Synthesis of D-xylopyranan by the ring-opening polymerization of 3-O-benzyl-alpha-D-xylopyranose 1,2,4-orthopivalate. Attempts to synthesize a stereoregular polymer.

3-O-Benzyl-alpha-D-xylopyranose 1,2,4-orthopivalate (1) was newly synthesized and polymerized under cationic polymerization reaction conditions in order to synthesize stereoregular (1-->4)-beta-D-xylopyranan. Although the polymerization of orthopivalate 1 was carried out under various reaction conditions, a non-stereoregular polymer, but mainly consisting of (1-->4)-beta-xylopyranose units, was obtained. Comparing these results with those of glucose 1,2,4-orthopivalates, it was revealed that not only the substituents in the C-2 and C-3 positions, but also the CH(2)OR group in glucose 1,2,4-orthopivalate, largely contribute to (1-->4)-beta-glucosidic bond formation by the ring-opening polymerization.     

A practical synthesis of beta-D-GlcA-(1-->3)-beta-D-Gal-(1-->3)-beta-D-Gal-(1-->4)-D-Xyl,a part of the common linkage region of a glycosaminoglycan

A practical synthesis of beta-D-GlcA-(1-->3)-beta-D-Gal-(1-->3)-beta-D-Gal-(1-->4)-beta-D-Xyl-(1-->OMe) was achieved by coupling of methyl 2,3,4-tri-O-acetyl-alpha-D-glucopyranosyluronate trichloroacetimidate with a trisaccharide acceptor. The trisaccharide acceptor was obtained by condensation of 3-O-allyl-2,4,6-tri-O-benzoyl-beta-D-galactopyranosyl-(1-->3)-2,4,6-tri-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate with methyl 2,3-di-O-benzoyl-beta-D-xylopyranoside, followed by deallylation. The beta-(1-->3)-linked disaccharide was prepared readily with p-methoxyphenyl 3-O-allyl-2,4,6-tri-O-benzoyl-beta-D-galactopyranoside as the key synthon. The alpha-(1-->3)-linkage was formed in considerable amount with galactose mono- and disaccharide trichloroacetimidate donors with C-2 neighboring group participation.     

Syntheses of arabinogalactans consisting of beta-(1-->6)-linked D-galactopyranosyl backbone and alpha-(1-->3)-linked L-arabinofuranosyl side chains

Two arabinogalactosyl nonasaccharides, beta-D-Galp-(1-->6)-[alpha-L-Araf-(1-->3)]-beta-D-Galp-(1-->6)-beta-D-Galp-(1-->6)-beta-D-Galp-(1-->6)-[alpha-L-Araf-(1-->5)-alpha-L-Araf-(1-->3)]-beta-D-Galp-(1-->6)-beta-D-Galp and beta-D-Galp-(1-->6)-[alpha-L-Araf-(1-->5)-alpha-L-Araf-(1-->3)]-beta-D-Galp-(1-->6)-beta-D-Galp-(1-->6)-beta-D-Galp-(1-->6)-[alpha-L-Araf-(1-->3)]-beta-D-Galp-(1-->6)-beta-D-Galp, were synthesized as their 4-methoxyphenyl glycosides with 2,3,4,6-tetra-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate (1), 6-O-acetyl-2,3,4-tri-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate (14), 4-methoxyphenyl 3-O-allyl-2,4-di-O-benzoyl-beta-D-galactopyranoside (2), 4-methoxyphenyl 2,3,4-tri-O-benzoyl-beta-D-galactopyranoside (5), 2,3,5-tri-O-benzoyl-alpha-L-arabinofuranosyl trichloroacetimidate (8), and 2,3,5-tri-O-benzoyl-alpha-L-arabinofuranosyl-(1-->5)-2,3-di-O-benzoyl-alpha-L-arabinofuranosyl trichloroacetimidate (11), as the key synthons. The tetra- (10) and pentasaccharide donor (13), and the tetra- (20) and pentasaccharide acceptor (22) were synthesized based on these synthons through simple transformations. Coupling of 22 with 10, and coupling of 20 with 13 and subsequent deacylation gave nonasaccharides 24 and 26, respectively, consisting of beta-(1-->6)-linked glactopyranosyl backbone and alpha-(1-->3)-linked arabinofuranosyl side chains of different size.     

