Investigation of the Surface State of Zeolite HZSM-5 Pretreated with Toluene by Using Fast Atom Bombardment Mass Spectrometry (FABMS)

Fastatombombardmentmassspectrometry(FABMS),asamodificationofSIMSbombingthesamplewithabeamofatomsinsteadofions,hasbeenusedtostudythesurfacecomPositionandstructureofinsulatormaterialssuchaszeolites,andaclearrelationshipbetweenFABMSspectrumandchemicalstructurewasobserved'.ZeoliteHZSM-5exhibitedadramaticallyenhancedactivityintolueneethylationwhiIethepara-selectivitykeptconstant,uponpretreatedwithasmallamountoftolueneathightemperature,whichwasattributedtoadelicatemodificationontheacidstrengt…     

Stereochemical Effects in Mass Spectrometry ( Ⅶ )——Negative Ion Fast Atom Bombardment Mass Spectro-metry of Saccharides with Areneboronic Acids as Reagents

1-Naphthylboronic acid and 2, 4-dimethylphenylboronic acid can react stereospecif-ically with hydroxy groups of saccharides on the probe tip of a fast atom bombardment mass spectrometer to form characteristic negatively-charged boronate ions. On the basis of the relative abundances of these characteristic ions, the epimers of mono- and di-saccharides may be distinguished. This approach was proved to be a simple and effective means for identifying sugars. The collisional activation moss spectra of these characteristic ions are also discussed.     

Formation of the [M+NH_4]~+ Ious of Some Mouo-and Di-saccharides in Fast Atom Bombardment Mass Spectrometry

Fastatombombardment(FAB)ionhaonhasbeenshowntobeaveryusefulmethodinthemassspetrometricanalysisofawidrangeofnaturalcompounds,panicularlyglycoaideS,saccharides,antibiohcsandotherhighlypolarcompoundsl'l.However,a1thoughFABitSeifcanproviderelativemolecularmassinformationofglycosboandsaCCharides,thelowabundanceof[M+H1+ionandchetnicalnoisefromionsoftheFABmatrixlimitthesmo1ecularmassinformation.FenselauetaI[2]andTakayamaetaI[3lhadreportedthattheFABspectraofcomplexorganiccompoundssuchasglycosid…     

An Efficient Synthesis of the α-D-Glucopyranosyl-(1−>2)-α-L-Rhamnopyranosidic Unit

Abstract

The α-D-glucopyranosyl-(1?>2)-L-rhamnopyranosyl sequence is present in some repeating units of bacterial polysaccharides,¹ as those found in the Shigella type or in various Streptococcal strains.     

Studies on Fragmentation Regularity of 5-Methoxycarbonyl-4-substit uted-6-methyl-3,4-dihydropyrimidin-2（1H）-ones by Time-of-flight Mass Spectrometry

The electron impact time-of-flight(TOF) mass spectra of the title compounds were studied to establish their fragmentation processes. With the high resolution of the TOF instrument, the exact mass for each fragment was determined. These data were used to infer the molecular formulas and the elemental compositions for all the molecular ions and fragments through software interpretation. By further applying the fragmentation regularity, the majority of ions were fully assigned. The main fragmentation pathways of the title compounds include the formation of molecular ions by the loss of R^1 groups in the 4-position and the ester groups in the 5-position. The formed ion can be further fragmented by the elimination of MeOH.     

Synthesis of p-Trifluoroacetamidophenylethyl O-(2-Acetamido-2-Deoxy-β-D-Galactopyranosyl)-(1→4)-O-β-D- Galactopyanosyl-(1→4)-O-β-D-Glucopyranoside,Containing the Trisaccharide Portion of the Asialo-GM2 Glycolipid

ABSTRACT

The p-trifluoroacetamidophenylethyl β-glycoside 9 of the trisaccharide O-(2-acetamido-2-deoxy-β-D-galactopyranosyl)-(1→4)-O-β-D-galactopyranosyl-(1→4)-D-glucopyranose (gangliotriose, asialo-GM2) was synthesised. The key step was coupling of a suitably protected lactose derivative with a galactosamine thioglycoside derivative using sulfuryl chloride/trifluoromethanesulfonic acid activation.     

