Exploiting Chitin as a Source of Biologically Fixed Nitrogen: Formation and Full Characterization of Small-Molecule Hetero- and Carbocyclic Pyrolysis Products

Synthesis of Pyrrole-2-Carboxylic Acid from Cellulose- and Chitin-Based Feedstocks Discovered by the Automated Route Search

The shift towards sustainable feedstocks for platform chemicals requires new routes to access functional molecules that contain heteroatoms, but there are limited bio-derived feedstocks that lead to heteroatoms in platform chemicals. Combining renewable molecules of different origins could be a solution to optimize the use of atoms from renewable sources. However, the lack of retrosynthetic tools makes it challenging to examine the extensive reaction networks of various platform molecules focusing on multiple bio-based feedstocks. In this study, a protocol was developed to identify potential transformation pathways that allow for the use of feedstocks from different origins. By analyzing existing knowledge on chemical reactions in large databases, several promising synthetic routes were shortlisted, with the reaction of D-glucosamine and pyruvic acid being the most interesting to make pyrrole-2-carboxylic acid (PCA). The optimized synthetic conditions resulted in 50 % yield of PCA, with insights gained from temperature variant NMR studies. The use of substrates obtained from two different bio-feedstock bases, namely cellulose and chitin, allowed for the establishment of a PCA-based chemical space.

Biomass to Aromatic Amine Module: Alkali Catalytic Conversion of N-Acetylglucosamine into Unsubstituted 3-Acetamidofuran by Retro-Aldol Condensation

Aminofurans are widely used in drug synthesis as aromatic modules analogous to aniline. However, unsubstituted aminofuran compounds are difficult to prepare. In this study, a process for the selective conversion of N-acetyl-d-glucosamine (NAG) into unsubstituted 3-acetamidofuran (3AF) is developed. The yield of 3AF from NAG catalyzed by a ternary Ba(OH)₂ -H₃ BO₃ -NaCl catalytic system in N-methylpyrrolidone at 180 °C for 20 min can reach 73.9 %. Mechanistic studies reveal that the pathway to 3AF starts with a base-promoted retro-aldol condensation of the ring-opened NAG, affording the key intermediate N-acetylerythrosamine. Judicious selection of the catalyst system and conditions enables the selective conversion of biomass-derived NAG into 3AF or 3-acetamido-5-acetylfuran.

Deep Chemical and Physico-Chemical Characterization of Antifungal Industrial Chitosans-Biocontrol Applications

Five different chitosan samples (CHI-1 to CHI-5) from crustacean shells with high deacetylation degrees (>93%) have been deeply characterized from a chemical and physicochemical point of view in order to better understand the impact of some parameters on the bioactivity against two pathogens frequently encountered in vineyards, Plasmopara viticola and Botrytis cinerea. All the samples were analyzed by SEC-MALS, ¹H-NMR, elemental analysis, XPS, FTIR, mass spectrometry, pyrolysis, and TGA and their antioxidant activities were measured (DPPH method). Molecular weights were in the order: CHI-4 and CHI-5 (MW >50 kDa) > CHI-3 > CHI-2 and CHI-1 (MW < 20 kDa). CHI-1, CHI-2 and CHI-3 are under their hydrochloride form, CHI-4 and CHI-5 are under their NH₂ form, and CHI-3 contains a high amount of a chitosan calcium complex. CHI-2 and CHI-3 showed higher scavenging activity than others. The bioactivity against B. cinerea was molecular weight dependent with an IC50 for CHI-1 = CHI-2 (13 mg/L) ≤ CHI-3 (17 mg/L) < CHI-4 (75 mg/L) < CHI-5 (152 mg/L). The bioactivity on P. viticola zoospores was important, even at a very low concentration for all chitosans (no moving spores between 1 and 0.01 g/L). These results show that even at low concentrations and under hydrochloride form, chitosan could be a good alternative to pesticides.

