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Nonbiodegradable Hyaluronan Derivative Prepared by Reaction with a Water-Soluble Carbodiimide

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Nonbiodegradable Hyaluronan Derivative Prepared by Reaction with a Water-Soluble Carbodiimide Nonbiodegradable Hyaluronan Derivative Prepared by Reaction with a Water-Soluble Carbodiimide aS. BYSTRICKÝ, aJ. ALFÖLDI, aE. MACHOVÁ, aB. STEINER, and bL. SOLTÉS aInstitute of Chemistry, Slovak Academy of Sciences, SK-842 38 Bratislava bInstitute of Experimental Pharmacology, Slovak Academy of Sciences, SK-842 16 Bratislava Received 26 May 2000 Reaction of hyaluronan (HA) with l-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) yielded a water-soluble polysaccharide with 40 % of modified HA carboxyl groups. XH and 13C NMR mea­ surements revealed that hyaluronan contained EDC bound by a nonspecific acylurea-type linkage. A test with testicular hyaluronidase showed that the modified hyaluronan was resistant to enzymic degradation. Hyaluronan (hyaluronic acid, HA), discovered 65 product enabled its analyses by conventional NMR as years ago, belongs to the most attractive biomateri- well as testing of its resistance to the enzymic (testic­ als. HA is composed of disaccharide repeating units ular hyaluronidase) degradation. of D-glucuronic acid and iV-acetyl D-glucosamine. The unique viscoelastic properties of its aqueous solution EXPERIMENTAL are exploited widely in e.g. medical, pharmacologi­ cal, and cosmetic applications. In the biological en­ The sample of the high-molecular-mass hyaluro­ vironment, HA can be depolymerized by action of nan (Mr = 250 000, polydispersity D = 1.15) was enzymes as well as oxygen radicals. Many hyaluro­ from CONTIPRO Chemical Co. (Czech Republic). 1- nan derivatives and conjugates with chemotherapeu- Ethyl-3-(3-dimethylaminopropyl)carbodiimide(EDC) tics and physiologically active substances have been and 2-(AT-morpholino)ethanesulfonic acid (MES) and prepared and commercialized [1]. Hydroxyl and car­ its sodium salt were from Sigma (U.S.A.), other chemi­ boxyl groups in HA are the sites for linking other cals were from Lachema (Czech Republic). The bovine molecules. Activation of the HA hydroxyl groups is testicular hyaluronidase (EC 3.2.1.35) was purchased usually performed by the cyanylation agents such as from the SEVAC a.s., Prague (Czech Republic). cyanogen bromide [2]. More efficient and less haz­ The content of the free carboxyl groups in the ardous chemistry employs the HA functionalization original HA and the final product of EDC-HA was through the carboxyl groups. determined by the method of potentiometrical titra­ Water-soluble carbodiimide is a widely used acti­ tion. The solution of the polysaccharide, after passing vator of carboxyl groups in the glycoconjugate chem­ through the cation exchanger Dowex 50X x 2 (H+- istry. Recently, we have provided evidence of high re­ form), was titrated with aqueous solution of KOH us­ activity of polysaccharide carboxyls with hydrazide ing a combined electrode to the point of equivalence. groups of adipic acid dihydrazide in the presence of 1- The degree of substitution was calculated as the dif­ ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) ference in the contents of carboxyl groups determined [3]. Attempts of other authors to couple amino groups for EDC-HA and HA. to HA in the presence of EDC failed or led to very For NMR measurements the samples were dis­ 3 low yields [4—6]. Instead, coupling reaction of car- solved in 0.5 cm of D20 (99.99 mole %) in 5-mm bodiimides to HA resulted in acylurea-type adducts. tubes. Spectra were recorded at 25°C, on a Bruker To differentiate between the two types of possi­ DPX AVANCE 300 spectrometer, operating at 300 ble acylurea products, namely 7V-acylurea and O- MHz for lE and 75.46 MHz for 13C. The acetone was acylisourea derivatives of HA, the solid-state NMR used as internal standard (S = 2.225 for *H and S = spectroscopy was employed [7]. The exclusive presence 31.07 for 13C). The *H spectra were measured imme­ of iV-acylurea derivatives of high-molecular-mass HA diately after dissolving HA-EDC adduct. was deduced. Here we report the characterization of water- Modified Hyaluronan soluble derivative of HA prepared by reaction with EDC at mild conditions. Good water solubility of the HA (130 mg) was dissolved in 20 cm3 of MES buffer Chem. Pap. 55(1)49—52 (2001) 49 S. BYSTRICKÝ. J. ALFÖLDI, E. MACHOVÁ, В. STEINER, L. ŠOLTÉS 1 2 о O HN—R (orR ) 1 2 НА-С-ОН + R -N=C=N-R *- HA-C-0-C=N-R2(orR1) • O-acylisourea О О • HA-C-N-C-NH-R2 (or R1) k1(orR2) /V-acylurea 1 R =CH3-CH2- 2 R = (CH3)2N - CH2 - CH2 - CH2 - Scheme 1 (с = 0.05 mol dm"3, pH 6.0) and 100 mg of EDC wawass The reaction of a carbodiimide with carboxyl added. The