Tailoring multivalent interactions of biopolymers with a polyproline scaffold

Abstract

A glycopeptide, comprising a polyproline backbone and one or more carbohydrate molecules.

Claims

1. A glycopeptide, comprising a polyproline backbone and one or more carbohydrate molecules, wherein the polyproline backbone has the following general formula (I): ##STR00010## wherein R is independently H or N.sub.3; wherein at least one R is N.sub.3; n is 1 or more; the one or more carbohydrate molecules is selected from the group consisting of a chondroitin sulfate, a heparin, a heparan sulfate, a dermatan sulfate, a hyaluronan, and a keratan sulfate; and wherein the one or more carbohydrate molecules is alkyne-functionalized and attached to the polyproline backbone at R by forming a 1,2,3-triazole linkage when R is N.sub.3.

2. The glycopeptide according to claim 1, wherein n is 8 or more.

3. The glycopeptide according claim 1, wherein the carbohydrate molecules are attached at pre-determined positions along the polyproline backbone at one or more of the following positions: at equal distances from each other along the polyproline backbone, and along the same face of the polyproline backbone.

4. The glycopeptides according to claim 1, wherein the chondroitin sulphate is selected from the group consisting of chondroitin sulfate A, chondroitin sulfate C, chondroitin sulfate D and chondroitin sulfate E.

5. The glycopeptide according to claim 1, further comprising one or more of the following: polyethylene glycol (PEG) at one end of the polyproline backbone, a biotin-conjugated PEG at one end of the polyproline backbone, and a lipid.

6. A glycopeptide comprising a polyproline backbone and one or more carbohydrate molecules having the following general formula (II): ##STR00011## wherein R is independently H or N.sub.3; wherein at least one R is N.sub.3; n is 1 or more; the one or more carbohydrate molecules is selected from the group consisting of a chondroitin sulfate, a heparin, a heparan sulfate, a dermatan sulfate, a hyaluronan, and a keratan sulfate; and wherein the one or more carbohydrate molecules is alkyne-functionalized and attached to the polyproline backbone at R by forming a 1,2,3-triazole linkage when R is N.sub.3.

7. The glycopeptide according to claim 6, wherein the polyproline backbone is a formula selected from the group consisting of: (P.sub.E).sub.4G(P.sub.E).sub.4G(P.sub.E).sub.4, (PP.sub.E).sub.12, (PPP.sub.E).sub.12, (PE).sub.12, (PP.sub.EP.sub.E).sub.6 and (PPP.sub.U).sub.12, wherein P is proline; G is glycine; P.sub.E is; ##STR00012## and P.sub.U is ##STR00013##

8. A method of synthesising a glycopeptide according to claim 1, comprising attaching one or more carbohydrate molecules to a polyproline backbone; wherein the one or more carbohydrate molecules is selected from the group consisting of a chondroitin sulfate, a heparin, a heparan sulfate, a dermatan sulfate, a hyaluronan, and a keratan sulfate.

9. The method according to claim 8, wherein the carbohydrate molecules are alkyne-functionalised chondroitin sulfate disaccharides.

10. The method according to claim 8, wherein the one or more carbohydrate molecules are attached to the polyproline backbone via a click reaction.

11. The method according to claim 10, comprising one or more of the following steps: conducting the click reaction in DMSO at ambient temperature for 7 days in the presence of copper (I) iodide, N,N-diisopropylethylamine (DIPEA) and tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA) under argon atmosphere; precipitating the reaction mixture resulting from the click reaction from a THF/methanol mixture; converting the reaction mixture into their sodium salt form; and purifying the salt by size-exclusion chromatography.

12. The method according to claim 9, wherein the alkyne-functionalised chondroitin sulfate disaccharides are synthesised by: (i) converting tricholoroacetimidate 8 ##STR00014## to the fully protected disaccharide 9 ##STR00015## using trimethylsilyl triflate; (ii) reducing N-trichloroactyl group to N-acetyl congener with n-tributylstannane and AIBN by radical-mediated reduction to yield the acetamide 10 ##STR00016## (iii) hydrolysing the benzylidene acetal followed by removing the TMS group to produce the diol 11 ##STR00017## (iv) optionally treating the diol 11 with SO.sub.3.trimethylamine complex; and (v) treating the resultant mixture with LiOOH and NaOH.

13. The method according to claim 12, comprising synthesising the polyproline backbone via solution-phase peptide synthesis.

14. The method according to claim 13, wherein the solution-phase peptide synthesis comprises the steps of: (i) coupling the Boc protected amino acid with amino acid methyl ester using O-(Benzotriazol-1-yl)-N,N,N,N-tetramethyluronium tetrafluoroborate (TBTU) as the coupling reagent; (ii) removing Boc and methyl ester protective groups of the resulting peptides prior to the next coupling reactions by treatment with a CF.sub.3CO.sub.2H/CH.sub.2Cl.sub.2 mixture and aqueous NaOH, respectively; (iii) repeating steps (i) and (ii) until the desired polyproline derivates are obtained; and (iv) purifying the polyproline derivatives by flash column chromatography on silica or reverse phase HPLC.

15. A method of controlling the binding affinity of a glycopeptide to one or more binding molecules, comprising attaching one or more alkyne-functionalized carbohydrate molecules at pre-determined positions along an azido-functionalized polyproline backbone by forming a 1,2,3-triazole linkage; wherein the one or more carbohydrate molecules is selected from the group consisting of a chondroitin sulfate, a heparin, a heparan sulfate, a dermatan sulfate, a hyaluronan, and a keratan sulfate.

16. The method according to claim 15, wherein the polyproline backbone is one having the following general formula (I): ##STR00018## wherein R is independently H or N.sub.3; wherein at least one R is N.sub.3; n is 1 or more; and wherein the one or more carbohydrate molecules are attached to the polyproline backbone at R by forming a 1,2,3-triazole linkage when R is N.sub.3.

17. The method according to claim 15, comprising attaching the carbohydrate molecules at pre-determined positions along the polyproline backbone at one or more of the following positions: at equal distances from each other along the polyproline backbone, and along the same face of the polyproline backbone.

18. The method according to claim 15, further comprising administering the glycopeptide to a patient in need of target-specific therapy, wherein the glycopeptide is a glycopeptide as defined in claim 1.

19. The method according to claim 18, wherein the glycopeptide binds to a target selected from the group consisting of E-selectin, L-selectin, P-selectin, nerve growth factor, growth factor, chemokine and cytokine.

20. The method according to claim 18, wherein the patient in need of a target-specific therapy is a patient suffering from a disease selected from a group consisting of cancer and neurodegenerative disease.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

(2) FIG. 1 shows the .sup.1H NMR spectra of the fully protected disaccharide 9, after conversion from trichloroacetimidate 8 in one embodiment of the method of synthesizing the glycopeptide as defined above as depicted in the schematic of FIG. 30.

(3) FIG. 2 shows the .sup.13C NMR spectra of the fully protected disaccharide 9, after conversion from trichloroacetimidate 8 in one embodiment of the method of synthesizing the glycopeptide as defined above as depicted in the schematic of FIG. 30.

(4) FIG. 3 shows the .sup.1H NMR spectra of the acetamide 10 after radical-mediated reduction of N-trichloroacytl group to N-acetyl congener with n-tributylstannane and AIBN in one embodiment of the method of synthesizing the glycopeptide as defined above as depicted in the schematic of FIG. 30.

(5) FIG. 4 shows the .sup.13C NMR spectra of the acetamide 10 after radical-mediated reduction of N-trichloroacytl group to N-acetyl congener with n-tributylstannane and AIBN in one embodiment of the method of synthesizing the glycopeptide as defined above as depicted in the schematic of FIG. 30.

