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Several spiro-bicyclo[2.2.2]octane derivatives are prepared as paclitaxel mimetics via a double Michael addition of enol ether (I) with methyl acrylate (II) and a ring-closing metathesis as key steps.

beta-1,4-Gatactosyltransferase 7 (beta 4GalT7) is an essential enzyme in the biosynthesis of glycosaminoglycan (GAG) chains of proteoglycans (PGs). Mammalian cells produce PGs, which are involved in biological processes such as cell growth and differentiation. The PGs consist of a core protein, with one or several GAG chains attached. Both the structure of the PGs and the GAG chains, and the expression of the enzymes involved in their biosynthesis and degradation, vary between normal cells and tumor cells. The biosynthesis of GAG chains is initiated by xylosylation of a serine residue of the core protein, followed by galactosylation by beta 4GalT7. The biosynthesis can also be initiated by exogenously added beta-D-xylopyranosides with hydrophobic aglycons, which thus can act as acceptor substrates for beta 4GalT7. To determine the structural requirements for beta 4GalT7 activity, we have cloned and expressed the enzyme and designed a focused library of 2-naphthyl beta-D-xylopyranosides with modifications of the xylose moiety. Based on enzymatic studies, that is galactosylation and its inhibition, conformational analysis and molecular modeling using the crystal structure, we propose that the binding pocket of beta 4GalT7 is very narrow, with a precise set of important hydrogen bonds. Xylose appears to be the optimal acceptor substrate for galactosylation by beta 4GalT7. However, we show that modifications of the xylose moiety of the beta-D-xylopyranosides can render inhibitors of galactosylation. Such compounds will be valuable tools for the exploration of GAG and PG biosynthesis and a starting point for development of anti-tumor agents. AuthorCount:12

Paclitaxel is one of the most important anti-cancer agents introduced during the last 20 years. However, the use of paclitaxel is limited by undesirable side effects as well as the development of drug resistance. Here, we report a synthetic strategy towards spiro-bicyclo[2.2.2]octane derivatives, which includes double Michael addition and ring-closing metathesis as key synthetic steps. This strategy was used to synthesize a series of spiro-bicyclic compounds designed to be paclitaxel mimetics, which were evaluated in human breast-derived cell lines. One of these paclitaxel mimetics showed toxicity, although at higher concentrations than paclitaxel itself. In addition, two other spiro-bicyclic compounds, lacking the paclitaxel side chain, showed toxicity.

N-Troc-protected (Troc = 2,2,2-trichloroethoxycarbonyl) glucosamine and galactosamine glycosyl donors (1-O-acetyl sugar, bromo sugar, and thioglycoside) were compared with the corresponding N-Phth-protected derivatives in glycosylations of 2-(trimethylsilyl)ethanol, 2-bromoethanol, methyl 3-mercaptopropionate, N-Fmoc-protected serine, and 2-(trimethylsilyl)ethyl 6-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranoside. The N-Troc-protected donors gave pure beta-glycosides in somewhat higher yields than the N-Phth-protected counterparts. The N-Troc protecting group can be removed by reduction with zinc, which allows selective N-deprotection in oligosaccharides containing both N-Troc and N-Phth groups.

Anthraldehyde acetals can be introduced regioselectively to carbohydrates in high yields. Advantages over conventional acetal protecting groups are increased crystallinity and strong absorbance and fluorescence which facilitate purification and reaction monitoring. The anthraldehyde acetals can be deprotected selectively in the presence of benzylidene acetals and can be cleaved regioselectively to yield 6-O-(9-anthracenyl)methyl ethers.

The minimum energy conformations of the four sterically reasonable SLe x and SLe a lactones were calculated using the molecular mechanics force-field MM2(91). The tetrasaccharide lactone involving the 3- and 2-position of the Gal moiety was found to be more stable than the 3,4-lactone both for SLe x and SLe a .

The use of benzylidene acetals as protecting groups in carbohydrate chemistry is utterly important. The main advantage of benzylidene acetal is the ability for regioselective openings. 4,6-benzylidene acetal can be opened selectively under reductive conditions to yield either free 4-OH or 6-OH. There are a plethora of methods available for regioselective openings, but only a few of these are widely used. In recent years, the mechanism has been investigated for borane mediated openings and it seems likely that the regioselectivity is determined by borane, rather than Lewis acid. When borane is activated by Lewis acids, borane is the most electrophilic species that consequently coordinates to the most nucleophilic oxygen of the acetals, usually O-6. This results in the formation of 6-O-benzyl ethers. If borane is not activated, Lewis acid is the most electrophilic species that thus adds to O-6 and hence generates the 4-O-benzyl ether.

