Free Radical Depolymerization Research Articles

Depolymerization of lignin model compounds by reactive oxygen species generated from peroxymonosulfate under mild conditions

Directional cleavage the linkages bonds between the lignin units is of great scientific interest although technically challenging. In this work, free radical depolymerization of lignin was investigated by using three model compounds. Peroxymonosulfate (PMS) was activated by N-doped carbon and thermal method, and could generate reactive oxygen species (ROS), including hydroxyl radical (OH∙), sulfate radical anion (SO4∙−), superoxide anion (O2∙−) and singlet oxygen(O12). pH of solution was used to regulate the types of ROS. The results showed that 1) pH value can tune the reaction pathway by regulating the type of ROS; 2) There should be an optimal temperature for maximum selectivity of monomer products in the depolymerization proces of lignin model compounds by ROS; 3) Hydroxyl group and Methoxy group can activate the reactivity of lignin model compounds, which is conductive to the directional generation of monomer products. In addition, the depolymerization mechanism of lignin model compound by PMS was proposed.This work illustrated the reaction characters and the influence factors of the lignin depolymerization by PMS, the results would facilitate the optimization of the lignin valorization process.

Structural requirements of Holothuria floridana fucosylated chondroitin sulfate oligosaccharides in anti-SARS-CoV-2 and anticoagulant activities.

Fucosylated chondroitin sulfate (FucCS) is a unique glycosaminoglycan found primarily in sea cucumbers. This marine sulfated glycan is composed of a chondroitin sulfate backbone decorated with fucosyl branches attached to the glucuronic acid. FucCS exhibits potential biological actions including inhibition of blood clotting and severe acute respiratory syndrome coronavirus (SARS-CoV-2) infection. These biological effects have been attributed to certain structural features, including molecular weight (MW), and/or those related to fucosylation, such as degrees of fucosyl branches, sulfation patterns and contents. In a previous work, we were able to generate oligosaccharides of the FucCS from Pentacta pygmaea (PpFucCS) with reduced anticoagulant effect but still retaining significant anti-SARS-CoV-2 activity against the delta strain. In this work, we extended our study to the FucCS extracted from the species Holothuria floridana (HfFucCS). The oligosaccharides were prepared by free-radical depolymerization of the HfFucCS via copper-based Fenton reaction. One-dimensional 1H nuclear magnetic resonance spectra were employed in structural analysis. Activated partial thromboplastin time and assays using protease (factors Xa and IIa) and serine protease inhibitors (antithrombin, and heparin cofactor II) in the presence of the sulfated carbohydrates were used to monitor anticoagulation. Anti-SARS-CoV-2 effects were measured using the concentration-response inhibitory curves of HEK-293T-human angiotensin-converting enzyme-2 cells infected with a baculovirus pseudotyped SARS-CoV-2 wild-type and delta variant spike (S)-proteins. Furthermore, the cytotoxicity of native HfFucCS and its oligosaccharides was also assessed. Like for PpFucCS, we were able to generate a HfFucCS oligosaccharide fraction devoid of high anticoagulant effect but still retaining considerable anti-SARS-CoV-2 actions against both variants. However, compared to the oligosaccharide fraction derived from PpFucCS, the average MW of the shortest active HfFucCS oligosaccharide fraction was significantly lower. This finding suggests that the specific structural feature in HfFucCS, the branching 3,4-di-sulfated fucoses together with the backbone 4,6-di-sulfated N-acetylgalactosamines, is relevant for the anti-SARS-CoV-2 activity of FucCS molecules.

Anti-SARS-CoV-2 and anticoagulant properties of Pentacta pygmaea fucosylated chondroitin sulfate depend on high molecular weight structures.

