Discovery of novel N-sulfonamide-tetrahydroisoquinolines as potent retinoic acid receptor-related orphan receptor γt agonists

Cancer immunotherapy has become a research hotspot in recent years. A variety of targets were developed for small molecule immuno-oncology agents, including retinoic acid-related orphan receptor gamma t (RORγt), chemokine receptor, stimulator of interferon genes (Sting), indoleamine 2,3-dioxygenase (IDO), toll-like receptors (TLR), etc. Among them, the retinoic acid receptor-related orphan receptor γt (RORγt) has gradually attracted more attention in these years. In particular, LYC-55716 (cintirorgon), a small molecule RORγt agonist developed by Lycera, has entered the phase II clinical study. In this work, starting from compound 7, compound 28 was obtained after 4 rounds of compound design, synthesis and SAR studies, which had an EC₅₀ of 0.021 ± 0.002 μM in dual Fluorescence Resonance Energy Transfer (dual-FRET) assay and an EC₅₀ of 0.021 ± 0.002 μM in mouse Th17 cell differentiation assay. It indicated that compound 28 had excellent RORγt agonistic activity and was expected to be developed as a new type of small molecule drug for cancer immunotherapy. The molecular dynamic simulation revealed that the agonist 28 formed a strong HYF triplet intramolecular interaction to stabilize H12, which helped RORγt to form the protein-binding site and therefore made the receptor ready to recruit coactivator. When the inverse agonist s27 bound with RORγt, the steric hindrance between s27 and H479 caused the destruction of the HYF triplet, leading to the collapse of H12, thus the transcription function of RORγt was interrupted due to the failure of recruiting a coactivator molecule. The triplet HYF in RORγt and the rigidity of 28 and s27 were identified to be the structural determinants for the functional switch of RORγt.

New approaches towards the synthesis of 1,2,3,4-tetrahydro isoquinoline-3-phosphonic acid (TicP)

Two new strategies for the efficient synthesis of racemic 1,2,3,4-tetrahydroisoquinoline-3-phosphonic acid (Tic^P) (±)-2 have been developed. The first strategy involves the electron-transfer reduction of the easily obtained α,β-dehydro phosphonophenylalanine followed by a Pictet-Spengler cyclization. The second strategy involves a radical decarboxylation-phosphorylation reaction on 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic). In both strategies, the highly electrophilic N-acyliminium ion is formed as a key intermediate, and the target compound is obtained in good yield using mild reaction conditions and readily available starting materials, complementing existing methodologies and contributing to the easy accessibility of (±)-2 for further research.

Synthesis and Evaluation of a Novel Series of 2,7-Substituted-6-tetrazolyl-1,2,3,4-tetrahydroisoquinoline Derivatives as Selective Peroxisome Proliferator-Activated Receptor γ Partial Agonists

A novel series of 7-substituted-2-[3-(2-furyl)acryloyl]-6-tetrazolyl-1,2,3,4-tetrahydroisoquinoline derivatives were synthesized to clarify structure-activity relationships for peroxisome proliferator-activated receptor γ (PPARγ) partial agonist activity and identify more efficacious PPARγ partial agonists with minor adverse effects. Among the derivatives synthesized, compound 26v with a 2-(2,5-dihydropyrrol-1-yl)-5-methyloxazol-4-ylmethoxy group at the 7-position of the tetrahydroisoquinoline structure exhibited stronger PPARγ agonist and antagonist activities (EC50 = 6 nM and IC50 = 101 nM) than previously reported values for compound 1 (EC50 = 13 nM and IC50 = 512 nM). Compound 26v had very weak protein tyrosine phosphatase 1B (PTP1B) inhibitory activity and showed higher oral absorption (Cmax = 11.4 µg/mL and area under the curve (AUC) = 134.7 µg·h/mL) than compound 1 (Cmax = 7.0 µg/mL and AUC = 63.9 µg·h/mL) in male Sprague-Dawley (SD) rats. A computational docking calculation revealed that 26v bound to PPARγ in a similar manner to that of compound 1. In male Zucker fatty rats, 26v and pioglitazone at 10 and 30 mg/kg for 4 weeks similarly reduced plasma triglyceride levels, increased plasma adiponectin levels, and attenuated increases in plasma glucose levels in the oral glucose tolerance test, while only pioglitazone decreased hematocrit values. In conclusion, 6-tetrazolyl-1,2,3,4-tetrahydroisoquinoline derivatives provide a novel scaffold for selective PPARγ partial agonists and 26v attenuates insulin resistance possibly by adiponectin enhancements with minor adverse effects.

