[Advances in synthesis of 2-phenylethanol].

2-phenylethanol (2-PE), an aromatic alcohol with a rose fragrance, is the second most widely used flavoring substance in the world. It is widely used in the cosmetic, food, and pharmaceutical industries. This paper introduces the chemical synthesis methods of 2-PE and the synthetic pathways in plants and microorganisms, summarizes the strategies to improve the microbial synthesis of 2-PE, reviews the research progress in de novo synthesis of 2-PE in microorganisms, and makes an outlook on the research prospects, aiming to provide a theoretical basis for the industrial production of 2-PE.

Efficiently Enantioselective Hydrogenation Photosynthesis of (R)-1-[3,5-Bis(trifluoromethyl)phenyl] ethanol over a CLEs-TiO2 Bioinorganic Hybrid Materials.

Engineering of biological pathways with man-made materials provides inspiring blueprints for sustainable drug production. (R)-1-[3,5-Bis(trifluoromethyl)phenyl]ethanol [(R)-3,5-BTPE], as an important artificial chiral intermediate for complicated pharmaceutical drugs and biologically active molecules, is often synthesized through a hydrogenation reaction of 3,5-bis(trifluoromethyl)acetophenone (3,5-BTAP), in which enantioselectivity and sufficient active hydrogen are the key to restricting the reaction. In this work, a biohybrid photocatalytic hydrogenation system based on an artificial cross-linked enzymes (CLEs)-TiO2-Cp*Rh(bpy) photoenzyme is developed through a bottom-up engineering strategy. Here, TiO2 nanotubes in the presence of Cp*Rh(bpy) are used to transform NADP+ to NADPH during the formation of chiral alcohol intermediates from the catalytic reduction of a ketone substrate by alcohol dehydrogenase CLEs. Hydrogen and electrons, provided by water and photocatalytic systems, respectively, are transferred to reduce NADP+ to NADPH via [Cp*Rh(bpy)(H2O)]2+. With the resulting NADPH, [(R)-3,5-BTPE] is synthesized using our efficient CLEs obtained from the cell lysate by nonstandard amino acid modification. Through this biohybrid photocatalytic system, the photoenzyme-catalyzed combined reductive synthesis of [(R)-3,5-BTPE] has a yield of 41.2% after reaction for 24 h and a very high enantiomeric excess value (>99.99%). In the case of reuse, this biohybrid system retained nearly 95% of its initial catalytic activity for synthesizing the above chiral alcohol. The excellent reusability of the CLEs and TiO2 nanotubes hybrid catalytic materials highlights the environmental friendliness of (R)-3,5-BTPE production.

Caffeic Acid Phenethyl Ester-Incorporated Radio-Sensitive Nanoparticles of Phenylboronic Acid Pinacol Ester-Conjugated Hyaluronic Acid for Application in Radioprotection.

We synthesized phenylboronic acid pinacol ester (PBPE)-conjugated hyaluronic acid (HA) via thiobis(ethylamine) (TbEA) linkage (abbreviated as HAsPBPE conjugates) to fabricate the radiosensitive delivery of caffeic acid phenetyl ester (CAPE) and for application in radioprotection. PBPE was primarily conjugated with TbEA and then PBPE-TbEA conjugates were conjugated again with hyaluronic acid using carbodiimide chemistry. CAPE-incorporated nanoparticles of HAsPBPE were fabricated by the nanoprecipitation method and then the organic solvent was removed by dialysis. CAPE-incorporated HAsPBPE nanoparticles have a small particle size of about 80 or 100 nm and they have a spherical shape. When CAPE-incorporated HAsPBPE nanoparticles were irradiated, nanoparticles became swelled or disintegrated and their morphologies were changed. Furthermore, the CAPE release rate from HAsPBPE nanoparticles were increased according to the radiation dose, indicating that CAPE-incorporated HAsPBPE nanoparticles have radio-sensitivity. CAPE and CAPE-incorporated HAsPBPE nanoparticles appropriately prevented radiation-induced cell death and suppressed intracellular accumulation of reactive oxygen species (ROS). CAPE and CAPE-incorporated HAsPBPE nanoparticles efficiently improved survivability of mice from radiation-induced death and reduced apoptotic cell death. We suggest that HAsPBPE nanoparticles are promising candidates for the radio-sensitive delivery of CAPE.

