Building blocks for glycopeptide synthesis: glycosylation of 3-mercaptopropionic acid and Fmoc amino acids with unprotected carboxyl groups

Synthesis of N-glycosyl amides: conformational analysis and evaluation as inhibitors of β-galactosidase from E. coli

The synthesis of N-glycosyl amides typically involves the use of glycosyl amines as direct precursors, resulting in low yields due to hydrolysis and the loss of stereocontrol through anomerization processes. In this study, a sequential synthesis of N-glycosyl amides is proposed, employing glycosyl amines as intermediates obtained from glycosyl azides. Derivatives with gluco, galacto, or xylo configurations were synthesized. Hexose derivatives were obtained under stereocontrol to give only the β anomer, while the xylo derivatives provided a mixture of α and β anomers. Conformational analysis revealed that all β anomers adopted the 4C1 conformation, while α anomers were found in the 1C4 chair as the major conformer. After de-O-acetylation, the derivatives containing a galactose unit were evaluated as inhibitors of β-galactosidase from E. coli and were found to be moderate inhibitors.

Glycopeptide drugs: A pharmacological dimension between "Small Molecules" and "Biologics"

Peptides are an important class of molecules with diverse biological activities. Many endogenous peptides, especially neuropeptides and peptide hormones, play critical roles in development and regulating homeostasis. Furthermore, as drug candidates their high receptor selectivity and potent binding leads to reduced off-target interactions and potential negative side effects. However, the therapeutic potential of peptides is severely hampered by their poor stability in vivo and low permeability across biological membranes. Several strategies have been successfully employed over the decades to address these concerns, and one of the most promising strategies is glycosylation. It has been demonstrated in numerous cases that glycosylation is an effective synthetic approach to improve the pharmacokinetic profiles and membrane permeability of peptides. The effects of glycosylation on peptide stability and peptide-membrane interactions in the context of blood-brain barrier penetration will be explored. Numerous examples of glycosylated analogues of endogenous peptides targeting class A and B G-protein coupled receptors (GPCRs) with an emphasis on O-linked glycopeptides will be reviewed. Notable examples of N-, S-, and C-linked glycopeptides will also be discussed. A small section is devoted to synthetic methods for the preparation of glycopeptides and requisite amino acid glycoside building blocks.

Recovery, Purification, and Reusability of Building Blocks for Solid Phase Synthesis

Solid phase synthesis (SPS) is well established for the synthesis of biomacromolecules such as peptides, oligonucelotides, and oligosaccharides, and today is also used for the synthesis of synthetic macromolecules and polymers. The key feature of this approach is the stepwise assembly of building blocks on solid support, enabling monodispersity and monomer sequence control. However, in order to achieve such control, a high excess of building blocks is required during the reaction. Herein, the recovery, purification, and reusability of building blocks used in SPS, including representative examples of tailor-made building blocks, Fmoc-protected amino acids, and functionalized carbohydrate ligands, are reported for the first time. Results demonstrate the general applicability with recovery in high yields and high purity. Furthermore, the described recovery process can be applied in both manual and automated synthesis using a standard peptide synthesizer. Overall, this process is envisioned to be applicable for a large variety of building blocks used in the SPS of different types of molecules, and to contribute to more resourceful SPS syntheses.

Glycosylation of α-amino acids by sugar acetate donors with InBr3. Minimally competent Lewis acids

A simplified method for the preparation of Fmoc-serine and Fmoc-threonine glycosides for use in O-linked glycopeptide synthesis is described. Lewis acids promote glycoside formation, but also promote undesired reactions of the glycoside products. Use of 'minimally competent' Lewis acids such as InBr(3) promotes the desired activation catalytically, and with greatly reduced side products from sugar peracetates.

