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Two previously unknown lumazine derivatives, 1 and 2, have been isolated from the parasitic freshwater leech Limnatis nilotica. The structures of the compounds have been elucidated by NMR and unambiguously corroborated by chemical synthesis.

The use of platinum drugs in antitumour therapy is well established. An important drawback of these chemotherapeutics is the lack of selectivity for tumour cells, usually resulting in severe toxic side effects. A glucuronyl-platinum conjugate was designed and synthesised to test the compatibility of platinum compounds with beta-glucuronidase-based prodrug therapy. Instantaneous cleavage of the beta-glucuronic bond in the glucuronyl-platinum conjugate was observed upon addition of beta-glucuronidase resulting in Pt(II)(dach)(4-hydroxybenzylmalonate) and glucuronic acid.

The synthesis of naturally occurring D-erythro-(2R,3S,4E)-sphingosine from commercially available D-ribo-(2S,3S,4R)-phytosphingosine is described. The key step in the reaction sequence comprises TMSI/DBN promoted regio- and stereoselective oxirane opening of intermediate 2-phenyl-4-(S)-[(1S,2S)-1,2-epoxyhexadecyl]-1,3-oxazoline followed by the in situ trans-elimination of 2-phenyl-4-(S)-[(1S,2R)-1,2-dideoxy-2-iodo-1-trimethylsilyloxyhexadecyl]-1,3-oxazoline.

The three-dimensional solution structure of two DNA decamers of sequence d(CCACXGGAAC)-(GTTCCGGTGG) with a modified nucleotide containing a cholesterol derivative (X) in its C1 ′(chol)α or C1 ′(chol)β diastereoisomer form has been determined by using NMR and restrained molecular dynamics. This DNA derivative is recognized with high efficiency by the UvrB protein, which is part of the bacterial nucleotide excision repair, and the α anomer is repaired more efficiently than the β one. The structures of the two decamers have been determined from accurate distance constraints obtained from a complete relaxation matrix analysis of the NOE intensities and torsion angle constraints derived from J-coupling constants. The structures have been refined with molecular dynamics methods, including explicit solvent and applying the particle mesh Ewald method to properly evaluate the long range electrostatic interactions. These calculations converge to well defined structures whose conformation is intermediate between the A- and B-DNA families as judged by the root mean square deviation but with sugar puckerings and groove shapes corresponding to a distorted B-conformation. Both duplex adducts exhibit intercalation of the cholesterol group from the major groove of the helix and displacement of the guanine base opposite the modified nucleotide. Based on these structures and molecular dynamics calculations, we propose a tentative model for the recognition of damaged DNA substrates by the UvrB protein.

In this paper, a glycosylation-based approach towards novel aminoglycoside analogues is presented. Three different cyclitol building blocks were condensed with different thioglycosides to give, after removal of the protective groups, several neamine-type analogs varying in the positioning and the stereochemistry of the amino functions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

[reaction: see text] Partially protected thioglycuronic acids are prepared efficiently by chemo- and regioselective oxidation of the corresponding thioglycosides using the TEMPO/BAIB reagent combination. After esterification, the thioglycuronic acids proved to be useful as both donor and acceptor in sulfonium-mediated condensations toward acidic di- and trisaccharides.

We report the synthesis of novel artificial ribonucleases with potentially improved cellular uptake. The design of trifunctional conjugates 1a and 1b is based on the specific RNA-recognizing properties of PNA, the RNA-cleaving abilities of diethylenetriamine (DETA), and the peptide (KFF)(3)K for potential uptake into E. coli. The conjugates were assembled in a convergent synthetic route involving native chemical ligation of a PNA, containing an N-terminal cysteine, with the C-terminal thioester of the cell-penetrating (KFF)(3)K peptide to give 12a and 12b. These hybrids contained a free cysteine side-chain, which was further functionalized with an RNA-hydrolyzing diethylenetriamine (DETA) moiety. The trifunctional conjugates (1a, 1b) were evaluated for RNA-cleaving properties in vitro and showed efficient degradation of the target RNA at two major cleavage sites. It was also established that the cleavage efficiency strongly depended on the type of spacer connecting the PNA and the peptide.

Enantiomerically pure 4,6-diaminocyclohexenols are obtained from carbohydrate derived 1,7-dienes by ring-closing metathesis and palladium catalyzed allylic amination using o-nitrobenzenesulfonylamides as nucleophiles. In the latter reaction the use of a cyclic carbonate as a leaving group proved to be essential to facilitate a smooth substitution. The obtained compounds were converted into orthogonally protected diaminocyclitols, which are stereoisomers of the naturally occurring 2-deoxystreptamine, a constituent of aminoglycoside antibiotics.