A concise and practical synthesis of antigenic globotriose, alpha-D-Gal-(1-->4)-beta-D-Gal-(1-->4)-beta-D-Glc

A concise and practical synthesis of the antigenic globotriose, alpha-D-Gal-(1-->4)-beta-D-Gal-(1-->4)-beta-D-Glc (13), was achieved by coupling of a monosaccharide donor, 3-O-allyl-2-O-benzoyl-4,6-O-benzylidene-alpha-D-galactopyranosyl trichloroacetimidate (4) with a disaccharide acceptor, p-methoxyphenyl 2,3,6-tri-O-benzoyl-beta-D-galactopyranosyl-(1-->4)-2,3,6-tri-O-benzoyl-beta-D-glucopyranoside (8), followed by deprotection. In spite of the existence of a C-2-ester substituent capable of neighboring-group participation in the donor, the coupling gave exclusively the alpha-linkage in satisfactory yield. The acceptor 8 was readily obtained from selective 3-O-benzoylation of the galactosyl ring of p-methoxyphenyl 2,6-di-O-benzoyl-beta-D-galactopyranosyl-(1-->4)-2,3,6-tri-O-benzoyl-beta-D-glucopyranoside (7), which was prepared from p-methoxyphenyl beta-D-lactoside (5) via isopropylidenation, benzoylation, and deisopropylidenation. Donor 4 was obtained from p-methoxylphenyl 3-O-allyl-2,4,6-tri-O-benzoyl-beta-D-galactopyranoside (1) via selective 4,6-di-O-debenzoylation, oxidative removal of 1-O-MP, benzylidenation, and trichloroacetimidate formation.     

Studies on the stereoselective synthesis of a protected α-D-Gal-(1→2)-D-Glc fragment

A novel 1,2-cis stereoselective synthesis of protected α-D-Gal-(1→2)-D-Glc fragments was developed. Methyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-α-D-galactopyranosyl-(1→2)-3-O-benzoyl-4,6-O-benzylidene-α-D-glucopyranoside (13), methyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-α-D-galactopyranosyl-(1→2)-3,4,6-tri-O-benzoyl-α-D-glucopyranoside (15), methyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-α-D-galactopyranosyl-(1→2)-3-O-benzoyl-4,6-O-benzylidene-β-D-glucopyranoside (17), and methyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-α-D-galactopyranosyl-(1→2)-3,4,6-tri-O-benzoyl-β-D-glucopyranoside (19) were favorably obtained by coupling a new donor, isopropyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-1-thio-β-D-galactopyranoside (2), with acceptors, methyl 3-O-benzoyl-4,6-O-benzylidene-α-D-glucopyranoside (4), methyl 3,4,6-tri-O-benzoyl-α-D-glucopyranoside (5), methyl 3-O-benzoyl-4,6-O-benzylidene-β-D-glucopyranoside (8), and methyl 3,4,6-tri-O-benzoyl-β-D-glucopyranoside (12), respectively. By virtue of the concerted 1,2-cis α-directing action induced by the 3-O-allyl and 4,6-O-benzylidene groups in donor 2 with a C-2 acetyl group capable of neighboring-group participation, the couplings were achieved with a high degree of α selectivity. In particular, higher α/β stereoselective galactosylation (5.0:1.0) was noted in the case of the coupling of donor 2 with acceptor 12 having a β-CH(3) at C-1 and benzoyl groups at C-4 and C-6.     

Enzymatic glycosidation of sugar oxazolines having a carboxylate group catalyzed by chitinase

Enzymatic glycosidation using sugar oxazolines 1-3 having a carboxylate group as glycosyl donors and compounds 4-6 as glycosyl acceptors was performed by employing a chitinase from Bacillus sp. as catalyst. All the glycosidations proceeded with full control in stereochemistry at the anomeric carbon of the donor and regio-selectivity of the acceptor. The N,N'-diacetyl-6'-O-carboxymethylchitobiose oxazoline derivative 1 was effectively glycosidated, under catalysis by the enzyme, with methyl N,N'-diacetyl-beta-chitobioside (4), pent-4-enyl N-acetyl-beta-D-glucosaminide (5), and methyl N-acetyl-beta-D-glucosaminide (6), affording in good yields the corresponding oligosaccharide derivatives having 6-O-carboxymethyl group at the nonreducing GlcNAc residue. The N,N'-diacetyl-6-O-carboxymethylchitobiose oxazoline derivative 2 was subjected to catalysis by the enzyme catalysis; however, no glycosidated products were produced through the reactions with 4, 5, and 6. Glycosidation reactions of the beta-d-glucosyluronic-(1-->4)-N-acetyl-D-glucosamine oxazoline derivative 3 proceeded with each of the glycosyl acceptors, giving rise to the corresponding oligosaccharide derivative having a GlcA residue at their nonreducing termini in good yields.     

