Ligustrazinyl amides: a novel class of ligustrazine-phenolic acid derivatives with neuroprotective effects

Natural Products-Pyrazine Hybrids: A Review of Developments in Medicinal Chemistry

Pyrazine is a six-membered heterocyclic ring containing nitrogen, and many of its derivatives are biologically active compounds. References have been downloaded through Web of Science, PubMed, Science Direct, and SciFinder Scholar. The structure, biological activity, and mechanism of natural product derivatives containing pyrazine fragments reported from 2000 to September 2023 were reviewed. Publications reporting only the chemistry of pyrazine derivatives are beyond the scope of this review and have not been included. The results of research work show that pyrazine-modified natural product derivatives have a wide range of biological activities, including anti-inflammatory, anticancer, antibacterial, antiparasitic, and antioxidant activities. Many of these derivatives exhibit stronger pharmacodynamic activity and less toxicity than their parent compounds. This review has a certain reference value for the development of heterocyclic compounds, especially pyrazine natural product derivatives.

An Overview of Tetramethylpyrazine (Ligustrazine) and its Derivatives as Potent Anti-Alzheimer’s Disease Agents

Abstract:

Tetramethylpyrazine (TMP), or ligustrazine, is an alkaloid isolated from the Chinese herb Ligusticum wallichii. It is known for its broad-spectrum medicinal properties against several diseases, and various studies have shown that it can modulate diverse biological targets and signaling pathways to produce neuroprotective effects, especially against Alzheimer’s disease (AD). This has attracted significant research attention evaluating TMP as a potent multitarget anti-AD agent. This review compiles the results of studies assessing the neuroprotective mechanisms exerted by TMP as well as its derivatives prepared using a multi-target-directed ligand strategy to explore its multitarget modulating properties. The present review also highlights the work done on the design, synthesis, structure-activity relationships, and mechanisms of some potent TMP derivatives that have shown promising anti-AD activities. These derivatives were designed, synthesized, and evaluated to develop anti-AD molecules with enhanced biological and pharmacokinetic activities compared to TMP. This review article paves the way for the exploration and development of TMP and TMP derivatives as an effective treatment for AD.

Novel Neuroprotective Lead Compound Ligustrazine Derivative Mass Spectrometry Fragmentation Rule and Metabolites in Rats by LC/LTQ-Orbitrap MS

The neuroprotective evaluation of ligustrazine derivatives has become a research focus all over the world. A novel ligustrazine derivative, (3,5,6-Trimethylpyrazin-2-yl)methyl(E)-3-(4-((3,5,6-trimethylpyrazin-2-l)methoxy)phenyl)acrylate (T-CA), has shown protective effects against CoCl₂-induced neurotoxicity in a differentiated PC12 cell model and middle cerebral artery occlusion (MCAO) model in our previous studies. However, nearly none of the parent drugs existed after rapid metabolism due to uncertain reasons. Thus, the fragmentation regularities of mass spectra, and metabolites, of T-CA in rats were examined using liquid chromatography-electrospray ionizationion trap mass spectrometry (LC/LTQ-Orbitrap MS) in this research. The main fragment ion, mass spectrum characteristics, and the structural information were elucidated. When compared with a blank sample, we identified five kinds of T-CA metabolites, including three phase I metabolites and two phase II metabolites. The results showed that the metabolic pathways of T-CA in rats via oral administration were hydrolysis (ether bond rupture, ester bond rupture), oxidation, reduction, glucose aldehyde acidification, etc. In addition, three main metabolites were synthesized and their structures were identified by superconducting high-resolution NMR and high-resolution mass spectroscopy (HR-MS). The neuroprotective activity of these metabolites was validated in a PC12 cell model. One of the metabolites (M2) showed significant activity (EC₅₀ = 9.67 μM), which was comparable to the prototype drug T-CA (EC₅₀ = 7.97 μM). The current study provides important information for ligustrazine derivatives, pertaining to the biological conversion process in vivo.