Design and Synthesis of Tetrahydroisoquinoline Derivatives as Anti-Angiogenesis and Anti-Cancer Agents

AIM

The aim of our research work is the synthesis of tetrahydroisoquinoline derivatives as anti-Angiogenesis and anti-cancer agents.

BACKGROUND

Cancer is the second leading cause of deaths in the United States. The current recovery rate from the advanced treatment for the cancer is excessively low. Therefore, the identification of novel, potent, and less toxic anticancer agents remains a top priority.

OBJECTIVE

To evaluate anti-angiogenesis and anticancer activities of THIQs on different colorectal cancer cell lines (CRC) viz., Colo320, DLD-1, HCT116, SNU-C1, SW480, and GSK3b in pre-treated viability HCT116. and to carry out molecular docking studies of THIQs.

METHODS

Twenty synthesized THIQs were screened in the Eli Lilly's Open Innovation Drug Discovery Program and selected twelve compounds for in vitro primary screening in the KRas (Kirsten rat sarcoma)-Wnt SL (Synthetic Lethal) in the basal viability of different colon cancer cell lines. Docking studies of the active THIQs were also performed in our laboratory, targeting the active sites of KRas and VEGF receptors.

RESULTS

Compound GM-3-18 was found to possess significant activities for KRas inhibition, with IC50 values in the range of 0.9 μM to 10.7 μM, for all colon cancer cell lines. Compound GM-3-121 showed potent anti-angiogenesis activity with IC50 = 1.72 μM. Molecular docking studies showed that the carbonyl oxygen atoms of GM-3-18 and GM-3-121 showed hydrogen bonding interactions with the hydrogen of - OH groups of THR 74 (A).

CONCLUSION

The results indicated that all the compounds showed moderate to high activity for KRas inhibition. The THIQs bearing the chloro group at the 4-position of the phenyl ring (GM-3-18) exhibited significant KRas inhibition against all colon cancer cell lines.

6,7-Dimethoxy-2-phenethyl-1,2,3,4-tetrahydroisoquinoline amides and corresponding ester isosteres as multidrug resistance reversers

Aiming to deepen the structure-activity relationships of the two P-glycoprotein (P-gp) modulators elacridar and tariquidar, a new series of amide and ester derivatives carrying a 6,7-dimethoxy-2-phenethyl-1,2,3,4-tetrahydroisoquinoline scaffold linked to different methoxy-substituted aryl moieties were synthesised. The obtained compounds were evaluated for their P-gp interaction profile and selectivity towards the two other ABC transporters, multidrug-resistance-associated protein-1 and breast cancer resistance protein, showing to be very active and selective versus P-gp. Two amide derivatives, displaying the best P-gp activity, were tested in co-administration with the antineoplastic drug doxorubicin in different cancer cell lines, showing a significant sensitising activity towards doxorubicin. The investigation on the chemical stability of the derivatives towards spontaneous or enzymatic hydrolysis, showed that amides are stable in both models while some ester compounds were hydrolysed in human plasma. This study allowed us to identify two chemosensitizers that behave as non-transported substrates and are characterised by different selectivity profiles.

