Synthesis and Anti-HIV Activity of Further Examples of 1-[3-Deoxy-3-(N-hydroxyamino)-β-d-threo-(and β-d-erythro)-pentofuranosyl]thymine Derivatives1

Abstract

Upon sodium cyanoborohydride reduction followed by de-O-silylation, the O-methyloxime and N-benzylnitrone of 5′-TBDMS-3′-ketothymidine gave resolvable epimeric mixtures of 1-[2,3-dideoxy-3-(N-methoxyamino)-β-d-threo-and β-d-erythro-pentofuranosyl]thymine and 1-[3-(N-benzyl-N-hydroxyamino)-2,3-dideoxy-β-d-threo- and β-d-erythro-pentofuranosyl]thymine respectively. These compounds were inactive against HIV. On the other hand, 1-[2,3-dideoxy-3-(N-hydroxyamino)-5-O-TBDMS-β-d-threo-pentofuranosyl]thymine, upon treatment with acetone, then de-O-silylation, gave the bicyclonucleoside analogue 15, slightly more active against HIV in vitro than DDI.     

Syntheses,characterization, and crystal structures of ruthenium(II)/(III) complexes with tridentate salicylaldiminato ligands

Treatment of [Ru(PPh₃)₃Cl₂] with one equivalent of tridentate Schiff base 2-[(2-dimethylamino-ethylimino)-methyl]-phenol (HL) in the presence of triethylamine afforded a ruthenium(III) complex [RuCl₃(κ²-N,N-NH₂CH₂CH₂NMe₂)(PPh₃)] as a result of decomposition of HL. Interaction of HL and one equivalent of [RuHCl(CO)(PPh₃)₃], [Ru(CO)₂Cl₂] or [Ru(tht)₄Cl₂] (tht = tetrahydrothiophene) under different conditions led to isolation of the corresponding ruthenium(II) complexes [RuCl(κ³-N,N,O-L)(CO)(PPh₃)] (2), [RuCl(κ³-N,N,O-L)(CO)₂] (3), and a ruthenium(III) complex [RuCl₂(κ³-N,N,O-L)(tht)] (4), respectively. Molecular structures of 1·CH₂Cl₂, 2·CH₂Cl₂, 3 and 4 have been determined by single-crystal X-ray diffraction.     

Synthesis, structure and spectral characterisation of a hydrogen-bonded polymeric manganese(III) Schiff base complex

A new hydrogen-bonded polymeric Mn(III) complex C₁₉H₂₀Mn₁N₃O₃S₁ (1) has been synthesised by conventional procedure with a new Schiff base ligand (2Z,3Z)-N ¹,N ²-bis(1-(2-hydroxyphenyl)ethylidene)ethane-1,2-diamine (H ₂ L) bearing a tetradentate N₂O₂ donor site. The complex has been characterised with several spectroscopic techniques like FT-IR, UV/Vis and EPR and also well supported by variable temperature magnetic susceptibility study. The structure of the co-ordination complex has been unequivocally confirmed from single crystal X-ray diffraction study. The redox stability of the metal chelate complex has been investigated with a slow scan cyclic voltammetry.     

A Novel Keggin Units-Supported Complex: Synthesis,Characterization and Crystal Structure of [(CH3)2NH2]6[Cu(DMF)4(GeW12O40)2] · 2DMF

A novel hybrid compound, [(CH₃)₂NH₂]₆[Cu(DMF)₄(GeW₁₂O₄₀ ^4-)₂] [sdot] 2DMF, has been synthesized from H₄GeW₁₂O₄₀ [sdot] n H₂O, CuCl₂ and N, N -dimethylformamide (DMF) in aqueous solution and characterized by elemental analysis, UV and IR spectra. Single crystal X-ray structure analysis shows that the crystal consists of a α-Keggin heteropolyanion-supported anion [Cu(DMF)₄(GeW₁₂O₄₀ ^4-)₂], two free N, N-dimethylformamide molecules, six protonated dimethylamine (DMA) molecules, and that the coordinating atoms of DMF are the oxygen atoms of C=O group. Thermal analysis indicates that the thermal stability of the GeW₁₂O₄₀ ^4- anion in the title compound is stronger than that in acid.     

