A novel caffeic acid-based deep eutectic solvent as caffeoyl donor to enhance glycerol caffeates synthesis

Studies on the Enzymatic Synthesis and Antioxidant Properties of Phenolic Acid Glycerols

The potentially wide application of Phenolic acids (PAs) in industries was severely limited by their inadequate solubility and stability in polar/non-polar media. To overcome these limits, studies on the enzymatic esterification of PAs with glycerol were carried out to reach a yield of 95% of phenolic acid glycerols (PAGs) under the following reaction conditions: 1:150 molar ratio of PAs to glycerol; 25% of Lipozyme 435 relative to the weight of total substrates; 80°C, 500 rpm, 86.7 kPa and 10 h. Three resulting PAGs including caffeoyl glycerol (CG), feruloyl glycerol (FG), and p-hydroxycinnamoyl glycerol (p-HCG) were confirmed by MS, 1H NMR and 13C NMR. Among them, CG showed a comparative free radical scavenging ability to CA, indicating its potential use as a water-soluble antioxidant alternative to CA for food and cosmetic applications.

Synthesis of hydrophilic glyceryl monocaffeate with economical catalyst cation-exchange resin Amberlyst-35

BACKGROUND

Caffeic acid (CA) has anti-oxidation and anti-inflammatory. However, the poor hydrophilicity of CA limits its biological activities. In this work, hydrophilic glyceryl monocaffeate (GMC) was synthesized by esterification using different caffeoyl donors (deep eutectic solvent and solid CA). Cation-exchange resins were used as the catalysts. The effects of reaction conditions were also investigated.

RESULTS

The mass transfer limitation of esterification was eliminated using deep eutectic solvent. Compared with the previous catalysts (immobilized lipase Novozym 435), an economic cation-exchange resin, Amberlyst-35 (A-35), showed good catalytic performance for GMC preparation. The activation energies of GMC synthesis and CA conversion were 43.71 kJ mol^-1 and 43.07 kJ mol^-1 , respectively. The optimal reaction conditions were a temperature reaction of 90 °C, catalyst load of 7%, glycerol/CA molar ratio of 5:1 (mol mol^-1 ), and reaction time of 24 h, which resulted in a maximum GMC yield and CA conversion of 69.75 ± 1.03% and 82.23 ± 2.02%, respectively.

CONCLUSION

The results of the work showed a promising alternative for the synthesis of GMC. © 2023 Society of Chemical Industry.

Catalytic Routes to Produce Polyphenolic Esters (PEs) from Biomass Feedstocks

Polyphenolic esters (PEs) are valuable chemical compounds that display a wide spectrum of activities (e.g., anti-oxidative effects). As a result, their production through catalytic routes is an attractive field of research. The present review aims to discuss recent studies from the literature regarding the catalytic production of PEs from biomass feedstocks, namely, naturally occurred polyphenolic compounds. Several synthetic approaches are reported in the literature, mainly bio-catalysis and to a lesser extent acid catalysis. Immobilized lipases (e.g., Novozym 435) are the preferred enzymes thanks to their high reactivity, selectivity and reusability. Acid catalysis is principally investigated for the esterification of polyphenolic acids with fatty alcohols and/or glycerol, using both homogeneous (p-toluensulfonic acid, sulfonic acid and ionic liquids) and heterogeneous (strongly acidic cation exchange resins) catalysts. Based on the reviewed publications, we propose some suggestions to improve the synthesis of PEs with the aim of increasing the greenness of the overall production process. In fact, much more attention should be paid to the use of new and efficient acid catalysts and their reuse for multiple reaction cycles.