An expeditious route to peptide-PNA-peptide conjugates following a two-step native chemical ligation (NCL) strategy is described. A cys-PNA-thioester is immobilized on PEGA-aldehyde resin by thiazolidine formation, followed by capping of excess resin aldehydes. The first NCL reaction is then performed with the immobilized PNA-thioester, to give, after release from the solid support, the cys-PNA-peptide intermediate with relatively high purity. The latter is then converted into the target compound by the second NCL reaction with a thioester peptide, the excess of which is captured using a cysteine-PEGA resin. The resulting peptide-PNA-peptide can then be readily isolated by a simple purification step. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

A combinatorial library of 32 tricomponent bisubstrate fucosyltransferase analogs has been generated using solid-phase peptide synthesis with orthogonally protected lysine as a scaffold.

As part of a program towards the development of specific inhibitors of human lysosomal beta-hexosaminidase for use as chemical chaperones in therapy of G(M2) gangliosidosis related diseases, the synthesis of 2-acetamidomethyl derivatives of isofagomine has been undertaken. Key event in this synthesis is the conversion of a C-2 substituted gluconolactone derivative into the corresponding lactam, followed by reduction to the corresponding amine. The 1-N-imino-2 acetamidomethyl derivative 5 proved to be a rather selective inhibitor with a K(i) of 2.4 microM for homogenate of human spleen lysosomal beta-hexosaminidase.

A novel chemoselective glycosylation sequence is described that employs the recently developed BSP/Tf2O and DPS/Tf2O reagent systems to activate thioglycosides. In the first glycosylation event a relatively armed thioglycoside is activated with the BSP/Tf2O activator system and condensed with an acceptor thioglycoside to yield the thiodisaccharide, which is activated with the more potent DPS/Tf2O activator in the next glycosylation event. Quenching of (N-piperidino)phenyl(S-thiophenyl)sulfide triflate, which is formed upon activation of the first thioglycoside, with triethyl phosphite is crucial for a productive glycosylation.

A novel triene linker system, that can be cleaved by a tandem ring-closing metathesis (RCM) reaction, is presented. The tandem RCM cleavage, that regenerates the active ruthenium catalyst without the need of additives like ethylene, proceeded very clean and fast to liberate cyclopent-2-enyl mannosides from the solid support. A cyclopent-2-enyl mannoside was isomerized to the corresponding vinyl ether glycoside, which could be readily deprotected by iodine-mediated hydrolysis.

Ring opening of the epoxide function in α‐1,2‐anhydrosugars with alkynyl zinc and titanium compounds proceeds with retention of configuration to afford α‐C‐alkynyl‐glycosides in reasonable to good yields, while the use of the corresponding alkynyltrifluoroborates results in the formation α/β mixtures. Vinyl nucleophiles predominantly afford α‐products, whereas allyl and allenyl species almost exclusively yield β‐C‐glycosides. †This paper is dedicated to Professor Gerard Descotes on the occasion of his 70th birthday.

A new, base-labile fluorous tag based on the Msc amine protecting group was synthesized. Its use in the purification of synthetic peptides by fluorous HPLC or fluorous SPE was demonstrated.

In this paper, a rapid route toward functionalized bicyclic alkaloids is presented. In only three steps, an easily accessible carbohydrate derivative was converted into iodomethyl indolizidine 13, which can equilibrate to the corresponding iodoquinolizidine 15. We provide strong evidence that this equilibration proceeds via an aziridinium ion intermediate. Furthermore, nucleophilic substitution of the iodomethyl indolizidine as well as the aziridinium intermediate gives access to highly functionalized indolizidine and quinolizidine alkaloids.

Peptide nucleic acids (PNA's) have shown to hold potential as antisense drugs. In this study we have designed PNA drugs for the microsomal triglyceride transfer protein (MTP), which is known to play a critical role in the assembly of atherogenic lipoproteins, and have converted the most potent drug into a liver-targeted prodrug. First, we have synthesized three PNA sequences targeting domains on the mouse MTP mRNA, which were not involved in intrastrand base-pairing interactions as jugded from its secondary structure. Only one of the PNA's, PNA569, showed dose-dependent inhibition of MTP expression in a cell-free system for coupled transcription/translation of MTP. Second, to improve the cellular uptake of this PNA drug, we have conjugated PNA569 to a high affinity ligand for the asialoglycoprotein receptor, K(GalNAc)(2). As compared to the parent PNA, the prodrug PNA-K(GalNAc)(2) was found to display to a markedly improved capacity to inhibit MTP mRNA expression in parenchymal liver cells. A glycoconjugated nonsense control appeared to be ineffective. In conclusion, the design of a targeted PNA is described to reduce MTP expression in parenchymal liver cells by 70%. The presented approach for targeted tissue-specific down-regulation of genes by PNA's may be valid for other genes as well.