Multivalent dendrimeric compounds containing carbohydrates expressed on immune cells inhibit infection by primary isolates of HIV-1

Specific glycosphingolipids (GSL), found on the surface of target immune cells, are recognized as alternate cell surface receptors by the human immunodeficiency virus type 1 (HIV-1) external envelope glycoprotein. In this study, the globotriose and 3'-sialyllactose carbohydrate head groups found on two GSL were covalently attached to a dendrimer core to produce two types of unique multivalent carbohydrates (MVC). These MVC inhibited HIV-1 infection of T cell lines and primary peripheral blood mononuclear cells (PBMC) by T cell line-adapted viruses or primary isolates, with IC(50)s ranging from 0.1 to 7.4 μg/ml. Inhibition of Env-mediated membrane fusion by MVC was also observed using a dye-transfer assay. These carbohydrate compounds warrant further investigation as a potential new class of HIV-1 entry inhibitors. The data presented also shed light on the role of carbohydrate moieties in HIV-1 virus-host cell interactions.

Facile synthesis of glycosylated Fmoc amino acid building blocks assisted by microwave irradiation

The synthesis of glycosylated Fmoc amino acids by reaction of mono- and disaccharide peracetates with Fmoc amino acids having free carboxyl groups was rapidly promoted by Lewis acids (SnCl(4), BF(3)·Et(2)O) under microwave irradiation. The products are useful building blocks for the synthesis of glycopeptides.

Radiolabelled153Sm-chelates of glycoconjugates: multivalence and topology effects on the targeting of the asialoglycoprotein receptor

In this paper we report and discuss the biodistribution studies with Wistar rats of a series of153Sm(III)-glycoconjugates, based on DO3A and DO2A(cis) scaffolds (DO3A=1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane; DO2A(cis) = 1,4-bis(carboxymethyl)-1,4,7,10-tetraazacyclododecane). The effects of changing the sugar type (galactose, lactose and glucose), valency (mono and divalent) and topology on the targeting ability of the liver asialoglycoprotein receptor (ASGPR) are evaluated. Divalent glycoconjugates with different topologies were generated by a pendant glycodendrimeric (generation 1) architecture on a DO3A scaffold and by a linear DO2A(cis)-bis derivative. The results show that the galactose conjugates are more target efficient than the lactose analogues, while the glucose conjugates have no liver targeting ability. Divalent galactose conjugates are more efficiently targeted to the liver than the monovalent ones, while the dendrimeric topology of DO3A-Gal2has higher targeting efficiency than that of the DO2A(cis)-Gal2.

Conformational consequences of protein glycosylation: preparation of O-mannosyl serine and threonine building blocks, and their incorporation into glycopeptide sequences derived from alpha-dystroglycan

With the goal to investigate the structural impact of O-mannosyl glycosylation on alpha-dystroglycan, a glycoprotein that has an important role in the extracellular organization of muscle, glycopeptides derived from its mucin-like sequence have been prepared by solid-phase peptide synthesis. Two approaches have been explored to obtain needed mannosylated serine and threonine building blocks. With the alpha-carboxyl group unprotected, and with tetraaceto-1-fluoro-alpha-D-mannose as the sugar donor, the desired alpha-O-mannosyl-Fmoc-Ser/Thr formed, along with mannosyl ester isomers and the species with mannose attached to both hydroxyl and carboxyl functions. Relevant mechanistic questions and stability issues were elucidated. Alternatively, building blocks were made with the alpha-carboxyl protected/activated as the pentafluorophenyl (Pfp) ester. Glycopeptides synthesized herein contained 5-9 residues, and featured one, two, and four consecutive Ser and/or Thr residues O-glycosylated with mannose. Circular dichroism (CD) spectra for Man-containing glycopeptides recorded in water show them to be not well ordered. For one of the alpha-dystroglycan-derived sequences, the comparative conformational consequences of glycosylation by either Man or GalNAc have been examined by CD and NMR, with both methods showing a more organized structure when GalNAc is present.

