Synthesis, protein-binding ability and phytoalexin-elicitor activity of epoxyalkyl (1→3)-β-D-oligoglucosides

We describe a approach for the synthesis of (1→3)-β-D-oligosaccharide derivatives 10–18. 1–9 were synthesized by treating peracetylated (1→3)-β-D-oligosaccharides with the corresponding alkenyl alcohols and Lewis acid (SnCl₄) catalyst. Epoxidation of the corresponding alkenyl oligoglucosides took place by m-CPBA. NaOMe in dry methanol was used for the deacetylation of the blocked derivatives, to give 10–18 in an overall yields of 25–32%. In subsequent glucan-binding protein of soybean assays, we found that 16 was most active, with an IC₅₀ value of 9 mM. However, the activities of 17, 18, 13, 14, 15, 10, 11, and 12 were gradually decreased. At the same time, we found 16 was most active as compared to the other (1→3)-β-D- oligoglucoside derivatives in eliciting phytoalexin accumulation in soybean cotyledon tissue, and 16 was kept longer time than (1→3)-β-D-glucohexaose, which indicated 16 is much more stable than (1→3)-β-D-glucohexaose. Published in 2004.     

Hexadecanoid pathway in plants: Lipoxygenase dioxygenation of (7<Emphasis Type="Italic">Z</Emphasis>,10<Emphasis Type="Italic">Z</Emphasis>,13<Emphasis Type="Italic">Z</Emphasis>)-hexadecatrienoic acid

7,10,13-Hexadecatrienoic acid (16:3) is abundant in many plant species. However, its metabolism through the lipoxygenase pathway is not sufficiently understood. The goal of present work was to investigate the oxygenation of 16:3 by different plant lipoxygenases and to study the occurrence of oxygenated derivatives of 16:3 in plant seedlings. The recombinant maize 9-lipoxygenase specifically converted 16:3 into (7S)-hydroperoxide. Identification of this novel oxylipin was substantiated by data of GC-MS, LC-MS/MS, ¹H-NMR, and 2D-COSY as well as by deuterium labeling from [²H₆]16:3. Soybean lipoxygenase 1 produced 91% (11S)-hydroperoxide and 6% racemic 14-hydroperoxide. Recombinant soybean lipoxygenase 2 (specifically oxidizing linoleate into 13-hydroperoxide) lacked any specificity towards 16:3. Lipoxygenase 2 produced 7-, 8-, 10-, 11-, 13-, and 14-hydroperoxides of 16:3, as well as a significant amount of bis-allylic 9-hydroperoxide. Seedlings of several examined plant species possessed free hydroxy derivatives of 16:3 (HHTs), as well as their ethyl esters. Interestingly, HHTs occur not only in “16:3 plants”, but also in typical “18:3 plants” like pea and soybean seedlings.     

Thio-sugars VII. Effect of 3-deoxy-4-S-(beta-D-gluco- and beta-D-galactopyranosyl)-4-thiodisaccharides and their sulfoxides and sulfones on the viability and growth of selected murine and human tumor cell lines

The first conversion of (1-->4)-thiodisaccharides into corresponding sulfoxides and sulfones by conventional oxidation with m-chloroperoxybenzoic acid (MCPBA) is reported. The effects of alpha-(1-->4)-3'-deoxythiodisaccharides (8-9) and their sulfoxide (14-15) and sulfone (16-17) derivatives on murine leukemia and human colon and pancreatic carcinoma cell viability were studied. Concentrations of thio-sugars that decreased tumor cell line viability by 50% (IC(50)), measured via the MTT assay, ranged from 6.4 to 38.3 microg/mL. The effect of alpha-(1-->4)-3'-deoxythiodisaccharide derivatives were most profound on human pancreatic epithelial carcinoma (PANC-1) cells with compounds 8 and 9 having IC(50) values of 6.4 microg/mL and 8.2 microg/mL, respectively. Sulfone derivatives 16 and 17 also had pronounced effects on PANC-1 cell viability (IC(50)=10.2 microg/mL and 9.6 microg/mL, respectively). These results indicate that deoxythio-disaccharide analogs generated by functionalization of the universal chiral precursor levoglucosenone may have cytotoxic properties and therapeutic potential as anticancer agents.     