Fucosylated chondroitin sulfate (FucCS) is a unique marine glycosaminoglycan that exhibits diverse biological functions, including antiviral and anticoagulant activity. In previous work, the FucCS derived from Pentacta pygmaea (PpFucCS) showed moderate anticoagulant effect but high inhibitory activity against the Wuhan strain of severe acute respiratory syndrome coronavirus (SARS-CoV-2). In this study, we perform free-radical depolymerization of PpFucCS by the copper-based Fenton method to generate low molecular weight (MW) oligosaccharides. PpFucCS oligosaccharides were structurally analyzed by 1H nuclear magnetic resonance spectroscopy and were used to conduct structure-activity relationship studies regarding their effects against SARS-CoV-2 and clotting. Anticoagulant properties were measured by activated partial thromboplastin time, protease (factors Xa and IIa) inhibition by serine protease inhibitors (antithrombin [AT] and heparin cofactor II [HCII]), and competitive surface plasmon resonance (SPR) assay using AT, HCII, and IIa. Anti-SARS-CoV-2 properties were measured by the concentration-response inhibitory curves of HEK-293T-human angiotensin-converting enzyme-2 cells infected with a baculovirus pseudotyped SARS-CoV-2 Delta variant spike (S)-protein and competitive SPR assays using multiple S-proteins (Wuhan, N501Y [Alpha], K417T/E484K/N501Y [Gamma], L542R [Delta], and Omicron [BA.2 subvariant]). Cytotoxicity of native PpFucCS and oligosaccharides was also assessed. The PpFucCS-derived oligosaccharide fraction of the highest MW showed great anti-SARS-CoV-2 Delta activity and reduced anticoagulant properties. Results have indicated no cytotoxicity and MW dependency on both anti-SARS-CoV-2 and anticoagulant effects of PpFucCS, as both actions were reduced accordingly to the MW decrease of PpFucCS. Our results demonstrate that the high-MW structures of PpFucCS is a key structural element to achieve the maximal anti-SARS-CoV-2 and anticoagulant effects.

Structural characterization of oligosaccharides from free radical depolymerized fucosylated glycosaminoglycan and suggested mechanism of depolymerization

Free radical depolymerization is a common method in structural analysis of polysaccharides, the major challenge is the analysis of the cleavage site and characterization of newly formed ends in this reaction. Here, a fucosylated glycosaminoglycan from H. fuscopunctata (HfFG) was depolymerized by H2O2 and a series of oligosaccharides were purified and their structures were elucidated. For non-reducing ends of the trisaccharides were intact GalNAc4S6S, the cleavage site should mainly be the β(1,3) linkages between GlcA and GalNAc in the backbone of FG. Meanwhile, the reducing ends of the disaccharides and trisaccharides were almost dicarboxylic acid derivatives of GlcA, possibly arising from oxidative breaking of the CC bond of GlcA at the reducing ends. In addition, glycosidic linkages in D-GalNAc-β(1,4)-D-GlcA and L-FucS-α(1,3)-D-GlcA located at the reducing end could be cleaved, and the released GalNAc4S6S were oxidized to N-acetylgalactosaminic acid.

Depolymerization Kinetics of Aqueous Cassava Starch under Sonication Process using Free-Radical Depolymerization Model and its Correlation with Radical Production from Acoustic Cavitation

The technology of biopolymer degradation to produce its derivative compounds is an important topic nowadays. The use of environmentally friendly methods, such as sonication, is a promising method for obtaining biopolymer derivative compounds. Sonication creates acoustic cavitation in the liquid body to produce radicals and microjets that can substitute acid substances in the degradation process. Through the sonication process, starch-based compounds can be degraded to oligosaccharides and reducing sugars, which have a variety of benefits in the food, pharmaceutical, and fermentation industries. Many experiments have been conducted to investigate the role of sonication in starch degradation. However, there is much process model that can describe the role of sonication in depolymerization. This work aims to evaluate the ability of sonication in producing reducing sugars and lower-molecular-weight starch by using the Free-radical depolymerization model and correlating it with the production of radicals from acoustic cavitation. Experiments were carried out using horn-type sonication with a power of 500W with various amplitudes. The reducing sugar analysis was carried out by the DNS method and the average molecular weight was estimated with Ubbelohde viscosimetry. From the simulation results, sonication with 30% of the maximum amplitude gives the largest radical production, which well correlates with the production of reducing sugar. The experimental results show a maximum yield of reducing sugar of 0.570 g / L in the process using S30 for 60 minutes.

