arabino-tetritol-1-yl)-pyrazolo[3,4-b]quinoxaline 7, respectively. The structure and anomeric configuration of the products were determined by n.m.r. spectroscopy. The mass spectra and biological activities in connection with chemical constitution are discussed.