From biomass to the karrikins via selective catalytic oxidation of hemicellulose-derived butyl xylosides and glucosides

Funding: This work was supported by a China Scholarship Council-University of St Andrews PhD Fellowship (GX) and an IBioIC funded PhD studentship in collaboration with Scottish Forestry and the Scottish Forestry Trust (GS).Members of the karrikin family of bioactive small molecules are known to promote germination of a range of plants following large scale fires. As a result, they are relevant and interesting compounds. This report describes their synthesis from a biomass-derived product stream. During work to fractionate biomass with the goal of obtaining high quality lignins, an interesting co-product stream derived from the hemicellulose in the biomass, was obtained. Whilst many applications of this co-product stream can be proposed, in this case the major monosaccharides have been converted to relevant karrikins in short reaction sequences. Key results include a highly selective catalytic oxidation reaction, conversion of the resulting ketone to a butenolide by two alternative approaches, a selective acetal reductive opening reaction, X-ray crystallographic analysis of two compounds and detailed comparison of the final products with previous literature reports. Only through successful use of all the components generated during biomass refining, can economic sustainability be potentially achieved.Publisher PDFPeer reviewe

Copper-mediated conversion of complex ethers to esters : enabling biopolymer depolymerisation under mild conditions

Authors acknowledge the China Scholarship Council (G.X. studentship), the University of St Andrews (G.X. and J.R.D.M. studentships) and the EPSRC-funded CRITICAT Centre for Doctoral Training (studentship to I.P.; EP/L016419/1) for PhD funding. C.S.L. thanks the Leverhulme Trust Early Career Fellowship (ECF-2018-480) and the University of St Andrews.Selective processing of the β-O-4 unit in lignin is essential for the efficient depolymerisation of this biopolymer and therefore its successful integration into a biorefinery set-up. An approach is described in which this unit is modified to incorporate a carboxylic ester with the goal of enabling the use of mild depolymerisation conditions. Inspired by preliminary results using a Cu/TEMPO/O2 system, a protocol was developed that gave the desired β-O-4-containing ester in high yield using certain dimeric model compounds. The optimised reaction conditions were then applied to an oligomeric lignin model system. Extensive 2D NMR analysis demonstrated that analogous chemistry could be achieved with the oligomeric substrate. Mild depolymerisation of the ester-containing oligomer delivered the expected aryl acid monomer.Publisher PDFPeer reviewe

Cleavage of organosolv lignin to phenols using nitrogen monoxide and hydrazine

Funding: The authors are grateful to the support by the Deutsche Bundesstiftung Umwelt (DBU).From the variety of methods known for the depolymerization of organosolv lignin, a broad range of diversely substituted aromatic compounds are available today. In the present work, a novel two-step reaction sequence is reported, which is focused on the formation of phenols. While the first step of the depolymerization strategy comprises the 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)-catalyzed oxidation of organosolv lignin with nitrogen monoxide so that two waste materials are combined, cleavage to the phenolic target compounds is achieved in the second step employing hydrazine and potassium hydroxide under Wolff–Kishner-type conditions. Besides the fact that the novel strategy proceeds via an untypical form of oxidized organosolv lignin, the two-step sequence is further able to provide phenols as cleavage products, which bear no substituent at the 4-position.Publisher PDFPeer reviewe

Chemical transformations of biomass-derived fractions : studies on lignin models and selected monosaccharides

"This work was supported by China Scholarship Council-St Andrews PhD Fellowship [G.X. studentship]" -- Fundin

Selective depolymerisation of γ-oxidised lignin <i>via </i>NHC catalysed redox esterification

The development of new catalytic methods for the processing of lignocellulose‐derived renewable feedstocks continues to gain momentum, despite the considerable challenges associated with the use of complex biopolymers such as lignin. Here, we report a new two‐step depolymerisation method for lignin involving primary alcohol oxidation followed by a NHC‐mediated redox esterification‐depolymerisation step. The process takes advantage of the inherent structure of the β‐aryl ether units present in the specific type of lignin that was used (butanosolv) and delivers 4 novel aromatic monomers which retain the C3 side chain present in the lignin subunits. The utility of the major product is assessed suggesting that rapid access to a wide range of interesting chemical could be achieved from this renewable building block

CCDC 2117933 & 2117934: Experimental Crystal Structure Determination

Related Article: Ganyuan Xiao, Gerard Su, Alexandra M. Z. Slawin, Nicholas Westwood|2022|Eur.J.Org.Chem.|||doi:10.1002/ejoc.20210130

Next generation glucose-1-phosphate thymidylyltransferase (RmlA) inhibitors : an extended SAR study to direct future design

Funding: This work was supported by grants from The Scottish Universities Life Science Alliance (L.P., Ph.D. studentship), a China Scholarship Council-University of St Andrews PhD Fellowship (GX). JHN is funded by the Wellcome Trust (100209/Z/12/Z).The monosaccharide L-Rhamnose is an important component of bacterial cell walls. The first step in the L-rhamnose biosynthetic pathway is catalysed by glucose-1-phosphate thymidylyltransferase (RmlA), which condenses glucose-1-phosphate (Glu-1-P) with deoxythymidine triphosphate (dTTP) to yield dTDP-D-glucose. In addition to the active site where catalysis of this reaction occurs, RmlA has an allosteric site that is important for its function. Building on previous reports, SAR studies have explored further the allosteric site, leading to the identification of very potent P. aeruginosa RmlA inhibitors. Modification at the C6-NH2 of the inhibitor’s pyrimidinedione core structure was tolerated. X-ray crystallographic analysis of the complexes of P.aeruginosa RmlA with the novel analogues revealed that C6-aminoalkyl substituents can be used to position a modifiable amine just outside the allosteric pocket. This opens up the possibility of linking a siderophore to this class of inhibitor with the goal of enhancing bacterial cell wall permeability.Publisher PDFPeer reviewe

Cleavage of organosolv lignin to phenols using nitrogen monoxide and hydrazine (dataset)

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