Bioorganic synthesis, characterization and antioxidant activity of esters of natural phenolics and α-lipoic acid

Synthesis of lipoic acid ferulate and evaluation of its ability to preserve fish oil from oxidation during accelerated storage

Lipoic acid ferulate (LAF) was synthesized and its anti-free radical ability in vitro was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonicacid) (ABTS) assays. Protective effects of LAF in stabilizing fish oil were tested, compared to antioxidants such as lipoic acid, ferulic acid and tert-butylhydroxyquinone (TBHQ) by measuring peroxide values, thiobarbituric acid reactants, p-anisidine values, nuclear magnetic resonance (NMR) spectra and gas chromatography-mass spectrometry (GC-MS) spectra of fish oil during accelerated storage (12 days, 80 °C). The inhibitory effect of these antioxidants on fish oil oxidation followed the order TBHQ ≧ LAF > ferulic acid > lipoic acid. In addition, the omega-3 polyunsaturated fatty acids were the first to be oxidized. The formation of oxidation products followed a first-order kinetic model, and the addition of LAF effectively reduced the reaction rate constants. Therefore, LAF can effectively slow down the formation of oxidative products and prolong the shelf life of fish oil.

Enhanced antioxidant capacity of lipoic acid in different food systems through lipase-mediated esterification with phytosterols

BACKGROUND

α-Lipoic acid has excellent antioxidant activity, but its poor lipid solubility greatly limits its practical application. This study was undertaken (i) to develop a novel and efficient enzymatic synthesis of lipophilic lipoic acid esters using Candida sp. 99-125 lipase as a catalyst; and (ii) to systematically evaluate their antioxidant potential against bulk oil, oil-in-water emulsion (O/W) and cooked ground meat.

RESULTS

Lipophilic lipoic acid esters were successfully and efficiently synthesized using phytosterols as acyl receptor in the presence of Candida sp. 99-125 lipase. The product was identified as phytosterol lipoate by mass spectrometry, Fourier transform infrared spectroscopy and nuclear magnetic resonance. The maximum conversion of phytosterol lipoate surpassed 90% within 12 h and its final yield exceeded 81%. Interestingly, the oil solubility of lipoic acid was increased at least 25-fold and other physicochemical properties were significantly improved. Most importantly, phytosterol lipoate exhibited higher antioxidant activity than lipoic acid in bulk oil, O/W emulsions and cooked ground meat.

CONCLUSION

The antioxidant capacity of lipoic acid can be significantly enhanced by esterification with phytosterols. Therefore, phytosterol lipoate could be further developed as a new antioxidant for use in oil- and fat-based foods. © 2022 Society of Chemical Industry.

Oleil Hydroxytyrosol (HTOL) Exerts Anti-Myeloma Activity by Antagonizing Key Survival Pathways in Malignant Plasma Cells

Polyphenols from olive oil are endowed with several biological activities. Chemical modifications have been recently applied to these compounds to improve their therapeutic activity in different pathological settings, including cancer. Herein, we describe the in vitro effects on multiple myeloma (MM) cells of oleil hydroxytyrosol (HTOL), a synthetic fatty ester of natural hydroxytyrosol with oleic acid. HTOL reduced the viability of various human MM cell lines (HMCLs), even when co-cultured with bone marrow stromal cells, triggering ER stress, UPR and apoptosis, while it was not cytotoxic against healthy peripheral blood mononuclear cells or B lymphocytes. Whole-transcriptome profiling of HTOL-treated MM cells, coupled with protein expression analyses, indicate that HTOL antagonizes key survival pathways for malignant plasma cells, including the undruggable IRF4–c-MYC oncogenic axis. Accordingly, c-MYC gain- and loss-of-function strategies demonstrate that HTOL anti-tumor activity was, at least in part, due to c-MYC targeting. Taken together, these findings underscore the anti-MM potential of HTOL, providing the molecular framework for further investigation of HTOL-based treatments as novel anti-cancer agents.

Tailored Functionalization of Natural Phenols to Improve Biological Activity

Phenols are widespread in nature, being the major components of several plants and essential oils. Natural phenols' anti-microbial, anti-bacterial, anti-oxidant, pharmacological and nutritional properties are, nowadays, well established. Hence, given their peculiar biological role, numerous studies are currently ongoing to overcome their limitations, as well as to enhance their activity. In this review, the functionalization of selected natural phenols is critically examined, mainly highlighting their improved bioactivity after the proper chemical transformations. In particular, functionalization of the most abundant naturally occurring monophenols, diphenols, lipidic phenols, phenolic acids, polyphenols and curcumin derivatives is explored.