Mass spectrometric evidence for the mechanism of free-radical depolymerization of various types of glycosaminoglycans

Glycosaminoglycans (GAGs) are large, complex carbohydrate molecules that interact with a wide range of proteins involved in physiological and pathological processes. Several naturally derived GAGs have emerged as potentially useful therapeutics in clinical applications. Natural polysaccharides, however, generally have high molecular weights with a degree of polydispersity, making it difficult to investigate their structural properties. In this study, we establish a free-radical–mediated micro-reaction system and use hydrophilic interaction chromatography (HILIC)–Fourier transform mass spectrometry (FTMS) to profile the degraded products of various types of GAGs, heparin, chondroitin sulfate A, NS-heparosan, and oversulfated chondroitin sulfate (OSCS), to reveal the free-radical degradation mechanism of GAGs. The results show that the bulk fragments of GAGs generated by free-radical degradation can maintain their basic structural units and sulfate substituents. In addition, an abundance of oligomers modified with oxidation at their reducing ends or by dehydration also appeared. We discovered that these modifications were related in terms of the degree of sulfation and the α- or β-linkage of HexNY (Y = SO3− or Ac), and especially that the different linkage of the disaccharide unit is the main factor in modification. In addition, the method based on micro-free-radical reaction and HILIC-FTMS is both effective and sensitive, thus suggesting its broad practical value for the structural characterization and in the biological structure-function studies of GAGs.

Characterization of New Oligosaccharides Obtained by An Enzymatic Cleavage of the Exopolysaccharide Produced by the Deep-Sea Bacterium Alteromonas infernus Using its Cell Extract.

Bacteria from deep-sea hydrothermal vents constitute an attractive source of bioactive molecules. In particular, exopolysaccharides (EPS) produced by these bacteria become a renewable source of both biocompatible and biodegradable molecules. The low molecular weight (LMW) derivatives of the GY785 EPS produced by the deep-sea hydrothermal vent strain Alteromonas infernus have previously displayed some biological properties, similar to those of glycosaminoglycans (GAG), explored in cancer and tissue engineering. These GAG-mimetic derivatives are obtained through a free radical depolymerization process, which could, however, affect their structural integrity. In a previous study, we have shown that A. infernus produces depolymerizing enzymes active on its own EPS. In the present study, an enzymatic reaction was optimized to generate LMW derivatives of the GY785 EPS, which could advantageously replace the present bioactive derivatives obtained by a chemical process. Analysis by mass spectrometry of the oligosaccharide fractions released after enzymatic treatment revealed that mainly a lyase activity was responsible for the polysaccharide depolymerization. The repeating unit of the GY785 EPS produced by enzyme cleavage was then fully characterized.

Sulfated polysaccharide from sea cucumber modulates the gut microbiota and its metabolites in normal mice

Sulfated polysaccharide from sea cucumber (SCSP) has been demonstrated with various health effects, the mechanism of which, however, remains poorly understood. This study aimed to investigate the possible mechanism exhibited by gut microbiota in response to SCSP. BALB/c mice were fed diets supplemented with SCSP and depolymerized SCSP (d-SCSP) for 42 days. The microbiota composition, short chain fatty acids (SCFAs), lipopolysaccharide-binding protein (LBP), body weight and gut tissue index were analyzed. Results revealed that both SCSP and d-SCSP positively regulated the gut microbiota as indicated by the enriched microbiota diversity, SCFA-producing bacteria and sulfide-degrading bacteria, and decreased harmful bacteria. Moreover, SCSP and d-SCSP not only significantly improved the levels of microbial metabolites including SCFAs and LBP, but also effectively adjusted body weight and gut tissue index. The microbial metabolites were identified to strongly correlate with the growth performance using Pearson's correlation coefficient. We further showed that the modulating effect of SCSP on the gut microbiota was altered by free-radical depolymerization, while the microbial metabolites and related growth performance were not. These findings suggest that SCSP can be used as a gut microbiota manipulator for health promotion and alter the gut microbiota in a molecular weight (Mw) dependent manner.

Structural characterization and in vitro antioxidant activities of chondroitin sulfate purified from Andrias davidianus cartilage