Strukturelle Abwandlungen anN-Acetylneuraminsäure, 3

From methyl-5-acetylamino-7,8-anhydro-4,9-O-bis-(t-butyldimethylsilyl)-3,5-dideoxy--D-glycero-D-galacto-2-nonulopyranosidonic acid methylester (1) the derivatives1 a and1 b were obtained by removing the 9-O-(t-butyldimethylsilyl)group withBu ₄NF, followed by acetylation. Treatment of1 b with 80% acetic acid and acetanhydride/pyridine yields the 8-epi-N-acetylneuraminic acid derivative2 a and the 7-epi-N-acetylneuraminic acid derivative3 a in a ratio of 3:1 (Scheme 1). The structure elucidation of2 b was achieved by converting2 b via the 4,9-bis-O-(tBDMSi)-8-O-tosyl-derivative2 d into the epoxide1 (Scheme 2). Using the same sequence the epoxides4 and5 were transformed into theN-acetylneuraminic acid derivative6 a and the 7,8-bis-epi-N-acetylneuraminic acid derivative7 a (Scheme 3). After treatment with sodium hydroxide and 0.025m HCl and Dowex 50 H⁺ the 8-epi-, 7-epi- and 7,8-bis-epi-N-acetylneuraminic acids2,3, and7 were obtained. These three compounds were tested withCMP-N-acetylneuraminic acid synthetase.

Herrn KollegenK. Schlögl mit den besten Wünschen zum 60. Geburtstag.     

Hydrothermal Syntheses and Crystal Structures of Compounds Based on <Emphasis Type="Italic">α</Emphasis>- or <Emphasis Type="Italic">β</Emphasis>-[Mo<Subscript>8</Subscript>O<Subscript>26</Subscript>]<Superscript>4−</Superscript> Isomers

Using Cu(II/I)/Ni(II) complex fragments and [Bu₄N]₄[α-Mo₈O₂₆] as precursors, four compounds based on α- or β- octamolybdate isomers, [{Cu(tpdoen)}₂][α-Mo₈O₂₆]·3H₂O 1 (tpdoen = 2-(pyridin-2-ylmethoxy)-N-(2-(pyridin-2-ylmethoxy)ethyl)-N-(pyridin-2-ylmethyl)ethanamine); [{Cu(dpoen)}₂(α-Mo₈O₂₆)] 2 (dpoen = 2-(pyridin-2-ylmethoxy)-N-(pyridin-2-ylmethyl)ethanamine); [{Cu(dpmea)}₂(β-Mo₈O₂₆)] 3 (dpmea = N,N-diethyl-N-(pyridin-2-ylmethyl)ethanaminium); [{Ni(tpoen)}₂(β-Mo₈O₂₆)]·5H₂O 4 (tpoen = 2-(pyridin-2-ylmethoxy)-N,N-bis(pyridin-2-ylmethyl)ethanamine) were hydrothermally synthesized. They have been characterized by elemental analysis, FT-IR, TG analysis and single-crystal X-ray diffraction. Compound 1 is a discrete structure constructed from [α-Mo₈O₂₆]⁴⁻ anions and [Cu(tpdoen)]²⁺ coordination cations. The coordination cations aggregate around an octamolybdate anion via hydrogen bonding interactions, forming a “flowerpot” supramolecular network. Compound 2 is constructed from [α-Mo₈O₂₆]⁴⁻ anions bridged through [Cu(dpoen)]²⁺ fragments into a 2D layered grid. Compounds 3 and 4 are Cu(I) and Cu(II) complexes bis-supported by [β-Mo₈O₂₆]⁴⁻ anions, respectively. The electrochemical behaviors of compounds 1–4 modified solid bulk-modified carbon paste electrodes (1-MCPE-4-MCPE) have been studied.     

Studies on two cadmium(II) and two zinc(II) complexes of 4′-chloro-2,2′ : 6′,2″-terpyridine with 1 : 1 or 1 : 2 ratio of metal and ligand

The reaction between 4′-chloro-2,2′ : 6′,2″-terpyridine (tpyCl) with d¹⁰ transition-metal ions produced two cadmium(II) and two zinc(II) metal complexes, formulated as [Cd(tpyCl-κ ³ N,N′,N″)(NO₃-κ ² O,O′)(NO₃-κO)(H₂O-κO)] (1), [Cd(tpyCl-κ ³ N,N′,N″)₂](ClO₄)₂ (2), [Zn(tpyCl-κ ³ N,N′,N″)₂](ClO₄)₂ (3), and [Zn(tpyCl-κ ³ N,N′,N″)₂](BF₄)₂ (4). Supramolecular interactions include coordinative bonding, O–H ··· O, O–H ··· Cl, C–H ··· F, and C–H ··· Cl hydrogen bonding and π–π stacking, all of which play essential roles in forming different frameworks of 1–4.     