Synthetic Antigens: Synthesis of 4-Aminophenyl O-α-D-Mannopyranosyl-(1→2)-O-α-D-mannopyranosyl-(1→6)-O-α-D-Mannopyranoside and A Related Di- and A Trisaccharide

Abstract

4-Nitrophenyl 2,3-O-isopropylidine-α-D-mannopyranoside 2 was condensed with O-(2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl)-(1→2)-3,4,6-tri-O-acetyl-α-D-mannopyranosyl bromide 1 and 2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl bromide 11 in the presence of mercuric cyanide. Products were deprotected to yield, respectively, 4-nitrophenyl O-α-D-mannopyranosyl-(1→2)-O-α-D-mannopyranosyl-(1→6)-α-D-mannopyranoside 6 and 4-nitrophenyl O-α-D-mannopyranosyl-(1→6)-α-D-mannopyranoside 14. The 4-nitrophenyl group of 6 was reduced to give title trisaccharide. Bromide 1 was also condensed with methyl 2,3,4-tri-O-benzyl-α-D-manopyranoside 3 in the presence of silver trifluoromethanesulfonate and tetramethylurea to give protected trisaccharide derivative which was deprotected to furnish, methyl O-α-D-mannopyranosyl-(1→2)-O-α-D-mannopyranosyl-(1→6)-α-D-mannopyranoside 10. The identities of all protected and deprotected compounds were supported by ¹H and ¹³C NMR spectral data.     

Synthesis of O-α-L-Fucopyranosyl-(1→2)-O-β-D-galactopyranosyl-(1→4)-2-acetamido-2-deoxy-D-glucopyranose. The H-Blood Group Specific Trisaccharide

Abstract

Different reaction conditions were investigated for the preparation of benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-β-D-glucopyranoside (5). Compound 5 on reaction with 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl bromide afforded the 4-O-substituted 2-acetamido-2-deoxy-β-D-glucopyranosyl derivative which, on O-deacetylation, gave benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-4-O-β-D-galactopyranosyl-β-D-glucopyranoside (8). The trimethylsilyl (Me₃Si) derivative of 8, on treatment with pyridineacetic anhydride-acetic acid for 2 days, gave the disaccharide derivative having an O-acetyl group selectively introduced at the primary position and Me₃Si groups at the secondary positions. The latter groups were readily cleaved by treatment with aqueous acetic acid in methanol to afford benzyl 2-acetamido-4-O-(6-O-acetyl-β-D-galactopyranosyl)-3,6-di-O-benzyl-2-deoxy-β-D-glucopyranoside, which on isopropylidenation gave the desired, key intermediate benzyl 2-acetamido-4-O-(6-O-acetyl-3,4-O-isopropylidene-β-D-galactopyranosyl)-3,6-di-O-benzyl-2-deoxy-β-D-glucopyranoside (12). Reaction of 12 with 2,3,4-tri-O-benzyl-α-L-fucopyranosyl bromide under catalysis by bromide ion afforded the trisaccharlde derivative from which the title trisaccharide was obtained by systematic removal of the protective groups. The structures of the final trisaccharide and of various intermediates were established by ¹H and ¹³C NMR spectroscopy.     

Direct Thin – Layer Chromatographic Separation of Enantiomers of Six selected Amino Acids Using 2-O-[(R)-2-Hydroxypropyl]-β-CD as a Mobile Phase Additive

Abstract

Compared with β-Cyclodextrin (β-CD), 2-O-[_(R)-2-hydroxypropyl]-β-CD (A) is more sensitive for chiral recognition. When (A) was used as the chiral mobile phase additive, some racemic amino acids were directly separated on silica gel TLC for the first time.     

Mass Spectral Studies Reveal the Structure of Aβ1-16-Cu(2+) Complex Resembling ATCUN Motif

In Alzheimer's disease, copper binds to amyloid beta (Aβ) peptide and generates oxidative stress. The coordination of histidine (His) residues to Cu(2+) is still uncertain. We studied Cu(2+) binding to Aβ1-16 peptide using the diethyl pyrocarbonate (DEPC) assay and mass spectrometry. Our results show that only one His is involved in Cu(2+) coordination, which is identified as His6 using mass spectral studies. Novel nickel displacement studies have further supported the proposal that the Cu(2+) binding site of Aβ1-16 peptide resembles the ATCUN motif of human serum albumin.     