Design and synthesis of 1H-1,2,3-triazoles derived from econazole as antitubercular agents

Econazole has been known to be active against Mycobacterium tuberculosis. We have designed and synthesized 1H-1,2,3-triazoles derived from econazole as antitubercular agents. The majority of triazole derivatives have been prepared by microwave-assisted click chemistry. It turned out that all of the prepared triazoles had no antifungal activities. However, most of the hydroxy-triazoles (6a and 10) apparently turned out to have antitubercular activities. Overall, hydroxy-triazoles 10 were more active than their corresponding ether-triazoles 11. While the MIC value of hydroxy-triazole 10d was as good as econazole (16 μg/mL), the MIC value of 10a was two-fold more active than econazole, suggesting that this 1H-1,2,3-triazole scaffold (3) could be further optimized to develop Mtb specific agents.     

Facile synthesis of the heptasaccharide repeating unit of O-deacetylated GXM of C. neoformans serotype B

A heptasaccharide, beta-D-Xylp-(1-->2)-alpha-D-Manp-(1-->3)-[beta-D-Xylp-(1-->2)]-alpha-D-Manp-(1-->3)-[beta-D-GlcpA-(1-->2)][beta-D-Xylp-(1-->4)]-alpha-D-Manp, the repeating unit of the exopolysaccharide from Cryptococcus neoformans serovar B, was synthesized as its methyl glycoside. Thus 2,3,4-tri-O-benzoyl-beta-D-xylopyranosyl-(1-->2)-3,4,6-tri-O-benzoyl-alpha-d-mannopyranosyl trichloroacetimidate (7) and allyl 2,3,4-tri-O-benzoyl-beta-D-xylopyranosyl-(1-->2)-4,6-di-O-benzoyl-alpha-D-mannopyranoside (8), readily obtained from the corresponding monosaccharide derivatives via simple transformation, were coupled to give a (1-->3)-linked tetrasaccharide 9. Deallylation of 9 followed by trichloroacetimidate formation produced the tetrasaccharide donor 11. Condensation of methyl 2,3,4-tri-O-benzoyl-beta-d-xylopyranosyl-(1-->4)-2-O-acetyl-6-O-benzoyl-alpha-D-mannopyranoside (18) with 11 followed by selective deacetylation yielded hexasaccharide acceptor 20. Coupling of 20 with methyl 2,3,4-tri-O-acetyl-alpha-D-glucopyranosyluronate bromide (21) and subsequent deprotection furnished the target heptaoside. A hexasaccharide fragment, alpha-D-Manp-(1-->3)-[beta-D-Xylp-(1-->2)]-alpha-D-Manp-(1-->3)-[beta-D-GlcpA-(1-->2)][beta-D-Xylp-(1-->4)]-alpha-D-Manp, was also similarly synthesized as its methyl glycoside.     

Synthesis of new glycyrrhetinic acid (GA) derivatives and their effects on tyrosinase activity

To synthesize glycyrrhetinic acid (GA) derivatives (3, 4, 5, 10, 13, 14, 15, and 16), we first removed the ketonic group in the C-11 position, and the carboxylic function at the C-30 position was kept intact, reduced to an alcohol, or transformed to an aldehyde corresponding derivatives 10 and 13. Glycyrrhetinic acid (GA) derivatives (3, 4, 5, 15, and 16) were coupled with 4-amino piperpyridine derivatives (12 and 14) and 4-fluorobenzyl bromide at C-30 carboxylic acid position of glycyrrhetinic acid. In subsequent tyrosinase assays, we found that GA derivatives 4, 5, and 16 were not active at early time points, but strongly inhibited tyrosinase activity at late time points. Of the GA derivatives examined, derivative 5 was most active, with an IC₅₀ value of 50 μM after 2 h reaction. IC₅₀ values of derivatives 4 and 16 were 120 and 170 μM, respectively. Further kinetic data indicated that these derivatives are slow-binding inhibitors of tyrosinase. The time-dependent inhibition was reversed when vitamin C or kojic acid was used, that is, both compounds showed active inhibition at early time points. These results suggest that GA derivatives are much more stable than vitamin C or kojic acid, although their intrinsic inhibitory potentials are relatively low. Higher stability and activity suggest that GA derivative 5 might be a useful candidate for skin whitening.     