Epidemic keratoconjunctivitis (EKC) is a severe disease of the eye, caused by members of the Adenoviridae (Ad) family, with symptoms such as keratitis, conjunctivitis, pain, edema, and reduced vision that may last for months or years. There are no vaccines or antiviral drugs available to prevent or treat EKC. It was found previously that EKC-causing Ads use sialic acid as a cellular receptor and demonstrated that soluble, sialic acid-containing molecules can prevent infection. In this study, multivalent sialic acid constructs based on 10,12-pentacosadiynoic acid (PDA) have been synthesized, and these constructs are shown to be efficient inhibitors of Ad binding (IC(50) = 0.9 μM) and Ad infectivity (IC(50) = 0.7 μM). The mechanism of action is to aggregate virus particles and thereby prevent them from binding to ocular cells. Such formulations may be used for topical treatment of adenovirus-caused EKC.

The novel promoter system iodine monochloride/silver trifluoromethanesulfonate (ICl/AgOTf) was evaluated with various thioglycoside donors and saccharide acceptors, and O-glycosides were obtained in 46-82% yield. Several practical advantages of the ICl/AgOTf system over known promoter systems were observed, such as convenient handling of the reagents and absence of byproducts related to N-succinimide.

N-Troc-protected (Troc = 2,2,2-trichloroethoxycarbonyl) glucosamine and galactosamine glycosyl donors (1-O-acetyl sugar, bromo sugar, and thioglycoside) were compared with the corresponding N-Phth-protected derivatives in glycosylations of 2-(trimethylsilyl)ethanol, 2-bromoethanol, methyl 3-mercaptopropionate, N-Fmoc-protected serine, and 2-(trimethylsilyl)ethyl 6-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranoside. The N-Troc-protected donors gave pure beta-glycosides in somewhat higher yields than the N-Phth-protected counterparts. The N-Troc protecting group can be removed by reduction with zinc, which allows selective N-deprotection in oligosaccharides containing both N-Troc and N-Phth groups.

Treatment of O-acetyl-protected sugars with a methanolic solution of guanidine/guanidinium nitrate caused the removal of the acetyl groups (91–99% isolated yield), without affecting other protecting groups. Removal of O-benzoyl groups required a longer reaction time. Of special merit is the stability of the 2,2,2-trichloroethoxycarbonylamino (N-Troc) group under these weakly basic reaction conditions.

Virtually complete regioselective galactosylation of the diol acceptor p-methoxyphenyl 6-O-benzyl-2-deoxy-2-tetrachlorophthalimido-β-d-glucopyranoside (8) with the donor phenyl 2,3,4-tri-O-acetyl-6...

The antiproliferative activity, and the capability of priming of glycosaminoglycan chains, of two series of peracetylated mono- and bis-xylosylated dihydroxynaphthalenes have been investigated for normal HFL-1 cells, as well as transformed T24 cells, and compared to the unprotected analogs. Our data show increased antiproliferative activity upon peracetylation, but a loss of selectivity towards T24 cells.

The reaction kinetics for a number of reductive openings of methyl 2,3-di-O-benzyl-4,6-O-benzylidene-alpha-D-glucopyranoside have been investigated. Openings to give free HO-6 (using BH(3) x THF-AlCl(3)-THF or LiAlH(4)-AlCl(3)-Et(2)O) follow first order kinetics, while reactions yielding free HO-4 (using BH(3) x NMe(3)-AlCl(3)-THF or BH(3) x NMe(3)-BF(3) x OEt(2)-THF) follow higher order kinetics. The addition of water to the BH(3) x NMe(3)-AlCl(3)-THF results in faster reactions. The BH(3) x SMe(2)-AlCl(3)-THF system constitutes a borderline case, yielding both free HO-6 (by a first order reaction) and free HO-4 (by a higher order reaction). These results correlate well with the concept of regioselectivity by activation of borane complexes.