Synthesis and activity towards Alzheimer's disease in vitro: Tacrine, phenolic acid and ligustrazine hybrids

A series of novel tacrine-phenolic acid dihybrids and tacrine-phenolic acid-ligustrazine trihybrids were synthesized, characterized and screened as novel potential anti-Alzheimer drug candidates. These compounds showed potent inhibition activity towards cholinesterases (ChEs), among of them, 9i was the most potent one towards acetylcholinesterase (eeAChE, IC₅₀ = 3.9 nM; hAChE, IC₅₀ = 65.2 nM). 9i could also effectively block β-amyloid (Aβ) self-aggregation with an inhibition ratio of 47% at 20 μM. In addition, its strong anti-oxidation activity could protect PC12 cells from CoCl₂-damage in the experimental condition while no neurotoxicity. Furthermore, its hepatotoxicity was lower than tacrine in vitro and in vivo. Kinetic and molecular modeling studies revealed that 9i worked in a mixed-type way, could interact simultaneously with catalytic active site (CAS) and peripheral anionic site (PAS) of AChE. Therefore, 9i was a promising multifunctional candidate for the treatment of AD.

Recent progress in the structural modification and pharmacological activities of ligustrazine derivatives

Ligustrazine is a main active fraction of the traditional medicine known as Ligusticum chuanxiong hort, which has been used as clinical medication for cerebral thrombosis, coronary heart disease and stenocardia recently. The rapid metabolism and short half-life of ligustrazine seriously limits its application in clinical practice. Therefore, derivatives of ligustrazine are designed and synthesized in our and other labs, including piperazine, cinnamic acid, styrene, acylguanidine, amides, curcumin and triterpenes derivatives of ligustrazine. Most of these compounds present better pharmacodynamics activities and more favorable pharmacokinetic properties compared to the parent compound. Besides, some new biological activities of these compounds are discovered. Hence, this review continues the previous review of our group as well as aims to highlight recent prominent advances in this field in the past ten years.

Neuroprotection by new ligustrazine-cinnamon acid derivatives on CoCl2-induced apoptosis in differentiated PC12 cells

A new series of ligustrazine-cinnamon acid derivatives had been designed and synthesized as potential neuro-protective agents. Among the derivatives, 3a exhibited the promising neuroprotective activity (EC₅₀ = 3.68 μM). Moreover, with the deep research of the drug pathway, it (the further mechanism researches) suggested compound 3a could inhibit the apoptosis of injured PC12 cells via blocking the mitochondria apoptosis pathway including up-regulation the ratio of Bcl-2/Bax, down-regulation the expression of cytochrome-c (Cyt-c) and inhibition of the activity of caspase-9 and -3. In addition, the structure-activity relationships (SARs) of novel compounds were also discussed.

Synthesis and protective effect of new ligustrazine-vanillic acid derivatives against CoCl2-induced neurotoxicity in differentiated PC12 cells

Ligustrazine-vanillic acid derivatives had been reported to exhibit promising neuroprotective activities. In our continuous effort to develop new ligustrazine derivatives with neuroprotective effects, we attempted the synthesis of several ligustrazine-vanillic acid amide derivatives and screened their protective effect on the injured PC12 cells damaged by CoCl₂. The results showed that most of the newly synthesized derivatives exhibited higher activity than ligustrazine, of which, compound VA-06 displayed the highest potency with EC₅₀ values of 17.39 ± 1.34 μM. Structure-activity relationships were briefly discussed.Graphical abstractNew series of ligustrazine-vanillic acid amide derivatives were synthesized and evaluated for their protective effect on the injured PC₁₂ cells damaged by CoCl₂. VA-06 was found to be the most active one.

Design, synthesis and evaluation of new ligustrazine derivatives as potential plasma-stable neuroprotective agents

A series of ligustrazine-phenolic acid esters which exhibited promising neuroprotective activities have previously been reported. Nevertheless, we found that these ester compounds (like T-VA) were not stable in plasma by further in vivo studies. To investigate plasma-stable neuroprotective agents, a series of new ligustrazine derivatives were synthesized by conjoining ligustrazine and phenols with ester, ether and amide bonds. Most of the compounds exhibited higher protective effects against CoCl₂-induced neurotoxicity in differentiated PC12 cells than ligustrazine. Structure-activity relationships were also briefly discussed. We found that compound 2c (2-((2-methoxy-4-(((3,5,6-trimethylpyrazin-2-yl)methoxy) methyl)phenoxy)methyl)-3,5,6-trimethylpyrazine) displayed the highest protective effect on the PC12 cells damaged by CoCl₂ (EC₅₀ = 1.07 μM). Preliminary stability investigation in rat plasma was verified in vitro and better plasma stability was observed with 2c in comparison to T-VA.