Semi-synthesis as a tool for broadening the health applications of bioactive olive secoiridoids: a critical review

Covering: 2005 up to 2020Olive bioactive secoiridoids are recognized as natural antioxidants with multiple beneficial effects on human health. Nevertheless, the study of their biological activity has also disclosed some critical aspects associated with their application. Firstly, only a few of them can be extracted in large amounts from their natural matrix, namely olive leaves, drupes, oil and olive mill wastewater. Secondly, their application as preventive agents and drugs is limited by their low membrane permeability. Thirdly, the study of their biological fate after administration is complicated by the absence of pure analytical standards. Accordingly, efficient synthetic methods to obtain natural and non-natural bioactive phenol derivatives have been developed. Among them, semi-synthetic protocols represent efficient and economical alternatives to total synthesis, combining efficient extraction protocols with efficient catalytic conversions to achieve reasonable amounts of active molecules. The aim of this review is to summarize the semi-synthetic protocols published in the last fifteen years, covering 2005 up to 2020, which can produce natural olive bioactive phenols scarcely available by extractive procedures, and new biophenol derivatives with enhanced biological activity. Moreover, the semi-synthetic protocols to produce olive bioactive phenol derivatives as analytical standards are also discussed. A critical analysis of the advantages offered by semi-synthesis compared to classical extraction methods or total synthesis protocols is also performed.

Synthesis of Feruloyl Ester Using Bacillus subtilis AKL 13 Lipase Immobilized on Celite® 545

The lipophilic antioxidants, glyceryl ferulate and feruloyl glyceryl linoleate, were synthesized using lipase from Bacillus subtilis AKL 13. The extracellular lipase was produced by cultivation of the strain in modified minimal medium and the enzyme was recovered by fractionation at 80% ammonium salt saturation. The concentrated enzyme with the specific activity of (4647±66) U/mg was immobilized on Celite® 545 and crosslinked using glutaraldehyde. The prepared enzyme catalyst was used for esterification of ferulic and linoleic acids with glycerol separately in hexane butane solvent system at 50 °C and 3.144×g agitation. The maximum ester conversion of 94% of feruloyl glyceryl linoleate was achieved at 48 h, whereas only 35% of glyceryl ferulate was synthesized. The reaction products were characterized using RP-HPLC, FTIR, ¹H NMR, ¹³C NMR and fluorescence spectrophotometry. The kinetic parameters of esterification reaction were determined according to ping-pong bi-bi model. The K_m and υ_max were found to be 69.37 and 3.46 mmol, and 0.387 and 1.02 mmol/(min·g) for glyceryl ferulate and feruloyl glyceryl linoleate, respectively. The kinetic parameters were simulated in MATLAB and the experimental data were in good agreement. Furthermore, 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity of the blend of feruloyl ester and palm oil was higher than of the plain palm oil and was closer to α-tocopherol.

Enzymatic alkylsuccinylation of tyrosol: Synthesis, characterization and property evaluation as a dual-functional antioxidant

This work reports a novel approach to generate a new group of tyrosol-based amphiphilic lipid alkylsuccinylated tyrosol by lipase-catalyzed succinylation of tyrosol with alkylsuccinic anhydrides of varying alkyl chain lengths, in high yields (80-95%). The structures of the compounds were confirmed by MS, FTIR &¹H NMR; and their properties were characterized by Temperature-Ramp FTIR, DSC & CMC measurements. The synthesized compounds integrate water-soluble phenylethanoid and hydrophobic alkyl into one molecule thus are endowed with dual functions: retaining the antioxidant property of tyrosol and entailing tyrosol with new surface-active property. The DPPH activity of tyrosol (13.77%) was significantly enhanced by 2-dodecen-1-ylsuccinylated tyrosol (16.01%). Compared to tyrosol-based emulsions (76.63%), the lipid oxidation is reduced to 21.57% and 42.32% in 2-octen-1-ylsuccinylated/2-dodecen-1-ylsuccinylated tyrosol emulsions, respectively. This work brings new members to the library of functional lipid excipients and open a novel and effective synthetic pathway for derivation of phenyl alcohols.

Enzymatic synthesis of bioactive compounds with high potential for cosmeceutical application

Cosmeceuticals are cosmetic products containing biologically active ingredients purporting to offer a pharmaceutical therapeutic benefit. The active ingredients can be extracted and purified from natural sources (botanicals, herbal extracts, or animals) but can also be obtained biotechnologically by fermentation and cell cultures or by enzymatic synthesis and modification of natural compounds. A cosmeceutical ingredient should possess an attractive property such as anti-oxidant, anti-inflammatory, skin whitening, anti-aging, anti-wrinkling, or photoprotective activity, among others. During the past years, there has been an increased interest on the enzymatic synthesis of bioactive esters and glycosides based on (trans)esterification, (trans)glycosylation, or oxidation reactions. Natural bioactive compounds with exceptional theurapeutic properties and low toxicity may offer a new insight into the design and development of potent and beneficial cosmetics. This review gives an overview of the enzymatic modifications which are performed currently for the synthesis of products with attractive properties for the cosmeceutical industry.