reaction mixture was stirred for 10 h at groups of HA starts with the addition of diimide room temperature. The pH was maintained at 6.0.0— system of EDC to carboxylate to give O-acylisourea 6.5 with addition of 0.1 mol dm"3 HCl. After compleiple­- product (Scheme 1). In the absence of strong nu- tion of the reaction, the mixture was filtered throug>ugh cleophile (e.g. hydrazine) O-acylisourea can further a paper filter (Whatman No. 3). The reagent ex-­ undergo a structural rearrangement or less proba- cess and the low-relative-molecular-mass componentents bly slowly hydrolyze back to carboxylic groups [9]. were removed by repeated ultrafiltration (Amicon PM Structural rearrangement of O-acylisourea proceeds 10) of solution. The purification process effectivenesness through an intramolecular acyl transfer to stable Ac­ was monitored by using HPLC. The high-relativetive- acylureas (Scheme 1). By keeping the set of experi- molecular-mass product was freeze-dried. The yielidd of mental conditions (see Experimental) we have received EDC-HA product was 105 mg. The infrared spectrctra 40 % conversion of carboxyl group as found by po- were taken using a Nicolet Magna-IR 750 instrumentLent.. tensometric titration. As HA is considered to be very sensitive to acid or basic degradation, the reaction was Kinetics of Enzymatic Degradation carried out at pH 6 for prolonged time. However, the small degradation was still unavoidable. The chemi- Commercial testicular hyaluronidase, 135 TRľRU cal bond formation of HA with EDC was observed on (turbidity-reducing units), was added to 10 cm33 oof infrared spectra by appearing of new bands at 1701 a solution (p = 0.002 g cm-3) of the biopolymeTr in cm-1 v(C=0), 1645 cm"1 v (amide I), and 1555 cm-1 aqueous NaNC>3 (c = 0.1 mol dm-3). The reactiotion v (amide II). was carried out under a gentle shaking at 37XI. Samam-­ In the XH NMR spectrum of product, the signals ple aliquots (200 mm3), withdrawn in the intervalvals in the range 3.4—4.8 were assigned to HA [10]. and r 5, 10. 30, 60 min were heated for 5 min in a boilDoil­- singlet at 2.17 was attributed to CH3 group of A - ing water bath. After cooling, the precipitated en­- Ac. The remaining signals belong to acylurea parts zyme was separated by centrifugation and the clea:lear of the structure: 1.35 (t) CH3CH2N, 3.07, 3.06 (both supernatant was submitted to HPLC analysis. TwГ wo s) N(CH3)2, 2.09 (overlapped multiplets) CH2CH2N. columns in series packed with Biospher GM 300 and The chemical shift of the CH3 proton at 1.35 suggests GM 1000 were used with HPLC instrument (Vývopvo-­ the O-acylisourea structure [6]. jové dílny, Czech Republic) equipped with differentiaitial In the 13C NMR spectrum (Fig. 1) of HA-EDC refractometric detector. Pullulan standards were useised adduct, except of signals of HA [10], there are also as molecular-mass reference materials [8]. the chemical shifts of acylurea: 14.47 CH3CH2, 25.11 CH3CH2, 37.10, 56.00, 50.60 CH2CH2CH2. The pres­ RESULTS AND DISCUSSION ence of CH2 groups was confirmed using the DEPT pulse sequence. The signals for C=0 group at 156.72, Attempt of chemical binding of amines to HA byу aаnл 156.20 indicate the presence of two TV-acylurea iso- EDC activation of HA carboxyl groups revealed tha:hat mers. The more intensive signal at 156.20 may belong the only product detected was an acylurea adduct:t of to isomer with NHCH2CH3 arrangement [7]. EDC and HA. As the acylurea products of HA coul>uld Fig. 2 presents dependence of the Mr values on be also commercially interesting [6], we have focuseised the time of enzymic reaction. As expected, the native on the more detailed chemical characterization includlud-­ HA showed depolymerization with the highest rate at ing their enzymic degradability. first 10 min. (The degree of polydispersity increased 50 Chem. Pap. 55(1)49—52 (2001) HYALURONAN DERIVATIVE N(CH3)2 CH2 CH3 CH2 CH2 C-O CH2 \}ш^№^^ Wv^ ^УЦ\^Ц^ *чК i i i i i i i "i i r" ,,,I""",,T,,"""I i i I I 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 S 13 Fig. 1. Proton-decoupled C NMR spectrum of EDC-HA in D20 at 25°C. 200 о 100- * Fig. 2. Depolymerization kinetics of HA and EDC-HA by action of hyaluronidase. from D = 1.15 to D = 1.33 at the same time.) On REFERENCES the contrary, EDC-modified HA did not show any de­ polymerization at all. This observation unveiled that 1. Vercruysse, K. P. and Prestwich, G. D., Critical Re­ roughly half of carboxyl groups that were modified can views in Therapeutic Drug Carrier Systems 15, 513 be enough to prevent the effective enzymatic attack by (1998). hyaluronidase. The chemical modification of HA with 2. Cera, C, Terbojevich, M., Cosani, A., and Palumbo, EDC can reduce biodegradability of HA while its bio- M., Int.
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