Synthesis and Conformational Analysis of Novel Trimeric Maleimide Cross-Linking Reagents

Nine homotrifunctional cross-linking reagents are presented. Their synthesis and chemical properties as well as their characterization by classical mechanical conformational searching techniques is reported. Mixed Low Mode and Monte Carlo searching techniques were used to exhaustively sample the OPLS2005/GBSA(water) potential energy surface of trisubstituted cyclohexane and benzene derivatives of C3 symmetry. Geometric structure, molecular length, and hydrogen-bonding patterns were analyzed. Nonaromatic compounds exhibited exclusively chair conformations at low energies, with a preference for axial or equatorial arms depending upon the presence of additional ring substituent Me groups. Increasing chain length often resulted in overall shorter molecular length due to additional chain flexibility. These results were consistent with one- and two-dimensional temperature-dependent NMR studies.

Synthesis and anti-HIV activity of trivalent CD4-mimetic miniproteins

A series of trivalent CD4-mimetic miniproteins was synthesized, in which three CD4M9 miniprotein moieties were tethered on a threefold-symmetric scaffold. The trivalent miniproteins were designed to target the CD4-binding sites displayed in the trimeric gp120 complex of HIV-1. The synthesis takes advantage of the highly efficient ligation between a cysteine-tagged CD4M9 miniprotein and a suitable trivalent maleimide that varied in the nature and length of spacer. Antiviral assay revealed that most of the synthetic trivalent miniproteins demonstrated significantly enhanced anti-HIV activities over the monomeric CD4M9 against both R5- and X4-tropic viruses, indicating the beneficial multivalent effects. One compound that possesses a hydrophobic linker was shown to be 140-fold more active than CD4M9 against HIV-1(Bal) infection, implicating a positive contribution of the lipid portion to the antiviral activity. It was also found that most of the trivalent miniproteins showed comparable anti-HIV activities in comparison with a typical bivalent miniprotein, regardless of the length of the linker. The results implicate a novel mechanism of the interactions between the multivalent inhibitors and the trimeric gp120 complex.

Effects of ethylene glycol addition on the aggregation and micellar growth of gemini surfactants

Micellization of three didodecyl dicationic dibromide gemini surfactants with different methylene spacer lengths, 12-s-12,2Br- where s = 3-5 methylene groups, has been investigated in water-ethylene glycol, EG, mixtures with weight percentages of EG up to 50%. Subsequently, effects of the addition of the organic solvent on the micellar growth of these surfactants and on the surfactant concentration range where sphere-to-rod transitions occur were studied by means of steady-state and time-resolved fluorescence quenching and spectroscopic measurements. Results show that an increase in the weight percentage of ethylene glycol added to aqueous 12-s-12,2Br- (s = 3-5) micellar solutions causes the sphere-to-rod transition to occur at higher surfactant concentrations than in pure water. The diminution in the average aggregation number, N(agg), when wt % EG increases, provoked by the decrease in the interfacial Gibbs energy contribution to DeltaG degrees M, is the main factor responsible for this observation. The decrease in N(agg) is accompanied by a decrease in the ionic interactions and the extra packing contribution to the deformation of the surfactants tails, making formation of cylindrical micelles less favorable. Besides, an increase in the solvent content and polarity of the interfacial region does not favor formation of direct ion pairs, decreasing the tendency of micelles to grow.

Glycosidase inhibitors as potential HIV entry inhibitors?

A few alpha-L-fucosidase inhibitors and alpha-D-glucosidase inhibitors have shown in vitro anti-HIV activities, that have been attributed to their ability to inhibit HIV entry. The mechanism of action of inhibitors such as 1-deoxynojirimycin (1) is not clearly established. One possible hypothesis is that the glycosidase inhibition affects the final conformation of the glycoproteins involved in the virus/cell recognition and fusion phenomena. This hypothesis is presented critically and the mechanisms of some glycoprotein biosynthesis are out-lined. Up to now, very few glycosidase inhibitors have been assayed for their potential as HIV entry inhibitors. Further assaying should be done and larger collections of glycosidase inhibitors should be prepared. To help investigations in that perspective, the inhibitory activities of alpha-glucosidase and alpha-L-fucosidase inhibitors have been summarized.

