Structure–Activity Relationships and Structural Design Optimization of a Series of p-Hydroxycinnamic Acids-Based Bis- and Trisphenols as Novel Sustainable Antiradical/Antioxidant Additives

Abstract

Chemo-enzymatic synthesis and screening of a library of renewable saturated and unsaturated bis- and trisphenols deriving from p-hydroxycinnamic acids (i.e., p-coumaric acid, ferulic acid, and sinapic acid) and biobased diols/triol (i.e., isosorbide, 1,4-butanediol, glycerol) showed that these compounds were potent antioxidants/antiradicals. To optimize their antiradical activities, we assessed the structure–activity relationships (SAR) of these phenolics focusing on the internal diol/triol linker, the degree of methoxylation on the aromatic rings, and the CC double bond of the α,β-unsaturated esters. We found that methoxylation degree and the unsaturation were critical for antiradical activity while the nature of the diol had a small impact. Indeed, SAR revealed that, for saturated compounds, the higher the methoxylation degree, the higher the antiradical activity; on the other hand, unexpectedly, the presence of the unsaturation had a negative impact on the activity. The antiradical activities of these bis- and trisphenols were then compared to that of Irganox 1010, a widely used antioxidant additive in polypropylene. The optimized compounds, i.e. those deriving from sinapic acid and with saturated esters, proved as effective while being 100% biobased and obtained through a more sustainable synthetic pathway. Thermal analyses (TGA) demonstrated that these bis- and trisphenols exhibit high thermal stability and that their T d5% can be easily tailored by playing with the structure of the bisphenol core. p-Hydroxycinnamic acids-based bis- and trisphenols are thus promising easily accessible, eco-friendly, and biocompatible antiradical additives for a sustainable approach to the stabilization of polymers in packaging and other applications.

Selective Depolymerisation of γ‐Oxidised Lignin via NHC Catalysed Redox Esterification

“…For example, NHC‐catalysed decarboxylation of 5 b gives 4‐vinylsyringol 6 (Scheme (reaction c)) a potent antimutagenic compound, whilst palladium catalysed decarboxylative coupling with arylboronic acids gives stilbenes such as 7 (Scheme (reaction d)) . 5 b can also serve as the starting point for the synthesis of more complex molecules such as the potential antioxidant dimer 8 and structures 9 and 10 …”

“… Conversion of selected lignin depolymerisation products to cinnamate‐type esters and acids and examples of literature conversions of sinapic acid ( 5 b ). Reaction conditions: This work: a) MsOH, d 8 ‐toluene, 90 °C, 10 min, 93 % ( 4 a ), 91 % ( 4 b ); b) KO t Bu, i ‐PrOH, 120 °C, 24 h, 96 % ( 5 a ), 94 % ( 5 b ); Literature reports using 5 b : c) 1‐Ethyl‐3‐methyl imidazolium acetate, DMSO, 100 °C, 60 min, 100 %; d) Phenylboronic acid, Pd(acac) 2 , Cu(OAc) 2 , LiOAc, DMF, 60 °C, 8 h, 89 %; e) (i): HCl, EtOH, reflux, 2d; (ii): H 2 , Pd/C, EtOAc, 10 °C, 45 min; (iii) 1,4‐Butanediol, CAL−B, 75 °C, 4–72 h, 87 %; f) (i): Horseradish peroxidase−H 2 O 2 , aq. acetone; (ii) acetic anhydride/pyridine; (iii) bromine, NH 4 OAc, AcOH, 50 °C, 6 h; (iv) AcCl−MeOH, 16 h; (v) Pd/C−Et 3 N, H 2 , MeOH, 2d, 80 %; (vi) DIBAL−H, toluene, 2 h; (vii) pyrrolidine, 3 min; g) (i) FeCl 3 , EtOH, RT., 1 h; (ii) 1 N NaOH, RT., 5 min, 62 % …”

“…[31] 5 b can also serve as the starting point for the synthesis of more complex molecules such as the potential antioxidant dimer 8 and structures 9 and 10. [32][33][34] In summary, several different elegant methods have previously been reported for the selective oxidation and depolymerisation of lignins, either via the oxidation of the secondary or primary alcohols. Here we have demonstrated, for the first time, that the same general approach can be used for the selective depolymerisation of butanosolv lignins, that contain high degrees of α-butoxylation in their β-aryl ether linkages.…”

“…Given the requirement for monomer production from lignin via approaches of this type required that there are two adjacent β-O-4 units, the yields of 3 a, 3 b, 3 c and 3 d could alternatively be stated as 10 wt %, 20 wt %, 10 wt % and 43 wt % respectively, based on a theoretical monomer yield of~5 mol % or~6 wt % accounting for butanol incorporation. [15,16] [29,30] d) Phenylboronic acid, Pd(acac) 2 , Cu(OAc) 2 , LiOAc, DMF, 60°C, 8 h, 89 %; [31] e) (i): HCl, EtOH, reflux, 2d; (ii): H 2 , Pd/C, EtOAc, 10°C, 45 min; (iii) 1,4-Butanediol, CALÀ B, 75°C, 4-72 h, 87 %; [32] f) (i): Horseradish peroxidaseÀ H 2 O 2 , aq. acetone; (ii) acetic anhydride/pyridine; (iii) bromine, NH 4 OAc, AcOH, 50°C, 6 h; (iv) AcClÀ MeOH, 16 h; (v) Pd/CÀ Et 3 N, H 2 , MeOH, 2d, 80 %; (vi) DIBALÀ H, toluene, 2 h; (vii) pyrrolidine, 3 min; [33] g) (i) FeCl 3 , EtOH, RT., 1 h; (ii) 1 N NaOH, RT., 5 min, 62 %.…”

Processing, Valorization and Application of Bio-Waste Derived Compounds from Potato, Tomato, Olive and Cereals: A Review

“…The derivatization of FA and its use as antioxidant additives were reported [336,337]. The authors enzymatically synthesized bis-and trisphenols from FA and bio-based diols (butenediols, propanediols and isosorbide) or triols (glycerol).…”