(6) FIG. 5 shows the .sup.1H NMR spectra of the diol 11 after hydrolysis of the benzylidene acetal of 10 followed by removal of the TMS group in one embodiment of the method of synthesizing the glycopeptide as defined above as depicted in the schematic of FIG. 30.

(7) FIG. 6 shows the .sup.13C NMR spectra of the diol 11 after hydrolysis of the benzylidene acetal of 10 followed by removal of the TMS group in one embodiment of the method of synthesizing the glycopeptide as defined above as depicted in the schematic of FIG. 30.

(8) FIG. 7 shows the .sup.1H NMR spectra of the unsulfated disaccharide 12 after deprotection of 11 in one embodiment of the method of synthesizing the glycopeptide as defined above as depicted in the schematic of FIG. 30.

(9) FIG. 8 shows the .sup.13C NMR spectra of the unsulfated disaccharide 12 after deprotection of 11 in one embodiment of the method of synthesizing the glycopeptide as defined above as depicted in the schematic of FIG. 30.

(10) FIG. 9 shows the .sup.1H NMR spectra of the sulfate motif after treatment of 11 with SO.sub.3.trimethylamine complex in one embodiment of the method of synthesizing the glycopeptide as defined above as depicted in the schematic of FIG. 30.

(11) FIG. 10 shows the .sup.13C NMR spectra of the sulfate motif after treatment of 11 with SO.sub.3.trimethylamine complex in one embodiment of the method of synthesizing the glycopeptide as defined above as depicted in the schematic of FIG. 30.

(12) FIG. 11 shows the .sup.1H NMR spectra of the desired CS-E disaccharide 13 after sequential treatment of LiOOH and NaOH in one embodiment of the method of synthesizing the glycopeptide as defined above as depicted in the schematic of FIG. 30.

(13) FIG. 12 shows the .sup.13C NMR spectra of the desired CS-E disaccharide 13 after sequential treat of LiOOH and NaOH in one embodiment of the method of synthesizing the glycopeptide as defined above as depicted in the schematic of FIG. 30.

(14) FIG. 13 shows the general structure of biotin-PEG.sub.12-azidopolyproline-OCH.sub.3, and formulae for exemplary polyprolines 1 to 5.

(15) FIG. 14 shows the analytical HPLC traces (top) and ESI mass data (bottom) of polyproline 1.

(16) FIG. 15 shows the analytical HPLC traces (top) and ESI mass data (bottom) of polyproline 2.

(17) FIG. 16 shows the analytical HPLC trace (top) and ESI mass data (bottom) of polyproline 3.

(18) FIG. 17 shows the analytical HPLC traces (top and ESI mass data (bottom) of polyproline 4.

(19) FIG. 18 shows the analytical HPLC traces (top) and ESI mass data (bottom) of polyproline 5.

(20) FIG. 19 shows the FT-IR spectra of exemplary polyprolines 1 to 5 and glycopeptides 1 to 7. The disappearance of the azide band in the spectra of the glycopeptides indicates completion of coupling of the CS-disaccharides to the polyproline backbone.

(21) FIG. 20 shows the .sup.1H NMR spectrum of glycopeptide 1.

(22) FIG. 21 shows the .sup.1H NMR spectrum of glycopeptide 2.

(23) FIG. 22 shows the .sup.1H NMR spectrum of glycopeptide 3.

(24) FIG. 23 shows the .sup.1H NMR spectrum of glycopeptide 4.

(25) FIG. 24 shows the .sup.1H NMR spectrum of glycopeptide 5.

(26) FIG. 25 shows the .sup.1H NMR spectrum of glycopeptide 6.

(27) FIG. 26 shows the .sup.1H NMR spectrum of glycopeptide 7.

(28) FIG. 27 shows the CD spectra of compounds 12 and 13 (2.4 mM) at 25 C.

(29) FIG. 28 shows the CD spectra of glycopeptides 1 to 7 (0.2 mM) at 25 C.

(30) FIG. 29 shows (A) a model of an oligoproline PPII helix with CS-E disaccharides, (B) structures of modified polyproline glycopeptides 1 to 7 containing CS disaccharides, and (C) configurations of carbohydrate display of glycopeptides 1 to 7.

(31) FIG. 30 shows (A) a schematic of the synthesis of alkyne-functionalized CS disaccharides, (B) the synthesis of biotinylated azido polyprolines, and (C) the click reaction for the synthesis of glycopeptides 1 to 7.

(32) FIG. 31 shows (A) the comparison of the binding affinities of glycopeptides 1 to 7 to NGF at various concentrations, and (B) an expanded view of glycopeptides 1 to 3 from FIG. 31(A); 1, .box-tangle-solidup.2, 3, .circle-solid.4, .square-solid.5, 6, .diamond-solid.7. All data presented as meanSD of triplicates.

(33) FIG. 32 shows the surface plasmon resonance of NGF binding at varying concentrations (185, 93, 46, 23, and 11 nM from top to bottom) to immobilized CS glycopeptides. The binding analysis was performed at 25 C., (A) with glycopeptide 5, and (B) with glycopeptide 1.

(34) FIG. 33 shows one embodiment of the use of a glycopeptide as defined above as a glycomimetic in binding -NGF.

(35) FIG. 34 demonstrates the effects of the glycopeptides 1 to 7 on NGF-induced neurite outgrowth in PC12 cells. Cells were grown in the presence or absence of NGF (4 ng/ml) and different glycopeptides (10 M) for 72 hr. (A) Control/NGF only; (B) glycopeptide 5; (C) glycopeptide 7; (D) CS-E polysaccharide; (E) glycopeptide 1; (F) glycopeptide 4; (G) Semi-Flexible glycopeptide 2; (H) Random Coil glycopeptide 3; (I) glycopeptide 5 only.

(36) FIG. 35 demonstrates the quantification of neurite-bearing cells for two sets of experimental conditions. Left: 4 ng/ml NGF and 10 M glycopeptide, grown for 3 days. Right: 2 ng/ml NGF and 6 M glycopeptide, grown for 5 days and media with complete supplements were changed at day 3. Data are average SD values from three separate experiments for each condition.

(37) FIG. 36 shows that glycopeptide 5 enhances NGF-mediated TrkA activation in PC12 cells. The ratio for the NGF-treated control sample is normalized to 1. Data are averageSD values from five separate experiments for each condition (****p<0.0001).

(38) FIG. 37 shows the predicted glycopeptide 5 binding site with NGF/TrkA complex (basic residues are circled in white).

DETAILED DESCRIPTION OF DRAWINGS

Examples

(39) Non-limiting examples of the invention, including the best mode, and a comparative example will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Example 1General Methods

(40) Unless otherwise stated, reactions were performed in flame-dried glassware under argon atmosphere and using dry solvents. All commercially obtained reagents were used as received unless otherwise noted. Thin layer chromatography (TLC) was performed using E. Merck silica gel 60 F254 precoated plates (0.25 mm). Visualization of the developed chromatogram was performed by UV, cerium ammonium molybdate or ninhydrin stain as necessary. Merck silica gel 60 (particle size 0.040-0.063 mm) was used for flash chromatography. Gel filtration chromatography (Sephadex G-15 ultrafine) was used in order to achieve purification of the glycopeptides.