Synthesis of O-(2-Acetamido-2-Deoxy-β-D-Glucopyranosyl)-(l→2)-O-α-D-Mannopyranosyl-(l→6)-O-β-D-Glucopyranosyl-(1→4)-2-Acetamido-2-Deoxy-D-Glucopyranose. A Potential Acceptor-Substrate for N-Acetylglucosaminyltransferase-V (GnT-V)

Abstract

The reaction of phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-phthaIimido-l-thio-β-D-glucopyranoside with methyl 3,4,6-tri-O-benzyl-α-D-mannopyranoside catalysed by iodonium ion (TfOH-NIS) followed by deacylation-acetylarion afforded disaccharide 11. which was readily converted (in four steps) to bromide 12. A similar glycosylarion with phenyl 2,3,4,6-tetra-O-acetyl-l-thio-D-glucopyranoside of benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-α-D-glucopyranoside 16 followed by O-deacetylation of the resulting intermediate gave disaccharide 18. The 4,6-O-benzylidene derivative of 18 was acetylated then deacetaled to give diol 21. This diol acceptor was condensed with bromide 12 (promoted by mercuric cyanide) to give the partially protected tetrasaccharide derivative 22 which was O-deacetylated and then subjected to catalytic hydrogenation to furnish the title tetrasaccharide 6. The structure assigned to 6 was supported by ¹H and ¹³C NMR spectral data and FAB mass spectroscopy.     

Synthetic Studies on Selectin Ligands/Inhibitors: One-Pot Synthesis of the Mono- and Oligo-Sulfated 2-(Tetradecyl)Hexadecyl β-D-Galacto- and Lactopyranosides as the Sulfatide Mimetics 1

Abstract

The ¹³C NMR spectra of inulin oligomers in D₂O with degree of polymerization (DP) of 3 through 9, along with two other inulin oligomer mixtures of average DP = 17 and DP = 31 were recorded. Significant variations in the chemical shift of some fructofuranose carbon signals indicates that unlike glucans, simple helical structures are not the predominant conformation for inulin oligomers—at least up to DP = 9. Models of the DP = 5 oligomer show that it should prefer a single helical conformation which however, would not be accessible to longer DP oligomers due to severe steric interactions.     

Fragmentation of the conjugate base of 2-(1-hydroxybenzyl)thiamin: does benzoylformate decarboxylase prevent orbital overlap to avoid it?

The base-catalyzed addition of thiamin to benzaldehyde produces 2-(1-hydroxybenzyl)thiamin (HBnT), but in neutral solution HBnT undergoes base-catalyzed irreversible fragmentation into pyrimidine and thiazole derivatives. The fragmentation (rather than elimination) occurs in proportion to the extent that N1' is protonated or alkylated. Generating the conjugate base of HBnT by decarboxylation surprisingly leads to fragmentation independent of the state of N1'. Therefore, a cationic state at N1' specifically promotes removal of the C2alpha proton rather than the fragmentation process itself. It is suggested that benzoylformate decarboxylase, which generates a similar intermediate, exerts stereoelectronic control of the conformation of the carbanion, blocking fragmentation and facilitating protonation.     

Studies on the Effect of Various Anions and Pyridine on the Stereochemistry of Lanthanide(III) Coordination Compounds of 4[N-(2′-Hydroxy-1′-Naphthalidene)Amino] Antipyrine Thiosemicarbazone

In the present studies, the effect of pyridine on stereochemistry of the coordination compounds of lanthanide(III) derived from 4[N-(2′-hydroxy-1′-naphthalidene)amino] antipyrine thiosemicarbazone (HNAAPTS) has been studied. The general composition of the present complexes is LnX₃·n(HNAAPTS)·Py (Ln = La, Pr, Nd, Sm, Gd, Tb, Dy, or Ho; X = NO₃, n = 1, x = Cl, NCS or ClO₄, n = 2, Py = pyridine). All the complexes were characterized by elemental analyses, molecular weight, molar conductance, magnetic susceptibilities, infrared and electronic spectral studies. The infrared studies reveal that the HNAAPTS behaves as a neutral tridentate (N, N, S), while pyridine is coordinated to metal ions via its nitrogen atom. Nitrates are bicovalently bonded, while thiocyanate is coordinated through a strong N-atom. Perchlorate ions are not coordinating in coordination sphere. From electronic spectral data, nephelauxetic effect (β), covalence factor (b^½), Sinha parameter (δ%), and the covalence angular overlap parameter (η) have been calculated. Thermal stabilities of these complexes were studied by thermogravimetric analysis. In conclusion, the coordination number of lanthanides(III) in the present compounds is either seven or ten depending on the coordinating anions.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Synthesis of enantiomerically pure (Z)-(2′R)-1-O-(2′-methoxyhexadec-4′-enyl)-sn-glycerol present in the liver oil of cartilaginous fish