Targeting the central nervous system: In vivo experiments with peptide-derivatized nanoparticles loaded with Loperamide and Rhodamine-123

Polymeric nanoparticles (Np) represent one of the most innovative non-invasive approaches for the drug delivery to the central nervous system (CNS). It is known that the ability of the Np to cross the Blood Brain Barrier (BBB), thus allowing the drugs to exert their pharmacological activity in the central nervous district, is linked to their surface characteristics. Recently it was shown that the biocompatible polyester poly(d,l-lactide-co-glycolide) (PLGA) derivatized with the peptide H(2)N-Gly-l-Phe-d-Thr-Gly-l-Phe-l-Leu-l-Ser(O-beta-d-Glucose)-CONH(2) [g7] was a useful starting material for the preparation of Np (g7-Np); moreover, fluorescent studies showed that these Np were able to cross the BBB. In this research, g-7 Np were loaded with Loperamide in order to assess their ability as drug carriers for CNS, and with Rhodamine-123, in order to qualitatively determine their biodistribution in different brain macro-areas. A pharmacological evidence is given that g7-Np are able to cross the BBB, ensuring, for the first time, a sustained release of the embedded drug, and that these Np are able to reach all the brain areas here examined. The ability to enter the CNS appears to be linked to the sequence of the peptidic moiety present on their surface.

N-Terminal Sugar Conjugation and C-Terminal Thr-for-Thr(ol) Exchange in Radioiodinated Tyr3-octreotide: Effect on Cellular Ligand Trafficking in Vitro and Tumor Accumulation in Vivo

For effective targeting of somatostatin receptor (sst) expressing tumors by radiolabeled octreotide analogues, high ligand uptake into sst-positive cells is mandatory. To optimize it, two modifications have been introduced into [(125)I]Tyr(3)-octreotide ([(125)I]TOC): C-terminal Thr-for-Thr(ol) exchange (leading to Tyr(3)-octreotate (TOCA)) and N-terminal derivatization with different carbohydrates. Both have significant impact on radioligand uptake into sst(2)-expressing cells in vitro and in vivo. Glucose conjugation via Amadori reaction by itself led to improved tumor uptake of [(123)I]Gluc-TOC in vivo, which is based on an enhancement of peptide internalization despite a reduction in receptor affinity. In the case of the doubly modified analogues [(123)I]Gluc-TOCA, [(123)I]Gluc-S-TOCA, and [(123)I]Gal-S-TOCA, a cumulative effect of both structural modifications was observed, leading up to a 5-fold increased uptake of these compounds in sst-expressing tumors compared to [(125)I]TOC. Thus, glycosylation with small carbohydrates was found to be a suitable tool to enhance receptor-mediated uptake of radiolabeled octreotide analogues into sst-positive malignancies, leading to tracers with excellent characteristics for in vivo sst-imaging applications.

Modulation of Pharmacokinetics of Radioiodinated Sugar-Conjugated Somatostatin Analogues by Variation of Peptide Net Charge and Carbohydration Chemistry