Here we demonstrate a synergistic and tumor selective cytotoxic effect by combined treatment with naphthoxylosides, polyamine synthesis inhibitor, and polyamine based nitric oxide (NO) donor, using in vitro human tumor models. We have earlier reported that heparan sulfate priming naphthoxyloside, 2-(6-hydroxynaphthyl)-O-beta-D-xylopyranoside, which inhibits growth of human tumor cells in vitro and in vivo models, undergoes NO dependent cleavage and accumulates in the nuclei of tumor cells. Polyamine depletion using alpha-difluoromethylornithine (DFMO) increases both the number of NO sensitive sites in heparan sulfate and uptake of the polyamine based NO donor, spermineNONOate, thereby enhancing formation of growth-inhibitory NO induced heparan sulfate products with specific cytotoxic effect on tumor cells. We also show that peracetylation of xylosides doubles the antiproliferative effect towards human cancer cells by making these compounds more permeable to the cells.

A xylosylated carborane was synthesized by standard carbohydrate methodology and tested on normal HFL-1 cells as well as transformed T24 cells. The xylosylated carborane initiated glycosaminoglycan (GAG) synthesis in both cell lines and treatment with the carborane gave a pronounced translocation of proteoglycans to the nuclei of T24 cells. However, most of the boron-containing compounds were secreted to the medium. We conclude that xylosides carrying carboranes are not suitable for boron neutron capture therapy (BNCT) for T24 cells. However, the uptake of boron-containing xyloside, the GAG priming capacity, and the nuclear translocation of glypican-1 make this xyloside a candidate for further investigation for selectivity toward other tumor cell lines.

A new fluorescent analog to the antiproliferative 2-(6-hydroxynaphthyl)-beta-D-xylopyranoside has been synthesized and tested on a T24 cell line. The new analog was efficiently uptaken by the T24 cells but did not initiate priming of GAG chains. The results are similar to other fluorescently labeled analogs and we propose that these compounds are too large and unpolar to efficiently function as GAG-primers. (c) 2007 Elsevier Ltd. All rights reserved.

A series of conformationally restricted N-"furanosides" has been synthesized, where the carbons of the tetrahydrofuran ring are kept in one plane by a rigid norbornane skeleton, permitting only the ring oxygen to move above or below the tetrahydrofuran ring plane. This causes the substituents of the anomeric carbon to occupy a pseudoaxial or a pseudoequatorial position. On protonation of these "norbornane-furanosides" with trifluoromethanesulfonic acid, all three compounds exhibited decreasing coupling constants for the anomeric proton, indicating a shift toward the pseudoaxial conformation. The coupling constant measurements were supported by volume integration of NOESY cross-peaks, which also showed a change toward the pseudoaxial conformation upon protonation of the nitrogen. These results provide no evidence for the so-called reverse anomeric effect; on the contrary they are in full agreement with a small normal anomeric effect.

Regioselective reductive openings of mixed phenolic-benzylic acetals, using BH3 center dot NMe3 center dot AlCl3, was investigated, and a mechanism where the outcome is directed by the electrostatic potential of the two oxygen atoms is presented. The regioselective acetal opening was used in the synthesis of a fluorescently labeled analogue to antiproliferative xylosides. The fluorescently labeled xyloside was tested for uptake, anti proliferative activity, and glycosaminoglycan priming in different cell lines. The xyloside was taken up by all cell lines but did not initiate glycosaminoglycan biosynthesis.

The antiproliferative activity of the 14 isomeric monoxylosylated dihydroxynaphthalenes has been tested in vitro toward normal HFL-1 and 3T3 A31 cells as well as transformed T24 and 3T3 SV40 cells. The antiproliferative effect toward HFL-1 cells was correlated with the polarity of the compounds. However, in the case of transformed T24 cells, some compounds showed a clearly different behavior resulting in a selective antiproliferative effect. No such correlation was found for normal 3T3 A31 or virus transformed 3T3 SV40 cells, nor for the free aglycon. These results suggest that the antiproliferative activity shown by naphthoxylosides is diverse in different cell lines and dependent on the nature of the aglycon. The antiproliferative effect of 2-(6-hydroxynaphthyl)-beta-D-xylopyranoside, in contrast to inactive 2-naphthyl-beta-D-xylopyranoside, on T24 cells was accompanied by increased apoptosis as indicated by a TUNEL assay.