A reinvestigation into the synthesis of oligonucleotides containing 5-(β-D-glucopyranosyloxymethyl)-2′-deoxyuridine revealed that existing procedures for the preparation of these DNA fragments suffered from decomposition at the final deprotection step. The decomposition product was identified as the corresponding 5-(aminomethyl)-2′deoxyuridyl derivative arising from amino substitution of the β-D-glucosyl moiety during ammonolysis. This was shown to be suppressed by the use of phosphoramidite 21 in place of 12 for solid-phase oligonucleotide synthesis, in conjunction with short ammonia treatment at room temperature. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

G protein-coupled receptors (GPCRs) mediate the perception of smell, light, taste, and pain. They are involved in signal recognition and cell communication and are some of the most important targets for drug development. Because currently no direct structural information on high-affinity ligands bound to GPCRs is available, rational drug design is limited to computational prediction combined with mutagenesis experiments. Here, we present the conformation of a high-affinity peptide agonist (neurotensin, NT) bound to its GPCR NTS-1, determined by direct structural methods. Functional receptors were expressed in Escherichia coli , purified in milligram amounts by using optimized procedures, and subsequently reconstituted into lipid vesicles. Solid-state NMR experiments were tailored to allow for the unequivocal detection of microgram quantities of 13 C, 15 N-labeled NT(8–13) in complex with functional NTS-1. The NMR data are consistent with a disordered state of the ligand in the absence of receptor. Upon receptor binding, the peptide undergoes a linear rearrangement, adopting a β-strand conformation. Our results provide a viable structural template for further pharmacological investigations.

Differently functionalized tetrahydropyran-based dipeptide isosters have been efficiently synthesized from 3,4,6-tri-O-acetyl-D-glucal. Analogues of the hsp65 p2−13 epitope of Mycobacterium tuberculosis and Mycobacterium leprae were prepared by replacement of the Ala−Tyr or Glu−Glu moiety in the native dodecapeptide with the prepared dipeptide isosters. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Colchicine, an established tubulin inhibitor, interferes with the trafficking of endocytotic vesicles and thereby promotes the escape of lysosome-entrapped compounds. To improve its potency and cell specificity, a targeted prodrug of colchicine was synthesized by conjugation to a high-affinity ligand (di-N(alpha),N(epsilon)-(5-(2-acetamido-2-deoxy-beta-D-galactopyranosyloxy)pentanomido)lysine, K(GalNAc)(2)) for the asialoglycoprotein receptor on parenchymal liver cells. The resulting colchicine-K(GalNAc)(2) conjugate bound to this receptor with an affinity of 4.5 nM. Confocal microscopy studies confirmed rapid uptake and receptor dependency of a prodrug conjugated with fluorescein isothiocyanate. Colchicine-K(GalNAc)(2) substantially increased the transfection efficiency of polyplexed DNA in parenchymal liver cells in a concentration- and receptor-dependent fashion. Colchicine-K(GalNAc)(2) was found to enhance the transfection efficiency by 50-fold at 1 nM, whereas the parental colchicine was ineffective. In conclusion, this nontoxic colchicine-K(GalNAc)(2) conjugate can be a useful tool to improve the transfection efficiency of hepatic nonviral gene transfer vehicles.

Cyclic oligomers composed of amide-linked furanoid (i.e., 1, 3) and pyranoid (i.e., 2, 4) ϵ-sugar amino acids (SAAs) were prepared by a cyclization/cleavage approach with use of the oxime resin. These cyclic homooligomers were constructed by use of the known N-Boc protected furanoid ϵ-SAA 11 and the novel pyranoid hydroxymethylene homologue 22. Conformational analysis of cyclic trimer 1 by an unrestrained simulated annealing technique showed that the furanoid rings of the residues I flip between a twist (north, P = 0°) and an envelope (south, P = 167°) conformation. Furthermore, the side chains connecting the carbonyl functionality (i.e. C2) proved to be rigid, while the other side chains (C7) are conformationally flexible. Similar conformational behaviour is observed for the side chains of the pyranoid ϵ-SAA II residues in trimer 2, but the pyranoid ring chair conformation remains stable during the calculation. These conformational details may have important implications in the future design of SAA-based artificial receptors or peptidomimetics. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Sugar amino acids (SAAs) bearing an amine group on the anomeric position are a challenging class of SAAs to synthesize due to the inherent instability of glycosylamines. We developed a novel synthetic strategy towards both furanoid and pyranoid δ-SAAs of this type, based on a Curtius rearrangement. The latter reaction, which is known to proceed with retention of configuration, was performed on carboxylic acids derived from the oxidation of glycosidic primary hydroxyls. Leu-enkephalin analogs were prepared by replacing the Gly-Gly moiety in the parent Leu-enkephalin pentapeptide with the furanoid and pyranoid δ-SAA. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