Sugar conjugation of biooactive peptides has been shown to be a powerful tool to modulate peptide pharmacokinetics. In the case of radiolabeled somatostatin analogues developed for in vivo scintigraphy of somatostatin receptor (sst) expressing tumors, it generally led to tracers with predominant renal excretion and low uptake in nontarget organs, and in some cases also with enhanced tumor accumulation. Especially with respect to endoradiotherapeutic applicability of these tracers, however, understanding the structural requirements for minimal kidney accumulation and maximal tumor uptake is important. The aim of this study was therefore the evaluation of the potential of specific glycoside structures in combination with reduced peptide net charge to reduce kidney accumulation without affecting tumor accumulation. Three glyco analogues of radioiodinated Tyr(3)-octreotate (TOCA) with z = 0 were evaluated in a comparative study using [(125)I]Mtr-TOCA (z = +1), the maltotriose-Amadori analogue of [(125)I]TOCA, as a reference, [(125)I]Glucuron-TOCA, the Amadori conjugate with glucuronic acid, and [(125)I]Gluc-S- and [(125)I]Gal-S-TOCA, the coupling products with glucosyl- and mannosyl-mercaptopropionate. In cells transfected with sst(1)-sst(5), all three new analogues show sst-subtype binding profiles similar to I-Mtr-TOCA with high, but somewhat reduced, affinity for sst(2). In contrast, internalization into sst(2)-expressing cells (in % of [(125)I]Tyr(3)-octreotide ([(125)I]TOC)) as well as the EC(50,R) of unlabeled TOC for internalization determined in dual-tracer experiments are substantially enhanced for [(123)I]Gal-S-TOCA and [(123)I]Gluc-S-TOCA (internalization, 190% +/- 12% and 265% +/- 20%, respectively, vs 168% +/- 6% of [(125)I]TOC for [(123)I]Mtr-TOCA; EC(50,R), 2.62 +/- 0.07 and 2.96 +/- 0.14, respectively, vs 1.81 +/- 0.07 for [(123)I]Mtr-TOCA). The tumor accumulation of [(125)I]Gal-S-TOCA and [(125)I]Gluc-S-TOCA in AR42J tumor-bearing nude mice 1 h p.i. is consequently very high (22.6 +/- 2.2 and 26.2 +/- 5.6%ID/g) and comparable to that of [(125)I]Mtr-TOCA (25.1 +/- 4.4%ID/g). [(125)I]Glucuron-TOCA showed lower uptake in sst-expressing tissues than did [(125)I]Mtr-TOCA, but considerably enhanced accumulation in nontarget organs such as liver, intestine, and kidney. Due to increased lipophilicity, hepatic and intestinal uptake 1 and 4 h p.i. of [(125)I]Gal-S-TOCA and [(125)I]Gluc-S-TOCA was also slightly higher than that of [(125)I]Mtr-TOCA. Kidney accumulation, however, was reduced by approximately 50% for both compounds (2.6 +/- 0.3 and 2.2 +/- 0.4, respectively, vs 4.0 +/- 0.7%ID/g at 1 h p.i.). Because no sugar-specific effect was detected in the latter case, it is concluded that general ligand pharmacokinetics and especially kidney accumulation of the tracers investigated are mainly determined by physicochemical characteristics such as lipophilicity, net charge, and also charge distribution ([(125)I]Glucuron-TOCA vs [(125)I]Gal-S- and [(125)I]Gluc-S-TOCA). With respect to receptor targeting, however, the structure of the carbohydrate moiety plays an important role, leading to dramatically enhanced ligand internalization, especially in the case of [(123)I]Gluc-S-TOCA. Taking into account the combined effects of the Gluc-S-moiety both on kidney and on tumor accumulation, this group seems to be a promising synthon for the synthesis of other radiolabeled peptide analogues with improved pharmacokinetics.

First (18)F-labeled tracer suitable for routine clinical imaging of sst receptor-expressing tumors using positron emission tomography

PURPOSE

Despite excellent radionuclide characteristics, no (18)F-labeled peptides are available for quantitative peptide receptor mapping using positron emission tomography (PET) so far, mainly due to time-consuming multistep radiosyntheses with limited overall yields. A newly developed two-step chemoselective conjugation method allows rapid and high-yield [(18)F]fluorination of peptides via oxime formation and was applied for the synthesis of new (18)F-labeled carbohydrated Tyr(3)-octreotate (TOCA) analogs with optimized pharmacokinetics suitable for clinical routine somatostatin-receptor (sst) imaging.

EXPERIMENTAL DESIGN

(18)F-labeled glucose (Gluc-S-) and cellobiose (Cel-S-) derivatives of aminooxy-functionalized TOCA were synthesized via oxime formation with 4-[(18)F]fluorobenzaldehyde ([(18)F]FBOA-peptides). Both the in vitro internalization profile of Gluc-S-Dpr([(18)F]FBOA)TOCA and Cel-S-Dpr([(18)F]FBOA)TOCA in hsst(2)-expressing Chinese hamster ovary cells (dual tracer protocol) and their biodistribution in AR42J tumor-bearing mice were investigated and compared with two [(18)F]fluoropropionylated ([(18)F]FP) analogs, Gluc-Lys([(18)F]FP)TOCA and Gluc-S-Dpr([(18)F]FP)TOCA.