(41) .sup.1H NMR and proton decoupling experiments were recorded on a Bruker AVIII (400 MHz) spectrometer and are reported in parts per million () relative to CDCl.sub.3 (7.26 ppm), CD.sub.3OD (4.87 ppm), and D.sub.2O (4.80 ppm). Data for the .sup.1H NMR spectra are reported as follows: chemical shift (5 ppm), multiplicity (s=singlet, bs=broad singlet, d=doublet, t=triplet, q=quartet, m=multiplet), coupling constant in Hz, and integration. .sup.13C NMR spectra were obtained on a Bruker AVIII (100 MHz) spectrometer and are reported in terms of chemical shift. Mass spectra were obtained from Chemical, Molecular and Materials Analysis Centre at the National University of Singapore.

3-Trimethylsilylpropargyl O-(methyl 2,3,4-tri-O-acetyl--D-glucopyranosyluronate)-(13)-4,6-O-benzylidene-2-deoxy-2-trichloroacetamido--D-galactopyranoside 9

(42) Donor 8 (0.500 g, 0.573 mmol) was co-evaporated with toluene (35 mL) and dried under vacuum overnight. To a solution of 8 and 3-trimethylsilylpropargyl alcohol (0.425 mL, 2.863 mol) in dry CH.sub.2Cl.sub.2 (7.35 mL) was added 4 powdered molecular sieves. The reaction was stirred at room temperature for 30 min, cooled to 78 C., and then stirred for an additional 30 min. Trimethylsilyl trifluoromethanesulfonate (0.227 mM in CH.sub.2Cl.sub.2, 0.115 mmol, 500 L) at 78 C. was added to the reaction dropwise. The reaction was warmed to 15 C., stirred for 2 hrs, and quenched with triethylamine. The reaction mixture was filtered through Celite and concentrated to afford yellow syrup. The product was purified by flash chromatography (1%.fwdarw.2% 2-propanol:CH.sub.2Cl.sub.2) to afford slightly impure 9 as a light yellow solid. The impure 9 was then purified one more time by flash chromatography (2%.fwdarw.5% THF:[2:1 hexanes:CH.sub.2Cl.sub.2]) to afford pure 9 (0.295 g, 61%) as a white solid. R.sub.f=0.45 (6:3:1 CH.sub.2Cl.sub.2:hexanes:THF). .sup.1H NMR (400 MHz, CDCl.sub.3): 7.53 (m, 2H, ArH), 7.387.33 (m, 3H, ArH), 6.97 (d, J=6.8 Hz, 1H, NH), 5.59 (s, 1H, PhCH), 5.23 (d, J=8.2 Hz, 1H, H-1), 5.23 (t, J=9.4 Hz, 1H, H-4), 5.16 (t, J=8.8 Hz, 1H, H-3), 5.04 (t, J=7.8 Hz, 1H, H-2), 4.90 (d, J=7.5 Hz, 1H, H-1), 4.77 (dd, J=11.1, J=3.4 Hz, 1H, H-3), 4.46 (d, J=3.3 Hz, 1H, H-4), 4.40 (s, 2H, CH.sub.2CC), 4.33 (d, J=12.4 Hz, 1H, H-6), 4.10 (d, J=11.6 Hz, 1H, H-6), 4.03 (d, J=9.7 Hz, 1H, H-5), 3.833.77 (m, 1H, H-2), 3.72 (s, 3H, OCH.sub.3), 3.55 (s, 1H, H-5), 2.01 (s, 3H, C(O)CH.sub.3), 2.01 (s, 3H, C(O)CH.sub.3), 2.00 (s, 3H, C(O)CH.sub.3), 1.99 (s, 3H, C(O)CH.sub.3), 0.16 (s, 3H, SiCH.sub.3); .sup.13C NMR (100 MHz, CDCl.sub.3): 170.20, 169.57, 169.32, 167.32, 162.27, 137.80, 128.99, 128.24, 126.33, 100.83, 100.40, 100.17, 96.10, 92.54, 92.48, 75.76, 74.22, 72.57, 72.12, 71.40, 69.22, 69.14, 66.76, 56.53, 55.03, 53.04, 20.97, 20.72, 20.63, 0.06; ESI MS: m/z calcd for [C.sub.34H.sub.42Cl.sub.3NO.sub.15Si+Na].sup.+: 860.1287, obsd 860.1296. The .sup.1H NMR spectrum of 9 is shown in FIG. 1, and its .sup.13C NMR spectrum is shown in FIG. 2.

3-Trimethylsilylpropargyl O-(methyl 2,3,4-tri-O-acetyl--D-glucopyranosyluronate)-(13)-4,6-O-benzylidene-2-deoxy-2-acetamido--D-galactopyranoside 10

(43) Reduction of the trichloroacetamide group was performed using a procedure modified from Blot et. al..sup.[1] Disaccharide 9 (0.353 g, 0.421 mmol) was dissolved in toluene (8.7 mL), and tributylstannane (1132 L, 4.21 mmol) and 2,2-azobisisobutyronitrile (34.5 mg, 0.211 mmol) were added. After stirring at room temperature for 30 min, the reaction mixture was heated to 80 C. and stirred for an additional 4 h 30 min. The reaction was then cooled to room temperature and concentrated to afford a white solid. The product was purified by flash chromatography (3.fwdarw.11% THF:CH.sub.2Cl.sub.2) to afford the desired acetamide (0.281 g, 91%) as a white solid. R.sub.f=0.25 (4% THF:CH.sub.2Cl.sub.2). .sup.1H NMR (400 MHz, CDCl.sub.3): 7.53 (m, 2H, ArH), 7.377.32 (m, 3H, ArH), 5.81 (d, J=6.6 Hz, 1H, NH), 5.56 (s, 1H, PhCH), 5.255.18 (m, 3H, H-3, H-4, H-1), 5.01 (t, J=7.7 Hz, 1H, H-2), 4.924.88 (m, 2H, H-1, H-3), 4.434.36 (m, 3H, H-4, CH.sub.2CC), 4.30 (d, J=12.5 Hz, 1H, H-6), 4.084.02 (m, 2H, H-5, H-6), 3.70 (s, 3H, OCH.sub.3), 3.53 (s, 1H, H-5), 3.473.41 (m, 1H, H-2), 2.02 (s, 6H, NHC(O)CH.sub.3, C(O)CH.sub.3), 2.00 (s, 3H, C(O)CH.sub.3), 1.98 (s, 3H, C(O)CH.sub.3), 0.18 (s, 3H, SiCH.sub.3); .sup.13C NMR (100 MHz, CDCl.sub.3): 171.31, 170.29, 169.59, 169.18, 167.47, 137.90, 128.92, 126.37, 100.85, 100.81, 100.57, 97.07, 91.88, 75.98, 75.16, 72.52, 72.03, 71.74, 69.29, 69.18, 66.60, 56.75, 54.31, 52.98, 23.98, 20.86, 20.75, 20.65, 0.07; ESI MS: m/z calcd for [C.sub.34H.sub.45NO.sub.15Si+Na].sup.+: 758.2456, obsd 758.2469. The .sup.1H NMR spectrum of 10 is shown in FIG. 3, and its .sup.13C NMR spectrum is shown in FIG. 4.

2-Propargyl-O-(methyl 2,3,4-tri-O-acetyl--D-glucopyranosyluronate)-(13)-2-deoxy-2-acetamido--D-galactopyranoside 11

(44) The acetamide (0.353 g, 0.480 mmol) was dissolved in AcOH/water (4:1, 3.0 mL) and stirred at 80 C. After 30 min, the reaction mixture was cooled and concentrated. The resulting concentrate was co-evaporated with toluene (33 mL) for the complete removal of AcOH.