Order of Reactivity of OH/NH Groups of Glucosamine Hydrochloride and N-Acetyl Glucosamine Toward Benzylation Using NaH/BnBr in DMF

The order of reactivity of OH and NH groups of glucosamine hydrochloride (GlcNH₂^.HCl) and N-acetyl glucosamine (GlcNAc) toward benzylation with NaH/BnBr in DMF was investigated. For GlcNH₂^.HCl, benzyl groups were introduced in the order of N-Bn > N-Bn₂ > 1-O-Bn > 6-O-Bn > 4-O-Bn > 3-O-Bn; for GlcNAc, benzyl groups were introduced in the order of 1-O-Bn > 6-O-Bn > 4-O-Bn > 3-O-Bn > N-Bn. A range of partially benzylated 2-N,N′-dibenzyl glucopyranosides and GlcNAc derivatives were obtained in a single step.     

Synthesis,characterization, thermogravimetry,and structural study of uranium complexes derived from dibasic S-alkylated thiosemicarbazone ligands

Two pentagonal bipyramidal complexes, ethanol-(S-ethyl-N¹,N⁴-bis(3-methoxy-2-hydroxybenzaldehyde)-isothiosemicarbazide-N,N′,O,O′)-dioxidouranium(VI) (1) and ethanol-(S-ethyl-N¹-(2-hydroxyacetophenone)-N⁴-(5-bromo-2-hydroxybenzaldehyde)-isothiosemicarbazide-N,N′,O,O′)-dioxidouranium(VI) (2), have been prepared and characterized. Their structures have been determined by X-ray crystallography, and the structural parameters are discussed with those observed in related complexes. Electronic absorption, proton magnetic resonance, and FT-IR spectra have been recorded and analyzed. In both complexes, the U(VI) centers are surrounded by N₂O₂ donor ligands, two oxido groups, and one ethanol in a distorted pentagonal bipyramid. The thermal stability of the new complexes has also been determined.     

SYNTHESIS AND CONFORMATIONAL INVESTIGATIONS OF SULFATED CARBOHYDRATES[1]

Starting from the finding that methyl 2,3,4,6-tetra-O-sulfonato-β-D-glucopyranoside (3) existed in a conformational equilibrium of the two chair conformers, the effect of sulfation on conformational equilibria was further investigated using a number of sulfated saccharides. Three sulfate groups on positions 3,4, and 6 or two on positions 2 and 3 were not sufficient to induce the conformational change as shown with methyl 2-amino-2-deoxy-3,4,6-tri-O-sulfonato-β-D-glucopyranoside. N-Sulfation of the amino group of the latter compound furnished an equilibrium of chair conformers with less ¹ C ₄ conformer content than for 3. The presence of persulfated methyl β-D-galactopyranoside in the usual ⁴ C ₁ conformation suggested the involvement of the 4-O-sulfate in the effect. Methyl 2,3,4-tri-O-sulfonato-β-D-xylopyranoside was found to prefer the “all-axial” ¹ C ₄ conformation demonstrating that O-sulfates facilitate 1,3-O/O-diaxial interactions better than ester groups and in particular benzoates. Also, sulfated 1,5-anhydro-D-glucitol occurred as a conformational mixture, the influence of the anomeric effect may thus have been overestimated in the previous discussion of this conformational effect.     

Template-directed syntheses of two 3D metal oxalates: in situ N-methylation and crystal structures

Two isomorphic organically templated zinc/cobalt oxalates, (dmdabco)[Zn₂(C₂O₄)₃]·4H₂O (1), and (dmdabco)[Co₂(C₂O₄)₃]·4H₂O (2) (C₂O₄^2? = oxalate; dmdabco = N,N′-dimethyl-1,4-diazabicyclo[2,2,2]octane), have been prepared under solvothermal conditions and characterized by X-ray structural analyses. The dmdabco²⁺ templating agent was derived from simple in situ N-alkylation between methanol and 1,4-diazabicyclo[2,2,2]octane (dabco). Distinct from conventional Eschweiler-Clarke methylation containing excess formic acid and formaldehyde, such one-step methylation from methanol molecules is convenient. Both 1 and 2 exhibit a uninodal 3-connected 3-D interrupted open-framework, in which oxalate ligands have in-plane and out-of-plane connection modes.     

