Synthesis and cytotoxicity of novel N-sulfonyl-1,2,3,4-tetrahydroisoquinoline thiosemicarbazone derivatives

The modified Pictet–Spengler reaction of phenylethylbenzene sulfonamide with a commercially available glyoxal to construct 1-benzoyl- and 1-acetyl-1,2,3,4-tetrahydroisoquinolines 9a–n has been reported. The reaction could be accomplished, regardless of the oxygenation pattern on the aromatic ring, leading to the N-sulfonyltetrahydroisoquinoline analogs which are versatile intermediates for the synthesis of new thiosemicarbazone analogs of 1,2,3,4-tetrahydroisoquinoline. Bioactivity test revealed that most thiosemicarbazones displayed cytotoxic potency against MOLT-3 cell lines with an IC₅₀ less than 20 μg/mL. Significantly, the thiosemicarbazone analog of 1-acetyltetrahydroisoquinoline 9j was the most potent cytotoxic compound against HuCCA-1, HepG2, and MOLT-3 cells. This study provides the novel lead molecules for further development.     

Comparative anticonvulsant activity of N-acetyl-1-aryl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline derivatives in rodents

The anticonvulsant activity of competitive 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo (F)-quinoxaline (NBQX) and noncompetitive 2,3-benzodiazepines and tetrahydroisoquinolines (THIQs) AMPA/kainate receptor antagonists, was tested in different experimental seizure models and compared with diazepam, a conventional antiepileptic drug acting on GABAergic neurotransmission. In particular, the compounds were evaluated against audiogenic and maximal electroshock seizures (MES) test and pentetrazol (PTZ) seizures model, and all of them showed protective action. In addition, NBQX, 2,3-benzodiazepines and THIQs, but not diazepam, were also protective against clonic and tonic seizures and lethality induced by kainate, AMPA and ATPA, but were ineffective against NMDA-induced seizures. Only 2,3-benzodiazepines and some THIQs were able to affect 4-aminopyridine- and mercaptopropionic-acid-induced seizures. The duration of anticonvulsant action of 33 micromol/kg of some 2,3-benzodiazepines and THIQs was also investigated in DBA/2 mice, a strain genetically susceptible to audiogenic seizures, and it was observed that the derivative THIQ-10c, possessing an acetyl group at the N-2 and a chlorine atom on the C-1 phenyl ring, showed higher anticonvulsant activity and longer-lasting protective effects.     

1,2,3,4-tetrahydroisoquinoline derivatives; lipophilicity evaluation vs. 5-HT1A receptor affinity

Retention parameters (log k') of 1,2,3,4-tetrahydroisoquinoline derivatives--a new class of 5-HT1A receptor ligands--were determined on the basis of reversed-phase HPLC experiments. Good correlations were found between the log k' values and the calculated log Pc, van der Waals volume of the R substituent (VR) as well as the 5-HT1A receptor affinity (Ki) of the investigated compounds. It was demonstrated that hydrophobic forces played a pivotal role in stabilizing the ligand-receptor bioactive complex for that group of compounds.     

Parkinsonism-preventing activity of 1-methyl-1,2,3,4-tetrahydroisoquinoline derivatives in C57BL mouse in vivo

1-Methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), an endogenous parkinsonism-preventing substance, and its 5-, 6-, and 7-hydroxylated derivatives are reported to show in vitro neuroprotective activity against toxicity due to salsolinol in SH-SY5Y human neuroblastoma cells. In the present study, we tested the parkinsonism-preventing potential of these derivatives by means of the pole test in C57BL mice in vivo, and measured brain dopamine contents by liquid chromatography-tandem mass spectrometry. Parkinsonism was induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydroisoquinoline(MPTP), and pretreatment with any of the 1MeTIQ derivatives prevented its induction. 6-Hydroxy-1MeTIQ showed the greatest preventive activity. The amount of dopamine in the brain was reduced by MPTP treatment, and this reduction was suppressed by pretreatment with 1MeTIQ derivatives. These hydroxy-1MeTIQ derivatives may have potential for the treatment of Parkinson's disease as well as 1MeTIQ itself.     

Discovery of antiglioma activity of biaryl 1,2,3,4-tetrahydroisoquinoline derivatives and conformationally flexible analogues

Cultured rat astrocytes and C6 rat glioma were used as a differential screen for a variety of 1,2,3,4-tetrahydroisoquinoline (THI) derivatives. Compound 1 [1-(biphenyl-4-ylmethyl)-1,2,3,4-tetrahydroisoquinoline-6,7-diol hydrochloride] selectively blocked the growth of C6 glioma leaving normal astrocytes relatively unaffected. The potential for clinical utility of 1 was further substantiated in human gliomas and other tumor cell lines. Preliminary SAR of this activity was characterized by synthesis and testing of several THI and conformationally flexible variants.     

3D pharmacophore models for 1,2,3,4-tetrahydroisoquinoline derivatives acting as anticonvulsant agents

A 3D pharmacophore model predicting anticonvulsant activity was obtained for a series of 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline derivatives recently disclosed as a new class of noncompetitive AMPA receptor antagonists. The training set included 17 compounds with varying potency against audiogenic seizures in DBA/2 mice. The best statistical hypothesis, generated with the HypoGen module of Catalyst 4.9, consisted of five features: two hydrogen bond acceptors, two hydrophobic features, and one hydrophobic aromatic region, providing a model with a correlation coefficient of 0.919. The obtained model was an efficient tool in the design of some new anticonvulsant agents containing the tetrahydroisoquinoline scaffold. Moreover, in order to explain the different degree of efficacy of the newly designed N-substituted derivatives, excluded volumes were also considered.     