(45) To a solution of crude diol (0.242 g, 0.374 mmol) in THF (3.7 mL) was added TBAF (1 M solution in THF, 18.8 mmol, 448 L) and the mixture stirred at 0 C. for 1.5 hr. At this time the addition of Amberlyst IR-120 resin was made and the reaction stirred for a further 30 min. After filtration, the mixture was concentrated to afford a light yellow solid. The residue was purified via flash chromatography (5.fwdarw.7% MeQH:CH.sub.2Cl.sub.2) to afford the desired compound (0.147 g, 53%) as a white solid. R.sub.f=0.30 (10% MeOH:CH.sub.2Cl.sub.2). .sup.1H NMR (400 MHz, CD.sub.3OD): 5.35 (t, J=6.6 Hz, 1H, H-3), 5.11 (t, J=9.8 Hz, 1H, H-4), 5.00 (dd, J=8.0 Hz, J=9.4 Hz, 1H, H-2), 4.91 (d, J=8.0 Hz, 1H, H-1), 4.66 (d, J=8.2 Hz, 1H, H-1), 4.434.37 (m, 2H, CH.sub.2CC), 4.29 (d, J=10.0 Hz, 1H, H-5), 4.07 (bs, 1H, H-4), 4.003.98 (m, 1H, H-2), 3.913.89 (m, 1H, H-3), 3.813.72 (m, 2H, H-6), 3.75 (s, 3H, OCH.sub.3), 3.54 (t, J=5.8 Hz, 1H, H-5), 2.87 (t, J=2.32 Hz, 1H, CCH), 2.06 (s, 3H, NHC(O) CH.sub.3), 2.03 (s, 3H, C(O)CH.sub.3), 2.01 (s, 3H, C(O)CH.sub.3), 2.00 (s, 3H, C(O)CH.sub.3);.sup.13C NMR (100 MHz, CD.sub.3OD): 173.41, 171.48, 171.21, 169.31, 102.60, 100.50, 81.36, 80.14, 76.47, 76.13, 73.45, 72.95, 72.57, 70.84, 69.17, 62.40, 56.43, 53.41, 52.56, 23.40, 20.97, 20.77, 20.49, 20.41; ESI MS: m/z calcd for [C.sub.24H.sub.33NO.sub.15+Na].sup.+: 598.1748, obsd 598.1760. The .sup.1H NMR spectrum of 11 is shown in FIG. 5, and its .sup.13C NMR spectrum is shown in FIG. 6.

2-Propargyl O-(sodium--D-glucopyranosyluronate)-(13)-2-deoxy-2-acetamido--D-galactopyranoside 12

(46) Compound 11 (40 mg, 0.0695 mmol) was dissolved in THF (684 L) and H.sub.2O (388 L) and cooled to 0 C. To this were added 1 M aq. LiOH (270 L) and 30% H.sub.2O.sub.2 (135 L). The reaction stirred at 0 C. for 1 hr and at room temperature for 12 hr. At this time, 4 M NaOH (203 L) and MeOH (1008 L) were added and the reaction stirred for another 12 hr..sup.[2] It was neutralized with Amberlyst IR-120 resin, filtered, and lyophilized to afford an orange solid. The product was purified by Sephadex G-15 (100% H.sub.2O) and lyophilized to afford 12 as a white solid (28.7 mg, 95%). .sup.1H NMR (400 MHz, D.sub.2O): 4.70 (d, J=8.6 Hz, 1H, H-1), 4.52 (d, J=7.8 Hz, 1H, H-1), 4.444.42 (m, 2H, CH.sub.2CC), 4.18 (d, J=3.1 Hz, 1H, H-4), 4.02 (dd, J=10.9, J=9.8 Hz, 1H, H-2), 3.86 (dd, J=10.8, J=3.2 Hz, 1H, H-3), 3.813.69 (m, 4H, H-5, H-5, H-6, H-6), 3.533.46 (m, 2H, H-3, H-4), 3.373.32 (m, 1H, H-2), 2.91 (t, J=2.4 Hz, 1H, CCH), 1.94 (s, 3H, NHC(O)CH.sub.3); .sup.13C NMR (100 MHz, D.sub.2O): 175.38, 174.93, 104.10, 99.57, 80.11, 78.84, 78.83, 76.07, 75.85, 75.25, 75.01, 72.64, 71.68, 67.67, 60.98, 56.56, 50.94, 22.25; ESI MS: m/z calcd for [C.sub.17H.sub.25NO.sub.12H].sup. 434.1299, obsd 434.1308. The .sup.1H NMR spectrum of 12 is shown in FIG. 7, and its .sup.13C NMR spectrum is shown in FIG. 8.

2-Propargyl O-(methyl 2,3,4-tri-O-acetyl--D-glucopyrano syluronate)-(13)-4,6-di-O-sodium sulfonato-2-deoxy-2-acetamido--D-galactopyranoside

(47) To a solution of diol 11 (0.050 g, 0.087 mmol) in DMF (3.9 mL) was added sulfur trioxide trimethylamine complex (SO.sub.3.TMA) (0.305 g, 2.17 mmol). The reaction mixture was stirred at 50 C. overnight and then cooled to room temperature. The product was purified on Sephadex LH-20 (50% MeOH:CH.sub.2Cl.sub.2), followed by silica gel chromatography (5%.fwdarw.20% MeOH:CH.sub.2Cl.sub.2) to afford a sulfated disaccharide (0.053 g, 82%) as a white solid. R.sub.f=0.20 (20% MeOH:CH.sub.2Cl.sub.2). .sup.1H NMR (400 MHz, D.sub.2O): 5.435.39 (m, 1H, H-3), 5.27 (t, J=9.9 Hz, 1H, H-4), 5.025.00 (m, 2H, H-1, H-2), 4.89 (bs, 1H, H-4), 4.78 (d, J=8.6 Hz, 1H, H-1), 4.46 (dd, J=4.0, J=2.4 Hz, 2H, CH.sub.2CC), 4.42 (d, J=9.9 Hz, 1H, H-5), 4.32 (dd, J=11.5, J=3.4 Hz, 1H, H-6), 4.264.21 (m, 1H, H-6), 4.114.01 (m, 3H, H-2, H-3, H-5), 3.80 (s, 3H, OCH.sub.3), 2.85 (bs, 1H, CCH), 2.11 (s, 3H, NHC(O)CH.sub.3), 2.10 (s, 6H, C(O)CH.sub.3, C(O)CH.sub.3), 2.07 (s, 3H, C(O)CH.sub.3); .sup.13C NMR (100 MHz, D.sub.2O): 174.45, 173.01, 172.70, 172.43, 169.34, 100.59, 100.00, 99.27, 78.72, 78.70, 76.34, 76.29, 75.73, 72.52, 72.39, 71.44, 71.32, 69.43, 67.67, 56.91, 53.50, 51.09, 22.23, 20.15, 20.00, 19.92; ESI MS: m/z calcd for [C.sub.24H.sub.33NO.sub.21S.sub.2H].sup.: 734.0908, obsd 734.0903. The .sup.1H NMR spectrum of the sulfated disaccharide is shown in FIG. 9, and its .sup.13C NMR spectrum is shown in FIG. 10.