Synthesis of alpha-Manp-(1-->2)-alpha-Manp-(1-->3)-alpha-Manp-(1-->3)-Manp, the tetrasaccharide repeating unit of Escherichia coli O9a, and alpha-Manp-(1-->2)-alpha-Manp-(1-->2)-alpha-Manp-(1-->3)-alpha-Manp-(1-->3)-Manp, the pentasaccharide repeating unit of E. coli O9 and Klebsiella O3

The tetrasaccharide repeating unit of Escherichia coli O9a, alpha-D-Manp-(1-->2)-alpha-D-Manp-(1-->3)-alpha-D-Manp-(1-->3)-D-Manp, and the pentasaccharide repeating unit of E. coli O9 and Klebsiella O3, alpha-D-Manp-(1-->2)-alpha-D-Manp-(1-->2)-alpha-D-Manp-(1-->3)-alpha-D-Manp-(1-->3)-D-Manp, were synthesized as their methyl glycosides. Thus, selective 3-O-allylation of p-methoxyphenyl alpha-D-mannopyranoside via a dibutyltin intermediate gave p-methoxyphenyl 3-O-allyl-alpha-D-mannopyranoside (2) in good yield. Benzoylation (-->3), then removal of 1-O-methoxyphenyl (right arrow4), and subsequent trichloroacetimidation afforded the 3-O-allyl-2,4,6-tri-O-benzoyl-alpha-D-mannopyranosyl trichloroacetimidate (5). Condensation of 5 with methyl 4,6-O-benzylidene-alpha-D-mannopyranoside (6) selectively afforded the (1-->3)-linked disaccharide 7. Benzoylation of 7, debenzylidenation, benzoylation, and deallylation gave methyl 2,4,6-tri-O-benzoyl-alpha-D-mannopyranosyl-(1-->3)-2,4,6-tri-O-benzoyl-alpha-D-mannopyranoside (11) as the disaccharide acceptor. Coupling of 11 with (1-->2)-linked mannose disaccharide donor 17 or trisaccharide donor 21, followed by deacylation, furnished the target tetrasaccharide and pentasaccharide, respectively.     

Concise syntheses of arabinogalactans with beta-(1-->6)-linked galactopyranose backbones and alpha-(1-->3)- and alpha-(1-->2)-linked arabinofuranose side chains

4-methoxyphenyl glycosides of 2,3'-bis-alpha-L-arabinofuranosyl branched beta-D-(1-->6)-linked galactopyranosyl tetraose (16), 3',2'-bis-alpha-L-arabinofuranosyl branched beta-D-(1-->6)-linked galactopyranosyl hexaose (27), and a twentyose (42) consisting of beta-(1-->6)-linked D-galactopyranosyl pentadecaoligosaccharide backbone with alpha-L-arabinofuranosyl side chains alternately attached at C-2 and C-3 of the middle galactose residue of each consecutive beta-(1-->6)-linked galactotriose unit of the backbone, were synthesized with isopropyl 3-O-allyl-2,4-di-O-benzoyl-1-thio-beta-D-galactopyranoside (6), 2,3,4,6-tetra-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate (7), 2,3,5-tri-O-benzoyl-alpha-L-arabinofuranosyl trichloroacetimidate (12), 6-O-acetyl-2,3,4-tri-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate (17), 4-methoxyphenyl 2,3,4-tri-O-benzoyl-beta-D-galactopyranoside (19), and 2,6-di-O-acetyl-3,4-di-O-benzoyl-alpha-D-galactopyranosyl trichloroacetimidate (28) as the key synthons. Condensation of 6 with 7 gave the disaccharide donor 8, and subsequent condensation of 8 with 4-methoxyphenyl 2,3,4-tri-O-benzoyl-beta-D-galactopyranosyl-(1-->6)-2-O-acetyl-3,4-di-O-benzoyl-beta-D-galactopyranoside (9) followed by selective deacetylation afforded the tetrasaccharide acceptor 11. Coupling of 11 with 12 gave the pentasaccharide 13, its deallylation followed by coupling with 12, and debenzoylation gave the hexasaccharide 16 with beta-(1-->6)-linked galactopyranose backbone and 2- and 3'-linked alpha-L-arabinofuranose side chains. The octasaccharide 27 was similarly synthesized, while the twentyoside 42 was synthesized with tetrasaccharides 33 or 24 as the donors and 23, 36, 38, and 40 as the acceptors by consecutive couplings followed by deacylation.     