RESULTS

In contrast to [(18)F]FP-labeling (3 h), chemo-selective [(18)F]FBOA-formation (50 min) afforded the respective radiopeptides in high yields (65-85%). In vitro, Gluc-S-Dpr([(18)F]FBOA)TOCA and Cel-S-Dpr([(18)F]FBOA)-TOCA showed high internalization (139 +/- 2 and 163 +/- 8 of the reference [(125)I]Tyr(3)-octreotide, respectively), which was reflected by high tumor accumulation in vivo [21.8 +/- 1.4 and 24.0 +/- 2.5% of injected dose/g (1 h), respectively]. How-ever, only Cel-S-Dpr([(18)F]FBOA)TOCA and Gluc-S-Dpr([(18)F]FP)TOCA (tumor: 15.1 +/- 1.5% of injected dose/g) with its very low accumulation in all of the nontarget organs showed improved tumor:organ ratios compared with Gluc-Lys([(18)F]FP)TOCA. For Cel-S-Dpr([(18)F]FBOA)TOCA,tumor:organ ratios (1 h) were 42:1, 27:1, 15:1, 3:1, and 208:1 for blood, liver, intestine, kidney, and muscle, respectively.

CONCLUSION

Due to the fast and high-yield chemoselective radiofluorination strategy and to its excellent pharmacokinetics, Cel-S-Dpr([(18)F]FBOA)TOCA represents the first tracer suitable for routine clinical application in PET somatostatin receptor imaging.

Influence of saccharide size on the cellular immune response to glycopeptides

Glycopeptides that bind to MHC molecules on antigen presenting cells may elicit carbohydrate selective T cells. In order to investigate how the cellular immune response depends on the size of the carbohydrate moiety, a trigalactosylated derivative of an immunogenic peptide from hen egg-white lysozyme (HEL52-61) was prepared. Synthesis was accomplished by assembly of an alpha-1,4-linked trigalactose peracetate which was coupled to Fmoc serine. After activation as a pentafluorophenyl ester the resulting building block was used in solid-phase synthesis In contrast to the corresponding mono- and digalactosylated derivatives of HEL52-61, the trigalactosylated HEL52-61 was not immunogenic. Somewhat surprisingly, this was found to be because the trigalactosyl derivative bound approximately two orders of magnitude weaker to I-Ak MHC molecules than the mono- and digalactosyl peptides. Our observation suggests an explanation for previous findings, which show that glycopeptides isolated from MHC molecules in nature usually carry small saccharides.

"Multivalent" saccharides: development of new approaches for inhibiting the effects of glycosphingolipid-binding pathogens

A number of diseases are initiated by the adherence of viruses, bacteria, or bacterial toxins to cell surface carbohydrates, a number of which are components of glycosphingolipids (GSLs). Studies of the binding of lectins indicated that many adhered weakly to monomeric carbohydrate ligands. The seminal observation that lectins adhered more strongly to a ligand with multiple carbohydrate binding sites initiated a plethora of studies designed to identify effective "multivalent" carbohydrate ligands for pathogens expressing multiple carbohydrate-binding sites. In addition to more completely defining ligand specificity of the carbohydrate-binding pathogen, identification of "multivalent" carbohydrate ligands has led to studies of their efficacy as pathogen inhibitors. This commentary focuses on pathogens that recognize the carbohydrate portion of GSLs. Because many GSL-binding pathogens have been shown to bind "multivalent" saccharides, approaches for identifying and preparing them as well as methods for characterizing their effectiveness as ligands are reviewed. Also discussed are areas of promise that should be investigated and pitfalls that might be encountered in the development of "multivalent" saccharides as pharmacologic agents.

Carbohydrate–protein interactions at interfaces: comparison of the binding of Ricinus communis lectin to two series of synthetic glycolipids using surface plasmon resonance studies

Two C-lactosyl lipids and the related C-galactosyl lipids have been synthesised and their binding to RCA120 plant lectin was compared with a second series of thiolactosylethoxyalkanes. The interactions were measured quantitatively in real time by surface plasmon resonance (BIAcore) at a range of concentrations and temperatures from 5 to 30 degrees C. The C-galactosyl lipid (1,3-dimethyl-5-[beta-D-galactopyranosyl]-5-(4-octadecyloxybenzyl)pyrimidine-2,4,6-trione) bound much more weakly with a K(A) = 8.86 x 10(5) than the corresponding C-lactosyl lipid (1,3-dimethyl-5-[beta-D-galactopyranosyl-(1 --> 4)-beta-D-glucopyranosyl]-5-(4-octadecyloxybenzyl)pyrimidine-2,4,6-trione) (K(A) = 2.31 x 10(7)). The influence of the linker region of the two different series of lactosyl lipids was clearly demonstrated by the differences in the binding to RCA120 lectin. The changes in kinetic values and in the enthalpic and entropic contribution to the free energy of binding reflected the importance of the linker and the hydrocarbon anchor holding the synthetic glycolipids in the neomembrane.