Chemistry of Renieramycins. Part 19: Semi-Syntheses of 22-O-Amino Ester and Hydroquinone 5-O-Amino Ester Derivatives of Renieramycin M and Their Cytotoxicity against Non-Small-Cell Lung Cancer Cell Lines

Two new series of synthetic renieramycins including 22-O-amino ester and hydroquinone 5-O-amino ester derivatives of renieramycin M were semi-synthesized and evaluated for their cytotoxicity against the metastatic non-small-cell lung cancer H292 and H460 cell lines. Interestingly, the series of 22-O-amino ester derivatives displayed a potent cytotoxic activity greater than the hydroquinone derivatives. The most cytotoxic derivative of the series was the 22-O-(N-Boc-l-glycine) ester of renieramycin M (5a: IC₅₀ 3.56 nM), which showed 7-fold higher potency than renieramycin M (IC₅₀ 24.56 nM) and 61-fold more than jorunnamycin A (IC₅₀ 217.43 nM) against H292 cells. In addition, 5a exhibited a significantly higher cytotoxic activity than doxorubicin (ca. 100 times). The new semi-synthetic renieramycin derivatives will be further studied and developed as potential cytotoxic agents for non-small-cell lung cancer treatment.

Concise total syntheses of (-)-jorunnamycin A and (-)-jorumycin enabled by asymmetric catalysis

The bis-tetrahydroisoquinoline (bis-THIQ) natural products have been studied intensively over the past four decades for their exceptionally potent anticancer activity, in addition to strong Gram-positive and Gram-negative antibiotic character. Synthetic strategies toward these complex polycyclic compounds have relied heavily on electrophilic aromatic chemistry, such as the Pictet-Spengler reaction, that mimics their biosynthetic pathways. Herein, we report an approach to two bis-THIQ natural products, jorunnamycin A and jorumycin, that instead harnesses the power of modern transition-metal catalysis for the three major bond-forming events and proceeds with high efficiency (15 and 16 steps, respectively). By breaking from biomimicry, this strategy allows for the preparation of a more diverse set of nonnatural analogs.

Synthesis of 1-(para-methoxyphenyl)tetrazolyl-Substituted 1,2,3,4-Tetrahydroisoquinolines and Their Transformations Involving Activated Alkynes

1-(p-Methoxyphenyl)tetrazolyl-substituted 6,7-dimethoxy(6,7-methylenedioxy)-1,2,3,4-tetrahydroisoquinolines formed tetrazolyl-substituted azocines in high yields by using activated alkynes. Unsubstituted at 6,7,8-aromatic fragment 1-tetrazolylisoquinoline interacted in several pathways forming tetrazolyl-substituted azocines, 1-tetrazolyl-1-R-vinylisoquinolines and 3-azaspiro[5.5]undeca-1,7,9-triene.

Application of the Asymmetric Pictet-Spengler Reaction in the Total Synthesis of Natural Products and Relevant Biologically Active Compounds

Tetrahydroisoquinolines are the framework of numerous natural products predominantly alkaloids, an important and one of the most wide spread families of naturally occurring compounds in the plant kingdom. Tetrahydroisoquinolines are commonly constructed through an old reaction, the so-called Pictet−Spengler Reaction (PSR). In this reaction, a β-aryl ethylamine undergoes an acid mediated condensation with a suitable aldehyde or ketone, followed by ring closure. In this review, we aim to highlight the applications of the asymmetric variant of this old name reaction in the total synthesis of natural products, chiefly, alkaloids, which exhibit significant biological properties.

Synthesis and Structure-Activity Relationships of a Series of Aporphine Derivatives with Antiarrhythmic Activities and Acute Toxicity

Some aporphine alkaloids, such as crebanine, were found to present arrhythmic activity and also higher toxicity. A series of derivatives were synthesized by using three kinds of aporphine alkaloids (crebanine, isocorydine, and stephanine) as lead compounds. Chemical methods, including ring-opening reaction, bromination, methylation, acetylation, quaternization, and dehydrogenation, were adopted. Nineteen target derivatives were evaluated for their antiarrhythmic potential in the mouse model of ventricular fibrillation (VF), induced by CHCl₃, and five of the derivatives were investigated further in the rat model of arrhythmia, induced by BaCl₂. Meanwhile, preliminary structure-activity/toxicity relationship analyses were carried out. Significantly, N-acetamidesecocrebanine (1d), three bromo-substituted products of crebanine (2a, 2b, 2c), N-methylcrebanine (2d), and dehydrostephanine (4a) displayed antiarrhythmic effects in the CHCl₃-induced model. Among them, 7.5 mg/kg of 2b was able to significantly reduce the incidence of VF induced by CHCl₃ (p < 0.05), increase the number of rats that resumed sinus rhythm from arrhythmia, induced by BaCl₂ (p < 0.01), and the number of rats that maintained sinus rhythm for more than 20 min (p < 0.01). Therefore, 2b showed remarkably higher antiarrhythmic activity and a lower toxicity (LD50 = 59.62 mg/kg, mice), simultaneously, indicating that 2b could be considered as a promising candidate in the treatment of arrhythmia. Structural-activity analysis suggested that variationsin antiarrhythmic efficacy and toxicity of aporphines were related to the C-1,C-2-methylenedioxy group on ring A, restricted ring B structural conformation, N-quaternization of ring B, levoduction of 6a in ring C, and the 8-, 9-, 10-methoxy groups on ring D on the skeleton.