Defects in degradation of blood group A and B glycosphingolipids in Schindler and Fabry diseases

Skin fibroblast cultures from patients with inherited lysosomal enzymopathies, alpha-N-acetylgalactosaminidase (alpha-NAGA) and alpha-galactosidase A deficiencies (Schindler and Fabry disease, respectively), and from normal controls were used to study in situ degradation of blood group A and B glycosphingolipids. Glycosphingolipids A-6-2 (GalNAc (alpha 1-->3)[Fuc alpha 1-->2]Gal(beta1-->4)GlcNAc(beta 1-->3)Gal(beta 1--> 4)Glc (beta 1-->1')Cer, IV(2)-alpha-fucosyl-IV(3)-alpha-N-acetylgalactosaminylneolactotetraosylceramide), B-6-2 (Gal(alpha 1-->3)[Fuc alpha 1--> 2] Gal (beta 1-->4)GlcNAc(beta 1-->3)Gal(beta 1-->4)Glc(beta 1-->1')Cer, IV(2)- alpha-fucosyl-IV(3)-alpha-galactosylneolactotetraosylceramide), and globoside (GalNAc(beta 1-->3)Gal(alpha 1-->4)Gal(beta 1-->4)Glc(beta 1-->1') Cer, globotetraosylceramide) were tritium labeled in their ceramide moiety and used as natural substrates. The degradation rate of glycolipid A-6-2 was very low in fibroblasts of all the alpha-NAGA-deficient patients (less than 7% of controls), despite very heterogeneous clinical pictures, ruling out different residual enzyme activities as an explanation for the clinical heterogeneity. Strongly elevated urinary excretion of blood group A glycolipids was detected in one patient with blood group A, secretor status (five times higher than upper limit of controls), in support of the notion that blood group A-active glycolipids may contribute as storage compounds in blood group A patients. When glycolipid B-6-2 was fed to alpha-galactosidase A-deficient cells, the degradation rate was surprisingly high (50% of controls), while that of globotriaosylceramide was reduced to less than 15% of control average, presumably reflecting differences in the lysosomal enzymology of polar glycolipids versus less-polar ones. Relatively high-degree degradation of substrates with alpha-D-Galactosyl moieties hints at a possible contribution of other enzymes.     

Large-scale chemoenzymatic synthesis of blood group and tumor-associated poly-N-acetyllactosamine antigens

Poly-N-acetyllactosamines (pLNs) are common terminal sugars of many N- and O-linked glycan structures present in glycoproteins and glycolipids. Utilizing various glycosyltransferases, we developed new and efficient chemoenzymatic methods for the synthesis of pLNs in gram-scale. Specifically, the use of sialyltransferases and fucosyltransferases enabled us to synthesize and purify 24 blood group and tumor-associated pLN derivatives with alpha-(2-->3)- and alpha-(2-->6)-linked sialic acid, as well as with alpha-(1-->2)- and alpha-(1-->3)-linked fucose. All synthesized derivatives were linked to a short 2-azidoethyl spacer for further modification.     

Synthesis of lacto-N-neotetraose and lacto-N-tetraose using the dimethylmaleoyl group as amino protective group.