Enhancement of the hydrophilic feruloyl glycerol synthesis using A-35 as a catalyst and its functional characteristics

Feruloyl glycerol (FG) is the hydrophilic ester of ferulic acid (FA), which has a high solubility in water and a strong ability to resist ultraviolet (UV) radiation. In this work, several solid acids were used as novel economical catalysts and FA was used as a cheap substrate for FG preparation. The effects of reaction variables on the esterification of FA with glycerol were investigated and optimized by response surface methodology (RSM). Results showed that a cheap solid acid cation exchange resin A-35 showed the best performance for esterification. The reaction conditions were optimized by RSM as follows: 15 : 1 (glycerol/FA) substrate molar ratio and 14% catalyst loading at 90 °C for 7 h. The maximum FG yield (98.50 ± 0.58%) was achieved under the optimized conditions. The activation energy of the esterification was 53.71 kJ mol^-1. The results of UV absorbance showed that FG had good anti-UV activity and photostability, which can be used as a potential antioxidant and UV absorber in food and sunscreen products.

Lipase-catalysed synthesis of mono- and di-acyl esters of glyceryl caffeate in propylene carbonate and their antioxidant properties in tuna oil

Development of new non-toxic antioxidants with diverse hydrophobic properties is important due to growing concerns about the toxicity of artificial oil-soluble antioxidants, the comparatively low effectiveness of natural options, and the complex role hydrophobicity plays in antioxidant effectiveness. Using caffeic acid, a naturally occurring phenolic acid with potent antioxidant activity, a range of glyceryl caffeate esters (decanoate and palmitate) were prepared using lipase-catalysed esterification reactions. Glyceryl-1-caffeate (GC) was prepared from ethyl caffeate and glycerol (acting as both the solvent and the substrate), catalysed by immobilised Candida Antarctica lipase B (Novozym-435) at 80 °C under vacuum. Esterification of GC with decanoic acid using immobilised Thermomyces lanuginosus lipase (TLIM) or Novozym-435 was found to be selective towards mono-acylated or di-acylated products, respectively. The reaction was performed in an unconventional solvent, propylene carbonate (PC), which has many of the attributes of a green solvent. Product conversions in PC were comparable to the best performing conventional solvents. In contrast to conventional volatile solvents, the low volatility of PC allowed the reaction to be performed under vacuum, without the need for molecular sieves for removal of water produced during the reaction. Diisopropyl ether was effective at extracting the more lipophilic products from PC. Both the lipase (Novozym-435) and PC were reused four times with only a small loss in conversion efficiency. Glyceryl caffeate esters performed much better than α-tocopherol at protecting bulk tuna oil from oxidation (analysed using Rancimat). A comparison of glyceryl caffeate esters (decanoate/palmitate and mono-/di-acylated) showed that their antioxidant effectiveness in bulk tuna oil was not affected by chain-length, but compounds containing only one fatty ester were slightly more effective than those containing two fatty esters.

Synthesis of Lipophilic Caffeoyl Alkyl Ester Using a Novel Natural Deep Eutectic Solvent

In this work, a novel method for lipophilic caffeoyl alkyl ester production was developed using a natural deep eutectic solvent (DES) consisting of choline chloride and caffeic acid (CA) as the caffeoyl donor. Cation-exchange resins were used as the catalyst to catalyze the esterification of fatty alcohols with the DES. Effects of the caffeoyl donor and reaction variables were investigated. Reaction thermodynamics were also analyzed. The results showed that the lipophilic caffeoyl alkyl ester production can be enhanced using the DES as the caffeoyl donor, and cation-exchange resin A-35 showed the best catalytic activity for the reaction. Under the optimized conditions (85 °C, stearyl alcohol/CA 8:1 (mol/mol), A-35 load 5% and 24 h), the maximum octodecyl caffeate (OC) yield (90.69 ± 2.71%) and CA conversion (95.17 ± 2.76%) were obtained with the DES as the caffeoyl donor, which were much higher than those obtained with solid CA as the caffeoyl donor (OC yield 40.97 ± 2.37% and CA conversion 44.26 ± 1.69%). The activation energy of CA conversion (67.57 kJ/mol) with the DES was lower than that with solid CA (90.19 kJ/mol). In addition, the mass transfer limitation can be decreased with the DES. Compared with solid CA as the caffeoyl donor, a fast reaction rate and low mass transfer limitation were obtained using the DES as the caffeoyl donor.