Haber-independent, asymmetric synthesis of the marine alkaloid epi-leptosphaerin from a chitin-derived chiral pool synthon

Chitin-derived platforms are emerging as valuable chemical entities for the construction of nitrogenous fine chemicals in processes independent of Haber ammonia. However, much of the work in this area has focused on achiral platforms that limit routine entry into enantiopure, bio-based N-chemical space. Herein, dihydroxyethyl acetamidofuran (Di-HAF), a chiral synthon readily available from chitin, has been transformed into the marine alkaloid epi-leptosphaerin. This work extends the fledgling Haber-independent synthesis concept to enantiopure chemical space not routinely accessible from existing achiral platforms.

The dehydration of N-acetylglucosamine (GlcNAc) to enantiopure dihydroxyethyl acetamidofuran (Di-HAF)

The first multi-gram synthesis of enantiopure dihydroxyethyl acetamidofuran (Di-HAF) is reported. Under optimized conditions, GlcNAc dehydrates in pyridine in the presence of phenylboronic acid and triflic acid to afford Di-HAF in 73% yield and 99.3% ee in just 30 minutes. This protocol opens the door for further research on this bio-renewable building block which is now available as a chiral pool synthon. A plausible mechanism of its formation and of the subsequent dehydration of Di-HAF into well-known 3-acetamido-5-acetylfuran (3A5AF) is proposed.

Diverse anti-inflammation and anti-cancer polyketides isolated from the endophytic fungi Alternaria sp. MG1

Six new polyketides, alternaritins A-D [(±)-1-4] and isoxanalteric acid I (8), and 25 known Alternaria toxins were isolated from the culture of an endophytic fungi Alternaria sp. MG1. 3 is a rare fungal metabolite. 6 is a new natural product, and 5, 7, and 9 are known previously but their absolute configurations have not been determined. Three enantiomers [(±)-1, (±)-7, and (±)-15] were separated via chiral HPLC resolution. The structures of those polyketides (1-9) were elucidated by spectrometric analysis using MS and NMR. The absolute configurations were established using X-ray diffraction analysis and statistical comparative analysis of the experimental ECD and OR data, in conjunction with quantum mechanical calculations. All of the compounds were evaluated for their bioactivities. Known compound 27 exerted the most potent cytotoxic activities against HT-1080 and NCI-H1299 cell lines. The new compounds, 2 and 3, showed moderate inhibition on COX-2, while a pair of isomers, 8 and 9, exhibited medium activity on COX-2 and uropathogenic Escherichia coli.

Exploiting Nature's Most Abundant Polymers: Developing New Pathways for the Conversion of Cellulose, Hemicellulose, Lignin and Chitin into Platform Molecules (and Beyond)

The four most prominent forms of biomass are cellulose, hemicellulose, lignin and chitin. In efforts to develop sustainable sources of platform molecules there has been an increasing focus on examining how these biopolymers could be exploited as feedstocks that support the chemical supply chain, including in the production of fine chemicals. Many different approaches are possible and some of the ones being developed in the authors' laboratories are emphasised.

Facile Preparation of 3-Acetamido-5-acetylfuran from N-Acetyl-d-glucosamine by using Commercially Available Aluminum Salts

3-Acetamido-5-acetylfuran (3A5AF) is a promising intermediate obtained from chitin for the production of N-containing value-added chemicals. However, the synthetic method is complicated so far, which has limited further investigation using 3A5AF. Herein, a facile method was developed for synthesizing 3A5AF from N-acetyl-d-glucosamine (NAG), including a simple isolation procedure. A 30 % yield of 3A5AF was obtained by performing the dehydration of NAG in N,N-dimethylformamide (DMF) solvent in the presence of AlCl₃ ⋅6 H₂ O at a temperature as low as 120 °C by conventional heating for 30 min. This method tolerated a wide range of temperature and concentration of substrate, thus easily allowing scale-up of the reaction. The produced 3A5AF was isolated with 98 % purity by simple column chromatography. Additionally, a highly functionalized N-containing lactone was identified as a byproduct under these reaction conditions.

Further, Small-Molecule Pyrolysis Products Derived from Chitin

In an ongoing study of the products formed on pyrolysis of chitin (4) under a range of conditions, we now detail the isolation and characterisation of the crystalline and hitherto undetected pyridine N-oxide 18 and enamide 19. Pathways for the formation of these products have been proposed and subjected to both experimental and computational assessment.