Design, synthesis, and biological evaluation of the novel glycyrrhetinic acid-cinnamoyl hybrids as anti-tumor agents

Background

Glycyrrhetinic acid (GA) derivatives had shown not only cytotoxicity but also could trigger apoptosis in various human cancer cell lines. Moreover, cinnamic acid (CA) and its phenolic analogues as potent antitumor agents were employed in the design of anti-tumor drugs. To further improve the anti-tumor activity of GA and CA derivatives, a series of novel compounds were designed and synthesized using GA and CA derivatives fragments.

Results

The result showed that all the novel glycyrrhetinic acid-cinnamoyl (GA–CA) hybrids presented higher antitumor activity on the tumor cell lines of HepG2, HT-29, Hela and lower cytotoxicity on three non-tumor cells lines MDCK, HY926, H9C2 than the parent compounds (IC₅₀ > 50 μM). It was worth noting that 8a had a superior cytotoxicity effect on Hela cells (IC₅₀ = 8.54 μM) than on other cancer cell lines (IC₅₀ > 15 μM). And it also indicated that 8a showed lower cytotoxicity (IC₅₀ > 27 μM) towards MDCK, HY926 and H9C2 cells than cisplatin (DDP, IC₅₀ < 10 μM). Moreover, according to the acute toxicity, it could be indicated that the LD₅₀ of 8a exceeded 3.0 g/kg by oral administration in mice. The further research using Giemsa, H33342 staining, flow cytometric analysis and caspase-3 assay showed that 8a could cause Hela cell damage, nuclei lysis and apoptosis. In addition, the structure–activity relationships of these hybrids were briefly discussed.

Conclusions

Compared with GA, target compounds demonstrated better anti-tumor activity, among which 8a was the most active one. What’s more, structure–activity relationship analysis also revealed that hybrids with trans olefinic bond group show higher antitumor activity than those without olefinic bond, such as 1a > 1b, 6a > 2b, 8a > 3b, 9a > 4b. In addition, it was found that the methoxy substituent might enhance selectivity of GA–CA hybrids towards regular non-cancerous cells MDCK, HY926 and H9C2, such as 4a, 6a, 7a, 8a. However, there might be less relationship between the cytotoxicity and the quantity, position of methoxy moiety. Hence, it is urgent need to synthesize efficient, low toxicity and multi-target anti-tumor compounds based on the structure combination principle.

A Novel Ligustrazine Derivative T-VA Prevents Neurotoxicity in Differentiated PC12 Cells and Protects the Brain against Ischemia Injury in MCAO Rats

Broad-spectrum drugs appear to be more promising for the treatment of acute ischemic stroke. In our previous work, a new ligustrazine derivative (3,5,6-trimethylpyrazin-2-yl) methyl 3-methoxy-4-[(3,5,6-trimethylpyrazin-2-yl)methoxy]benzoate (T-VA) showed neuroprotective effect on injured PC12 cells (EC₅₀ = 4.249 µM). In the current study, we show that this beneficial effect was due to the modulation of nuclear transcription factor-κB/p65 (NF-κB/p65) and cyclooxygenase-2 (COX-2) expressions. We also show that T-VA exhibited neuroprotective effect in a rat model of ischemic stroke with concomitant improvement of motor functions. We propose that the protective effect observed in vivo is owing to increased vascular endothelial growth factor (VEGF) expression, decreased oxidative stress, and up-regulation of Ca²⁺–Mg²⁺ ATP enzyme activity. Altogether, our results warrant further studies on the utility of T-VA for the potential treatment of ischemic brain injuries, such as stroke.