The hydrolysis of the alkenyl group from enthanolamine-plasmalogen by oligodendroglial cell-enriched fractions

The rate of hydrolysis of the 1-0-alkenyl group of sn-1-alk-1′-enyl-2-acyl-glycerylphosphorylethanolamine (alkenyl, acyl-GPE; ethanolamine plasmalogen) by plasmalogenase is higher in oligodendroglial cell-enriched fractions from bovine brain compared with fractions enriched in neuronal perikarya and astroglia. The distribution of plasmalogenase activity in membrane fractions isolated from bovine oligodendroglia has been compared with that of ‘marker’ enzymes. The highest specific activity was in a fraction enriched in plasma membranes, whilst most activity was recovered in an endoplasmic reticulum membrane fraction. In bovine oligodendroglial cell homogenates, the enzyme had a neutral pH optimum, had no requirement for divalent cations and its activity towards 1-alkenyl-GPE (lysoplasmalogen) was half that with alkenyl, acyl-GPE. C₁₆ alkenyl groups were hydrolysed more rapidly than C₁₈ alkenyl groups. With ³H-labelled alkenyl, acyl-GPE as substrate, radioactivity in released aldehydes appeared in fatty acids esterified in phospholipid while the oxidation of fatty aldehydes was blocked by the addition of NADH. An NAD-dependent aldehyde dehydrogenase was found to be present in oligodendroglia which exhibited highest activity towards C₁₄C₁₈ aldehydes (K_m, 2 μM).     

Synthesis of novel 13α-18-nor-16-carboxamido steroids via a palladium-catalyzed aminocarbonylation reaction

13α-18-nor-16-Carboxamido steroids were synthesized via a palladium-catalyzed aminocarbonylation reaction of the corresponding iodoalkenes. The starting material was an unnatural 13α-16-keto steroid, obtained by a Wagner–Meerwein rearrangement of a 16α,17α-epoxide in the presence of [BMIM][BF₄]. The 13α-16-keto steroid was converted to a mixture of 16-iodo-16-ene and 16-iodo-15-ene derivatives in two steps by Barton’s methodology. Aminocarbonylation of the steroidal alkenyl iodides was carried out using different primary and secondary amines as nucleophiles. The products, 16-carboxamido-16-ene and 16-carboxamido-15-ene derivatives, were obtained in good yields and were characterized by ¹H and ¹³C NMR, IR and MS.The reduction of the above two unsaturated carboxamides resulted in the same product, 17α-methyl-16α-carboxamido-androstane.     

N-[(Dihydroxyphenyl)acyl]serotonins as potent inhibitors of tyrosinase from mouse and human melanoma cells

A series of N-acyl derivatives of tyramine, tryptamine, and serotonin were synthesized and tested on anti-melanogenic activity. The serotonin derivatives such as N-caffeoylserotonin (3) and N-protocatechuoylserotonin (9) were inhibitory to tyrosinase from mouse B16 and human HMV-II melanoma cells, while the corresponding derivatives of tryptamine and 5-methoxytryptamine were almost inactive or less active than the serotonin derivatives. The inhibitory activity of the serotonin derivatives increased with increasing number of phenolic hydroxyl groups in the acyl moiety. Melanin formation in the culture of B16 cells was suppressed by 3 and 9 with no cytotoxicity in the concentration range tested (IC₅₀ = 15, 3 and 111 μM for 3, 9, and kojic acid, respectively). Thus the N-acylserotonin derivatives having a dihydroxyphenyl group are potential anti-melanogenic agents. Their inhibition of tyrosinase is primarily performed through the 5-hydroxyindole moiety and further strengthened by the phenolic hydroxyl groups in the acyl moiety.     