Carbohydrates carrying an aromatic aglycon are important natural products and thus key synthetic targets. However, due to the electron-withdrawing properties of aromatic rings, phenols are difficult to glycosylate. This review covers the most common carbohydrate donors used for aromatic O-glycosylation (anomeric acetates, halides, trichloroacetimidates and thioglycosides) as well as some less common donors. The scope of the review is to give practical examples of aromatic O-glycosylations and to offer guidelines for glycosylation of typical aromatic residues. Anomeric acetates or trichloroacetimidates, activated under acidic conditions, are preferred for electron rich aromatic aglycons, while glycosyl halides, activated using basic conditions, are preferred for electron deficient aromatic residues.

We have used DNase I footprinting and fluorescence melting studies to study the interaction of the hairpin polyamide Im-Py-Py-Py-(R)H2Ngamma-Im-Py-Py-Py-beta-Dp with its preferred binding sites (5'-WGWWCW; W=A or T) and other sequences. DNase I footprinting confirmed that the ligand binds to the sequence AGAACA at nanomolar concentrations and that changing the terminal A to G causes a dramatic decrease in affinity, while there was no interaction with the reverse sequence WCWWGW. Fluorescence melting studies with 11-mer duplexes showed that the polyamide had very different effects on the forward (TGWWCT) and reverse (TCTAGT) sequences. At low concentrations, the polyamide produced biphasic melting curves with TGATCT, TGTACT and TGAACT, suggesting a strong interaction. In contrast, the melting profiles with TCTAGT were always monophasic and showed much smaller concentration dependent changes in Tm. The polyamide also showed weak binding to the sequence TGATCT when one of the central AT pairs was replaced with an AC mismatch. These melting profiles were compared with those produced by the AT-selective minor groove binding agents distamycin and Hoechst 33258 at the same sites and at similar sequences containing A5 and (AT)3, which are expected to bind distamycin in the 1:1 and 2:1 modes, respectively. These ligands produced simple monophasic melting curves in which the Tm steadily increased as the ligand concentration was raised.

The novel promoter system IX/AgOTf (X = Cl or Br) has been evaluated in the synthesis of two bislactam analogues of GD3. We have carried out two high-yielding galactosylations in 97% and 98% yield, respectively, using ICl/AgOTf, and four sialylations in 93%, 59%, 40%, and 44% yield, using IBr/AgOTf. The choice of interhalogen (IX) is determined by the donor type used in the glycosylation. We also report some mechanistic investigations leading to further optimization of the IX/AgOTf promoter system.

(Trimethylsilyl)ethyl 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside and (trimethylsilyl)ethyl 2,3,6-tri-O-acetyl-4-O-(2,3,6-tri-O-acetyl-4-O-[2-acetamido-4,6-di-O-ace tyl-2- deoxy-3-O-(2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-beta-D- galactopyranosyl]-beta-D-galactopyranosyl)-beta-D-glucopyranoside have been transformed in high yield into the corresponding 1-O-beta-acyl saccharides by treatment with various carboxylic anhydrides in the presence of boron trifluoride-diethyl ether in toluene. The carboxylic anhydrides (4-pentenoic, 2-cyclopentenylacetic, 2,4-dimethoxy-benzoic, and 2-methoxybenzoic anhydride) were synthesized from the corresponding carboxylic acids by treatment with N,N-bis[2-oxo-3-oxazolidinyl]phosphorodiamidic chloride.

A new aromatic pair, 2-hydroxy-6-methoxybenzamide/1-methylpyrrole at the terminal position of hairpin polyamides has been designed for distinguishing T·A from A·T base pairs and both from G·C/C·G in the minor groove of DNA. Four eight-ring hairpin polyamides with benzamide (Bz), 2-hydroxybenzamide (Hb-1), 2-hydroxy-6-methylbenzamide (Hb-2), and 2-hydroxy-6-methoxybenzamide (Hb-3) at the N-terminal position were synthesized. The equilibrium association constants (K_a) were determined at four DNA sites which differ at a single common position, 5‘-TNTACA-3‘ (N = T, A, G, C). Quantitative DNase I footprint titration experiments reveal that (Hb-3)PyPyPy-(R)^H2^Nγ-ImPyPyPy-β-Dp (4) bound the sequences 5‘-TTTACA-3‘ and 5‘-TATACA-3‘ with high affinity; K_a = 2.6 × 10^(10) M^(-1) and K_a = 8.4 × 10^9 M^(-1), respectively, a 3-fold specificity for T vs A was found. Importantly, the sequences 5‘-TGTACA-3‘ and 5‘-TCTACA-3‘ are bound with 50 and 200 times lower affinity, revealing an overall specificity of Hb-3/Py of T > A ≫ G > C. These results expand the repertoire of sequences targetable by hairpin polyamides.