2-Propargyl O-(sodium--D-glucopyranosyluronate)-(13)-4,6-di-O-sodium sulfonato-2-deoxy-2-acetamido--D-galacto pyranoside 13

(48) The sulfated compound (185 mg, 0.251 mmol) was dissolved in THF (684 L) and H.sub.2O (338 L) and cooled to 0 C. To this were added 1 M aq. LiOH (270 L) and 30% H.sub.2O.sub.2 (135 L). The reaction was stirred at 0 C. for 1 hr and at room temperature for 12 hr. At this time, 4 M aq. NaOH (203 L) and MeOH (1008 L) were added and the reaction was stirred for another 12 hr. It was then neutralized with Amberlyst IR-120 resin, filtered, and lyophilized to afford an orange solid. The product was purified by Sephadex G-15 (100% H.sub.2O) and lyophilized to afford 13 as a white solid (136 mg, 91%). .sup.1H NMR (400 MHz, D.sub.2O): 4.86 (d, J=2.4 Hz, 1H, H-4), 4.78 (d, J=9.0 Hz, 1H, H-1), 4.70 (d, J=7.8 Hz, 1H, H-1), 4.45 (dd, J=4.1, J=2.4 Hz, 2H, CH.sub.2CC), 4.31 (dd, J=11.4, J=3.3 Hz, 1H, H-6), 4.244.19 (m, 1H, H-6), 4.134.04 (m, 3H, H-2, H-3, H-5), 3.90 (d, J=9.8 Hz, 1H, H-5), 3.61 (t, J=9.1 Hz, 1H, H-4), 3.50 (t, J=9.3 Hz, 1H, H-3), 3.40 (dd, J=9.4, J=7.8 Hz, 1H, H-2), 2.92 (t, J=2.4 Hz, 1H, CCH), 2.04 (s, 3H, NHC(O) CH.sub.3); .sup.13C NMR (100 MHz, D.sub.2O): 177.46, 175.82, 106.10, 101.93, 81.26, 78.75, 78.60, 78.07, 77.57, 77.44, 74.95, 74.83, 73.81, 70.30, 59.45, 53.93, 24.81; ESI MS: m/z calcd for [C.sub.17H.sub.25NO.sub.18S.sub.2H].sup.: 594.0435, obsd 594.0429. The .sup.1H NMR spectrum of 13 is shown in FIG. 11, and its .sup.13C NMR spectrum is shown in FIG. 12.

(49) General Procedure for Solution Phase Peptide Synthesis:

(50) In a typical solution phase peptide synthesis, Boc-Peptide(1)-OH (1.0 equiv.) was dissolved in DMF (final concentration was adjusted to 0.1M). H-Peptide(2)-OCH.sub.3 (1.1 equiv.), TBTU (1.1 equiv.), and DIPEA (5.0 equiv.) were then added to the solution. The reaction mixture was stirred at room temperature until the reaction completed. After the completion, the solvent removed in vacuo to afford a yellow solid. Purification of this solid by either flash column chromatography on silica or reverse phase HPLC afforded Boc-Peptide(1)-Peptide(2)-OCH.sub.3.

(51) General Method for Boc Group Deprotection of Boc-Peptide(1)-Peptide (2)-OCH.sub.3

(52) Boc-Peptide(1)-Peptide(2)-OCH.sub.3 was dissolved in CH.sub.2Cl.sub.2/TFA (1:1) at 0 C., and stirred for 2 hrs. After the completion, the solvent was removed by blowing a slow stream of nitrogen gas and then diethyl ether was added to give H-Peptide(1)-Peptide(2)-OCH.sub.3 quantitatively as a white precipitate.

(53) General Procedure for Methyl Group Deprotection of Boc-Peptide(1)-Peptide (2)-OCH.sub.3:

(54) To a solution of Boc-Peptide(1)-Peptide(2)-OCH.sub.3 (1.0 equiv.) in THF/MeOH (1:1, final concentration was adjusted to 0.05M) was added aq. NaOH (2.0 equiv.) and sonicated for 5 min. At this time, the same volume of CH.sub.2Cl.sub.2 was added and the reaction was stirred for additional 2 hrs. It was then neutralized with Amberlyst IR-120 resin, filtered, and evaporated in vacuo to afford H-Peptide(1)-Peptide(2)-OCH.sub.3 quantitatively.

(55) General Procedure for the Synthesis of Biotin-PEG.sub.12-Azidopolyproline-OCH.sub.3:

(56) To a solution of H-Azidopolyproline-OCH.sub.3 (1.0 equiv.) in DMSO (final concentration was adjusted to 0.1M) were added EZ-link NHS-PEG.sub.12-Biotin (1.2 equiv., from Thermo Scientific) and DIPEA (5.0 equiv.), and stirred overnight at room temperature. After the completion, the solvent was removed in vacuo to afford a yellow sticky solid. Purification of this solid by reverse phase HPLC afforded biotin-PEG.sub.12-azidopolyproline-OCH.sub.3. The structures of the biotin-PEG.sub.12-azidopolyproline-OCH.sub.3 are shown in FIG. 13. The analytical HPLC conditions for biotin-PEG.sub.12-azidopolyproline-OCH.sub.3 are set out below in Table 1, while the ESI-MS data of biotin-PEG.sub.12-azidopolyproline-OCH.sub.3 are set out below in Table 2. The analytical HPLC traces and ESI mass data of polyprolines 1 to 5 are shown FIGS. 14 to 18, respectively.

(57) TABLE-US-00001 TABLE 1 Analytical HPLC conditions for biotin-PEG.sub.12- azidopolyproline-OCH.sub.3. Biotin-PEG.sub.12-azido poliproline-OCH.sub.3 HPLC condition* Retention time Polyproline 1 5-60% A over 8 min 7.35 min Polyproline 2 5-60% A over 8 min 5.30 min Polyproline 3 5-60% A over 8 min 4.27 min Polyproline 4 5-60% A over 8 min 2.40 min Polyproline 5 5-60% A over 8 min 4.93 min *A: CH.sub.3CN/0.1% TFA, B: H.sub.2O/0.1% TFA.

(58) TABLE-US-00002 TABLE 2 ESI-MS Data of biotin-PEG.sub.12-azidopolyproline-OCH.sub.3. Biotin-PEG.sub.12-azido poliproline-OCH.sub.3 MS, calculated ESI-MS, observed Polyproline 1 2538.29 1270.94 ([M + 2H].sup.2+), 847.62 ([M + 3H].sup.3+) Polyproline 2 2514.11 1258.87 ([M + 2H].sup.2+), 839.39 ([M + 3H].sup.3+) Polyproline 3 3678.74 1841.03 ([M + 2H].sup.2+), 1227.79 ([M + 3H].sup.3+), 921.35 ([M + 4H].sup.4+) Polyproline 4 4843.37 1616.56 ([M + 3H].sup.3+), 1212.66 ([M + 4H].sup.4+) Polyproline 5 2628.15 1315.81 ([M + 2H].sup.2+), 877.92 ([M + 3H].sup.3+)
General Procedure for the Synthesis of Glycopeptides Via Click Reaction:

(59) In a typical click reaction, a small vial was charged with alkyne-functionalized CS disaccharides (total 15.6 equiv., 1.3 equiv. per azide), biotin-PEG.sub.12-azidopolyproline-OMe (1.0 equiv.), Tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA, 0.3 equiv. per azide), and a small stir bar under argon atmosphere. The mixture was dissolved in degassed DMSO, and the desired amount of copper (I) iodide (0.3 mol % per azide) stock solution in DMSO and DIPEA (48 equiv.) were added. The reaction mixture was then stirred at room temperature for 7 days. The consumption of biotin-PEG.sub.12-azidopolyproline-OCH.sub.3 was monitored by analytical reverse phase HPLC equipped with C-18 column. After the completion, anhydrous THF/MeOH (9:1) was added to give a white precipitate (TBTA and DIPEA can be removed as the glycopeptides and excess CS-disaccharides are insoluble at this condition). The white precipitate was dissolved in 200 L of 6M aq. NaCl and purified by Sephadex G-15 column (100% H.sub.2O) to afford desired glycopeptides as white solids upon lyophilization.