Synthesis, SAR, and preliminary mechanistic evaluation of novel antiproliferative N⁶,5'-bis-ureido- and 5'-carbamoyl-N⁶-ureidoadenosine derivatives

We have developed efficient methods for the preparation of N(6),5'-bis-ureidoadenosine derivatives and their 5'-carbamoyl-N(6)-ureido congeners. Treatment of 5'-azido-5'-deoxy-N(6)-(N-alkyl or -arylurea)adenosine derivatives (6a-d) with H(2)/Pd-C or Ph(3)P/H(2)O, followed by N-methyl-p-nitrophenylcarbamate gave N(6),5'-bis-ureido products 7a-d in 49-78% yield. Analogous derivatives in the 5'-carbamoyl-N(6)-ureido series were prepared by treatment of 2',3'-bis-O-TBS-adenosine (11) with N-methyl-p-nitrophenylcarbamate followed by acylation with appropriate isocyanates which gave 13a-d in 45-69% yield. A more versatile route for obtaining potentially vast libraries of compounds from both series was achieved by treatment of 5'-N-methylureido- or 5'-N-methylcarbamoyladenosine derivatives with ethylchlorformate to give N(6)-ethoxycarbonyl derivatives (9 and 14) in 55-63% yields, respectively. Simple heating of 9 or 14 in the presence of primary alkyl- or arylamines gave the corresponding N(6),5'-bis-ureido- or 5'-carbamoyl-N(6)-ureidoadenosine derivatives in good yields (33-72% and 39-83%; 10a-e and 15a-e, respectively). Significant antiproliferative activities (IC(50)≈4-10 μg/mL) were observed for a majority of the N(6),5'-bis-ureido derivatives, whereas the 5'-carbamoyl-N(6)-ureido derivatives were generally less active (IC(50) >100 μg/mL). A 2',3'-O-desilylated derivative (5'-amino-5'-deoxy-5'-N-methylureido-N(6)-(N-phenylcarbamoyl)adenosine, 16) was shown to inhibit binding of 16 of 441 protein kinases to immobilized ATP-binding site ligands by 30-40% in a competitive binding assay at 10 μM. Compound 16 was also shown to bind to bone morphogenetic protein receptor 1b (BMPR1b) with a Kd=11.5 ± 0.7 μM.     

Synthesis and antiviral activities of 1'-carbon-substituted 4'-thiothymidines

4-Thiofuranoid glycals substituted at the 1-position with methyl (5), (t-butyldimethylsilyloxy)methyl (7), and acetoxymethyl (8) groups were prepared from the 3,5-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl) (TIPDS)-4-thiofuranoid glycal (3) by way of LDA-lithiation. N-Iodosuccimide-initiated electrophilic glycosidation between silylated thymine and these 1-carbon-substituted 4-thioglycals gave the respective beta-anomers (9, 10, and 13) stereoselectively. Tin radical-mediated removal of the 2'-iodine atom from these products provided the corresponding 1'-branched 4'-thiothymidine derivatives (11, 12, and 14) in good yields. The 1'-hydroxymethyl derivative (15) served as a precursor for the preparation of the formyl (16), cyanoethenyl (17), and cyano (19) derivatives. Among the deprotected 1'-branched 4'-thiothymidines (20-25), the 1'-methyl analogue 20 showed the most potent anti-HSV-1 activity, but it was much less active than the parent compound 4'-thiothymidine.     

Synthesis and biological evaluation of novel propargyl amines as potential fluorine-18 labeled radioligands for detection of MAO-B activity

The aim of this project was to synthesize and evaluate three novel fluorine-18 labeled derivatives of propargyl amine as potential PET radioligands to visualize monoamine oxidase B (MAO-B) activity.The three fluorinated derivatives of propargyl amine ((S)-1-fluoro-N,4-dimethyl-N-(prop-2-ynyl)-pent-4-en-2-amine (5), (S)-N-(1-fluoro-3-(furan-2-yl)propan-2-yl)-N-methylprop-2-yn-1-amine (10) and (S)-1-fluoro-N,4-dimethyl-N-(prop-2-ynyl)pentan-2-amine (15)) were synthesized in multi-step organic syntheses. IC₅₀ values for inhibition were determined for compounds 5, 10 and 15 in order to determine their specificity for binding to MAO-B. Compound 5 inhibited MAO-B with an IC₅₀ of 664 ± 48.08 nM. No further investigation was carried out with this compound. Compound 10 inhibited MAO-B with an IC₅₀ of 208.5 ± 13.44 nM and compound 15 featured an IC₅₀ of 131.5 ± 0.71 nM for its MAO-B inhibitory activity. None of the compounds inhibited MAO-A activity (IC₅₀ > 2 μM).The fluorine-18 labeled analogues of the two higher binding affinity compounds (10 and 15) (S)-N-(1-[¹⁸F]fluoro-3-(furan-2-yl)propan-2-yl)-N-methylprop-2-yn-1-amine (16) and (S)-1-[¹⁸F]fluoro-N,4-dimethyl-N-(prop-2-ynyl)pentan-2-amine (18) were both prepared from the corresponding precursors 9A, 9B and 14A, 14B by a one-step fluorine-18 nucleophilic substitution reaction. Autoradiography experiments on human postmortem brain tissue sections were performed with 16 and 18. Only compound 18 demonstrated a high selectivity for MAO-B over MAO-A and was, therefore, chosen for further examination by PET in a cynomolgus monkey.The initial uptake of 18 in the monkey brain was 250% SUV at 4 min post injection. The highest uptake of radioactivity was observed in the striatum and thalamus, regions with high MAO-B activity, whereas lower levels of radioactivity were detected in the cortex and cerebellum. The percentage of unchanged radioligand 18 was 30% in plasma at 90 min post injection.In conclusion, compound 18 is a selective inhibitor of MAO-B in vitro and demonstrated a MAO-B specific binding pattern in vivo by PET in monkey. It can, therefore, be considered as a candidate for further investigation in human by PET.     