[reaction: see text] A novel sequential glycosylation procedure is described that combines the use of 1-hydroxyl and thiodonors. The Ph(2)SO/Tf(2)O-mediated dehydrative condensation of 1-hydroxyl donors with thioglycosides affords in good yield the thiodisaccharides, which in turn can be activated by the same activator system to furnish trisaccharides. The alpha-Gal epitope and a hyaluronan trisaccharide were efficiently assembled in a one-pot procedure.

Undesired N(7) platination of 2'-deoxyguanosine residues at predetermined sites in an oligodeoxynucleotide (ODN) sequence is prevented by applying the sterically demanding diphenylcarbamoyl (DPC) as an O(6)-protecting group. The presence of a base-labile oxalyl linker between the immobilized 3'-nucleotide and controlled pore glass (CPG) allows cleavage of the protected ODN from the support and leaves DPC protection unaffected. This method provides an ODN with specifically blocked guanine-N(7) sites for platination. In the hexanucleotides prepared in this study, 5'-GGBGGT-3'(for B=T, C and A), a platinum GG adduct is introduced at G4,G5. These site-specific platinated hexamers were isolated in a yield of 65 %, and were fully characterized by using reversed-phase HPLC (high performance liquid chromotography), LCMS (liquid chromatography-mass spectrometry), MALDI-TOF MS (matrix-assisted laser desorption/ionization time-of-flight mass spectrometry), PAGE (polyacrylamide gel electrophoresis) and Maxam-Gilbert sequencing analysis.

Diphenylsulfoxide in combination with triflic anhydride provides a very potent thiophilic glycosylation promotor system, capable of activating disarmed thioglycosides. The usefulness of this novel thiophilic activator is illustrated in a successful chemoselective glycosylation sequence in which the donor thioglycoside in the first condensation step may be either armed or disarmed. [reaction: see text]

Gel-phase 195Pt NMR spectroscopy of dichloroplatinum peptide complexes attached to a solid support is described. The observed 195Pt chemical shifts of the support-bound platinum complexes are in good agreement with the solution-state 195Pt NMR spectra of the soluble and deprotected analogs. This non-destructive analytical method for on-resin-compound analysis was applied in the optimization of the solid-phase synthesis of the primary amine dichloroplatinum complex 6, which represents a new class of platinum complexes now available via solid-phase synthetic chemistry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The synthesis of three methylene bridged sugar amino acids is described. Key transformations in the synthetic strategy are a CO-insertion on fully protected ribose, an aldol condensation with formaldehyde and an oxetane forming cyclisation step. A novel Leu-enkephalin analogue containing the δ-SAA 1 was prepared using standard solution phase peptide chemistry.

The uridylylated amino acid building blocks 2-cyanoethyl-(Nα-9-fluorenylmethoxy-carbonyl-tyrosin-4-yl)-(2′,3′-di-O-acetyluridin-5′-yl) phosphate and 2-chlorophenyl-(Nα-fluorenyl-methoxycarbonyl-serin-3-yl)-(2′,3′-di-O-acetyluridin-5′-yl) phosphate have been used successfully in an on-line SPPS of the VPgpU from the polio, coxsackie and cowpea mosaic virus.

The highly functionalized piperidine 5a was synthesized in only 4 steps starting from ribose using a tandem retro‐Michael‐[2 + 3]‐cycloaddition process as the key transformation. The versatility of the tandem retro‐Michael‐[2 + 3]‐cycloaddition was demonstrated by the synthesis of novel piperidines 5b, 5c, 11 and 16.

A tethered nucleophilic substitution strategy for the stereoselective introduction of axially oriented amino functions on suitably protected gluco- and mannopyranosides is presented. The obtained oxazine is a versatile building block, which after some manipulation, could be used in the construction of highly functionalised oligosaccharides.