Biotransformation: a green and efficient way of antioxidant synthesis

Antioxidant compounds play a vital role in human physiology. They prevent the oxidation of biomolecules by scavenging free radicals produced during physiochemical processes and/or as a result of several pathological states. A balance between the reactive oxygen species (free radicals) and antioxidants is essential for proper physiological conditions. Excessive free radicals cause oxidative stress which can lead to several human diseases. Therefore, synthesis of the effective antioxidants is crucial in managing the oxidative stress. Biotransformation has evolved as an effective technique for the production of structurally diverse molecules with a wide range of biological activities. This methodology surpasses the conventional chemical synthesis due to the fact that enzymes, being specific in nature, catalyze reactions affording products with excellent regio- and stereoselectivities. Structural transformation of various classes of compounds such as alkaloids, steroids, flavonoids, and terpenes has been carried out through this technique. Several bioactive molecules, especially those having antioxidant potential have also been synthesized by using different biotransformation techniques and enzymes. Hydroxylated, glycosylated, and acylated derivatives of phenols, flavonoids, cinnamates, and other molecules have proven abilities as potential antioxidants. A critical review of the biotransformation of these compounds into potent antioxidant metabolites is presented here.

Bio-active nanoemulsions enriched with gold nanoparticle, marigold extracts and lipoic acid: In vitro investigations

A novel and efficient approach for the preparation of enriched herbal formulations was described and their potential applications including wound healing and antioxidant activity (cell based and cell free) were investigated via in vitro cell culture studies. Nigella sativa oil was enriched with Calendula officinalis extract and lipoic acid capped gold nanoparticles (AuNP-LA) using nanoemulsion systems. The combination of these bio-active compounds was used to design oil in water (O/W) and water in oil (W/O) emulsions. The resulted emulsions were characterized by particle size measurements. The phenolic content of each nanoemulsion was examined by using both colorimetric assay and chromatographic analyses. Two different methods containing cell free chemical assay (1-diphenyl-2-picrylhydrazyl method) and cell based antioxidant activity test were used to evaluate the antioxidant capacities. In order to investigate the bio-activities of the herbal formulations, in vitro cell culture experiments, including cytotoxicity, scratch assay, antioxidant activity and cell proliferation were carried out using Vero cell line as a model cell line. Furthermore, to monitor localization of the nanoemulsions after application of the cell culture, the cell images were monitored via fluorescence microscope after FITC labeling. All data confirmed that the enriched N. sativa formulations exhibited better antioxidant and wound healing activity than N. sativa emulsion without any enrichment. In conclusion, the incorporation of AuNP-LA and C. officinalis extract into the N. sativa emulsions significantly increased the bio-activities. The present work may support further studies about using the other bio-active agents for the enrichment of herbal preparations to strengthen their activities.

Behavioral and neurochemical effects of alpha-lipoic Acid in the model of Parkinson's disease induced by unilateral stereotaxic injection of 6-ohda in rat

This study aimed to investigate behavioral and neurochemical effects of α -lipoic acid (100 mg/kg or 200 mg/kg) alone or associated with L-DOPA using an animal model of Parkinson's disease induced by stereotaxic injection of 6-hydroxydopamine (6-OHDA) in rat striatum. Motor behavior was assessed by monitoring body rotations induced by apomorphine, open field test and cylinder test. Oxidative stress was accessed by determination of lipid peroxidation using the TBARS method, concentration of nitrite and evaluation of catalase activity. α -Lipoic acid decreased body rotations induced by apomorphine, as well as caused an improvement in motor performance by increasing locomotor activity in the open field test and use of contralateral paw (in the opposite side of the lesion produced by 6-OHDA) at cylinder test. α -lipoic acid showed antioxidant effects, decreasing lipid peroxidation and nitrite levels and interacting with antioxidant system by decreasing of endogenous catalase activity. Therefore, α -lipoic acid prevented the damage induced by 6-OHDA or by chronic use of L-DOPA in dopaminergic neurons, suggesting that α -lipoic could be a new therapeutic target for Parkinson's disease prevention and treatment.

Enzymatic hybridization of α-lipoic acid with bioactive compounds in ionic solvents

The lipase-catalyzed molecular hybridization of α-lipoic acid (LA) with bioactive compounds pyridoxine, tyrosol and tyramine was performed in ionic solvents and deep eutectic solvents. The biocatalytic reactions were catalyzed by Candida antarctica lipase B immobilized onto various functionalized multi-walled carbon nanotubes (f-CNTs-CaLB), as well as by commercial Novozym 435. The use of f-CNTs-CaLB leads, in most cases, to higher conversion yields as compared to Novozym 435. The nature and ion composition of ionic solvents affect the performance of the biocatalytic process. The highest conversion yield was observed in (mtoa)NTf2. The high enzyme stability and the relatively low solubility of substrates in specific media account for the improved biocatalytic synthesis of molecular hybrids of LA. Principal component analysis was used to screen for potential lipoxygenase inhibitors. In vitro studies showed that the synthesized compounds exhibit up to 10-fold increased inhibitory activity on lipoxygenase mediated lipid peroxidation as compared to parent molecules.