Synthesis of enantiopure (Z)-(2′R)-1-O-(2′-methoxyhexadec-4′-enyl)-sn-glycerol 1, the principal methoxylated glyceryl ether found in Nature, is described by a highly convergent five-step process taking place in 27% overall yield. The synthesis is based on an ether bond formation between the chiral synthon (R)-2,3-O-isopropylidene-sn-glycerol and (Z)-(R)-1-chlorohexadec-4-en-2-ol employing ground potassium hydroxide and tetra-n-butylammonium bromide as a catalyst under solvent free conditions.     

Studies on the Total Synthesis of Sarcophytol-A——Synthesis of 2-Isopropyl-2-(3-Methyl-1-Benzoxyl-5-Phenylsulfonyl-3E-Pentenyl )-1,3-Dithiocyclohexane

The key intermediate, 2-isopropyl-2-(3-methyl-1-benzoxyl-5-phenylsulfonyl-3E-pentenyl)-1, 3-dithiocycllohexane(Ⅲ), for the total synthesis of Sarcophytol-A (1)was prepared through 7 steps from acetone. The key steps are nucleophilic addition of 2-1ithio-2-isopropyl-1,3-dithiocyclohexane to aldehyde 5 and double bond migration reaction of allylic alcohol 9 and 10.     

The Steric Effect of trans-(1S,2S)-1-Substituted-2 (N,N-dialkyl-amino)-1-indanol Derivatives as Chiral Ligands in the Catalytic Enantioselective Addition of Diethylzinc to Aldehydes

Optically active trans-(12,2S)-1-substituted-2(N,N-dialkylamino)-1-indanol derivatives have been prepared and used in the asymmetric addition of diethylzinc to aldehydes to give sec-alcohol in good yield with up to 93.1% enantiomeric excess.     

Generalized Method for the Production of 1,3‐Benzoxazine, 1,3‐Benzothiazine,and Quinazoline Derivatives from 2‐(Hydroxy,Thio, or Amino) Aromatic Acids Using Triphenylphosphine Thiocyanogen

Abstract

A modified one‐pot method was developed for the synthesis of 1,3‐benzoxazines, in which the preparation of unstable thiocyanogen was omitted. The method was found to be general for substituted (methyl, methoxy, halo, and hydroxy) 2‐hydroxy benzoic acids and 2‐hydroxy naphthoic acids. The method was extended to 2‐thio, 2‐amino, and N‐methyl aminobenzoic acid with which the synthesis of 1,3‐benzothiazine and quinazoline derivatives has been achieved, respectively. It was also found that 3‐hydroxypyridine‐2‐carboxylic acid and 2‐hydroxynicotinic acid using a modified method gave 2‐thioxo‐2,3‐dihydro‐4H‐pyrido[2,3‐e][1,3]oxazin‐4‐one and 2‐thioxo‐2,3‐dihydro‐4H‐pyrido[3,2‐e][1,3]oxazin‐4‐one, respectively. The structures of the new compounds were confirmed by the analysis of their IR, ¹H, and ¹³C NMR spectra.     

Unexpected formation of 6,7-dihydrobenzo[4′,5′]imidazo-[1′,2′: 1,6]pyrimido[5,4-a]indolizine derivative in the alkylation of 2-amino-1-(benzimidazol-2-yl)-3-(4-methoxybenzoyl)indolizine

An attempt to effect exhaustive alkylation of 2-amino-1-(benzimidazol-2-yl)-3-(4-methoxybenzoyl) indolizine with alkyl iodides in boiling acetone led to the formation of 6,6-dimethyl-8-(4-methoxybenzoyl)-6,7-dihydrobenzo[4′,5′]imidazo[1′,2′: 1,6]pyrimido[5,4-a]indolizine instead of expected N-alkyl derivatives. The product structure was proved by X-ray analysis.