Immobilisation on polystyrene of diazirine derivatives of mono- and disaccharides: biological activities of modified surfaces

The potential of surface glycoengineering for biomaterials and biosensors originates from the importance of carbohydrate-protein interactions in biological systems. The strategy employed here utilises carbene generated by illumination of diazirine to achieve covalent bonding of carbohydrates. Here, we describe the synthesis of an aryl diazirine containing a disaccharide (lactose). Surface analysis techniques [X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectroscopy (ToF-SIMS)] demonstrate its successful surface immobilisation on polystyrene (PS). Results are compared to those previously obtained with an aryl diazirine containing a monosaccharide (galactose). The biological activity of galactose- or lactose-modified PS samples is studied using rat hepatocytes, Allo A lectin and solid-phase semi-synthesis with alpha-2,6-sialyltransferase. Allo A shows some binding to galactose-modified PS but none to lactose-modified surfaces. Similar results are obtained with rat hepatocytes. In contrast, sialylation of lactose-modified PS is achieved but not with galactose-modified surfaces. The different responses indicate that the biological activity depends not only on the carbohydrate per se but also on the structure and length of the spacer.

Solid-phase synthesis of O-linked glycopeptide analogues of enkephalin

The synthesis of 18 N-alpha-FMOC-amino acid glycosides for solid-phase glycopeptide assembly is reported. The glycosides were synthesized either from the corresponding O'Donnell Schiff bases or from N-alpha-FMOC-amino protected serine or threonine and the appropriate glycosyl bromide using Hanessian's modification of the Koenigs-Knorr reaction. Reaction rates of D-glycosyl bromides (e.g., acetobromoglucose) with the L- and D-forms of serine and threonine are distinctly different and can be rationalized in terms of the steric interactions within the two types of diastereomeric transition states for the D/L and D/D reactant pairs. The N-alpha-FMOC-protected glycosides [monosaccharides Xyl, Glc, Gal, Man, GlcNAc, and GalNAc; disaccharides Gal-beta(1-4)-Glc (lactose), Glc-beta(1-4)-Glc (cellobiose), and Gal-alpha(1-6)-Glc (melibiose)] were incorporated into 22 enkephalin glycopeptide analogues. These peptide opiates bearing the pharmacophore H-Tyr-c[DCys-Gly-Phe-DCys]- were designed to probe the significance of the glycoside moiety and the carbohydrate-peptide linkage region in blood-brain barrier (BBB) transport, opiate receptor binding, and analgesia.

Glycopeptide synthesis and the effects of glycosylation on protein structure and activity

Despite the omnipresence of protein glycosylation in nature, little is known about how the attachment of carbohydrates affects peptide and protein activity. One reason is the lack of a straightforward method to access biologically relevant glycopeptides and glycoproteins. The isolation of homogeneous glycopeptides from natural sources is complicated by the heterogeneity of naturally occuring glycoproteins. It is chemical and chemoenzymatic synthesis that is meeting the challenge to solve this availability problem, thus playing a key role for the advancement of glycobiology. The current art of glycopeptide synthesis, albeit far from being routine, has reached a level of maturity that allows for the access to homogeneous and pure material for biological and medicinal research. Even the ambitious goal of the total synthesis of an entire glycoprotein is within reach. It is demonstrated that with the help of synthetic glycopeptides the effects of glycosylation on protein structure and function can be studied in molecular detail. For example, in immunology, synthetic (tumour-specific) glycopeptides can be used as immunogens to elicit a tumour-cell-specific immune response. Again, synthetic glycopeptides are an invaluable tool to determine the fine specificity of the immune response that can be mediated by both carbohydrate-specific B and T cells. Furthermore, selected examples for the use of synthetic glycopeptides as ligands of carbohydrate-binding proteins and as enzyme substrates or inhibitors are presented.