Synthetic Studies on Sialoglycoconjugates 89: Synthesis of Ganglioside GM3 and KDN-GM3 Containing Different Carbon-Chain Length Fatty Acyl Groups at the Ceramide Residue

ABSTRACT

Ganglioside GM₃ and KDN-ganglioside GM₃, containing hexanoyl, decanoyl, and hexadecanoyl groups at the ceramide moiety have been synthesized. Selective reduction of the azido group in O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→3)-O-(2,4-di-O-acetyl-6-O-benzoyl-β-D-galactopyranosyl)-(1→4)-O-(3-O-acetyl-2,6-di-O-benzoyl-β-D-glucopyranosyl)-(1→1)-(2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (1) and O-(methyl 4,5,7,8,9-penta-O-acetyl-3-deoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→3)-O-(2,4-di-O-acetyl-6-O-benzoyl-β-D-galactopyranosyl)-(1→4)-O-(3-O-acetyl-2,6-di-O-benzoyl-β-D-glucopyranosyl)-(1→1)-(2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol (2), coupling with hexanoic, decanoic, and hexadecanoic acids, O-deacylation, and de-esterification gave the title gangliosides GM₃ (11→13) and KDN-GM₃ (14→16) in good yields. On the other hand, O-deacylation of 1 and subsequent de-esterification gave 2-azido-sphingosine containing-GM₃ analogue 17, which was converted into lyso-GM₃, in which no fatty acyl group was substituted at the sphingosine residue, by selective reduction of the azido group.     

Self-assembly of 1-D, 2-D,and 3-D transition-metal coordination polymers based on a T-shaped tripodal ligand 4-(4,5-dicarboxy-1H-imidazol-2-yl)pyridine 1-oxide

Three coordination polymers, {[Co(C₁₀H₅N₃O₅)(H₂O)₂]·H₂O}_n (1), {[Mn₃(C₁₀H₅N₃O₅)₂Cl₂(H₂O)₆]·2H₂O}_n (2), and {[Cu₃(C₁₀H₄N₃O₅)₂(H₂O)₃]·4H₂O}_n (3), based on a T-shaped tripodal ligand 4-(4,5-dicarboxy-1H-imidazol-2-yl)pyridine 1-oxide (H₃DCImPyO), were synthesized under hydrothermal conditions. The polymers showed diverse coordination modes, being characterized by elemental analysis, infrared spectroscopy, and single-crystal X-ray structure analysis. In 1, the HDCImPyO^2? generated a 1-D chain by adopting a μ₂-kN, O : kN′, O′ coordination mode to bridge two Co(II) ions in two bis-N,O-chelating modes. In 2, the HDCImPyO^2? adopted a μ₃-kN, O : kO′, O′′ : O′′′ coordination mode to bridge two crystallographically independent Mn(II) ions, forming a 2-D hcb network with {6³} topology. In 3, by adopting μ₄-kN, O : kO′, O′′ : kN′′, O′′′ : O′′′′ coordination, DCImPyO^3? bridged three crystallographically independent Cu(II) ions to form a 3-D framework having the stb topology.     

NMR and theoretical study on the linking properties of peroxovanadium(V) complexes with the 3-aminomethyl-pyridine derivatives

To understand the substitution effects of 3-aminomethyl-pyridine on the reaction equilibrium, the interactions between a series of 3-aminomethyl-pyridine derivatives and peroxovanadium(V) complex [OV(O₂)₂(D₂O)]^?/[OV(O₂)₂(HOD)]^? in solution were explored by the combined use of multinuclear (¹H, ¹³C, and ⁵¹V) magnetic resonance spectroscopy together with HSQC in 0.15 M NaCl ionic medium for mimicking the physiological conditions. Some direct NMR data are given for the first time. The relative reactivity among the 3-aminomethyl-pyridine derivative ligands are N-(pyridin-3-ylmethyl)acetamide (1) ≈ N-(pyridin-3-ylmethyl)propionamide (2) > N-(pyridin-3-ylmethyl)pivalamide (3) > t-butyl(pyridin-3-ylmethyl)carbamate (4). The competitive coordination results in the formation of a series of new six-coordinate peroxovanadium species [OV(O₂)₂L]^? (L = 1–4). The results of density functional calculations indicated that the solvation effects play an important role in these reactions, providing a reasonable explanation on the relative reactivity of the 3-aminomethyl-pyridine derivatives.     