Chemoenzymatic semisynthesis of caffeic acid ß-phenethyl ester, an antioxidative component in propolis, from raw coffee bean extract.

Caffeic acid ß-phenethyl ester (CAPE), an antioxidative bioactive catechol isolated from propolis, was semisynthesized from chlorogenic acid and related compounds in an extract of raw (unroasted) Robusta coffee (Coffea canephora) beans in 5 steps and a total yield of 31%. Oxidative degradation of the intermediates and target molecule was prevented by alkaline hydrolysis of the chlorogenic acids in the presence of sodium dithionite (Na2S2O4) and deprotection of the catecholic diacetate precursor by Candida antarctica lipase B-mediated transesterification as the final step.

Synthesis, α-Glucosidase inhibition and molecular docking studies of tyrosol derivatives.

To find a potent α-glucosidase inhibitor, 24 tyrosol derivatives with different substituents located at the meta, ortho, or para position of the phenyl group have been synthesised via the Mitsunobu reaction, characterised by 1H NMR, 13C NMR, ESI-MS and IR and evaluated for inhibition. The derivatives possessed varying degrees of in vitro inhibitory activity against α-glucosidase and a relationship between the structure and activity was subsequently established for all compounds. Two of these compounds with substituents at the para position showed significant inhibitory effects surpassing that of the control standard acarbose. Molecular docking studies performed to better understand the binding interactions between the enzyme and the two most active compounds showed substantial binding within the active site of α-glucosidase. Taken together, these results indicate that the position of the substituent plays a crucial role in this inhibition and may facilitate the development of new α-glucosidase inhibitors.

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.

FA-97, a New Synthetic Caffeic Acid Phenethyl Ester Derivative, Protects against Oxidative Stress-Mediated Neuronal Cell Apoptosis and Scopolamine-Induced Cognitive Impairment by Activating Nrf2/HO-1 Signaling.

Alzheimer's disease (AD) is an age-related neurodegenerative disorder with cognitive deficits, which is becoming markedly more common in the world. Currently, the exact cause of AD is still unclear, and no curative therapy is available for preventing or mitigating the disease progression. Caffeic acid phenethyl ester (CAPE), a natural phenolic compound derived from honeybee hive propolis, has been reported as a potential therapeutic agent against AD, while its application is limited due to the low water solubility and poor bioavailability. Here, caffeic acid phenethyl ester 4-O-glucoside (FA-97) is synthesized. We validate that FA-97 attenuates H2O2-induced apoptosis in SH-SY5Y and PC12 cells and suppresses H2O2-induced oxidative stress by inhibiting the ROS level, malondialdehyde (MDA) level, and protein carbonylation level, as well as induces cellular glutathione (GSH) and superoxide dismutase (SOD). Mechanistically, FA-97 promotes the nuclear translocation and transcriptional activity of Nrf2 associated with the upregulated expression of HO-1 and NQO-1. The prime importance of Nrf2 activation in the neuroprotective and antioxidant effects of FA-97 is verified by Nrf2 siRNA transfection. In addition, FA-97 prevents scopolamine- (SCOP-) induced learning and memory impairments in vivo via reducing neuronal apoptosis and protecting against cholinergic system dysfunction in the hippocampus and cortex. Moreover, the increased MDA level and low total antioxidant capacity in SCOP-treated mouse brains are reversed by FA-97, with the increased expression of HO-1, NQO-1, and nuclear Nrf2. In conclusion, FA-97 protects against oxidative stress-mediated neuronal cell apoptosis and SCOP-induced cognitive impairment by activating Nrf2/HO-1 signaling, which might be developed as a therapeutic drug for AD.

Synthesis of Forsythenethoside A, a Neuroprotective Macrocyclic Phenylethanoid Glycoside, and NMR Analysis of Conformers.

Forsythenethoside A (1) is a structurally unique macrocyclic phenylethanoid glycoside, which was isolated from Forsynthia suspensa and displayed considerable neuroprotective activities. Here, we report its first chemical synthesis via a longest linear sequence of 14 steps in 5% overall yield wherein intramolecular oxidative coupling was successfully employed to realize the pivotal macrocyclization. NMR analysis revealed the existence of an unexpected conformational interconversion of the congested macrocycles.

A Three-Step, Gram-Scale Synthesis of Hydroxytyrosol, Hydroxytyrosol Acetate, and 3,4-Dihydroxyphenylglycol.