Anthracyclines, e.g. daunorubicin, doxorubicin, and idarubicin, consist of a tetracycline moiety linked via a glycosidic bond to a sugar residue, usually the aminosugar daunosamine. The anthracyclines are efficient chemotherapeutic agents against cancer, but their use is limited due to cardiotoxicity and induction of multidrug resistance. In the search for new anthracycline analogs, a daunosamine donor that can be used to glycosylate suitable aglycons is of utmost importance. Here, we present a short and efficient synthesis of the versatile donor p-tolyl 4-O-acetyl-3-azido-2,3,6-trideoxy-1-thio-α-L-lyxo-hexopyranoside in 3 steps from commercially available L-fucal with an overall yield of 32%. The same procedure can be used to synthesize the donor p-tolyl 4-O-acetyl-3-azido-2,3,6-trideoxy-1-thio-α-L-arabino-hexopyranoside in 28% overall yield from L-rhamnal, for the synthesis of epirubicin analogs.

A new method for highly effective and selective 1-O-deacetylation of peracetylated carbohydrates using polymer-bound amines is presented.

The predominantly populated conformation of carbohydrates in solution does not necessarily represent the biologically active species; rather, any conformer accessible without too large an energy penalty may be present in a biological pathway. Thus, the conformational preferences of a naphthyl xyloside, which initiates in vivo synthesis of antiproliferative glycosaminoglycans, have been studied by using NMR spectroscopy in a variety of solvents. Equilibria comprising the conformations (4)C1, (2)SO and (1)C4 were found, with a strong dependence on the hydrogen bonding ability of the solvent. Studies of fluorinated analogues revealed a direct hydrogen bond from the hydroxyl group at C2 to the fluorine atom at C4 by a (1h)JF4,HO2 coupling. Hydrogen bond directionality was further established via comparisons of fluorinated levoglucosan molecules.

We describe the use of acrylic tanks (400 x 450 x 27 mm) for visualization of chemical demonstrations in aqueous solutions. Examples of well-suited demonstrations are oscillating reactions, pH indicators, photochemical reduction of Lauth's violet, and chemoluminiscent reactions.

Treatment of O-acetyl-protected sugars with a methanolic solution of guanidine/guanidinium nitrate caused the removal of the acetyl groups (91–99% isolated yield), without affecting other protecting groups. Removal of O-benzoyl groups required a longer reaction time. Of special merit is the stability of the 2,2,2-trichloroethoxycarbonylamino (N-Troc) group under these weakly basic reaction conditions.

A new method for performing flash chromatography is presented in which the solvent reservoir is at the side of the column, in a separate bottle, connected with a Teflon tube to an adapter for standard flash chromatography columns.

To improve microscale distillation in a basic organic chemistry course, a simple and highly efficient vacuum distillation apparatus was designed.

Glycosaminoglycans (GAGs) are essential polysaccharides in normal physiology and disease. However, understanding of the contribution of specific GAG structures to specific biological functions is limited, largely because of the great structural heterogeneity among GAGs themselves, as well as technical limitations in the structural characterization and chemical synthesis of GAGs. Here we describe a cell-based method to produce and display distinct GAGs with a broad repertoire of modifications, a library we refer to as the GAGOme. By using precise gene editing, we engineered a large panel of Chinese hamster ovary cells with knockout or knock-in of the genes encoding most of the enzymes involved in GAG biosynthesis, to generate a library of isogenic cell lines that differentially display distinct GAG features. We show that this library can be used for cell-based binding assays, recombinant expression of proteoglycans with distinct GAG structures, and production of distinct GAG chains on metabolic primers that may be used for the assembly of GAG glycan microarrays.