Glycosylation/Hydroxylation-induced stabilization of the collagen triple helix. 4-trans-hydroxyproline in the Xaa position can stabilize the triple helix

We have shown recently that glycosylation of threonine in the peptide Ac-(Gly-Pro-Thr)(10)-NH(2) with beta-d-galactose induces the formation of a collagen triple helix, whereas the nonglycosylated peptide does not. In this report, we present evidence that a collagen triple helix can also be formed in the Ac-(Gly-Pro-Thr)(10)-NH(2) peptide, if the proline (Pro) in the Xaa position is replaced with 4-trans-hydroxyproline (Hyp). Furthermore, replacement of Pro with Hyp in the sequence Ac-(Gly-Pro-Thr(beta-d-Gal))(10)-NH(2) increases the T(m) of the triple helix by 15.7 degrees C. It is generally believed that Hyp in the Xaa position destabilizes the triple helix because (Pro-Pro-Gly)(10) and (Pro-Hyp-Gly)(10) form stable triple helices but the peptide (Hyp-Pro-Gly)(10) does not. Our data suggest that the destabilizing effect of Hyp relative to Pro in the Xaa position is only true in the case of (Hyp-Pro-Gly)(10). Increasing concentrations of galactose in the solvent stabilize the triple helix of Ac-(Gly-Hyp-Thr)(10)-NH(2) but to a much lesser extent than that achieved by covalently linked galactose. The data explain some of the forces governing the stability of the annelid/vestimentiferan cuticle collagens.

Synthesis of single- and double-chain fluorocarbon and hydrocarbon galactosyl amphiphiles and their anti-HIV-1 activity

Galactosylceramide (GalCer) is an alternative receptor allowing HIV-1 entry into CD4(-)/GalCer(+) cells. This glycosphingolipid recognizes the V3 loop of HIV gp120, which plays a key role in the fusion of the HIV envelope and cellular membrane. To inhibit HIV uptake and infection, we designed and synthesized analogs of GalCer. These amphiphiles and bolaamphiphiles consist of single and double hydrocarbon and/or fluorocarbon chain beta-linked to galactose and galactosamine. They derive from serine (GalSer), cysteine (GalCys), and ethanolamine (GalAE). The anti-HIV activity and cytotoxicity of these galactolipids were evaluated in vitro on CEM-SS (a CD4(+) cell line), HT-29, a CD4(-) cell line expressing high levels of GalCer receptor, and/or HT29 genetically modified to express CD4. GalSer and GalAE derivatives, tested in aqueous medium or as part of liposome preparation, showed moderate anti-HIV-1 activities (IC50 in the 20-220 microM range), whereas none of the GalCys derivatives was found to be active. Moreover, only some of these anti-HIV active analogs inhibited the binding of [3H]suramin (a polysulfonyl compound which displays a high affinity for the V3 loop) to SPC3, a synthetic peptide which contains the conserved GPGRAF region of the V3 loop. Our results most likely indicate that the neutralization of the virion through masking of this conserved V3 loop region is not the only mechanism involved in the HIV-1 antiviral activity of our GalCer analogs.

The synthesis and structure of the derivatives of 2-deoxy-2-hydroxyimino-D-lyxo-hexopyranosyl-L-cysteine and -thiophenol

3,4,6-Tri-O-acetyl-2-deoxy-2-hydroxyimino-beta and -alpha-D-lyxo-hexopyranosides of thiophenol (3, 4) and the methyl ester of N-benzoyl-L-cysteine have been synthesised by condensation of 3,4,6-tri-O-acetyl-2-deoxy-2-nitroso-alpha-D-galactopyranosyl chloride with thiophenol and the L-cysteine derivative, respectively. The conformation of the sugar residue and configuration of the anomeric centre as well as of the hydroxyimino group were established on the basis of the 1H NMR (DQF-COSY, ROESY, TOCSY) spectrometric techniques and polarimetric data. Additionally, the structure of S-[3,4,6-tri-O-acetyl-2-deoxy-2-(Z)-hydroxyimino-beta-D-lyxo -hexopyranosyl]-thiophenol (3) was supported by X-ray diffraction data.