Hydroxytyrosol and two other polyphenols of olive tree, hydroxytyrosol acetate and 3,4-dihydroxyphenylglycol, are known for a wide range of beneficial activities in human health and prevention from diseases. The inability to isolate high, pure amounts of these natural compounds and the difficult and laborious procedures for the synthesis of them led us to describe herein an efficient, easy, cheap, and scaling up synthetic procedure, from catechol, via microwave irradiation.

Caffeic acid phenethyl ester (CAPE)-derivatives act as selective inhibitors of acetylcholinesterase.

Unexpected inhibitory effects against eeAChE could be found for a newly synthesized class of caffeic acid phenethyl ester (CAPE) derivatives. Thus, phenethyl-(E)-3-(3,5-dimethoxy-4-phenethoxyphenyl)-acrylate (Ki = 1.97 ±â€¯0.38 µM, Ki´â€¯= 2.44 ±â€¯0.07 µM) and 4-(2-(((E)-3-(3,4-bis(benzyloxy)phenyl)acryloyl)oxy)ethyl)-1,2-phenylene (2E,2'E)-bis(3-(3,4-bis(benzyloxy)phenyl)acrylate) (Ki = 0.72 ±â€¯0.31 µM, Ki´â€¯= 1.80 ±â€¯0.21 µM) showed very good inhibition of eeAChE, while being non cytotoxic for malignant human cancer cells and non-malignant mouse fibroblasts. Also, they are weak inhibitors for BChE (from equine serum).

Chemical, physical and biotechnological approaches to the production of the potent antioxidant hydroxytyrosol.

Hydroxytyrosol (HT) is a polyphenol of interest to the food, feed, supplements and pharmaceutical sectors. It is one of the strongest known natural antioxidants and has been shown to confer other benefits such as anti-inflammatory and anti-carcinogenic properties, and it has the potential to act as a cardio- and neuroprotectant. It is known to be one of the compounds responsible for the health benefits of the Mediterranean diet. In nature, HT is found in the olive plant (Olea europaea) as part of the secoiridoid compound oleuropein, in its leaves, fruit, oil and oil production waste products. HT can be extracted from these olive sources, but it can also be produced by chemical synthesis or through the use of microorganisms. This review looks at the production of HT using plant extraction, chemical synthesis and biotechnological approaches.

Chemoenzymatic Synthesis and Radical Scavenging of Sulfated Hydroxytyrosol, Tyrosol, and Acetylated Derivatives.

Potential metabolites of bioactive compounds are important for their biological activities and as authentic standards for metabolic studies. The phenolic compounds contained in olive oil are an important part of the human diet, and therefore their potential metabolites are of utmost interest. We developed a convenient, scalable, one-pot chemoenzymatic method using the arylsulfotransferase from Desulfitobacterium hafniense for the sulfation of the natural olive oil phenols tyrosol, hydroxytyrosol, and of their monoacetylated derivatives. Respective monosulfated (tentative) metabolites were fully structurally characterized using LC-MS, NMR, and HRMS. In addition, Folin-Ciocalteu reduction, 1,1-diphenyl-2-picrylhydrazyl radical scavenging, and antilipoperoxidant activity in rat liver microsomes damaged by tert-butylhydroperoxide were measured and compared to the parent compounds. As expected, the sulfation diminished the radical scavenging properties of the prepared compounds. These compounds will serve as authentic standards of phase II metabolites.

Synthesis and characterization of CAPE derivatives as xanthine oxidase inhibitors with radical scavenging properties.

Inhibitors of the enzyme xanthine oxidase (XO) with radical scavenging properties hold promise as novel agents against reperfusion injuries after ischemic events. By suppressing the formation of damaging reactive oxygen species (ROS) by XO or scavenging ROS from other sources, these compounds may prevent a buildup of ROS in the aftermath of a heart attack or stroke. To combine these two properties in a single molecule, we synthesized and characterized the non-purine XO inhibitor caffeic acid phenethylester (CAPE) and 19 derivatives using a convenient microwave-assisted Knoevenagel condensation protocol. Varying systematically the number and positions of the hydroxyl groups at the two phenyl rings, we derived structure-activity relationships based on experimentally determined XO inhibition data. Molecular docking suggested that critical enzyme/inhibitor interactions involved π-π interactions between the phenolic inhibitor ring and Tyr914, hydrogen bonds between inhibitor hydroxyl groups and Glu802, and hydrophobic interactions between the CAPE phenyl ring and non-polar residues located at the entrance of the binding site. To effectively scavenge the stable radical DPPH, two hydroxyl groups in 1,2- or 1,4-position at the phenyl ring were required. Among all compounds tested, E-phenyl 3-(3,4-dihydroxyphenyl)acrylate, a CAPE analog without the ethyl tether, showed the most promising properties.