Expeditious Synthesis of a Trisubstrate Analogue for α(1→3)Fucosyltransferase

Abstract

The synthesis of cyclohexyl 2-acetamido-2-deoxy-3-O-{2-O-[2-(guanosine 5′-O-phosphate)ethyl]-α-L-fucopyranosyl}-β-D-glucopyranoside (1), a potential inhibitor of α(1→3)fucosyltransferases, is described. Target compound 1 was assembled via fucosylation of cyclohexyl 2-acetamido-2-deoxy-4,6-O-isopropylidene-β-D-glucopyranoside (6) with ethyl 2-O-[2-(benzoylhydroxy)ethyl]-3,4-O-isopropylidene-1-thio-β-L-fucopyranoside (5) followed by debenzoylation, subsequent condensation of the resulting compound with 3′,4′ -di-O-benzoyl-5′ -O-(2-cyanoethyl-N,N-diisopropylphosphoramidite)-2-N-diphenylacetylguanosine (10) and deprotection.     

Synthesis,structural characterization,oxygen sensitivity,and antimicrobial activity of ruthenium(II) carbonyl complexes with thiosemicarbazones

[Ru(CO)(PPh₃)₂(η³-O,N³,S-TSC¹)] (1), [Ru(Cl)(CO)(PPh₃)₂(η²-N³,S-TSC²)] (2), and [Ru(Cl)(CO)(PPh₃)₂(η²-N³,S-TSC³)] (3) have been prepared by reacting [Ru(H)(Cl)(CO)(PPh₃)₃] with the respective thiosemicarbazones TSC¹ (2-hydroxy-3-methoxybenzaldehyde thiosemicarbazone), TSC² (3-hydroxybenzaldehyde thiosemicarbazone), and TSC³ (3,4-dihydroxybenzaldehyde thiosemicarbazone) in a 1?:?1 M ratio in toluene and all of the complexes have been characterized by UV–vis, FT-IR, and ¹H and ³¹P NMR spectroscopy. The spectroscopic studies showed that TSC¹ is coordinated to the central metal as a tridendate ligand coordinating via the azomethine nitrogen (C=N), phenolic oxygen, and sulfur to ruthenium in 1, whereas TSC² and TSC³ are coordinated to ruthenium as a bidentate ligand through azomethine nitrogen (C=N) and sulfur in 2 and 3. Oxygen sensitivities of 1–3 and [Ru(Cl)(CO)(PPh₃)₂(η²-N³,S-TSC⁴)] (4), and antimicrobial activities of 1–3 have been determined.     

SYNTHESIS OF SIALYL-α-(2→3)-NEOLACTOTETRAOSE DERIVATIVES MODIFIED AT C-2 OF THE N-ACETYLGLUCOSAMINE RESIDUE: PROBES FOR INVESTIGATION OF ACCEPTOR SPECIFICITY OF HUMAN α-1,3-FUCOSYLTRANSFERASES,FUC-TVII,AND FUC-TVI *

A variety of sialyl-α-(2→3)-neolactotetraose (IV³NeuAcnLcOse₄ or IV³NeuGcnLcOse₄) derivatives (23, 31–37, 58–60) modified at C-2 of the GlcNAc residue have been synthesized. The phthalimido group at C-2 of GlcNAc in 2-(trimethylsilyl)ethyl (3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-(2,4,6-tri-O-benzyl-β-d-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-d-glucopyranoside (5) was systematically converted to a series of acylamino groups, to give the per-O-benzylated trisaccharide acceptors (6–11). On the other hand, modification of the hydroxyl group at C-2 of the terminal Glc residue in 2-(trimethylsilyl)ethyl (4,6-O-benzylidene-β-d-glucopyranosyl)-(1→3)-(2,4,6-tri-O-benzyl-β-d-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-d-glucopyranoside (42) gave three different kinds of trisaccharide acceptors containing D-glucose (49), N-acetyl-d-mannosamine (50), and D-mannose (51) instead of the GlcNAc residue. Totally ten trisaccharide acceptors (5–11 and 49–51) were each coupled with sialyl-α-(2→3)-galactose donor 12 to afford the corresponding pentasaccharides (14–21 and 52–54) in good yields, respectively, which were then transformed into the target compounds. Acceptor specificity of the synthetic sialyl-α-(2→3)-neolactotetraose probes for the human α-(1→3)-fucosyltransferases, Fuc-TVII and Fuc-TVI, was examined.     

