Synthesis of carbamate-containing cyclodextrin analogues

[formula: see text] The one-pot cyclooligomerization of a saccharide-derived p-nitrophenyl carbamate monomer was developed to generate a series of novel carbamate-containing cyclodextrin analogues. The "transcarbamoylation" occurs by initial base-induced activation to the isocyanate, followed by polycondensation/cyclization of the isocyanato alcohol. In the presence of NaH, only cyclized oligomers were observed, suggesting the importance of Na+ in promoting the efficiency of the cyclization process. The facile deprotection of the oligomers was achieved.     

Synthesis and properties of a new family of cyclodextrin analogues

The chemical synthesis of a series of cyclic oligosaccharides built up from (14)-linked alternatingD– andl-pyranosidic units is described for the first time. Key intermediates employed were disaccharides representing minimal repeating units. These disaccharides (monomers) have been prepared in specifically modified forms so that they bear both glycosyl donor (cyanoethylidene group) and glycosyl acceptor (trityloxy group) functions. Polycondensation-cyclisation of these disaccharide monomers, catalysed by TrC1O₄ under normal conditions of dilution, has led to series of homologous cyclic oligosaccharides with an even number of sugar residues (6, 8, 10, 12,etc.) in each case. Cyclic hexa- and octa-saccharides, based onl-rhamnose andD-mannose as the alternating monosaccharides units, have been deprotected to produce analogues of - and -cyclodextrins (CDs) and the X-ray crystal structure of the cyclic octasaccharide has been determined.     

Synthesis of 2,4-methanoproline analogues via an addition-intramolecular substitution sequence

A new two-step synthetic approach toward 3-(chloromethyl)cyclobutanone is described and used in the synthesis of 2,4-methanoproline analogues. The key step consists of a reversible addition of hydrogen cyanide onto the imines 12 in 50-74% yield under conditions that allow ring closure. 2-Alkyl-2-azabicyclo[2.1.1]hexane-1-carbonitriles 19, synthesized in four steps, can also be converted to the corresponding amines.     

Synthesis of sulfonic acid analogues of the non-reducing end trisaccharide of the antithrombin binding domain of heparin

Three sulfonic acid trisaccharides related to the antithrombin-binding DEFGH domain of heparin were synthesised. Trisaccharides carrying the sulfonatomethyl moiety at position 2 or 6 were prepared in high yields by [DE+F] couplings using the same disaccharide uronate donor and the appropriate sulfonic acid acceptor, respectively. The trisaccharide with a 3-deoxy-3-sulfonatomethyl function could be obtained with high efficacy by a [D+EF] coupling where the carboxylic function of the EF uronate acceptor was created at a disaccharide level.     

Synthesis, structure, and inclusion capabilities of trehalose-based cyclodextrin analogues (cyclotrehalans)

Concise and efficient strategies toward the synthesis of D2h- and D3h-symmetric cyclodextrin analogues alternating alpha,alpha'-trehalose disaccharide subunits and pseudoamide segments (cyclotrehalans, CTs) are reported. The conformational properties of these cyclooligosaccharides are governed by the rigidity of the alpha,alpha'-trehalose disaccharide repeating unit and the partial double-bond character of the N-(C=X) linkages. In contrast to the typical concave-shaped cavity of cyclodextrins (CDs), CTs feature a convex-shaped hydrophobic cavity in which the beta-face of the monosaccharide subunits is oriented toward the inner side, as supported by NMR and modeling (molecular mechanics and dynamics) studies. In the case of cyclodimeric CTs (CT2s), the existence of intramolecular hydrogen bonds results in collapsed cavities, too small to allow the formation of inclusion complexes with organic molecules. Cyclotrimeric CTs (CT3s) display cavity sizes that are intermediate between those of alphaCD and betaCD, ideally suited for the complexation of complementary guests with ternary symmetry such as adamantane 1-carboxylate (AC). The higher flexibility of the pseudoamide bridges as compared with classical glycosidic linkages endow these glyconanocavities with some conformational adaptability properties, making them better suited than CDs for complexation of angular guests, as seen from comparative inclusion capability experiments against the fluorescent probes 6-p-toluidinonaphthalene-2-sulfonate (TNS; linear) and 8-anilinonaphthalene-1-sulfonate (ANS; angular).     

Synthesis of novel polyyne analogues of sphingoid base via an iterative acetylene homologation sequence

The first syntheses of polyyne-containing sphingoid base analogues were achieved by employing our iterative strategy that uses a two-step acetylene homologation sequence. In this process, a bromoalkyne is homologated by one acetylene unit through a Pd-catalyzed cross-coupling with a TIPS-protected acetylene and a subsequent in situ AgF-mediated desilylative bromination. Repeating this homologation sequence followed by cross-coupling with the long-chained terminal acetylene provides access to the polyyne framework in good overall yields.     

