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1-(1-Chloroethyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline was synthesized through the reaction of homoveratrylamine with racemic lactic acid. The formation of two enantiomers, RR and SS, was detected by performing X-ray diffraction analysis on their chloride salts. The asymmetric unit of the crystal consists of a C13H19ClNO2+ molecular cation and a Cl− anion. Two protonated enantiomers of the title compound, with RR and SS configurations of the chiral atoms, are connected into hydrogen-bonded dimers bridged by Cl− anions. Weak C—H...Cl interactions lead to the formation of a chain running along the a-axis direction of the unit cell, which corresponds to the longest dimension (the preferential growth direction) of the needle-shaped monocrystal. The crystal studied was refined as a two-component twin.

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.