Chemoenzymatic synthesis of hydroxytyrosol monoesters and their suppression effect on nitric oxide production stimulated by lipopolysaccharides.

Fatty acid monoesters of hydroxytyrosol [2-(3,4-dihydroxyphenyl)ethanol] were synthesized in two steps from tyrosol (4-hydroxyphenylethanol) by successive Candida antarctica lipase B-catalyzed chemoselective acylation on the primary aliphatic hydroxy group over phenolic hydroxy group in tyrosol, and 2-iodoxybenzoic acid (IBX)-mediated hydroxylation adjacent to the remaining free phenolic hydroxy group. Examination of their suppression effects on nitric oxide production stimulated by lipopolysaccharides in RAW264.7 cells showed that hydroxytyrosol butyrate exhibited the highest inhibition (IC50 7.0 µM) among the tested compounds.

Semisynthesis of ω-Hydroxyalkylcarbonate Derivatives of Hydroxytyrosol as Antitrypanosome Agents.

Several lipophilic ω-hydroxyalkylcarbonate hydroxytyrosol derivatives and also their corresponding dimeric derivatives have been synthesized, coupling the primary hydroxy group of this phenolic compound with several terminal diols of different chain lengths, by the use of a carbonate linker. The trypanocidal activity and cytotoxicity of these ω-hydroxyalkylcarbonate derivatives of hydroxytyrosol and known alkylcarbonate derivatives of hydroxytyrosol were assessed. Three of the hydroxytyrosol alkylcarbonate derivatives were active against Trypanosoma brucei: two with an alkyl chain of average size (0.2 and 0.5 µM) and another with a double bond in the alkyl chain (0.4 µM). These values suggest an increase in activity with respect to hydroxytyrosol (264-, 90-, and 116-fold, respectively). Furthermore, these compounds showed high selectivity indices against MRC-5, a nontumor human cell line (62, 71, and 39, respectively). Some other ω-hydroxyalkylcarbonate and alkylcarbonate derivatives of hydroxytyrosol were also active against T. brucei within a low micromolar range (about 1 µM).

Comparative Analysis of the Effects of Olive Oil Hydroxytyrosol and Its 5-S-Lipoyl Conjugate in Protecting Human Erythrocytes from Mercury Toxicity.

Oxidative stress is one of the underlying mechanisms of the toxic effects exerted by mercury (Hg) on human health. Several antioxidant compounds, including the olive oil phenol hydroxytyrosol (HT), were investigated for their protective action. Recently, we have reported that 5-S-lipoylhydroxytyrosol (Lipo-HT) has shown increased antioxidant activities compared to HT and exerted potent protective effects against reactive oxygen species (ROS) generation and oxidative damage in human hepatocellular carcinoma HepG2 cell lines. In this study, the effects of Lipo-HT and HT on oxidative alterations of human erythrocytes induced by exposure to 40 µM HgCl2 were comparatively evaluated. When administered to the cells, Lipo-HT (5-20 µM) proved nontoxic and it decreased the Hg-induced generation of ROS, the hemolysis, and the depletion of intracellular GSH levels. At all tested concentrations, Lipo-HT exhibited higher ability to counteract Hg-induced cytotoxicity compared to HT. Model studies indicated the formation of a mercury complex at the SH group of Lipo-HT followed by a redox reaction that would spare intracellular GSH. Thus, the enhanced erythrocyte protective action of Lipo-HT from Hg-induced damage with respect to HT is likely due to an effective chelating and reducing ability toward mercury ions. These findings encourage the use of Lipo-HT in nutraceutical strategies to contrast heavy metal toxicity in humans.

Discovery of caffeic acid phenethyl ester derivatives as novel myeloid differentiation protein 2 inhibitors for treatment of acute lung injury.