Stereoselective synthesis of (2S,3S,4R,5S)-5-methylpyrrolidine-3,4-diol derivatives that are highly selective α-l-fucosidase inhibitors

N-Phenylaminomethyl benzimidazolyl moieties attached at C-2 of (2S,3S,4R,5S)-5-methylpyrrolidine-3,4-diol increase the potency and selectivity of the inhibitory activity of these systems towards alpha-L-fucosidases.

Synthesis ofd- andl-2,3-trans-3,4-cis-4,5-trans-3,4-Dihydroxy-5-hydroxymethylproline and Tripeptides Containing Them

Enantiomerically pure (-)-(1R,4R,5R,6S)- and (+)-(1S,4S,5S,6R)-7-(tert-butoxycarbonyl)-5,6-exo-isopropylidenedioxy-7-azabicyclo[2.2.1]hept-2-one ((-)-3 and (+)-3) have been obtained from the Diels-Alder adduct of N-(tert-butoxycarbonyl)pyrrole and 2-bromo-1-(p-toluenesulfonyl)acetylene, including the Alexakis optical resolution of ketone (+/-)-3 via formation of cyclic aminals with (1R,2R)-diphenylethylenediamine. Compounds (-)-3 and (+)-3 were converted into d- and l-2,3-trans-3,4-cis-4,5-trans-N-(tert-butoxycarbonyl)-5-hydroxymethyl-3,4-isopropylidenedioxyprolines (-)-4 and (+)-4, respectively. Applying the Boc and Fmoc strategies of peptide synthesis, these compounds were used to construct two tripeptides containing the d- or l-2,3-trans-3,4-cis-4,5-trans-3,4-dihydroxy-5-hydroxymethylproline.

Synthesis and glycosidase inhibitory activities of 2-(aminoalkyl)pyrrolidine-3,4-diol derivatives

Several 2-(aminomethyl)-and 2-(2-aminoethyl)-pyrrolidine-3,4-diol derivatives have been assayed for their inhibitory activities towards glycosidases. Good inhibitors of alpha-mannosidases must have the (2R,3R,4S) configuration and possess 2-(benzylamino)methyl substituents. Stereomers with the (2S,3R,4S) configuration are also competitive inhibitors of alpha-mannosidases, but less potent as they share the configuration of C(1), C(2), C(3) of beta-D-mannosides rather than that of alpha-D-mannosides. Interestingly, (2S,3R,4S)-2-[2-[(4-phenyl)phenylamino]ethyl]pyrrolidine-3,4-diol (12g) inhibits several enzymes, for instance alpha-L-fucosidase from bovine epididymis (K(i)=6.5microM, competitive), alpha-galactosidase from bovine liver (K(i)=5microM, mixed) and alpha-mannosidase from jack bean (K(i)=102microM, mixed). Diamines such as (2R,3S,4R)-2-[2-(phenylamino) or 2-(benzylamino)ethyl]pyrrolidine-3,4-diol (ent-12a, ent-12b) inhibit beta-glucosidase from almonds (K(i)=13-40microM, competitive).

Specific activation of ERK pathways by chitin oligosaccharides in embryonic zebrafish cell lines

Chitin oligosaccharides (COs) play a role in plant development and are presumed to affect body plan formation during vertebrate embryogenesis. The mechanisms of COs recognition and cellular processes underlying embryonic development are still not understood. We analyze the possible link with the mitogen-activated protein kinase pathway that is conserved in evolution through the plant and animal kingdom and has been implicated in diverse cellular processes, including cell growth, proliferation, differentiation, survival, and vertebrate development. We show that in vivo stimulation of embryonic zebrafish cells ZF13 and ZF29 with chitin tetrasaccharides at 10-9 M concentration transiently induced activation/phosphorylation of extracellular regulated kinases (ERKs), with a maximum after 15 min. Furthermore the biological specificity of chitin tetrasaccharides and various derivatives was examined. The replacement of one or two GlcNAc residues of the chitin backbone by glucose and fucosylation of chitin tetrasaccharides at the reducing terminus caused a complete loss of their activity. We also tested a chitin tetrasaccharide analogue in which the oxygen atoms in glycosidic linkages were replaced by sulfur atoms. This analog, which could not be enzymatically hydrolyzed, was as potent an inducer as chitin tetrasaccharide. These results suggest that the observed activation of ERKs is chitin tetrasaccharide-specific and does not require further enzymatic processing. We examined possible signaling pathways leading to ERK activation by COs by use of phosphospecific antibodies and inhibitors. We conclude that a high-affinity CO receptor system exists that links to the Raf, MEK, and ERK pathway in zebrafish cells.