3-Thiomorpholin-8-oxo-8H-acenaphtho [1,2-b] pyrrole-9-carbonitrile (S1) derivatives as pan-Bcl-2-inhibitors of Bcl-2, Bcl-xL and Mcl-1

Based on the binding mode of our previously discovered dual inhibitor of Bcl-2 and Mcl-1, 3-thiomorpholin-8-oxo-8H-acenaphtho[1,2-b]pyrrole-9-carbonitrile (3, S1), a library of 9-substituted 3 derivatives was synthesized to further probe the p4 pocket of the two targets. By NMR, structure–activity relationship study, and site-directed mutation, compound 6d (3-(4-aminophenylthio)-8-oxo-8H-acenaphtho[1,2-b]pyrrole-9-3-phenyl)propylamine) was identified to span p2–p4 pockets of Mcl-1, Bcl-2 and Bcl-x_L, and then exhibited 9- to 35-fold better affinity to the three targets than 3 (IC₅₀ = 10, 20 and 18 nM, respectively), which led to greater activity in induction of apoptosis in multiple cancer cell lines. Different contribution of p4 pocket to binding Bcl-2 and Mcl-1 was also investigated by plotting the potency and the HAC of the derivatives.     

Solution properties of antitumor sulfated derivative of alpha-(1-->3)-D-glucan from Ganoderma lucidum

Four fractions of a water-insoluble alpha-(1-->3)-D-glucan GL extracted from fruiting bodies of Ganoderma lucidum were dissolved in 0.25 M LiCl/DMSO, and then reacted with sulfur trioxide-pyridine complex at 80 degrees C to synthesize a series of water-soluble sulfated derivatives S-GL. The degree of substitution of DS was measured by using IR infrared spectra, elemental analysis, and 13C NMR to be 1.2-1.6 in the non-selective sulfation. Weight-average molecular weight Mw and intrinsic viscosity [eta] of the sulfated derivatives S-GL were measured by multi-angle laser light scattering and viscometry. The Mw value (2.4 x 10(4)) of sulfated glucan S-GL-1 was much lower than that (44.5 x 10(4)) of original alpha-(1-->3)-D-glucan GL-1. The Mark-Houwink equation and average value of characteristic ratio C(infinity) for the S-GL in 0.2 M NaCl aqueous solution at 25 degrees C were found to be: [eta] = 1.32 x 10(-3) Mw(1.06) (cm3 g(-1)) and 16, respectively, in the Mw range from 1.1 x 10(4) to 2.4 x 10(4). It indicated that the sulfated derivatives of the alpha-(1-->3)-D-glucan in the aqueous solution behave as an expanded chain, owing to intramolecular hydrogen bonding or interaction between charge groups. Interestingly, two sulfated derivatives synthesized from the alpha-(1-->3)-D-glucan and curdlan, a beta-(1-->3)-D-glucan, all had significant higher antitumor activity against Ehrlich ascites carcinoma (EAC) than the originals. The effect of expanded chains of the sulfated glucan in the aqueous solution on the improvement of the antitumor activity could not be negligible.     