The disaccharide donor O-[2,3,4,6-tetra-O-acetyl-beta-D- galactopyranosyl)-(1-->4)-3,6-di-O-benzyl-2-deoxy-2-dimethylmaleimido - alpha,beta-D-glucopyranosyl] trichloroacetimidate (7) was prepared by reacting O-(2,3,4,6-tetra-O-acetyl- alpha-D-galactopyranosyl) trichloroacetimidate with tert-butyldimethylsilyl 3,6-di-O-benzyl-2-deoxy-2- dimethylmaleoylamido-glucopyranoside to give the corresponding disaccharide 5. Deprotection of the anomeric center and then reaction with trichloroacetonitrile afforded 7. Reaction of 7 with 3'-O-unprotected benzyl (2,4,6-tri-O-benzyl-beta-D-galactopyranosyl)- (1-->4)-2,3,6-tri-O-benzyl-beta-D-glucopyranoside (8) as acceptor afforded the desired tetrasaccharide benzyl (2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-(1-->4)-(3,6-di-O- benzyl-2-deoxy-2-dimethylmaleimido-beta-D-glucopyranosyl)-(1-->3)- (2,4,6- tri-O-benzyl-beta-D-galactopyranosyl)-(1-->4)-2,3,6-tri-O-benzyl-beta-D- glucopyranoside. Replacement of the N-dimethylmaleoyl group by the acetyl group, O-debenzylation and finally O-deacetylation gave lacto-N-neotetraose. Similarly, reaction of O-[(2,3,4,6-tetra-O-acetyl-beta- D-galactopyranosyl)-(1-->3)-4,6-O-benzylidene-2-deoxy-2-dimethylmalei mido- alpha,beta-D-glycopyranosyl] trichloroacetimidate as donor with 8 as acceptor afforded the desired tetrasaccharide benzyl (2,3,4,6-tetra-O-acetyl-beta-D- galactopyranosyl)-(1-->3)-(4,6-benzylidene-2-deoxy-2-dimethylmaleimid o- beta-D-glucopyranosyl)-(1-->3)-(2,4,6-tri-O-benzyl-beta-D-galactopyranos yl)- (1-->4)-2,3,6-tri-O-benzyl-beta-D-glucopyranoside. Removal of the benzylidene group, replacement of the N-dimethylmaleoyl group by the acetyl group and then O-acetylation afforded tetrasaccharide intermediate 15, which carries only O-benzyl and O-acetyl protective groups. O-Debenzylation and O-deacetylation gave lacto-N-tetraose (1). Additionally, known tertbutyldimethylsilyl (2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-(1-->3)-4,6-O-benzylide ne- 2-deoxy-2-dimethylmaleimido-beta-D-glucopyranoside was transformed into O-[2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)- (1-->3)-4,6-di-O-acetyl-2-deoxy-2-dimethylmaleimido-alpha,beta-D- glucopyranosyl] trichloroacetimidate as glycosyl donor, to afford with 8 as acceptor the corresponding tetrasaccharide 22, which is transformed into 15, thus giving an alternative approach to 1.     

Synthesis,docking simulation,biological evaluations and 3D-QSAR study of 5-Aryl-6-(4-methylsulfonyl)-3-(metylthio)-1,2,4-triazine as selective cyclooxygenase-2 inhibitors

A series of 5-Aryl-6-(4-methylsulfonyl)-3-(metylthio)-1,2,4-triazine derivatives were synthesized and their COX-1/COX-2 inhibitory activity as well as in vivo anti-inflammatory and analgesic effects were evaluated. All of compounds showed strong inhibition of COX-2 with IC₅₀ values in the range of 0.1–0.2 μM and in most cases had stronger anti-inflammatory and analgesic effects than indomethacin at doses 3 and 6 mg/kg. Among them, 5-(4-chlorophenyl)-6-(4-(methylsulfonyl) phenyl)-3-(methylthio)-1,2,4-triazine (9c) was the most potent and selective COX-2 compound; its selectivity index of 395 was comparable to celecoxib (SI = 405). Evaluation of anti-inflammatory and analgesic effects of 9c showed its higher potency than indomethacin and hence could be considered as a promising lead candidate for further drug development. Furthermore, the affinity data of these compounds were rationalized through enzyme docking simulation and 3D-QSAR study by k-Nearest Neighbour Molecular Field Analysis.     

Triterpenoid saponins with N-acetyl sugar from the bark of Albizia procera

Three (1,2,4) and one known (3) triterpenoid saponins were isolated from the bark of Albizia procera. The saponins were characterized as 3-O-[beta-D-xylopyranosyl-(1-->2)-alpha-L-arabinopyranosyl-(1-->6)-2-acetamido-2-deoxy-beta-D-glucopyranosyl] echinocystic acid (1), 3-O-[alpha-L-arabinopyranosyl-(1-->2)-beta-D-fucopyranosyl-(1-->6)-2-acetamido-2-deoxy-beta-D-glucopyranosyl] echinocystic acid (2) and 3-O-[beta-D-xylopyranosyl-(1-->2)-alpha-L-arabinopyranosyl-(1-->6)-2-acetamido-2-deoxy-beta-D-glucopyranosyl] acacic acid lactone (4). Their structures were elucidated by 1D and 2D NMR experiments, FABMS as well as chemical means. Saponins 1 and 3 exhibited cytotoxicity against HEPG2 cell line with IC50 9.13 microg/ml and 10 microg/ml, respectively.     