(60) FTIR was used to monitor the azide vibrational band (2100 cm.sup.1) for the completion of the click coupling reaction. Fourier transform infrared spectroscopy (FTIR) was carried out using a Perkin Elmer FTIR Spectrum 100 between 4000 and 800 cm.sup.1 at a spectral resolution of 4 cm.sup.1, and the number of scans was 4. Samples were placed on a germanium stage and pressed before every measurement. The disappearance of the azide band in the spectra of the glycopeptides indicated the completion of the coupling reactions (FIG. 19). The .sup.1H NMR spectra of glycopeptides 1 to 7 are shown in FIGS. 20 to 26.

(61) Circular Dichroism Analysis:

(62) CD spectra were recorded on an Aviv 410 circular dichroism spectrometer equipped with temperature controller. Glycopeptide solutions at concentrations of 200 M (2.4 mM for compounds 12 and 13) were used. All sample solutions made in 10 mM sodium phosphate-dibasic buffer, pH 7.0, were equilibrated for 24 hrs at 4 C. and then 1 hr at room temperature before CD measurements. Cells of 1 mm path length were used. Spectra were recorded from 260 to 190 mm at 25 C. Mean residue ellipticity [] was calculated as follows;
[]=/(10.Math.N.Math.c.Math.l)
represents the ellipticity in millidegrees, N the number of amino acid residues, c the molar concentration in mol.Math.L.sup.1, and l the cell path length in cm. The CD spectra of compounds 12 and 13 are shown in FIG. 27, while the CD spectra of glycopeptides 1 to 7 are shown in FIG. 28.
Enzyme-Linked Immunosorbent Assay (ELISA):

(63) The new plate was rinsed three times with PBS containing 0.05% Tween 20 and one time with PBS before the experiment. 100 L of biotinylated glycopeptide solutions (0.5 M) were added to required wells in the Pierce Streptavidin Coated High Binding Capacity plates (#15501), and incubated overnight at room temperature. After immobilization of glycopeptides, the plates were rinsed three times with PBS containing 0.05% Tween 20 and one time with PBS. The surface was then blocked with 125 L of 3% BSA in PBS for 1 hr, followed by rinsing three times with PBS containing 0.05% Tween 20 and one time with PBS. 100 L of varying concentrations (0 nM, 10 nM, 20 nM, 30 nM, 40 nM, 50 nM and 60 nM) of NGF in PBS containing 1% BSA was added to the wells and incubated for 2 hrs at 37 C. The surface was rinsed three times with PBS containing 0.05% Tween 20 and one time with PBS.

(64) Washing was done three times with pH 4.0 10 mM Sodium acetate buffer containing 0.05% Tween 20 and 0.5M NaCl for 10 min. The plate was then rinsed five times with 200 L of PBS 0.05% Tween 20. Following that, the plate was washed one time with 10 mM TBS 0.05% Tween 20 and 0.5M NaCl for 10 min. The wells were rinsed three times with PBS 0.05% Tween 20 and one time with PBS.

(65) The wells were then incubated with anti-NGF labeled with HRP in PBS containing 1% BSA. Absorbance signal was then developed with 100 L of TMB Substrate from Thermo Scientific Pierce (#0034021) for 20 to 30 min before quenching with 100 L of 2M H2SO4. Absorbance at 450 nm was then measured.

(66) Surface Plasmon Resonance:

(67) Affinity measurements were performed using a Biacore T100 system (GE Heathcare). The CM5 sensor chip was used for all measurements. At first, the instrument was primed with HBS-EP+ (GE Heathcare) buffer. Then, 700RU of streptavidin was immobilized on all flow cells. A 1:1 mixture of 0.4 M EDC and 0.1 M NHS was used to activate the flow cells, and 0.008 mg/mL streptavidin solution reconstituted in Acetate 5.0 buffer (GE Healthcare) was injected. Blocking of the remaining activated groups was done with a 1 M solution of ethanolamine (pH 8.5). Flow cell 1 (or 3) was used as a reference to subtract nonspecific binding, drift, and the bulk refractive index, while flow cell 2 (or 4) was further immobilized with glycol-peptide samples of varying structures. Biotinylated glycopeptides (20 nM) were dissolved in HBS-EP+ buffer and were injected to flow cell 2 (or 4) at 30 L/min until the baseline response increased by 104 or 127 RU. The instrument was then primed using running buffer (HBS-EP+). NGF was dissolved in HBS-EP+ buffer to produce a 185 nM stock solution, which was serially diluted to produce a concentration series down to 11 nM. For a given affinity measurement, these series of peptide solutions were successively injected into the flow cells for 240 seconds of contact time and 800 seconds of dissociation time using a flow rate of 50 L/min at 25 C. Flow cells were regenerated by 2.5 M MgCl2 at 30 L/min for 30 seconds after injection of each protein solutions.

Example 2Design of Glycopeptides

(68) CS disaccharide monomers were incorporated into the PPII helix by click reaction of azido groups with alkynes bearing CS disaccharide moieties.sup.[3c]. Furthermore, a minimum spacer length between proline and sugar units allowed us the maximal positional control of carbohydrate units. Finally, biotin-conjugated PEG.sub.12 were introduced at the end of peptide chain to facilitate the surface attachment (FIGS. 29A and 29B).

(69) Seven glycopeptides were designed on the basis of above considerations. These were: i) two glycopeptides (1 and 2) containing CS-E disaccharide motifs at all faces of helix with/without backbone flexibility; ii) one glycopeptide (3) containing a completely flexible backbone; iii) one glycopeptide (4) containing equally distributed CS-E disaccharides along the helix backbone but more space as compared to 1; iv) one glycopeptide (5) displaying all CS-E disaccharides along one face of PPII helix; and v) two control glycopeptides containing unsulfated CS disaccharide moieties (6 and 7).

(70) All CS-E glycopeptides differ only subtly in their orientation of functional motifs but have the same number of CS-E disaccharides. A comparison of the relative protein binding activity of 1 and 4 would allow for the evaluation of the importance of the distance between pendant groups. Inclusion of glycine residues on polyproline as in 2 was envisioned to introduce chain flexibility. Finally, glycopeptide 5 affords insight into not only the role of saccharide density but also the arrangement of active motifs (FIGS. 29B and 29C).

Example 3Preparation of CS Glycopeptides 1-7

(71) Studies began with the synthesis of biologically active CS-E and unsulfated CS disaccharide units containing alkyne functionality (FIG. 30). Briefly, the trichloroacetimidate 8.sup.[4] was converted to the fully protected disaccharide 9 mediated by trimethylsilyl triflate in good yield and stereoselectivity. Notably, terminal alkyne was protected to avoid free-radical hydrostannation..sup.[5] With the key intermediate in hand, the study was continued with the deprotection-sulfation steps. Radical-mediated reduction of N-trichloroactyl group to N-acetyl congener with n-tributylstannane and AIBN yielded the acetamide 10. Hydrolysis of the benzylidene acetal followed by removal of the TMS group afforded the diol 11. Treatment of 11 with SO.sub.3.trimethylamine complex delivered the sulfate motif efficiently. The desired CS-E disaccharide 13 was successfully elaborated by sequential treatment of LiOOH and NaOH. Deprotection of 11 under the similar conditions furnished the unsulfated disaccharide 12.

(72) As the typical Fmoc chemistry on solid-phase resulted in very low coupling efficiency, all polyproline derivatives containing azides were prepared via standard solution-phase peptide synthesis. Boc-protected amino acid was coupled with amino acid methyl ester using O-(Benzotriazol-1-yl)-N,N,N,N-tetramethyluronium tetra fluoroborate (TBTU) as the coupling reagent. Boc and methyl ester protective groups of resulting peptides were removed prior to the next coupling reactions by treatment of CF.sub.3CO.sub.2H/CH.sub.2Cl.sub.2 mixture and aqueous NaOH, respectively. Couplings and deprotections were repeated until the desired polyproline derivatives were obtained. All peptides were purified to homogeneity by flash column chromatography on silica or reverse phase HPLC and characterized by mass spectroscopy.