Four heparin pentasaccharides bearing either one (i.e. 3b and 4b) or two (i.e. 3c and 4c) positively charged amino groups at the reducing end have been synthesized and evaluated for their antithrombin III mediated anti-Xa activity. The positively charged groups were introduced to interact specifically with the negatively charged amino acid residues Glu113 and Asp117 of antithrombin III, which are located in the heparin binding site in close proximity to the reducing end of the saccharide. It turned out that the target compounds 3b,c and 4b,c exhibited relatively low anti-Xa activities, indicating unfavorable interactions between the new pentasaccharides and antithrombin III rather than the anticipated enhancement of association. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

A solid-phase approach is described that provides facile access to monofunctionally trans-PtII-modified PNA oligomers of arbitrary sequence for potential use both in antigene and antisense strategies. The approach includes the synthesis of a platinated building block 1 and its subsequent incorporation into three different PNA oligomers 5-7 by solid-phase synthesis. In a model cross-linking reaction one of the latter is found to recognize sequence-specifically a target oligonucleotide 8 and to cross-link to it. The resulting structure is the trans-PtII-cross-linked PNA/DNA duplex 9 as revealed by mass spectrometry in combination with a Maxam-Gilbert sequencing experiment.

A convenient solid-phase synthesis of a PNA sequence containing an N-terminal thiaproline and a C-terminal thioester is described. The usefulness of this bifunctional PNA molecule is illustrated by the construction, based on native ligation, of a peptide–PNA–peptide adduct.

d -erythro-Sphingosine ( 1 ) and d -erythro-2-azidosphingosine ( 2 ) are both prepared from commercially available and cheap d -ribo-phytosphingosine ( 3 ) in a yield of 58% and 70%, respectively. A key transformation in the synthesis of d -erythro-sphingosine ( 1 ) is the palladium catalyzed regiospecific reduction of the Z-enol triflate 9 . A crucial step in the synthesis of azidosphingosine 2 comprises a regio- and stereoselective in situ trans-elimination of the 4-O-triflate of azidophytosphingosine 13 .

The absolute configuration of the 2-substituted arabinitol 1-phosphate residue present in the repeating unit of the capsular polysaccharide (CPS) from Streptococcus pneumoniae Type 17F is confirmed as D, based on a comparison of proton and carbon chemical shifts in a synthetic oligosaccharide and in an oligosaccharide derived from the CPS by degradation.

Peptide nucleic acid (PNA) is a synthetic DNA analogue that is resistant to nucleases and proteases and binds with exceptional affinity to RNA. Because of these properties PNA has the potential to become a powerful therapeutic agent to be used in vivo. Until now, however, the use of PNA in vivo has not been much investigated. Here, we have attempted to reduce the expression of the bcr/abl oncogene in chronic myeloid leukaemia KYO-1 cells using a 13mer PNA sequence (asPNA) designed to hybridise to the b2a2 junction of bcr/abl mRNA. To enhance cellular uptake asPNA was covalently linked to the basic peptide VKRKKKP (NLS-asPNA). Moreover, to investigate the cellular uptake by confocal microscopy, both PNAs were linked by their N-terminus to fluorescein (FL). Studies of uptake, carried out at 4 and 37 degrees C on living KYO-1 cells stained with hexidium iodide, showed that both NLS-asPNA-FL and asPNA-FL were taken up by the cells, through a receptor-independent mechanism. The intracellular amount of NLS-asPNA-FL was about two to three times higher than that of asPNA-FL. Using a semi-quantitative RT- PCR technique we found that 10 micro M asPNA and NLS-asPNA reduced the level of b2a2 mRNA in KYO-1 cells to 20 +/- 5% and 60 +/- 10% of the control, respectively. Western blot analysis showed that asPNA promoted a significant inhibition of p210(BCR/ABL) protein: residual protein measured in cells exposed for 48 h to asPNA was approximately 35% of the control. Additionally, asPNA impaired cell growth to 50 +/- 5% of the control and inhibited completion of the cell cycle. In summary, these results demonstrate that a PNA 13mer is taken up by KYO-1 cells and is capable of producing a significant and specific down-regulation of the bcr/abl oncogene involved in leukaemogenesis.

A flexible synthetic route towards chirally pure 4,6-diaminocyclohexene derivatives based on palladium catalyzed allylic amination of carbohydrate derived cyclohexenes is presented.

A ring-closing metathesis (RCM) and a ring-opening metathesis (ROM) are combined in a domino process giving access to a variety of aza- and oxacyles, equipped with highly functionalized side chains, starting from readily accessible cyclopentenyl or cycloheptenyl ethers and amines. The role of different protective groups is examined as well as the influence of the relative configuration of stereocenters of the substrate molecules. Substituted 2,5-dihydro-furans and -pyrroles, 1,2,5,6-tetrahydropyranes and -pyridines as well as 2,3,4,7-tetrahydrooxepines are available via this methodology.