Protective effects of steroid saponins from Paris polyphylla var. yunnanensis on ethanol- or indomethacin-induced gastric mucosal lesions in rats: structural requirement for activity and mode of action

The methanolic extract from the rhizomes of Paris polyphylla SM. var. yunnanensis (FR.) H-M. was found to potently inhibit ethanol-induced gastric lesions in rats. Through bioassay-guided separation, four known spirostanol-type steroid saponins, pennogenin 3-O-alpha-L-rhamnopyranosyl(1-->2)-[alpha-L-arabinofuranosyl(1-->4)]-beta-D-glucopyranoside (1), pennogenin 3-O-alpha-L-rhamnopyranosyl(1-->4)-alpha-L-rhamnopyranosyl(1-->4)-[alpha-L-rhamnopyranosyl(1-->2)]-beta-D-glucopyranoside (2), diosgenin 3-O-alpha-L-rhamnopyranosyl(1-->2)-[alpha-L-arabinofuranosyl(1-->4)]-beta-D-glucopyranoside (3), and diosgenin 3-O-alpha-L-rhamnopyranosyl(1-->4)-alpha-L-rhamnopyranosyl(1-->4)-[alpha-L-rhamnopyranosyl(1-->2)]-beta-D-glucopyranoside (4), and a new furostanol-type steroid saponin, parisaponin I (5), together with two known furostanol-type steroid saponins, trigofoenoside A (6) and protogracillin (7), were isolated from the active fraction. Compounds 1-4 (1.25-10 mg/kg, po) strongly inhibited gastric lesions induced by ethanol and indomethacin. With regard to structural requirement of steroid saponins, the 3-O-glycoside moiety and spirostanol structure were found to be essential for the activity and the 17-hydroxyl group in the aglycon part enhanced the protective effects against ethanol-induced gastric lesions. The protective effects of 1 and 3 against ethanol-induced gastric lesions were attenuated by pretreatment with indomethacin and N-ethylmaleimide. Compounds 1 and 3 weakly inhibited acid secretions in pylorus-ligated rats. These findings suggested that endogenous prostaglandins and sulfhydryl compounds were involved in the protective activity.     

Synthesis of an alpha-linked dimer of the trisaccharide repeating unit of the exopolysaccharide produced by Pediococcus damnosus 2.6

A hexasaccharide, beta-D-Glcp-(1-->3)-[beta-D-Glcp-(1-->2)]-alpha-D-Glcp-(1-->3)-beta-D-Glcp-(1-->3)-[beta-D-Glcp-(1-->2)]-D-Glcp, the alpha-linked dimer of the trisaccharide repeating unit of the exopolysaccharide produced by Pediococcus damnosus 2.6, was synthesized as its methyl glycoside. Condensation of fully benzoylated alpha-D-glucopyranosyl trichloroacetimidate (1) with isopropyl 4,6-O-benzylidene-1-thio-beta-D-glucopyranoside (2) selectively furnished (1-->3)-linked disaccharide 3, and subsequent 2-O-acetylation, desulfation, and trichloroacetimidate formation afforded the disaccharide donor 6. Meanwhile, selective 3-O-coupling of methyl 4,6-O-benzylidene-alpha-d-glucopyranoside (8) with 3-O-allyl-2,4,6-tri-O-benzoyl-alpha-D-glucopyranosyl trichloroacetimidate (7), followed by coupling with 1 gave the trisaccharide 10. Removal of the benzylidene group of 10, benzoylation, and deallylation produced the trisaccharide acceptor 12. Condensation of 12 with 6 yielded a pentasaccharide mixture 13 with beta and alpha isomers in a ratio of 2:1. Removal of the benzylidene group of 13, followed by benzoylation gave the pentasaccharide mixture 14. Selective 2'-deacetylation of the isolated beta-linked 14beta with MeCOCl/MeOH/CH2Cl2 did not give the expected pentasaccharide acceptor, and serious decomposition occurred, indicating a large steric hindrance at C-2'. Alternatively, 2,3-di-O-glycosylation of allyl 4,6-O-benzylidene-beta-D-glucopyranoside (21) with 1 gave 22, then deallylation and trichloroacetimidate formation afforded the trisaccharide donor 24. Condensation of 12 with 24 furnished only the alpha-linked hexasaccharide 25, and its deprotection gave the free hexaoside 27.     

