Preparation Of Novel Chitooligosaccharide Amide Derivatives And Their Antioxidant Activities

Research has shown that ageing and many chronic diseases are directly linked to free radicals.The instability of free radicals stems from the fact that they are molecules containing unpaired electrons.These unpaired electrons are released under induced conditions（e.g.inflammation,drugs,alcohol consumption and stress）and tend to contribute to the accumulation of free radicals.This can cause oxidative damage to the body and disrupt normal physiological functions,leading to chronic diseases.The degree of oxidative damage in the body is regulated by antioxidants,and as research in the field of antioxidants becomes more extensive and intensive,the advantages of natural antioxidant polysaccharides have come to the fore.Chitooligosaccharide are abundant in nature,and they are a new kind of natural antioxidant polysaccharides.In this paper,12 new chitooligosaccharide amide derivatives were prepared by grafting six amino acids with two different molecular weights of chitooligosaccharide as lead compounds,and the molecular structures of the derivatives were characterized by infrared spectroscopy,NMR carbon spectroscopy and elemental analysis.The characteristic absorption peaks of the amide bonds of all derivatives are enhanced in the IR spectrum,indicating that the-NH₂of chitooligosaccharide has undergone an amide reaction with the-COOH of the amino acid.In the NMR carbon spectrum,none of the chemical shifts of the chitooligosaccharide sugar ring carbons（C1-C6）were altered and the amide bonds were chemically stable with each amino acid carbon skeleton.All spectral results indicate that the target derivatives were successfully synthesized:2-aminoacetyl chitooligosaccharide（2-Gly COS）,2-aminopropionyl chitooligosaccharide（2-Ala COS）,2-amino-3-methylbutanoylchitooligosaccharide（2-Val COS）,2-amino-4-methylpentanoylchitooligosaccharide（2-Leu COS）,2-amino-3-hydroxypropionyl chitooligosaccharide（2-Ser COS）and 2,6-diaminohexanoyl chitooligosaccharide（2-Lys COS）.The results of the elemental analysis showed that all derivatives had>60%substitution,with the highest substitution of 86.28%for 2-Gly COS.The solubility of derivatives of grafted 4 non-polar amino acids（Gly,Ala,Val,Leu）was assessed by solubility testing and it was found that the derivatives were able to overcome the hydrophobicity of the non-polar amino acids,resulting in a significant increase in solubility and facilitating many activity studies.After preparation,the in vitro antioxidant activities（hydroxyl radical,superoxide anion,DPPH radical scavenging capacity and reducing capacity）of each derivative were determined,and the antioxidant levels of each derivative were comprehensively examined.The antioxidant activity of the derivatives was positively correlated with the concentration in all the experiments.In the scavenging ability of hydroxyl radicals,2-Val HCOS and 2-Leu HCOS showed the best scavenging effect with the highest scavenging rate of 19.05%and 17.12%.In the scavenging ability of superoxide anion,2-Gly LCOS,2-Ala LCOS and 2-Leu LCOS showed the best scavenging effect,with the highest scavenging rate of 58.30%,67.70%and 57.13%.In the DPPH radical scavenging ability test,2-Ser HCOS and 2-Lys LCOS showed the best scavenging effect,with the highest scavenging rate of 74.82%and 40.62%.In the reduction ability test,2-Ala LCOS was particularly effective,with the highest absorbance value reaching 0.143 Abs.The overall results showed that the seven derivatives of 2-Gly LCOS,2-Ala LCOS,2-Val HCOS,2-Leu HCOS,2-Leu LCOS,2-Ser HCOS and 2-Lys LCOS have outstanding overall clearance and better antioxidant activity,and are worthy of further development and study.Finally,the antioxidant mechanism of the derivatives in this study was investigated in depth,and the effect of the introduction of new groups on the antioxidant activity of chitooligosaccharide was analysed from the perspectives of free radical scavenging mode and active hydrogen supply mechanism.To summarize the antioxidant pattern of chitooligosaccharide and its derivatives,so as to facilitate future research in the preparation of chitooligosaccharide antioxidants,provide a theoretical basis for the antioxidant mechanism of chitooligosaccharide and solidify the research framework.