(73) With CS disaccharides and polyproline derivatives in hand, the next focus was on synthesizing glycopolymers via conjugating the alkyne-functionalized CS disaccharides to the azido-functionalized polyprolines. The click reactions were conducted in DMSO at ambient temperature for 7 days in the presence of copper(I) idode, N,N-diisopropylethylamine (DIPEA), and tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA) under argon atmosphere. The complete conversion of azido groups into 1,2,3-triazoles was monitored by FT-IR and .sup.1H NMR spectroscopy (see FIG. 19 and NMR spectra shown in FIGS. 20 to 26)..sup.[6] While the FT-IR spectra of azido-polyprolines revealed the presence of a strong vibrational band at 2100 cm.sup.1, which is characteristic of azide moieties, the disappearance of the azide band in the spectra of the glycopeptide derivatives clearly demonstrated the completion of the coupling reactions. Moreover, .sup.1H NMR spectra revealed the new signals from CS disaccharides. In addition, the characteristic peak at 8.2 ppm after the click reaction indicated the formation of 1,2,3-triazole linkage. Both FT-IR and .sup.1H NMR spectra, hence, fully demonstrated the efficiency of click reaction for the disaccharides. The resulting reaction mixtures were precipitated from THF/methanol mixture and then converted to their sodium salts. Purification by size-exclusion chromatography furnished the desired CS glycopeptides 1-7.

Example 4Circular Dichroism Studies

(74) With the glycopeptides successfully prepared, circular dichroism (CD) studies were performed to investigate the PPII helix stability of the glycopeptides. Although several reports have suggested that polyprolines can be efficiently functionalized while retaining PPII conformations,.sup.[3b,3c,3d] an attempt was made to validate whether the bulky and highly charged pendant groups could induce the conformational change of backbones, thereby making it difficult to position functional groups at desired sites. For these studies, the peptide solutions (400 M) were incubated at 4 C. for 24 h to allow for complete folding and measured at room temperature. In order to examine the backbone conformation of glycopeptides, CD signals of corresponding CS disaccharides (see FIG. 27).sup.[7] were subtracted from those of glycopeptides. The CD traces (displayed in FIG. 28) show that, while the CD spectrum of 3 exhibited a random coil conformation as expected, other glycopeptides adopt a polyproline type II helical profile with a maximum positive band at 224-228 nm and minimum negative band at 208-213 nm, as is typically observed for a PPII helix..sup.[8] These data confirm that inclusion of CS disaccharides to polyproline does not affect the fold of the backbone, and the polyproline scaffold maintains the native structure even with anionic groups along the same face of the helix.

Example 5ELISA

(75) To evaluate the ability of the glycopeptides to interact with protein receptors, the binding affinity of each agent with nerve growth factor (NGF), which is known to bind CS-E sulfation motif selectively,.sup.[9] was examined by ELISA. For this study, glycopeptides at a constant concentration were immobilized on the streptavidin-coated 96-well plates followed by treating various concentrations of NGF into the solution as a mimic of GAG-extracellular protein interactions on the cell surface. The amount of glycopeptide-bound NGF was measured by HRP-conjugated polyclonal NGF antibody. Glycopeptides 1 and 6 served as initial compounds for this protein binding study. NGF turned out to bind to CS-E sulfated glycopeptide 1 in a concentration-dependent manner and displayed no significant binding to unsulfated glycopeptide 6 (FIG. 31A). Although 1 exhibited moderate binding affinity to NGF, these results are consistent with the previous reports in which CS-E sulfation motif provides a major binding epitope to NGF. To enhance the binding affinity, attempts were made to modify the agent 1. One expected consequence of polyproline scaffold is that rigidity of glycopeptide backbone would hamper the target protein binding as the flexibility of polymer chain is important for the interaction by accommodating the secondary structure of relevant proteins..sup.[10] To address this problem, two compounds were prepared containing either partially flexible chain by incorporating glycine residues (2) or entirely flexible chain (3). No enhancement of binding affinity, however, was observed compared to 1, indicating that the chain flexibility is not the crucial factor in the model system (FIG. 31B).

(76) Previous studies have shown that the binding elements density in multivalent ligands can affect the binding affinity towards the target protein..sup.[6d,10,11] To investigate the influence of the binding epitope density, the glycopeptide 4 was synthesized. In this design, proline residues were added between CS-E conjugated prolines to introduce more space while retaining the same spatial arrangements of sugar epitopes as the initial agent 1. This modification resulted in significant increase in NGF binding affinity by approximately 2.6-fold in comparison to 1 (FIG. 31A). It is noteworthy that this phenomenon arises entirely from the distance between binding epitopes over any other factors by taking advantage of rigid polyproline property without perturbing a steric and electronic environment. Finally, all CS units were deployed at one face, while the other two faces contained proline residues, resulting in the agents 5 and 7 with a repeating PPPE or PPPU unit (FIGS. 29B and 29C). The compound 5 was the most effective binding ligand to NGF by 4.6-fold increase as compared to 1, while 7 did not exhibit any binding (FIG. 31A). Thus, the results clearly demonstrate that the spatial arrangement of the binding epitopes in multivalent ligands has considerable effects on the binding affinity towards target receptors.

Example 6Surface Plasmon Resonance

(77) Surface plasmon resonance (SPR) technology was further employed to facilitate quantitative, real-time kinetic analysis of glycopeptide-NGF interaction. Streptavidin was coated on a carboxydextran CM5 sensor chip, using EDC/NHS coupling chemistry, at a relatively low density (700 RU) to prevent nonspecific interactions with NGF. Biotinylated glycopeptides were then immobilized on streptavidin-coated surface at normalized levels by molecular weights,.sup.[12] 104 and 127 RU for 1 and 5, respectively. Kinetics were monitored at 25 C. by injecting various concentrations of NGF (11-185 nM) over the surface for 240 s at 50 L.Math.min.sup.1 and recording the dissociation for 800 s before the surface was regenerated with 2.5 M solution of MgCl.sub.2. As shown in FIG. 32, both CS-E sulfated glycopeptides were efficiently recognized by NGF. In addition, the glycopeptide 5 gave higher overall responses than the glycopeptide 1, indicating that 5 recruits NGF more efficiently than 1. These results are consistent with those of ELISA described above. Further kinetic analysis was conducted using a two-state binding model for comprehensive understanding of this binding event. It is well known that many carbohydrate-protein binding processes are much more complex than a simple Langmuir 1:1 interaction and exhibit a two-state binding kinetics..sup.[13] In this model, surface-bound glycopeptide binds to NGF to form an initial complex and then undergoes conformational change to form a more stable complex..sup.[14] The complete kinetic parameters including equilibrium constants KD with standard errors in parentheses are given in Table 3 below. This kinetic analysis yielded an interesting result. A comparison of K.sub.D values revealed that the agent 5 (K.sub.D=137 nM) binds to NGF more strongly than the agent 1 (K.sub.D=2500 nM) by approximately 18-fold. Moreover, the kinetic result suggests that the higher binding affinity of 5 was mainly attributed to the relatively fast initial association rate (k.sub.a1 (5)=4.65 (0.16)104 M.sup.1 s.sup.1) compared to 1 (k.sub.a1 (1)=1.95 (0.39)103 M.sup.1 s.sup.1). This result suggests that a subtle change in binding epitope display can significantly impact the rate at which target receptor proteins are clustered. Previous investigations have focused on optimizing activity on the basis of binding epitope density by changing the ratio of biologically active to inactive monomers..sup.[10,11] Here, it is discovered that the simple conformational change of binding motifs is sufficient to manipulate receptor-ligand interactions.

