| Separating monomeric compounds from biomass resources and then using them to synthesize new compounds and research their biological activities are a significant way in deep processing of high value-added products from biomass resources. Lignin is the second most abundantly renewable natural plant resources except cellulose richly found in wood hydrolysis and papermaking waste, used as fuel and even discharged without any treatment process, causing severe environmental pollution because it?s complicated structure and low industrial application rate. Researching on the value-added utilization of lignin by reaction–separation and modification of lignin degradation products is of very significant importance to make full use of natural resource and also to waste water treatment.Reaction-separation technology is one of important method in modern separation and purification, which is particularly tremendous significance in separation of natural produacts. In this paper, syringaldehyde, vanillin and p-hydroxybenzaldehyde were prepared from lignin via alkaline nitrobenzene oxidation with total yield 18% (purity 98.4%, 99.1% and 97.6%, respectively); Guaiacol, lilac alcohol, acetovanillone, acetosyringone were also obtained from lignin through new and low-toxicity oxidants A and B. In addition, Several series of new compounds were prepared using aromatic aldehydes obtained from lignin and screened for their biological activities to research their Structure-activity relationship:1) A convenient protocol is described for the preparation of 3-amino-imidazo[1,2-a] pyridine derivatives via three-component reactions between 2-aminopyridine derivatives, aldehydes and isocyanides with excellent yields (83~94%). All the compounds were characterized by IR, 1H NMR, 13C NMR, and HPLC-ESI-MS. In addition, their antibacterial activities were tesed by filter paper method. The result showed that these compounds 4b(iii), 4f(iii) and 4s(iii) had no inhibiting effects on Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Streptococcus, but they are being screened for anti-schistosomiasis activities. 2) A series of novel bispyrazoles joined by arylmethylene at C-4 position were synthesized in good to excellent yield (≥82%) using aromatic aldehydes obtained from lignin and screened for their antioxidant activities by N,N-diphenyl-N′-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylenzothiazoline-sulphonic acid) (ABTS+) radical scavenging assays. All of these compounds exhibited good DPPH and ABST+ radical scavenging activities as compared to the standard, Trolox. Especially, the compound 4a(iv) and 4d(iv) had better antioxidant activities, which suggested their potential as promising agents for curing tumors or other free radical-related diseases.3) A series of 4-aryl-hexahydroquinolines were prepared by microwave assisted Hantzsch reaction using aromatic aldehydes obtained from lignin, 1,3-cyclohexanediones,β-ketoesters and ammonium carbonate with good yields (≥89%). The antioxidant properties of 5a-c(v), 5g-i(v) were evaluated by two methods: scavenging effect on DPPH radical and scavenging effect on ABTS+ radical. Compounds 5a and 5g showed the best antioxidant activities against DPPH and ABST+, 5b(v) and 5h(v) were second, 5c(v) and 5i(v) were relatively bad. In addition, the results showed that the compounds containing methoxy moiety linked at the aryl substituents of the 4-aryl-hexahydroquinolines increased their biological activities; the activity order of them is as follows: 4-(4-hydroxy-3,5-dimethoxyphenyl) hexahydroquinolines > 4-(4-hydroxy-3-methoxyphenyl) hexahydroquinolines >> 4-(4-hydroxyphenyl) hexahydroquinolines.4) One-pot condensation of 1,4-dihydropyridines and 9-arylpolyhydroacridines with aromatic aldehydes obtained from lignin in the presence of ammonium carbonate was carried out in water with good yields (≥79%) except compound 6c(vi). Antioxidant properties of compounds 4a(vi), 4b(vi), 4e(vi), 6a(vi) and 6b(vi) were evaluated by scavenging DPPH and ABTS+ radical effects. Compounds 4a(vi) and 6a(vi) showed the best antioxidant activities against DPPH and ABST+. In addition, Compounds 4a(vi) and 6a(vi) also exibited good hypotensive properties, which suggested them deserving to further development and application.5) A series of novel 1H,4H-dihydro-pyrano[2,3-c]pyrazoles were synthesized via muti-component reaction with aromatic aldehydes obtained from lignin, and screened for their antioxidant activities by DPPH and ABTS+ radical scavenging assays. Except compound 7e(vii) and 7g(vii), all the other compound yielded well (≥70%). In addition, to our surprise, those compouds 6a(vii), 6d(vii), 6j(vii), 7d(vii) and 7g(vii) showed excellent antioxidant properties. Their values of IC50 were lower than that of Trolox in the DPPH and ABST+ radical cation scavenging assays. Especially, their values of IC50 were 1 000 times lower than that of Trolox in reaction with ABST+ radical. The strong antioxidant abilities of these compounds indicated their potential usefulness in the drug development, thus providing an effective approach for value-added application of lignin.6) 27 kinds of 3-cyanopyridine derivatives were prepared via convenient, rapid and environmentally benign four-component reactions between 2-substituted acetophenones, aromatic aldehydes, malononitrile and ammonium acetate under microwave irradiation with good yield (63~85%); the compounds 5b(viii), 5h(viii), 5i(viii), 7d(viii), 7e(viii), 7f(viii) and 7k(viii) were screened for their antioxidant activities by DPPH radical scavenging assays. The results showed that they had poor antioxidant properties, but they are being screened for anti-schistosomiasis activities.Through structure-activity relationship analysis, it was found that 4-hydroxy-3,5-dimethoxyphenyl heterocyclic compounds had better antioxidant and hypotensive activities than 4-hydroxy-3-methoxyphenyl and 4-hydroxyphenyl heterocyclic compounds, i.e, syringaldehyde is the better material for synthsis of antioxidant and hypotensive agents than vanillin and p-hydroxybenzaldehyde.
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