Characterization of lyso-galactolipids, C-2 and C-3 O-acyl trigalactosylglycerol isomers, obtained from the lichenized fungus Dictyonema glabratum

A mixture of two lyso isomers of a galactolipid was obtained from Dictyonema glabratum. Aqueous hydrolysis gave rise to galactose and glycerol in a 3:1 molar ratio. ESI-MS spectroscopy gave, in the positive-ion mode, a pseudomolecular ion at m/z 839 and daughter ions with m/z 677, 600, 515 and 353, suggesting three galactosyl units linked to a glycerol moiety, substituted by one O-acyl group. 1D and 2D NMR experiments were used to characterize the glycolipid, and HMQC examination showed three anomeric signals, corresponding to two alpha-Galp and one beta-Galp residue liked to glycerol. The glycolipid structure was shown to be O-alpha-D-Galp-(1-->6)-O-alpha-D-Galp-(1-->6)-O-beta-D-Galp-(1<-->1)-2- and -3-monoacyl-D-glycerol, the latter structures not having been previously found in nature. The fatty acid composition was determined by GC-MS of derived methyl esters: that of palmitic acid C(16:0) was the most abundant, although the presence of C(12:0), C(14:0), C(16:1) and C(18:0) esters was observed.     

Effect of fat type and lysophosphatidylcholine addition to broiler diets on performance,apparent digestibility of fatty acids,and apparent metabolizable energy content

A completely randomized design study with a 3 × 2 factorial arrangement was conducted to evaluate the effects of three different fat sources (soybean oil, tallow, and poultry fat) with or without emulsifier supplementation on performance, coefficient of total tract apparent digestibility (CTTAD) of fatty acids, and apparent metabolizable energy (AME) content in broiler chickens. Two hundred and fifty-two one-day-old male Arbor Acres broiler chickens were randomly divided into 6 different treatments: (T1) basal diet containing soybean oil without lysophosphatidylcholine (LPC) supplementation, (T2) basal diet containing soybean oil with LPC supplementation, (T3) basal diet containing tallow without LPC supplementation, (T4) basal diet containing tallow with LPC supplementation, (T5) basal diet containing poultry fat without LPC supplementation, and (T6) basal diet containing poultry fat with LPC supplementation. Body weight gains from broiler chicks fed diets containing tallow were lower (P<0.05) than the body weight gains from chicks that were fed diets containing soybean oil or poultry fat in both the starter and grower periods. Birds fed diets containing tallow had the highest FCR (P<0.05), followed by the birds that were fed diets containing poultry fat, and soybean oil. The CTTAD of C16:0, C18:2, and C18:3n3 was greater (P<0.05) for broilers fed diets containing soybean oil than for those fed diets containing tallow or poultry fat in the starter period. The addition of LPC increased (P<0.05) body weight gain of broiler chickens in the starter period and the AME of the diets in the grower period, and tended to reduce FCR (P=0.072) in the starter period. LPC supplementation increased (P<0.05) the CTTAD of C16:0, C18:1n7 and C18:1n9 in the starter period, and of C18:2, and C18:3n3 in the grower period (P<0.05). There were no significant interactions between fat sources and the addition of LPC. These data indicated that LPC supplementation can improve body weight gain of broiler chickens in the starter period. This effect may be associated with an increase of CTTAD of FA due to LPC activity.     

Further probing of the substrate specificities and inhibition of enzymes involved at an early stage of glycosylphosphatidylinositol (GPI) biosynthesis

1-D-6-O-(2-amino-2-deoxy-alpha-D-glucopyranosyl)-1-O-hexadecyl-myo-inositol (14), 1-D-6-O-(2-amino-2-deoxy-alpha-D-glucopyranosyl)-myo-inositol 1-(octadecyl phosphate) (18), 1-D-6-O-(2-amino-2-deoxy-beta-D-glucopyranosyl)-myo-inositol 1-(1,2-di-O-hexadecanoyl-sn-glycerol 3-phosphate) (24), 1-D-6-O-(2-amino-2-deoxy-alpha-D-mannopyranosyl)-myo-inositol 1-(1,2-di-O-hexadecanoyl-sn-glycerol 3-phosphate) (30) and the corresponding 2-amino-2-deoxy-alpha-D-galactopyranosyl analogue 36 have been prepared and tested in cell-free assays as substrate analogues/inhibitors of alpha-(1 --> 4)-D-mannosyltransferases that are active early on in the glycosylphosphatidylinositol (GPI) biosynthetic pathways of Trypanosoma brucei and HeLa (human) cells. The corresponding N-acetyl derivatives of these compounds were similarly tested as candidate substrate analogues/inhibitors of the N-deacetylases present in both systems. Following on from an early study, 1-L-6-O-(2-amino-2-deoxy-alpha-D-glucopyranosyl)-2-O-methyl-myo-inositol 1-(1,2-di-O-hexadecanoyl-sn-glycerol 3-phosphate) (44) was prepared and tested as an inhibitor of the trypanosomal alpha-(1 --> 4)-D-mannosyltransferase. A brief summary of the biological evaluation of the various analogues is provided.     