Origin and manufacturing process are key factors affecting the biological activities of chondroitin sulfate (CS), which can be utilized as a nutraceutical in dietary supplements. Herein, we extracted and purified CS from the cartilage of artificially breeding Andrias davidianus (ADCS), i.e., Chinese giant salamander (CGS), one of the prospective functional food source materials in China. Low molecular weight CS (LMWADCS) was then prepared by free radical depolymerization of ADCS. High-performance gel permeation chromatography (HPGPC) analysis showed that the average molecular weight (Mw) of ADCS was 49.2 kDa, while the Mw of LMWADCS was 6.4 kDa. After the eliminative degradation of ADCS by chondroitinase ABC, strong anion-exchange high-performance liquid chromatography (SAX-HPLC) analysis showed that the disaccharide composition of ADCS was 14.6% ΔDi0S, 60.9% ΔDi6S and 24.5% ΔDi4S. Then, in vitro antioxidant assays were performed with ADCS, LMWADCS and CS from a commercial source. Our results showed that LMWADCS exerted the highest total antioxidant activity out of the total antioxidant capacity, including the capacity of scavenging DPPH radicals, hydroxyl radicals and superoxide anion radicals. From the results of this study, we can conclude that the Mw and composition of ADCS are different from those reported for bovine and shark CS, and LMWADCS can be utilized as a valuable and potential nutraceutical for the functional food industry.

Preparation of sodium cellulose sulfate oligomers by free-radical depolymerization

Sodium cellulose sulfates with various degree of substitution (DS) and degree of polymerization (DP) were synthesized by homogeneous sulfation of cellulose with different DP by using SO3/pyridine (Py) complex in N,N-dimethylacetamide/lithium chloride (DMA/LiCl). Sodium cellulose sulfate (SCS) samples obtained were free-radically depolymerized with hydrogen peroxide and copper (II) acetate at a controlled pH value of 7.5–8.0 and without control of the pH value (pH 2.5–4.0). The depolymerization process was studied with respect to changes in molecular mass, total DS, and substituent distribution of SCS. Elemental analysis, 13C NMR- and IR spectroscopic methods indicated that primary structures of SCS were retained with insignificant decreases in total sulfate content in the depolymerization. The depolymerization of SCS was randomly and obeyed pseudo first order kinetics under the conditions applied. SCS oligomers with low DP and very narrow molecular weight distribution were prepared by the depolymerization at pH 2.5–4.0.

Depolymerization of Fucosylated Chondroitin Sulfate with a Modified Fenton-System and Anticoagulant Activity of the Resulting Fragments.

Fucosylated chondroitin sulfate (fCS) from sea cucumber Isostichopus badionotus (fCS-Ib) with a chondroitin sulfate type E (CSE) backbone and 2,4-O-sulfo fucose branches has shown excellent anticoagulant activity although has also show severe adverse effects. Depolymerization represents an effective method to diminish this polysaccharide’s side effects. The present study reports a modified controlled Fenton system for degradation of fCS-Ib and the anticoagulant activity of the resulting fragments. Monosaccharides and nuclear magnetic resonance (NMR) analysis of the resulting fragments indicate that no significant chemical changes in the backbone of fCS-Ib and no loss of sulfate groups take place during depolymerization. A reduction in the molecular weight of fCS-Ib should result in a dramatic decrease in prolonging activated partial thromboplastin time and thrombin time. A decrease in the inhibition of thrombin (FIIa) by antithromin III (AT III) and heparin cofactor II (HCII), and the slight decrease of the inhibition of factor X activity, results in a significant increase of anti-factor Xa (FXa)/anti-FIIa activity ratio. The modified free-radical depolymerization method enables preparation of glycosaminoglycan (GAG) oligosaccharides suitable for investigation of clinical anticoagulant application.

Cytokine-inducing and anti-inflammatory activity of chitosan and its low-molecular derivative

A low-molecular derivative of the polysaccharide (5 kDa) was obtained and its cytokine-inducing and anti-inflammatory activity was studied by free radical depolymerization of chitosan (110 kDa). It was shown that high-molecular chitosan in vitro inhibited the synthesis of anti-inflammatory cytokine, the tumor necrosis factor alpha induced by endotoxin. In the case of peroral introduction to experimental animals, high- and low-molecular chitosans stimulated synthesis of the anti-inflammatory cytokine IL-10 in the blood serum of mice; in this case, the activity of the high-molecular derivative was two times higher as compared with the initial polysaccharide. With peroral introduction, the initial polysaccharide (50 mg/kg) and its derivative inhibited the development of chemically induced inflammation of experimental animals’ large intestines, which was manifested as a decrease in the affected area and the degree of damage to the large intestine wall, as well as a two-fold reduction of myeloperoxidase activity. According to morphological and biochemical characteristics, the effect of chitosans was similar to that of a hormone anti-inflammatory drug, prednisolone.

Depolymerization of Free-Radical Polymers with Spin Migrations.

