Insertion of Degradable Thioester Linkages into Styrene and Methacrylate Polymers

The thionolactone 3,3-dimethyl-2,3-dihydro-5H-benzo[e][1,4]dioxepine-5-thione (DBT) is shown to homopolymerize and, for the first time, copolymerize with styrene and methacrylates, introducing degradable thioester backbone functionality. The rapid copolymerization with styrene was exploited to produce copolymers through free-radical polymerization in a starve-fed semi-batch setup. The copolymerization of DBT with tert-butyl methacrylate under RAFT conditions was hypothesized to involve selective retardation of DBT-terminal chains that led to a more uniform distribution of degradable thioester linkages between chains. Surprisingly, the aminolysis of DBT homopolymers was accompanied by the intramolecular ether cleavage within the primary degradation product leading to the formation of 2,2-dimethylthiirane and salic-ylamides.

Oligomeric Aromatic Oxides (OAO) Production From Sugarcane Bagasse Lignin by Acid-Catalyzed Solvothermal Liquefaction in Methanol

Extracted alkali lignin (AL) and organosolv lignin (OL) from sugarcane bagasse were acid-catalyzed liquefied in methanol with the aim of producing oligomeric aromatic oxides. Acids were screened for their effects on the output of oligomeric aromatic oxides from alkali lignin liquefaction. Based on the highest amount of lignin conversion, the order of catalytic efficiency was: p-toluenesulfonic acid (TsOH) > CCl3COOH (TCA) > KHSO4 > AlCl3 > H3O40PW12 > H2SO4. The most alkali lignin conversion was 86.2 wt% when catalyzed by p-toluenesulfonic acid. Optimized liquefaction temperatures indicated that AL liquefaction optimum temperature was 250°C and OL was 175°C. GPC characterized AL, OL and resultant products implied that TsOH could degrade both lignins to about 780 g/mol of molecular weight. HSQC-NMR and GC-MS observations suggested that simultaneous vinyl ether cleavage and intermediate stabilization of phenolic hydroxyl group etherification at high temperatures achieved AL liquefaction. Acidolysis of β-ether linkages at mild temperatures was the mechanism of OL liquefaction.

Roles of two glutathione S-transferases in the final step of the β-aryl ether cleavage pathway in Sphingobium sp. strain SYK-6

Sphingobium sp. strain SYK-6 is an alphaproteobacterial degrader of lignin-derived aromatic compounds, which can degrade all the stereoisomers of β-aryl ether-type compounds. SYK-6 cells convert four stereoisomers of guaiacylglycerol-β-guaiacyl ether (GGE) into two enantiomers of α-(2-methoxyphenoxy)-β-hydroxypropiovanillone (MPHPV) through GGE α-carbon atom oxidation by stereoselective Cα-dehydrogenases encoded by ligD, ligL, and ligN. The ether linkages of the resulting MPHPV enantiomers are cleaved by stereoselective glutathione (GSH) S-transferases (GSTs) encoded by ligF, ligE, and ligP, generating (βR/βS)-α-glutathionyl-β-hydroxypropiovanillone (GS-HPV) and guaiacol. To date, it has been shown that the gene products of ligG and SLG_04120 (ligQ), both encoding GST, catalyze GSH removal from (βR/βS)-GS-HPV, forming achiral β-hydroxypropiovanillone. In this study, we verified the enzyme properties of LigG and LigQ and elucidated their roles in β-aryl ether catabolism. Purified LigG showed an approximately 300-fold higher specific activity for (βR)-GS-HPV than that for (βS)-GS-HPV, whereas purified LigQ showed an approximately six-fold higher specific activity for (βS)-GS-HPV than that for (βR)-GS-HPV. Analyses of mutants of ligG, ligQ, and both genes revealed that SYK-6 converted (βR)-GS-HPV using both LigG and LigQ, whereas only LigQ was involved in converting (βS)-GS-HPV. Furthermore, the disruption of both ligG and ligQ was observed to lead to the loss of the capability of SYK-6 to convert MPHPV. This suggests that GSH removal from GS-HPV catalyzed by LigG and LigQ, is essential for cellular GSH recycling during β-aryl ether catabolism.

Roles of two glutathione S-transferases in the final step of the β-aryl ether cleavage pathway in Sphingobium sp. strain SYK-6

ABSTRACTSphingobium sp. strain SYK-6 is an alphaproteobacterial degrader of lignin-derived aromatic compounds, which can degrade all the stereoisomers of β-aryl ether-type compounds. SYK-6 cells convert four stereoisomers of guaiacylglycerol-β-guaiacyl ether (GGE) into two enantiomers of α-(2-methoxyphenoxy)-β-hydroxypropiovanillone (MPHPV) through GGE α-carbon atom oxidation by stereoselective Cα-dehydrogenases encoded by ligD, ligL, and ligN. The ether linkages of the resulting MPHPV enantiomers are cleaved by stereoselective glutathione S-transferases (GSTs) encoded by ligF, ligE, and ligP, generating (βRβS)-α-glutathionyl-β-hydroxypropiovanillone (GS-HPV) and guaiacol. To date, it has been shown that the gene products of ligG and SLG_04120 (ligQ), both encoding GST, catalyze glutathione removal from (βRβS)-GS-HPV, forming achiral β-hydroxypropiovanillone. In this study, we characterized the enzyme properties of LigG and LigQ and elucidated their roles in β-aryl ether catabolism. Purified LigG showed an approximately 300-fold higher specific activity for (βR)-GS-HPV than that for (βS)-GS-HPV, whereas purified LigQ showed an approximately six-fold higher specific activity for (βS)-GS-HPV than that for (βR)-GS-HPV. Analyses of mutants of ligG, ligQ, and both genes revealed that SYK-6 converted (βR)-GS-HPV using both LigG and LigQ, whereas only LigQ was involved in converting (βS)-GS-HPV. Furthermore, the disruption of both ligG and ligQ was observed to lead to the loss of the capability of SYK-6 to convert MPHPV. This suggests that GSH removal from GS-HPV catalyzed by LigG and LigQ, is essential for cellular GSH recycling during β-aryl ether catabolism.IMPORTANCEThe β-aryl ether linkage is most abundant in lignin, comprising 45%–62% of all intermonomer linkages in lignin; thus, cleavage of the β-aryl ether linkage together with the subsequent degradation process is considered the essential step in lignin biodegradation. The enzyme genes for β-aryl ether cleavage are useful for decomposing high-molecular-weight lignin, converting lignin-derived aromatic compounds into value-added products, and modifying lignin structures in plants to reduce lignin recalcitrance. In this study, we uncovered the roles of the two glutathione S-transferase genes, ligG and ligQ, in the conversion of GS-HPV isomers, which are generated in the β-aryl ether cleavage pathway in SYK-6. Adding our current results to previous findings allowed us to have a whole picture of the β-aryl ether cleavage system in SYK-6.