Synthesis, conformational analysis and antinociceptive activity of 1-[N-methyl-(2-phenylethyl)amino]methyl-1,2,3,4-tetrahydroisoquinoline derivatives

New derivatives of 1-[N-methyl-(2-phenylethyl)amino]methyl-1,2,3,4-tetrahydroisoquinoline were synthesized. The antinociceptive activity of the compounds, determined by the mouse tail-flick test, showed that the introduction of a hydroxy substituent in position 5 of the isoquinoline nucleus generated compounds 4c and 5c, which were as potent as codeine. Conformational analysis and superimposition of energy minima conformers of the compounds on phenazocine revealed that the main proposed opioid pharmacophores were well matched.     

Metabolism and penetration through blood-brain barrier of parkinsonism-related compounds. 1,2,3,4-Tetrahydroisoquinoline and 1-methyl-1,2,3,4-tetrahydroisoquinoline.

14C-Labeled 1,2,3,4-tetrahydroisoquinoline (TIQ) and 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) were synthesized, and their metabolism and tissue distribution were studied. Both compounds showed similar metabolic patterns. In 24 hr after po administration (50 mg/kg) to rats, 76% of TIQ and 72% of 1MeTIQ were excreted unchanged, and 2.7 and 8.7% were excreted as the 4-hydroxyl derivatives, 4-hydroxy-TIQ and 4-hydroxy-1MeTIQ, respectively. Small amounts of N-methylated metabolites, 2-methyl-TIQ (0.4%) and 2-methyl-1MeTIQ (0.7%) were detected. Isoquinoline (2.5%) also was found as a metabolite of TIQ and 1-methyl-3,4-dihydroisoquinoline (1.0%) was found as a metabolite of 1MeTIQ. The concentration of labeled compounds in the brain was about 4.5-fold higher than the blood concentration at 4 hr after dosing, and over 90% was unchanged TIQ or 1MeTIQ. These data indicated that TIQ and 1MeTIQ easily passed through the blood-brain barrier and were concentrated in the brain. Thus, it appears that TIQ and 1MeTIQ as endogenous or exogenous amines may accumulate in the brain and may be related to the onset of Parkinson's disease.     

Effect of 1,2,3,4-tetrahydroimidazo[4,5-c]pyridine and 1,2,3,4-tetrahydroisoquinoline derivatives on the behavior and the brain receptor system in rats

Adducts obtained via the interaction of formaldehyde with histidine (1,2,3,4-tetrahydroimidazo[4, 5-c]pyridine-3-carboxylic acid (I)), tyrosine (7-hydroxy-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (II)), and dopamine (6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (III)) influence the behavior and the state of the brain receptor system of rats upon chronic administration (10-day treatment at a daily dose of 50 mg/kg, i.p.). All the compounds studied decrease the horizontal and (to a lower extent) vertical motor activity and increase the quiescence period duration. On the other hand, the effects of compounds tested on the vegetative reactions were different: compounds I and III increased, whereas compound II decreased these reactions. Using the radioligand binding method, it was established that the treatment with compound I led to a decrease in the density of benzodiazepine receptors (B max of [3H]-flunitrazepam was 78% of the control level) and to a significant (148%) increase in the density of specific binding sites for [3H]-spiperone (reflecting the total density of dopamine (D2) and serotonin (5-HT2) receptors. The chronic administration of compound III produced a reliable decrease (76% of the control level) only in the density of benzodiazepine receptors. None of the tested compounds influenced the affinity of receptors with respect to the radioactive ligands used.     

Effects, in an in-vivo model system, of 1,2,3,4-tetrahydroisoquinoline on glioma

The effects of 1-(biphenyl-4-ylmethyl)-1,2,3,4-tetrahydroisoquinoline-6,7-diol (EDL-155) on the growth of glioma was tested in vitro and in vivo. Normal cultured rat astrocytes and C6 rat glioma were used as a differential screen to test the effects of EDL-155. The compound was preferentially cytotoxic for C6 glioma (EC50=1.5 mumol/l) relative to cultured neonatal astrocytes (EC50=27.4 mumol/l). When compared with a standard chemotherapeutic agent, carmustine (1,3-bis[2-chloroethyl]-1-nitrosourea), or temozolomide, EDL-155 was more selective and more potent in our differential tissue culture assay. The effect of EDL-155 was also tested in an animal model in which C6 glioma was transplanted into the brains of Sprague-Dawley rats. EDL-155 was delivered directly onto the tumor by an osmotic minipump directly into the brain or by intraperitoneal injection. Animals treated with EDL-155 had significantly smaller tumors than did control animals treated with carrier solution. We observed anatomical changes in cultured glioma cells treated with EDL-155 that were consistent with selective destruction of mitochondria and the induction of autophagy. These changes were not observed in normal astrocytes cultured from rat pups. The selective killing of glioma in tissue culture and in the rat brain models indicates that EDL-155 has potential therapeutic value in treating this type of brain cancer.