Hetaryleneaminopolyols and hetarylenecarbopeptoids: a new type of glyco- and peptidomimetics. Syntheses and studies on solution conformation and dynamics

Ready access to a new class of oligomers has been demonstrated by the synthesis of hetaryleneaminopolyols and hetarylenecarbopeptoids using 3-hydroxymethyl-5-(4-amino-4-deoxy-d-arabinotetritol-1-yl)-2-methylfuran and 5-(4-amino-4-deoxy-d-arabinotetritol-1-yl)-2-methyl-3-furoic acid as novel scaffolds. The conformational behavior of peptidomimetics 22, 23, 25, 26, and 36 have been analyzed by NMR spectroscopy and extensive molecular dynamics simulations. MD simulations using the GB/SA continuum solvent model for water and the MM3 force field provide a population distribution of conformers which satisfactorily agrees with the experimental NMR data for the torsional degrees of freedom of the molecule.

Stereoselective syntheses of 1,4-dideoxy-1,4-imino-octitols and novel tetrahydroxyindolizidines

A new route for the preparation of four new indolizidines, (1R,2S,6S,7S,8aS)- and (1R,2S,6R,7R,8aS)-1,2,6,7-tetrahydroxyindolizidine (30 and 32) and (1S,2R,7S,8S,8aR)- and (1S,2R,7R,8R,8aR)-1,2,7,8-tetrahydroxyindolizidine (44 and 46), is reported. The synthesis is based on Knoevenagel homologation of the readily available enantiomerically pure pyrrolidin-carbaldehydes 13 and 37followed by asymmetric dihydroxylation of the subsequent alkenyl pyrrolidines and cyclization of the corresponding imino-octitols. The new indolizidines and their precursors (imino-octitols 20, 25, 26) and indolizidinones 28a and 28b have been tested for inhibitory activities toward 26 glycosidases. The enzymatic inhibition of trans-7-hydroxy-d-(-)-swainsonine (44) toward alpha-mannosidases is similar to that described for trans-7-hydroxy-l-(+)-swainsonine (11b) toward naringinase (alpha-l-rhamnosidase from Penicillium decumbens).

Synthesis of [(2S,3S,4R)-3,4-dihydroxypyrrolidin-2-yl]-5-methylfuran-4-carboxylic acid derivatives: new leads as selective beta-galactosidase inhibitors

The preparation of [(2S,3S,4R)-3,4-dihydroxypyrrolidin-2-yl]furan derivatives in a stereoselective route starting from D-glucose and ethyl acetoacetate is presented. Ethyl ester (6), N,N-diethylamide (7) and N-isopropylamide (8) have been tested towards 25 glycosidases. Ester (6) is a selective inhibitor of beta-galactosidases. The new compounds represent a new type of imino-C-nucleoside analogues.

New leads for selective inhibitors of alpha-L-fucosidases. Synthesis and glycosidase inhibitory activities of [(2R,3S,4R)-3,4-dihydroxypyrrolidin-2-yl]furan derivatives

Readily derived from D-glucose, 5-[(2R,3S,4R)-3,4-dihydroxypyrrolidin-2-yl]-2-methyl-3-furoic esters and amides are selective and competitive inhibitors (K(i)> or = 3 microM) of alpha-L-fucosidase from bovine epididymis and from human placenta.

Derivatives of (2R,3R,4S)-2-aminomethylpyrrolidine-3,4-diol are selective alpha-mannosidase inhibitors

A collection of (2R,3R,4S)-3,4-dihydroxypyrrolidin-2-yl derivatives have been tested for their inhibitory activities toward 25 glycosidases. Competitive (K(i)=7.4 microM) and selective inhibition of alpha-mannosidase from jack bean has been found for (2R,3R,4S)-2-[(benzylamino)methyl]pyrrolidine-3,4-diol and other derivatives.