Dialkylaluminum hydride-promoted cyclodimerization of silylated 1,3-enynes via skeletal rearrangement

The dialkylaluminum hydride-promoted reaction of 1-silylalk-3-en-1-ynes gave symmetrical 1,2,3,5-tetrasubstituted benzenes as single regioisomers. The novel cyclodimerization via skeletal rearrangement can be rationalized by an unprecedented mechanism involving sequential hydroalumination, alkene isomerization, carboalumination, carbon-carbon bond cleavage, and retro-hydroalumination.     

Synthesis of the non-reducing end trisaccharide of the antithrombin-binding domain of heparin and its bioisosteric sulfonic acid analogues

A glucoronic acid-containing trisaccharide related to the antithrombin-binding DEFGH domain of heparin and its methanesulfonic acid analogues were synthesized. Trisaccharides without sulfonic acid content or possessing a sulfonatomethyl moiety at position 2 or 6 of unit F were prepared in high yields by [DE+F] couplings using the same disaccharide uronate donor, respectively. Synthesis of the trisaccharide with a 3-deoxy-3-sulfonatomethyl function was accomplished in three different pathways, from which a [D+EF] coupling and applying a non-oxidized precursor of the glucuronic acid afforded the trisaccharide in the highest yield.     

Synthesis of S-linked carbohydrate analogues via a Ferrier reaction

In this work, the synthetic utility of the Ferrier reaction to access S-linked disaccharides and S-linked glycoamino acids has been probed. Significantly, entry to a range of 1,4- and 1,6-S-linked disaccharides has been achieved using glycals derived from glucose and galactose, and sulfur containing coupling partners derived from methyl α-d-glucopyranoside. Access to S-linked glycoamino acids and glycopeptides has also been achieved using protected cysteine and homocysteine coupling partners within the Ferrier reaction. Functionalisation of the Ferrier products, for example, via dihydroxylation using OsO₄ or amino acid coupling, and deprotection of the targets have also been achieved. In this way, entry to materials of interest as mimics of biologically interesting disaccharides and glycopeptides has been realised, including targets derived from rare sugars such as talopyranose and gulopyranose.     

Synthesis of the Lewis a trisaccharide based on an anomeric silyl fluorous tag

The synthesis of the trisaccharide Lewis a was performed using an anomeric fluorous silyl protective group. This methodology allowed us to fully characterize each product (NMR, MS) and monitor each synthetic step (TLC). Although the product purifications could be performed by fluorous-solid-phase extraction (F-SPE) technology, standard chromatography could be used to effect purification if necessary. Trichloroethoxy carbonyl (Troc) protection of the amino group of the glucosamine moiety was found essential to allow protecting group manipulation of the fluorous protected sugar.     

Synthesis of new furocoumarin analogues via cross-coupling reaction of triflate

Furocoumarins such as psoralen or angelicin showed important biological activities. We present here the synthesis of new furocoumarin analogues via Suzuki or Sonogashira cross-coupling reaction of triflate.     

Synthesis of Ugi-4CR boronate analogues via microwave irradiation

The synthetic condition for the synthesis of boronate ester Ugi-4CR analogs under mild conditions was developed. The reported reactions were carried out in methanol and promoted by microwave heating. This synthetic strategy could provide unique access to a broad range of boron-containing chemical libraries.     

Synthesis of chiral and modifiable hexahydroxydiphenoyl compounds

A reliable method for synthesizing each enantiomer of the hexahydroxydiphenoyl (HHDP) compounds has been developed. The synthesis involved atropselective construction of the aryl-aryl bond of the HHDP compounds. This construction relied on the CuCl(2)·n-BuNH(2)-mediated intramolecular coupling of bis(4-O-benzylgallate) on two simple chiral auxiliaries, both of which were derived from l-(+)-tartaric acid. The coupling reaction realized complete or near-perfect atropselectivity. The two auxiliaries induced opposite axial chirality despite their identical origin. The diastereoselectivities of these couplings were probably controlled kinetically. Modifications of the free phenolic hydroxy groups and the carbonyl groups in the resulting HHDP compounds demonstrated the potential derivatization of a wide variety of HHDP analogues.     

Synthesis of the pyridinyl analogues of dibenzylideneacetone (pyr-dba) via an improved Claisen-Schmidt condensation, displaying diverse biological activities as curcumin analogues

An efficient and easy procedure to synthesize the pyridinyl analogues of dibenzylideneacetone (pyr-dba) was developed by the condensation of substituted nicotinaldehyde and acetone in the presence of K(2)CO(3) in toluene-EtOH-H(2)O solvent system. Structurally diverse pyr-dba, including quinolinyl dba, can be prepared conveniently in moderate to excellent yields under mild conditions with this method. The resulting pyr-dba functioned as the enone analogs of curcumin and efficiently inhibited the activation of NF-κB and the growth of colorectal carcinoma HCT116 p53+/+ cells as well as the HIV-1 IN-LEDGF/p75 interaction.     

Synthesis of the trisaccharide portion of the immunologic adjuvant QS-21A via sulfonium-mediated oxidative and dehydrative glycosylation

[see structure]. The first synthesis of the trisaccharide fragment of the potent immunologic adjuvant QS-21A is reported. The key steps involve the application of sulfonium-mediated oxidative and dehydrative glycosidic couplings to construct the anomeric linkages in a short and convergent assembly of the branched trisaccharide.     