Sweet is stable: glycosylation stabilizes collagen

For most collagens, the melting temperature (T(m)) of the triple-helical structure of collagen correlates with the total content of proline (Pro) and 4-trans-hydroxyproline (Hyp) in the Xaa and Yaa positions of the -Gly-Xaa-Yaa- triplet repeat. The cuticle collagen of the deep-sea hydrothermal vent worm Riftia pachyptila, despite a very low content of Pro and Hyp, has a relatively high thermal stability. Rather than Hyp occupying the Yaa position, as is normally found in mammalian collagens, this position is occupied by threonine (Thr) which is O-glycosylated. We compare the triple-helix forming propensities in water of two model peptides, Ac-(Gly-Pro-Thr)(10)-NH(2) and Ac-(Gly-Pro-Thr(Galbeta))(10)-NH(2), and show that a collagen triple-helix structure is only achieved after glycosylation of Thr. Thus, we show for the first time that glycosylation is required for the formation of a stable tertiary structure and that this modification represents an alternative way of stabilizing the collagen triple-helix that is independent of the presence of Hyp.

Neuronorm is a potent and water soluble neurokinin A receptor antagonist

We report here the synthesis and preliminary pharmacological characterization of a novel water soluble Neurokinin A receptor antagonist named Neuronorm. The synthesis was achieved in high yield by a combination of classical peptide synthesis methodologies, in both solution and solid phase. The pharmacological properties as neurokinin A receptor antagonist were assessed in in vitro experiments on rat vas deferens and guinea pig trachea, and were compared to those of MEN10627.

RGDS glycosylated peptides as inhibitors of cell-attachment and platelet aggregation

Glycopeptides derived from the GRGDS sequence were synthesized to study the effect of the sugar residue on the activity of these peptides. The peptides were tested as inhibitors of cell adhesion to fibronectin and of platelet aggregation. The sugar moiety was found to reduce the biological activity of the parent compounds except for the cyclic derivatives P37 and P38 where the inhibition of platelet aggregation was increased. Some interesting differences were observed between the peptides bearing sugar residues with free hydroxyl groups and those with peracetylated sugars.

A novel biomarker for hyperglycemia, MRX isolated from hydrolysate of glycated proteins

Long-lived proteins can undergo non-enzymatic glycation to form highly crosslinked structures with characteristic fluorescence during aging and diabetes processes. In this paper, a typical fluorophore, named Maillard reaction product X (MRX), was isolated from the hydrolysate of glycated proteins. MRX could be formed by incubation of bovine serum albumin with glucose, followed by acid hydrolysis. The structure of MRX was determined to be 8-hydroxy-5-methyldihydrothiazolo[3,2-alpha] pyridinium-3-carboxylate. MRX was also found to be formed by the incubation of cysteine and arginine with glucose, followed by hydrolysis. We found the formation of MRX in the recently developed genetically diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats and compared them with that in the control Long-Evans Tokushima Otsuka (LETO) rats. Significantly higher levels of MRX were observed from the serum (p < 0.005) and urinary protein (p < 0.001) of OLETF rats in comparison with those of LETO rats. MRX must be a potential candidate as a biomarker for hyperglycemia.

Esterification of 9-fluorenylmethoxycarbonyl-glycosylated serine and cysteine derivatives with an hydroxymethyl resin

Esterification of glycosylated serine and cysteine derivatives with a 4-alkoxybenzyl alcohol (Wang) resin is described. The classical methods of ester bond formation (symmetrical anhydride, 2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate [TBTU]/4-dimethylaminopyridine [DMAP] with or without 1-hydroxybenzotriazole [HOBT], pentafluorophenyl [Pfp] esters gave high percentages of racemization of the glycosylated serine or cysteine residues. To reduce the D-amino acid content, we found that the best results were obtained with the highly efficient MSNT reagent (2,4,6-mesitylenesulfonyl-3-nitro-1,2,4-triazolide), which gave a high yield of substitution of the resin and the lowest percentage of racemization. A difference in behavior was observed between the two amino acids. The glycosylated cysteine derivative always gave lower racemization than the analogous glycosylated serine.