1,2,4-Triazino-[5,6b]indole derivatives: effects of the trifluoromethyl group on in vitro antimalarial activity

In an attempt to search for new and alternative antimalarial agents, a series of unsubstituted and 6-trifluoromethyl-1,2,4-triazino[5,6b]indole and 5H-1,2,4-triazolo[1',5',2,3]-1,2,4-triazino[5,6b]indole derivatives were synthesized and their chemical structures confirmed by 1H NMR and 13C NMR, elemental, IR and mass spectrophotometric analyses. The in vitro antimalarial activities of these compounds were evaluated against the chloroquine-sensitive (D10) and the chloroquine-resistant (RSA11) strains of Plasmodium falciparum. The 1,2,4-triazino[5,6b]indole derivatives (4, 6 and 8) with a trifluoromethyl group at position 6 exhibit increased in vitro activity when compared to the unsubstituted analogues, which are all devoid of activity. The presence of the trifluoromethyl group in the 5H-1,2,4-triazolo[1',5',2,3]-1,2,4-triazino[5,6b]indole ring system leads to compounds with diminished antimalarial activity when compared to the corresponding unsubstituted analogues. The compounds associate with ferriprotoporphyrin IX and interact with DNA to more or less the same extent.     

Synthesis of oligosaccharide derivatives related to those from sanqi, a Chinese herbal medicine from Panax notoginseng

Oligosaccharide derivatives from sanqi, a Chinese herbal medicine derived from Panax notoginseng, methyl beta-D-galactopyranosyl-(1-->3)-[alpha-L-arabinofuranosyl-(1-->6)]-alpha-D-galactopyranoside, diosgenyl beta-D-galactopyranosyl-(1-->3)-[alpha-L-arabinofuranosyl-(1-->6)]-alpha-D-galactopyranoside, and methyl beta-D-galactopyranosyl-(1-->3)-[alpha-L-arabinofuranosyl-(1-->6)]-alpha-D-galactopyranosyl-(1-->4)-beta-D-galactopyranosyl-(1-->3)-[alpha-L-arabinofuranosyl-(1-->6)]-alpha-D-galactopyranoside, were synthesized under standard glycosylation conditions. An unexpected alpha-(1-->4) linkage was formed predominantly in the presence of neighboring participation group during regioselective synthesis of hexasaccharide via 3+3 strategy.     

Synthesis of a spacer-containing repeating unit of the capsular polysaccharide of Streptococcus pneumoniae type 23F.

The synthesis is reported of 3-aminopropyl 4-O-(4-O-beta-D-glucopyranosyl-2-O-alpha-L-rhamnopyranosyl-beta-D- galactopyranosyl)-beta-L-rhamnopyranoside 3'-(glycer-2-yl sodium phosphate) (25 beta), which represents the repeating unit of the capsular polysaccharide of Streptococcus pneumoniae type 23F (American type 23) [(----4)-beta-D-Glcp-(1----4)-[Glycerol-(2-P----3)] [alpha-L- Rhap-(1----2)]-beta-D-Galp-(1----4)-beta-L-Rhap-(1----)n). 2,4,6-Tri-O-acetyl-3-O-allyl-alpha-D-galactopyranosyl trichloroacetimidate (5) was coupled with ethyl 2,3-di-O-benzyl-1-thio-alpha-L-rhamnopyranoside (6). Deacetylation of the resulting disaccharide derivative, followed by benzylidenation, and condensation with 2,3,4-trio-O-acetyl-alpha-L-rhamnopyranosyl trichloroacetimidate (10) afforded ethyl 4-O-[3-O-allyl-4,6-O-benzylidene-2-O-(2,3,4-trio-O-acetyl- alpha-L-rhamnopyranosyl)-beta-D-galactopyranosyl]-2,3-di-O-benzyl-1-thio - alpha-L-rhamnopyranoside (11). Deacetylation of 11, followed by benzylation, selective benzylidene ring-opening, and coupling with 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl trichloroacetimidate (15) gave ethyl 4-O-[3-O-allyl-6-O-benzyl-4-O-(2,3,4,6- tetra-O-acetyl-beta-D-glucopyranosyl)-2-O-(2,3,4-tri-O-benzyl-alpha-L- rhamnopyranosyl)-beta-D-galactopyranosyl]-2,3-di-O-benzyl-1-thio-alpha-L - rhamnopyranoside (16). Deacetylation of 16 followed by benzylation, deallylation, and acetylation yielded ethyl 4-O-[3-O-acetyl-6-O-benzyl-4-O-(2,3,4,6-tetra-O-benzyl-beta-D-glucopy ran osyl)- 2-O-(2,3,4-tri-O-benzyl-alpha-L-rhamnopyranosyl)-beta-D-galactopyranosyl ]-2,3- di-O-benzyl-1-thio-alpha-L-rhamnopyranoside (20). The glycosyl bromide derived from 20, when coupled with 3-benzyloxycarbonylamino-1-propanol, gave the beta-glycoside (21 beta) as the major product. Deacetylation of 21 beta followed by condensation with 1,3-di-O-benzylglycerol 2-(triethylammonium phosphonate) (27), oxidation, and deprotection, afforded 25 beta.     