The mechanism of depolymerization is one of the most essential issues in chemical engineering and materials science. In this work, we investigate the depolymerization reactions of three typical free-radical poly(alpha-methylstyrene) tetramers by using first-principles density functional theory. The calculated results show that these reactions all need to overcome the energy barriers in the range of 0.58 to 0.77 eV, and that breaking the C-C bond at the chain end leads to the dissociation of alpha-methylstyrene monomers from the polymers. Electronic-structure analysis indicates that the reactions occur easily at the CR3 unsaturated end, and that the frontier molecular orbitals that participate in the reactions are mainly localized at the unsaturated ends. Meanwhile, spin population analysis presents the unique net spin-transfer process in free-radical depolymerization reactions. We hope the current findings can contribute to understanding the free-radical depolymerization mechanism and help guide future experiments.

Depolymerization of polysaccharides from Opuntia ficus indica: Antioxidant and antiglycated activities

The extraction, purification and degradation of polysaccharides from Opuntia ficus indica cladodes, as well as the evaluation of their antioxidant and antiglycated activities in vitro were investigated. The optimization of the extraction showed that extraction by ultrasound at 40°C presented the best carbohydrates yield. The degradation of the extracted polysaccharides was achieved by free radical depolymerization with H2O2 in the presence of copper(II) acetate for various reaction times. Sugar contents were determined by colorimetric assays. The macromolecular characteristics of the different isolated and degraded carbohydrates were carried by size exclusion chromatography (SEC/MALS/VD/DRI). These experiments showed that all samples are polysaccharides, which are probably pectins and that molecular weight (Mw) has decreased from 6,800,000 to 14,000g/mol after 3h of depolymerization without changing the structure. Preliminary antioxidant and antiglycated tests indicated that degraded polysaccharides for 2 and 3h showed even better antioxidant and antiglycated activities.

Profiling pneumococcal type 3-derived oligosaccharides by high resolution liquid chromatography–tandem mass spectrometry

Pneumococcal type-3 polysaccharide (Pn3P) is considered a major target for the development of a human vaccine to protect against Streptococcus pneumoniae infection. Thus, it is critical to develop methods for the preparation and analysis of Pn3P-derived oligosaccharides to better understand its immunological properties. In this paper, we profile oligosaccharides, generated by the free radical depolymerization of Pn3P, using liquid chromatography (LC)–tandem mass spectrometry (MS/MS). Hydrophilic liquid interaction chromatography (HILIC)–mass spectrometry (MS) revealed a series of oligosaccharides with an even- and odd-number of saccharide residues, ranging from monosaccharide, degree of polymerization (dp1) to large oligosaccharides up to dp 20, generated by free radical depolymerization. Isomers of oligosaccharides with an even number of sugar residues were easily separated on a HILIC column, and their sequences could be distinguished by comparing MS/MS of these oligosaccharides and their reduced alditols. Fluorescent labeling with 2-aminoacridone (AMAC) followed by reversed phase (RP)-LC–MS/MS was applied to analyze and sequence poorly separated product mixtures, as RP-LC affords higher resolution of AMAC-labeled oligosaccharides than does HILIC-based separation. The present methodology can be potentially applied to profiling other capsular polysaccharides.

Structural characterization and antioxidant activities of κ-carrageenan oligosaccharides degraded by different methods

In the present study, four kinds of κ-carrageenan oligosaccharides were obtained by the degradation of parent κ-carrageenan using free radical depolymerization, mild acid hydrolysis, κ-carrageenase digestion and partial reductive hydrolysis, respectively. Their structure types were accurately and comparatively elucidated by ESI-MS and CID MS/MS. The antioxidant activities of different degraded products were investigated by four different antioxidant assays, including superoxide radical scavenging activity, hydroxyl radical scavenging activity, reducing power and DPPH radical scavenging activity. The methods of depolymerization had an influence on the antioxidant activities of κ-carrageenan oligosaccharides obtained from κ-carrageenan. These results indicated that the antioxidant activities of κ-carrageenan oligosaccharides could be related to the degree of polymerization, the content of reducing sugar and sulfate groups, and the structure of reducing terminus.