(78) TABLE-US-00003 TABLE 3 Calculated (two-state kinetic model) equilibrium binding constants of glycopeptide 1 and 5 to NGF. Glycopeptide 1 Glycopeptide 5 k.sub.a1 (M.sup.1s.sup.1) 1.95 (0.39) 10.sup.3 4.65 (0.16) 10.sup.4 k.sub.d1 (s.sup.1) 3.22 (0.07) 10.sup.2 2.74 (0.04) 10.sup.2 k.sub.a2 (M.sup.1s.sup.1) 3.62 (0.04) 10.sup.3 1.97 (0.02) 10.sup.3 k.sub.d2 (s.sup.1) 6.43 (0.13) 10.sup.4 6.00 (0.17) 10.sup.4 K.sub.D (M) 2.50 10.sup.6 1.37 10.sup.7

Example 7Glycopeptides for Use as Biological Mimetics

(79) Neurotrophins are a family of proteins that play important roles in the central nervous system to ensure proper brain functions. In particular, nerve growth factor (NGF) is critical for the survival and differentiation of certain neurons. It is distributed in many parts of the brain such as substantia nigra, basal forebrain and brain stem. Deprivation of NGF in these areas can lead to neuronal death and eventually neurodegenerative disorders including Parkinson's disease and Alzheimer's disease. To maintain neuronal survival and neurite outgrowth, NGF binds to a transmembrane receptor TrkA, induces receptor phosphorylation and activates the downstream signaling pathway. Interaction between NGF and TrkA requires glycosaminoglycan (GAG) chondroitin sulfate, which facilitates the formation of a stable complex. Glycopeptides that mimic the natural GAGs with binding specificity and affinity as well as biological activities in various systems were designed and synthesized.

Experimental Procedures

(80) Cell Culture

(81) Rat pheochromocytoma (PC12) cells were maintained in T75 tissue culture flask in complete RPMI 1640 growth medium containing 10% heat-inactivated horse serum (HI-HS), 5% fetal bovine serum (FBS) and 1% penicillin/streptomycin. Stock cultures from liquid nitrogen were grown at 37 C. with 5% CO.sub.2 in a humidified chamber for 72 hr before experiments.

(82) Preparation of Glass Coverslips

(83) 13 mm glass coverslips were submerged in 65% nitric acid for at least three days. The coverslips were washed with distilled water, 70% ethanol and 100% ethanol 3 each for 30 minutes with gentle rocking. The coverslips were dried in the cell culture hood overnight with UV sterilization. For coating, 60 l of laminin solution (25 g/ml in sterile PBS) was added to each coverslip, followed by 2 hr incubation at 37 C. The coverslips were rinsed 3 with PBS and dried in the hood before use.

(84) Neurite Outgrowth Assay

(85) PC12 cells were seeded on laminin-coated coverslips at a density of 100 cells/mm.sup.2 in RPMI 1640 differentiation medium containing 1% HI-HS. Cells were allowed to attach to the surface for 1 hr at 37 C. The coverslips were transferred to 24-well plates and the cells were incubated with fresh differentiation medium for 1 hr. Glycopeptides were incubated with NGF in differentiation medium for 1 hr at room temperature before adding to the cells together. At the end of culture period, the cells were fixed with 4% formaldehyde solution for 15 minutes at room temperature and rinsed 2 with PBS. All experiments were repeated three times and done in duplicate each time. For each treatment, 400-500 randomly selected single cells were counted. The percentage of neurite-bearing cells was determined by counting the number of cells with neurite length at least one cell body long.

(86) Western Blotting

(87) PC12 cells were seeded on laminin-coated coverslips at a density of 300 cells/mm.sup.2 and one coverslip was used for each treatment (40,000 cells in total). Cells were starved in differentiation medium for 12-18 hr before use. For glycopeptide treatment, cells were incubated with fresh differentiation medium containing 10 M glycopeptide for 1 hr at 37 C. To induce TrkA phosphorylation, cells were treated with NGF at a final concentration of 4 ng/ml for 5 minutes at 37 C. Cells were washed with ice cold PBS and lysed using RIPA lysis buffer containing protease and phosphatase inhibitors. The protein samples were separated on 4-12% SDS-PAGE gel and transferred to nitrocellulose membrane. Membranes were blocked for 1 h at room temperature and probed with anti-TrkA Ab (1:1500) and anti-pTrkA Ab (1:1500) overnight at 4 C., followed by 2 hr incubation with horseradish peroxidase-conjugated secondary antibodies. Enhanced chemiluminescence system was used for detection. The bands were quantified using the ImageJ program and the ratio of phosphor-TrkA to total TrkA was calculated and expressed as arbitrary units (a.u.).

(88) Results

(89) PPPE12 Promotes NGF-Mediated Neurite Outgrowth in PC12 Cells

(90) When PC12 cells were exposed to NGF in serum-free medium, extension of neurites was observed. Treatment of single-facial glycopeptide 5 significantly promoted neurite outgrowth compared to the control whereas other designs such as the equally distributed glycopeptide 1 and unsulfated glycopeptide 7 displayed no effect (FIG. 34). In the absence of NGF, PC12 cells treated with glycopeptide 5 only remained round-shaped and undifferentiated, indicating that the glycopeptide functions through the NGF-mediated pathway. Percentage of neurite-bearing cells was also greatly increased with the glycopeptide 5 treated samples (FIG. 35).

(91) TrkA Phosphorylation is Enhanced with PPPE12 Treatment

(92) The role of glycopeptide 5 in the NGF/TrkA pathway was examined by monitoring TrkA activation using Western blot. The addition of glycopeptide 5 increased NGF-induced TrkA phosphorylation by 40% compared to the control sample (FIG. 36). This finding further supports the cell culture data that the single-facial glycopeptide can act as a neuronal promoter in NGF-induced PC12 differentiation process.

(93) Glycopeptide 5 Facilitates the Formation of a Stable NGF/TrkA Complex

(94) Protein modeling studies were conducted to investigate the binding between glycopeptide 5 and NGF/TrkA complex. According to the crystal structure of NGF/TrkA complex, there are 6 basic residues arranged linearly at 1017 apart (FIG. 37). Glycopeptide 5 presents 12 disaccharide units with sulfate groups at 9-11 apart facing the same direction. This allows for a perfect geometric fit of sulfate groups to the basic residues, which maximizes the electrostatic interactions and stabilizes the NGF/TrkA complex.

Applications

(95) In summary, a new class of CS glycopeptides has been developed, in which the orientation of CS motifs is precisely controlled by taking advantage of rigid polyproline scaffold. The ability to manipulate multivalent interactions is significant as individual design, in spite of high charge density, showed a distinct binding affinity to target protein. Specifically, NGF exhibited the highest binding affinity to glycopeptide 5 that has all CS-E motifs along one face. Furthermore, the better binding affinity of agent 4 and 5 than 1 clearly demonstrated the influence of binding epitope on multivalent interactions without perturbing a steric and electronic environment. While the majority of research to-date has focused on optimizing activity on the basis of binding epitopes, the present invention underscores the importance of their spatial and conformational display in designing multivalent ligands. The present findings are anticipated to provide a useful tool for developing target-specific therapeutic agents, biopolymers and markers, and manipulating their functions in vivo.

(96) It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.

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