Myeloid differentiation protein 2 (MD2) is an essential molecule which recognizes lipopolysaccharide (LPS), leading to initiation of inflammation through the activation of Toll-like receptor 4 (TLR4) signaling. Caffeic acid phenethyl ester (CAPE) from propolis of honeybee hives could interfere interactions between LPS and the TLR4/MD2 complex, and thereby has promising anti-inflammatory properties. In this study, we designed and synthesized 48 CAPE derivatives and evaluated their anti-inflammatory activities in mouse primary peritoneal macrophages (MPMs) activated by LPS. The most active compound, 10s, was found to bind with MD2 with high affinity, which prevented formation of the LPS/MD2/TLR4 complex. The binding mode of 10s revealed that the major interactions with MD2 were established via two key hydrogen bonds and hydrophobic interactions. Furthermore, 10s showed remarkable protective effects against LPS-caused ALI (acute lung injury) in vivo. Taken together, this work provides new lead structures and candidates as MD2 inhibitors for the development of anti-inflammatory drugs.

Substituted Caffeic and Ferulic Acid Phenethyl Esters: Synthesis, Leukotrienes Biosynthesis Inhibition, and Cytotoxic Activity.

Glioblastoma multiforme (GBM) is an aggressive brain tumor that correlates with short patient survival and for which therapeutic options are limited. Polyphenolic compounds, including caffeic acid phenethyl ester (CAPE, 1a), have been investigated for their anticancer properties in several types of cancer. To further explore these properties in brain cancer cells, a series of caffeic and ferulic acid esters bearing additional oxygens moieties (OH or OCH3) were designed and synthesized. (CAPE, 1a), but not ferulic acid phenethyl ester (FAPE, 1b), displayed substantial cytotoxicity against two glioma cell lines. Some but not all selected compounds derived from both (CAPE, 1a) and (FAPE, 1b) also displayed cytotoxicity. All CAPE-derived compounds were able to significantly inhibit 5-lipoxygenase (5-LO), however FAPE-derived compounds were largely ineffective 5-LO inhibitors. Molecular docking revealed new hydrogen bonds and π-π interactions between the enzyme and some of the investigated compounds. Overall, this work highlights the relevance of exploring polyphenolic compounds in cancer models and provides additional leads in the development of novel therapeutic strategies in gliomas.

Synthesis and Biological Evaluation of New Tyrosol-Salicylate Derivatives as Potential Anti-Inflammatory Agents.

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the most commonly used medications in inflammatory illnesses. However, the gastrointestinal bleeding and toxicity associated with NSAIDs long term use prompted the quest towards investigations for new anti-inflammatory agents. Natural and natural-derived molecules proved its anti-inflammatory efficacy in vitro as well as in vivo. Given this background, the scope of this research involves structural changes of the natural polyphenol (tyrosol) generating two new salicylate derivatives and testing their biological properties, focusing on anti-inflammatory effects assessed in vitro and in vivo assays. The first molecular modification was the introduction of a carboxylic acid group adjacent to the phenol group present in this compound, which creates a new salicylate-like tyrosol. In addition, the acetylation of phenol group in this molecule produced an acetylsalicylate derivative, which may be regarded as aspirin-like natural polyphenol. Interestingly, tyrosol and its novel derivatives attenuated the edema in acute inflammatory response on carrageenan- induced local inflammation in mice. In addition, our results demonstrated that tyrosol and its novel derivatives were able to reduce the chemotaxis of neutrophil assessed in vitro model by chemo attractant (fMLP). Furthermore, only derivative 2 was able to reduce this effect in the acute inflammatory model. In (DPPH)- scavenging activity, tyrosol derivatives demonstrated a minor antioxidant activity, which may suggest that radical scavenging is not a major pathway involved in the anti-inflammatory effects of these derivatives. Salicylate-like tyrosol derivatives are of particular interest for future studies.

Antiproliferative activity and SARs of caffeic acid esters with mono-substituted phenylethanols moiety.

A series of CAPE derivatives with mono-substituted phenylethanols moiety were synthesized and evaluated by MTT assay on growth of 4 human cancer cell lines (Hela, DU-145, MCF-7 and ECA-109). The substituent effects on the antiproliferative activity were systematically investigated for the first time. It was found that electron-donating and hydrophobic substituents at 2'-position of phenylethanol moiety could significantly enhance CAPE's antiproliferative activity. 2'-Propoxyl derivative, as a novel caffeic acid ester, exhibited exquisite potency (IC50=0.4±0.02 & 0.6±0.03µM against Hela and DU-145 respectively).