Evaluation of the Local Anesthetic Activity, Acute Toxicity, and Structure–Toxicity Relationship in Series of Synthesized 1-Aryltetrahydroisoquinoline Alkaloid Derivatives In Vivo and In Silico

Abstract

Isoquinoline alkaloids constitute one of the most common classes of alkaloids that have shown a pronounced role in curing various diseases. Finding ways to reduce the toxicity of these molecules and to increase their therapeutic margin is an urgent matter. Here, a one-step method for the synthesis of a series of 1-aryl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolines was performed in 85–98% yield by the Pictet–Spengler reaction. This was accomplished using the reaction between 3,4-dimethoxyphenylethylamine and substituted benzaldehydes boiling in trifluoroacetic acid. Furthermore, 1-(3′-amino-, 4′-aminophenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolines were obtained in 94% and 97% yield by reduction in 1-(3′-nitro-, 4′-nitrophenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolines with SnCl2 × 2H2O. The structures of the substances obtained were confirmed by infrared (IR) and nuclear magnetic resonance (1H and 13C NMR) spectra. ADMET/TOPKAT in silico study concluded that the synthesized compounds exhibited acceptable pharmacodynamic and pharmacokinetic properties without carcinogenic or mutagenic potential but with variable hepatotoxicity. The acute toxicity and structure–toxicity relationship (STR) in the series of 20 derivatives of 1-aryl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolines (3a-r, 4a, b) was studied via determination of acute toxicity and resorptive action in white mice employing intragastric step-by-step administration. The first compound, 1-phenyl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline hydrochloride (3a), showed the highest toxicity with LD50 of 280 mg/kg in contrast to 1-(3′-bromo -4′-hydroxyphenyl)-6,7-methylenedioxy-1,2,3,4-tetrahydroisoquinoline hydrochloride (3e) which proved to be the safest of the compounds studied. Its toxicity was 13.75 times lower than that of the parent compound 3a. All compounds investigated showed high local anesthetic activity on rabbit eyes in the concentrations studied. Only 3r, 3n, and 4a caused eye irritation and redness. All investigated derivatives (except 4b) in 1% concentration were more active than lidocaine, providing longer duration of complete anesthesia. Therefore, based on the obtained results of in silico tests, local anesthesia, and acute toxicity, a conclusion can be drawn that the experimental compounds need further extensive future investigations and possible modifications so that they can act as promising drug candidates.

Analgesic and anti-inflammatory effects of galangin: a potential pathway to inhibit transient receptor potential vanilloid 1 receptor activation

“…Upon discovering the ability of galangin to inhibit the synthesis of pro-inflammatory mediators, specifically histamine and prostaglandins, induced by carrageenan and formalin, as well as its capacity to hinder acute inflammation and prevent the activation of pain-sensing nerve endings, this investigation delved deeper into the serum and local tissue levels of TNF-α, IL-6, IL-1β, IL-10, COX-2, and PGE2 in rats experiencing capsaicin-induced inflammatory pain. These findings revealed that galangin effectively suppresses the production and levels of these pro-inflammatory mediators, which aligns with previous studies on the efficacy of anti-inflammatory analgesic drugs [ 26 , 28 ]. This further suggests that galangin may inhibit cyclooxygenase activity, thus reducing prostaglandin synthesis and suppressing the levels of pro-inflammatory mediators to impede the development of inflammatory pain.…”

Anesthetic drug discovery with computer-aided drug design and machine learning

“…In a recent study, Azamatov et al introduced computational AMDET prediction methods to develop novel local anesthetics with lower toxicity. Through the study of a group of 1-aryl tetrahydroisoquinoline alkaloid derivatives, they also proposed explainable correlations between chemical structures and acute toxicity [152]. Another approach is to refine currently available drugs by optimizing PK/PD parameters.…”