A Convenient Synthesis of Simple Tetrahydroisoquinolines

Design, synthesis, and biological antitumor evaluation of tetrahydroisoquinoline derivatives

Cancer, as a public health issue, is the leading cause of death worldwide. Tetrahydroisoquinoline derivatives have effective biological activities and can be used as potential therapeutic agents for antitumor drugs. In this work, we designed and synthesized a series of novel tetrahydroisoquinoline compounds and evaluated their antitumor activity in vitro on several representative human cancer cell lines. The results showed that the vast majority of compounds showed good inhibitory activities against the cancer cell lines of HCT116, MDA-MB-231, HepG2, and A375.

A Cationic Catechol Derivative Binds Anions in Competitive Aqueous Media

A simple dihydroxy isoquinolinium molecule (3+ ) was prepared by a modification of a literature procedure. Interestingly, during optimisation of the synthesis a small amount of the natural product pseudopalmatine was isolated, and characterised for the first time by X-ray crystallography. Compound 3+ contains a catechol motif and positive charge on the same scaffold and was found to be a potent anion receptor, binding sulfate strongly in 8 : 2 d6 -acetone:D2 O and 7 : 3 d6 -acetone:D2 O (Ka >104 and 2,100 M-1 , respectively). Unsurprisingly, chloride binding was much weaker, even in the less polar solvent mixture 9 : 1 d6 -acetone:D2 O. The sulfate binding is remarkably strong for such a simple molecule, however anion binding studies were complicated by the tendency of the molecule to react with BPh4 - or BF4 - species during anion metathesis reactions. This gave two unusual zwitterions containing tetrahedral boronate centres, which were both characterised by X-ray crystallography.

Synthesis of carbon-11 labeled biaryl 1,2,3,4-tetrahydroisoquinoline derivatives and conformationally flexible analogues as new potential PET glioma tumor imaging agents

Carbon-11 labeled biaryl 1,2,3,4-tetrahydroisoquinoline derivatives and conformationally flexible analogues, 2-(2-(biphenyl-4-yl)ethyl)-6-[(11)C]methoxy-7-methoxy-1,2,3,4-tetrahydroisoquinoline ([(11)C]3); 1-(biphenyl-4-yl)methyl-6,7-dimethoxy-2-[(11)C]methyl-1,2,3,4-tetrahydroisoquinoline (N-[(11)C]7) and 1-(biphenyl-4-yl)methyl-6-[(11)C]methoxy-7-methoxy-2-methyl-1,2,3,4-tetrahydroisoquinoline (O-[(11)C]7); and 2-(biphenyl-4-yl)-N-(3,4-dimethoxy-phenethyl)-N-[(11)C]methyl-ethanamine (N-[(11)C]10) and 2-(biphenyl-4-yl)-N-(3-methoxy-4-[(11)C]methoxy-phenethyl)-N-methyl-ethanamine (O-[(11)C]10), have been synthesized as new potential positron emission tomography (PET) glioma tumor imaging agents, either by O-[(11)C]methylation or by N-[(11)C]methylation of the appropriate precursors using [(11)C]CH(3)OTf and isolated either by a simplified solid-phase extraction (SPE) purification procedure or by HPLC method in 30-55% radiochemical yields decay corrected to EOB, 15-25 min overall synthesis time, and 4.0-6.0 Ci/mumol specific activity at EOB.

Synthesis and in vitro evaluation of tetrahydroisoquinolinyl benzamides as ligands for sigma receptors

5-Bromo-N-[4-(6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)-butyl)]-2,3-dimethoxy-benzamide (1) is one of the most potent and selective sigma(2) receptor ligands reported to date. Previous structure-activity relationship studies of such tetrahydroisoquinolinyl benzamides have focused on the linker that connects the ring systems and the effects of benzamide ring substituents. The present study explores the effects of fusing methylene-, ethylene-, and propylenedioxy rings onto the tetrahydroisoquinoline in place of the two methoxy groups. These modifications decreased sigma(2) affinity by 8- to 12-fold, with no major differences noted with ring size. By contrast, the methylenedioxy analog showed a 10-fold greater sigma(1) affinity than 1, and progressively lower sigma(1) affinities were then noted with increasing ring size. We also opened the tetrahydroisoquinoline ring of 1 to study the effects of greater conformational fluidity on sigma receptor binding. The sigma(2) affinity of the open-ring compound decreased by 1700-fold, while sigma(1) affinity was not changed. Thus, a constrained tetrahydroisoquinoline ring system is key to the exceptional sigma(2) receptor binding affinity and selectivity of this active series.

Novel multidrug resistance reversal agents

A series of 59 alpha-aryl-alpha-thioether-alkyl, -alkanenitrile, and -alkanecarboxylic acid methyl ester tetrahydroisoquinoline and isoindoline derivatives (15a-48) were synthesized and evaluated as multidrug resistance (MDR) reversal agents. The compounds were tested on S1-B1-20 human colon carcinoma cells selected for resistance to bisantrene. Both the cytotoxicity of the reversal agents and their ability to resensitize the cells to bisantrene were determined. All but two of these compounds (15q, 40) were more effective MDR reversal agents in vitro than verapamil (VRP), a calcium channel antagonist which also has been shown to possess MDR modulating activity. Several showed good activity in this assay (IC50's < 0.5 microM), the most potent being isoindolines 44 (IC50 0.26 microM) and 46 (IC50 0.26 microM) and tetrahydroisoquinolines 47 (IC50 0.29 microM) and 15m (IC50 0.30 microM). A number of compounds were evaluated in vivo against vincristine (VCR)-resistant murine P388 leukemia, as well as against human epidermoid carcinoma KB/8.5 implanted sc in athymic mice. The reversal agents which consistently showed the highest activity, together with low toxicity, were alpha-aryl-alpha-thiotolylalkanenitrile tetrahydroisoquinoline derivatives with electron-rich alkoxy substituents on the aromatic rings. Of the tested compounds, the most effective reversal agents for both tumor lines were 15h (33% increased life span at 12.5 mg/kg, 0.2 mg/kg VCR versus VCR alone in the VCR-resistant P388 leukemia model and 59% relative tumor growth at 50 mg/kg, 8 mg/kg doxorubicin versus doxorubicin alone in the KB/8.5 model) and 39a (48% increased life span at 50 mg/kg, 0.2 mg/kg VCR versus VCR alone in the VCR-resistant P388 leukemia model and 46% relative tumor growth at 25 mg/kg, 8 mg/kg doxorubicin versus doxorubicin alone in the KB/8.5 model). The mechanism of action of these compounds is believed to involve blocking the drug efflux pump, P-glycoprotein.

Total Synthesis of (-)-Tetrahydropalmatine via Chiral Formamidine Carbanions: Unexpected Behavior with Certain Ortho-Substituted Electrophiles

A method has been developed by alkylation of chiral lithioformamidines to construct protoberberine alkaloids with a C(9) and C(10) D-ring substitution pattern. This ring pattern was established using an ortho-substituted hydroxymethylbenzene electrophile protected as a silyl ether to ultimately provide (-)-tetrahydropalmatine in 88% ee. Additionally, we have discovered limitations with ortho-substituted electrophiles in the asymmetric formamidine alkylation. These electrophiles have the potential to disrupt the lithium formamidine chelate and cause the selectivity in the alkylation to be uncharacteristically low. The total synthesis of (+/-)-canadine and (-)-tetrahydropalmatine along with the limitations to the formamidine alkylation technology are delineated herein.