Synthesis of glycosides of 3-deoxy-4-thiopentopyranosid-2-uloses and their reduction products: 3-deoxy-4-thiopentopyranosides

Michael addition of common thiols to the enone system of (2S)-2-benzyloxy-2H-pyran-3(6H)-one (1) afforded the corresponding 3-deoxy-4-thiopentopyranosid-2-ulose derivatives (2-4). The reaction was highly diastereoselective, and the addition was governed by the quasiaxially disposed 2-benzyloxy substituent of the starting pyranone. As expected from the enantiomeric excess of 1 (ee > 86%) the corresponding thiouloses 2-4 exhibited the same optical purity. However, the enantiomerically pure thioulose 5 was obtained by reaction of 1 with the chiral thiol, N-(tert-butoxycarbonyl)-L-cysteine methyl ester. The thio derivative 7 was also synthesized by reaction of 6 (enantiomer of 1) with the same chiral thiol. Alternatively, 4-thiopent-2-uloses 9-12 were prepared in high optical purity by 1,4-addition of thiols to (2S)-[(S)-2'-octyloxy]dihydropyranone 8. Similarly, reaction of 13 (enantiomer of 8) with benzenemethanethiol afforded 14 (enantiomer of 10). This way, the stereocontrol exerted by the anomeric center on the starting dihydropyranone led to 4-thiopentuloses of the D and L series. Sodium borohydride reduction of the carbonyl function of uloses 10 and 12 gave the corresponding 3-deoxy-4-thiopentopyranosid-2-uloses (16-19). The diastereomers having the beta-D-threo configuration (16, 18) slightly predominated over the beta-D-erythro (17, 19) analogues. However, the reduction of the enantiomeric pyranones 10 and 14 with K-Selectride was highly diastereofacial selective in favor of the beta-D- and beta-L-threo isomers 16 and 20, respectively.     

Synthesis of beta-(1-->6)-branched beta-(1-->3) glucohexaose and its analogues containing an alpha-(1-->3) linked bond with antitumor activity

A beta-(1-->6)-branched beta-(1-->3)-glucohexaose, present in many biologically active polysaccharides from traditionally herbal medicines such as Ganoderma lucidum, Schizophyllum commune and Lentinus edodes, was synthesized as its lauryl glycoside 32, and its analogues 18, 20 and 33 containing an alpha-(1-->3) linked bond were synthesized. It is interesting to find that coupling of a 3,6-branched acylated trisaccharide trichloroacetimidate donor 9 with 3,6-branched acceptors 13 and 16 with 3'-OH gave the alpha-(1--> 3)-linked hexasaccharides 17 and 19, respectively, in spite of the presence of C-2 ester capable of neighboring group participation. However, coupling of 9 with 4-methoxyphenyl 4,6-O-benzylidene-beta-D-glucopyranoside (27) selectively gave beta-(1-->3)-linked tetrasaccharide 28. Simple chemical transformation of the tetrasaccharide 28 gave acylated tetrasaccharide trichloroacetimidate 29. Coupling of 29 with lauryl (1-->6)-linked disaccharide 26 with 3-OH gave beta-(1-->3)-linked hexasaccharide 30 as the major product. Bioassay showed that in combination with the chemotherapeutic agent cyclophospamide (CPA), the hexaose 18 at a dose of 0.5-1mg/kg substantially increased the inhibition of S(180) for CPA, but decreased the toxicity caused by CPA. Some of these oligosaccharides also inhibited U(14) noumenal tumor in mice effectively.