Synthesis and structure elucidation of novel fused 1,2,4-triazine derivatives as potent inhibitors targeting CYP1A1 activity

Synthesis and structure elucidation of new series of novel fused 1,2,4-triazine derivatives 3a-3f, 4a-4i and 6a-6b and their inhibitory activities are presented. Molecular structures of the synthesized compounds were confirmed by (1)H NMR, (13)C NMR, MS spectra and elemental analyses. X-ray crystallographic analysis was performed on 2-acetyl-8-(N,N-diacetylamino)-6-(4-methoxybenzyl)-3-(4-methoxy-phenyl)-7-oxo-2,3-dihydro-7H-[1,2,4]triazolo[4,3-b][1,2,4]triazine 3d and 2-acetyl-8-(N-acetylamino)-6-benzyl-3-(4-chlorophenyl)-3-methyl-7-oxo-2,3-dihydro-7H-[1,2,4]triazolo[4,3-b][1,2,4]triazine 4e to secure their structures. The inhibitory effect of these compounds toward the CPY1A1 activity was screened to determine their potential as promising anticancer drugs. Our data showed that compounds 4e, 5a, 5b and 6b possess the highest inhibitory effects among all tested compounds. Furthermore, analysis of triazolotriazine derivatives docking showed that these compounds bind only at the interface of substrate recognition site 2 (SRS2) and (SRS6) at the outer surface of the protein. Amino-acids ASN214, SER216 and ILE462 participate in the binding of these compounds through H-bonds.     

Synthesis of 3-aminoimidazo[4,5-c]pyrazole nucleoside via the N-N bond formation strategy as a [5:5] fused analog of adenosine

3-Amino-6-(beta-D-ribofuranosyl)imidazo[4,5-c]pyrazole (2) was synthesized via an N-N bond formation strategy by a mononuclear heterocyclic rearrangement (MHR). A series of 5-amino-1-(5-O-tert-butyldimethylsilysilyl-2,3-O-isopropylidene-beta-D-ribofuranosyl)-4-(1,2,4-oxadiazol-3-yl)imidazoles (6a-d), with different substituents at the 5-position of the 1,2,4-oxadiazole, were synthesized from 5-amino-1-(beta-D-ribofuranosyl)imidazole-4-carboxamide (AICA Ribose, 3). It was found that 5-amino-1-(5-O-tert-butyldimethylsilyl-2,3-O-isopropylidene-beta-D-ribofuranosyl)-4-(5-methyl-1,2,4-oxadiazol-3-yl)imidazole (6a) underwent the MHR with sodium hydride in DMF or DMSO to afford the corresponding 3-acetamidoimidazo[4,5-c]pyrazole nucleoside(s) (7b and/or 7a) in good yields. A direct removal of the acetyl group from 3-acetamidoimidazo[4,5-c]pyrazoles under numerous conditions was unsuccessful. Subsequent protecting group manipulations afforded the desired 3-amino-6-(beta-D-ribofuranosyl)imidazo[4,5-c]pyrazole (2) as a 5:5 fused analog of adenosine (1).