Synthesis of benzaldehyde-functionalized LewisX trisaccharide analogs for glyco-SAM formation

LewisX (Le^x) antigen based carbohydrate–carbohydrate interactions are mediated by complexation of metal ions. Although theoretical studies about the influence of participating hydroxyl groups in the Le^x trisaccharide head group (Galβ(1-4)[Fucα(1-3)]GlcNAc) could gave same rudimental information about the basic mechanism behind this interaction, a little is known about orientation and configuration of the hydroxyl groups required for the specific interaction mediated by Ca²⁺ complexation. Therefore, there is a need of non-natural derivatives to provide detailed information about the requirements for hydroxyl group arrangement in Le^x head group surface plasmon resonance and gold nanoparticle techniques have shown to be powerful tools to investigate carbohydrate–carbohydrate interactions. Benzaldehyde-functionalized glycans can be used for attachment to both gold nanoparticles and surface plasmon resonance sensor surfaces. Therefore, seven benzaldehyde equipped Le^x analogs including the natural trisaccharide were synthesized utilizing convergent approach. The derivatives were applied in ongoing carbohydrate–carbohydrate interaction studies by surface plasmon resonance experiments to prove theoretical postulate about the structural requirements of hydroxyl group arrangements in Le^x trisaccharides.     

Synthesis of chiral pilocarpine analogues via a C-8 ketone intermediate

The synthesis of a chiral pilocarpine analogue 3 in which the lactone ring is replaced by an oxazolidinone and the bridging methylene group is in the ketone oxidation state has been accomplished. The utility of this compound as a key intermediate for the preparation of more complex structures was demonstrated by its reduction to two alcohol epimers and its reaction with a methylene ylide.     

Oligosaccharide Analogues of Polysaccharides. Part 7. Synthesis of a monosaccharide-derived monomer for amylose and cyclodextrin analogues

The synthesis of monomers of type C (Scheme 1) is described. In a first approach, chloro-acetyl-addition to the dioxolane 2 (Scheme 2), followed by treatment of the resulting chlorides 3 (α-D /β-D 1:3) with excess AgOTf and Bu₃SnC?CSiMe₃ gave the axial C-alkynyl-glycoside 4 (31%) and the C-arylglycoside 5 (29%). The structure of the dialkyne 6 , obtained by deacetylation of 4 , was established by X-ray analysis. The yield of the C-alkynyl-glycoside was slightly improved by protecting the C(4)-ethynyl group as the triethysilyl derivative, but not by substituting the benzyl by allyl or 2,6-difluorobenzyl groups. Silylation of the diol 1 with (chloro)diethyl[2-(trimethylsilyl)ethynyl]silane ( 19 ) resulted in 90% of the monosilyl ether 20 . HO? C(3) of 20 should favor coordination of a Lewis acid to O? C(6), and intramolecular, inverting acetal opening should lead to the product of axial alkynylation. Indeed, treatment of 20 with in situ generated BuAlCl₂, followed by treatment of the crude product with 0.1M HCl in MeOH, gave the dialkynylated triol 22 in yields of 85 to 90%. Under similar conditions, the disilyl ether 21 reacted more slowly to 22 (75%). The slower reaction correlates with the assumed intramolecular interaction of the precoordinated Lewis acid with O? C(6) in 20 .     

Synthesis of a library of complex macrodiolides employing cyclodimerization of hydroxy esters

The synthesis of complex macrodiolides involving microwave-accelerated transesterification of chiral, nonracemic, hydroxy esters is described. Methodology development studies indicate that both microwave power and reaction temperature play an important role in the efficiency of cyclodimerizations. Hydroxy ester monomer pairs were evaluated using an analytical rehearsal leading to the preparation of a 127-member library of highly diverse and stereochemically well-defined macrodiolides. Preliminary assays identified a novel macrodiolide antagonist of the kappa opioid receptor.     

Synthesis and electronic factors in thermal cyclodimerization of functionalized aromatic trifluorovinyl ethers

A series of 19 p-substituted aromatic trifluorovinyl ether compounds were prepared from versatile intermediate p-Br-C(6)H(4)-O-CF=CF(2) and underwent thermal radical mediated cyclodimerization to new difunctional compounds containing the 1,2-disubstituted perfluorocyclobutyl (PFCB) linkage. The synthetic scope demonstrates the functional group transformation tolerance of the fluorovinyl ether, and the dimers are useful as monomers for traditional step-growth polymerization methods. (19)F NMR spectra confirmed that p-substitution affects the trifluorovinyl ether group chemical shifts. The first kinetic studies and substituent effects on thermal cyclodimerization were performed, and the results indicated that electron-withdrawing groups slow the rate of cyclodimerization. The data were further analyzed using the Hammett equation, and reaction constants (rho) of -0.46 at 120 degrees C and -0.59 at 130 degrees C were calculated. This study presents the first liner free energy relationship reported for the cyclodimerization of aromatic trifluorovinyl ethers to PFCB compounds.