A new monoterpene glucoside and complete assignments of dihydroflavonols of Pulicaria jaubertii: potential cytotoxic and blood pressure lowering activity

One new monoterpene glucoside and five dihydroflavonols were isolated for the first time from the aerial parts of Pulicaria jaubertii and identified as p-menthane-2-O-β-D-glucopyranoside [1], dihydroquercetin (taxifolin) [2], 7,3′-di-O-methyltaxifolin [3], 3′-O-methyltaxifolin [4], 7-O-methyltaxifolin (padmatin) [5] and 7-O-methyl-dihydrokampferol (7-O-methylaromadenderin) [6]. The structures of these compounds were unambiguously assigned on the basis of NMR spectroscopic data (¹H, ¹³C, DEPT, HSQC, HMBC) and MS analysis. 2D-NMR methods required revision of assignments of H-6 and H-8 for dihydroflavonol compounds. Possible cytotoxic activity as well as blood pressure (BP) lowering activity were tested. The alcoholic extract showed cytotoxic activity against prostate carcinoma (PC-3), breast carcinoma (MCF-7) and hepatocellular carcinoma (HepG-2) human cell lines with IC₅₀ 19.1, 20.0 and 24.1 μg, respectively. The higher dose levels of the alcoholic extract significantly reduced normal BP of rats in a dose-dependent manner.     

Synthetic Studies on Sialoglycoconjugates 44: Synthesis of KDN-Gangliosides Gm4 and GM3

Abstract

Ganglioside GM₄ and GM₃ analogs, containing 3-deoxy-D-glycero-D-galacto-2-nonulopyranosonic acid (KDN) in place of N-acetylneuraminic acid, have been synthesized. KDN, prepared by the condensation of oxalacetic acid with D-mannose, was converted into methyl (phenyl 4,5,7,8,9-penta-O-acetyl-3-deoxy-2-thio-D-glycero-D-galacto-2-nonulopyranosid)onate (2) via methyl esterification, O-acetylation and replacement of the anomeric acetoxy group with phenyl thio. Glycosylation of 2 with 2-(trimethylsilyl)ethyl 6-O-benzoyl-β-D-galactopyranoside (3) or 2-(trimethylsilyl)ethyl O-(6-O-benzoyl-β-D-galactopyranosyl)-(1→4)-2,6-di-O-benzoyl-β-D-glucopyranoside (4) was performed, using N-iodosuccinimide-trimethylsilyl trifluoromethanesulfonate as the glycosyl promoter, to give 2-(trimethylsilyl)ethyl O-(methyl 4,5,7,8,9-penta-O-acetyl-3-deoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→3)-6-O-benzoyl-β-D-galacto-pyranoside (5) and 2-(trimethylsilyl)ethyl O-(methyl 4,5,7,8,9-penta-O-acetyl-3-deoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→3)-(6-O-benzoyl-β-D-galactopyrano-syl)-(l→4)-(2,6-di-O-benzoyl-β-D-glucopyranoside (9), respectively. Compounds 5 and 9 were converted via O-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group and subsequent imidate formation, into the corresponding trichloroacetimidates 8 and 12, respectively. Glycosylation of (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-l,3-diol (13) with 8 and 12 in the presence of boron trifluoride etherate afforded the expected β-glycosides 14 and 17, which were transformed via selective reduction of the azido group, coupling with octadecanoic acid, O-deacylation and de-esterification, into the target gangliosides 16 and 19 in high yields.     

Synthesis and structures of pyridoannelated 1,2,3,4-tetrazine 1,3-dioxides

Treatment of 2- and 4-amino-3-(tert-butyl-NNO-azoxy)pyridines with nitrating agents (N₂O₅or NO₂BF₄) afforded the first representatives of pyridoannelated 1,2,3,4-tetrazine di-N-oxides, viz., pyrido[2,3-e][1,2,3,4]tetrazine 1,3-dioxide (9), 7-nitropyrido[2,3-e][1,2,3,4]tetrazine 1,3-dioxide (10), and pyrido[3,4-e][1,2,3,4]tetrazine 2,4-dioxide (11). These compounds were studied by ¹H, ¹³C, and ¹⁴N NMR spectroscopy. The 1:1 complex of compound 10 with benzene was studied by X-ray diffraction analysis.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2471–2477, November, 2004.