Depolymerized glycosaminoglycan and its anticoagulant activities from sea cucumber Apostichopus japonicus

A controlled Cu2+ catalytic free-radical depolymerization process of fucosylated chondroitin sulfate from sea cucumber Apostichopus japonicus was established. The results showed a good linear relationship between 1/Mw and time during the depolymerization. A series of fractions with different molecular weight were obtained, and the physicochemical properties of them were investigated and compared utilizing the chemical method, IR spectra and NMR spectra. The results showed no significant variations of the backbone and branches structures during the depolymerization. Furthermore, the anticoagulant activities of the depolymerized fractions were evaluated by the activated partial thromboplastin time (APTT). The APTT decreases in proportion to the molecular weight following a linear relationship and the prolongation of APTT activity requires at least oligosaccharide of 4 trisaccharide units (about 4000Da). Their anticoagulant activity of low molecular weight fraction (Mw=24,755Da) is similar to LMWH with significantly less bleeding risk. The results suggest that the low molecular weight fraction could be used as a novel anticoagulant with less undesired side effects.

Structure and anticoagulant activity of fucosylated glycosaminoglycan degraded by deaminative cleavage

Fucosylated glycosaminoglycans (FGs) are complex glycosaminoglycans that exhibit potent anticoagulant activity. To study the relationship between molecular size and biological activity, oligosaccharides with (2,5)-anhydro-d-talose units at new reducing ends were prepared by hydrazine deacetylation and nitrous acid depolymerization. The product chemical structures were analyzed by one- and two-dimensional NMR methods. Additionally, anticoagulant activities were evaluated by clotting assay and chromogenic substrate cleavage. The results demonstrated that under mild deacetylation and deaminative cleavage conditions, both products were relatively homogeneous and sulfated fucose branch types and sulfate substituents remained stable. These depolymerized FGs with different molecular sizes had potent intrinsic anticoagulant activities, which were similar to those that were obtained by free-radical depolymerization with similar molecular weights. Decreasing molecular weight may weaken activity but not significantly affect factor Xase and heparin cofactor II (HCII)-mediated thrombin inhibition.

Extraction of a Polysaccharide from the Skin of Ray Raja montagui by Free-Radical Depolymerization with Metallic Catalysis

The large production of sulfated polysaccharides was routinely investigated by various procedures such as enzymatic method and acid hydrolysis. The free-radical depolymerization applied directly on the skin of ray constitutes an efficient method and an original process to produce bioactive compounds in large amount and good reproducibility. The depolymerized sulfated polysaccharides fractions obtained from the skin of ray Raja montagui have an average molecular weight ranging from 29 kDa to 5 kDa and were endowed with higher anticoagulant activity compared to mammalian dermatan sulfate from intestinal mucosa. Moreover, the anticoagulant effect of these fractions was 4 and 5-fold higher than the DS from porcine mucosa as shown by activated partial thromboplastin time and thrombin time, respectively. In particular, this was illustrated by lower IC50 as for the overall inhibition of thrombin in human plasma. Keywords: Anticoagulant activity, antithrombin, dermatan sulfate, free-radical depolymerization, ray skin, sulfated polysaccharide.

Low molecular weight derivatives of different carrageenan types and their antiviral activity

A number of low molecular weight (LMW) fractions of carrageenans with different structural types were obtained by free radical depolymerization (H2O2), mild acid hydrolysis (HCl), and a specific enzyme. Three samples of carrageenans were depolymerized: kappa-carrageenan from Chondrus armatus, kappa-carrageenan from Kappaphycus alvarezii, and kappa/beta-carrageenan from Tichocarpus crinitus with initial molecular weights of 250, 390, and 400 kDa, respectively. The chemical depolymerization by two methods resulted to LMW derivatives of carrageenans with molecular weight from 1.2 to 3.5 kDa. Oligosaccharides of kappa- and kappa/beta-carrageenans with molecular weight of 2.2 and 4.3 kDa, respectively, were obtained after enzymatic depolymerization by recombinant kappa-carrageenase from Pseudoalteromonas carrageenovora. It was shown that the antiviral activity of high molecular weight carrageenans against tobacco mosaic virus was higher than that of their LWM derivatives independently on the depolymerization method. The method of depolymerization had some influence on the antiviral activity of carrageenan. LMW derivatives of kappa- and kappa/beta-carrageenans obtained by mild acid hydrolysis showed higher antiviral activity than the products of free radical depolymerization. The oligosaccharides prepared by enzymatic degradation possessed the lowest activity.