Synthesis and evaluation of the structural elements in alkylated tetrahydroisoquinolines for binding to CNS receptors

Diseases of the CNS are often complex and involve multiple receptor systems and thus, the treatment options for these diseases must focus on targeting the multiple receptors implicated in the various disorders. Schizophrenia and depression are examples of such diseases and their pharmacotherapy thus depends on agents which target multiple receptors including the dopamine, serotonin and even cholinergic receptors at the same time. In our previous campaign to find multi-receptor ligands, we have identified the benzothiazole 1a as an initial lead molecule. In the current work, we have expanded the structure affinity relationship (SAFIR) of 1a resulting in the identification of a partially restrained butyrophenone 3j as a potent and selective dual 5-HT1A and 5-HT7 receptor ligand. It is expected that compound 3j may serve as a new lead for further development in our search for newer and novel ligands with the potential to treat diseases of CNS origin.

Studies relating to the synthesis, enzymatic reduction and cytotoxicity of a series of nitroaromatic prodrugs

A series of N-nitroarylated-3-chloromethyl-1,2,3,4-tetrahydroisoquinoline derivatives, several of which also possessed a trifluoromethyl substituent, were prepared and assessed as potential nitroaromatic prodrugs. The enzymatic reduction of these compounds and their cytotoxicities were studied. The compounds were cytotoxic, but this is probably not related to their enzymatic reduction.

Chemistry of Renieramycins. 15. Synthesis of 22-O-Ester Derivatives of Jorunnamycin A and Their Cytotoxicity against Non-Small-Cell Lung Cancer Cells

Eighteen 22-O-ester derivatives of jorunnamycin A (2) were prepared via 2, and their cytotoxicity against human non-small-cell lung cancer (NSCLC) cells was evaluated. Preliminary study of the structure-cytotoxicity relationship revealed that the ester part containing a nitrogen-heterocyclic ring elevated the cytotoxicity of the 22-O-ester derivatives. Among them, 22-O-(4-pyridinecarbonyl) ester 6a is the most potent compound (IC50 1.1 and 1.6 nM), exhibiting 21-fold and 5-fold increases in cytotoxicity against the H292 and H460 NSCLC cell lines, respectively, relative to renieramycin M (1), the major cytotoxic bistetrahydroisoquinolinequinone alkaloid of the Thai blue sponge Xestospongia sp.

Design, synthesis, and pharmacological evaluation of JDTic analogs to examine the significance of replacement of the 3-hydroxyphenyl group with pyridine or thiophene bioisosteres

The potent and selective KOR antagonist JDTic was derived from the N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine class of pure opioid antagonists. In previous studies we reported that compounds that did not have a hydroxyl on the 3-hydroxyphenyl group and did not have methyl groups at the 3- and 4-position of the piperidine ring were still potent and selective KOR antagonists. In this study we report JDTic analogs 2, 3a-b, 4a-b, and 5, where the 3-hydroxyphenyl ring has been replaced by a 2-, 3-, or 4-pyridyl or 3-thienyl group and do not have the 3-methyl or 3,4-dimethyl groups, remain potent and selective KOR antagonists. Of these, (3R)-7-hydroxy-N-(1S)-2-methyl-[4-methyl-4-pyridine-3-yl-carboxamide (3b) had the best overall binding potency and selectivity in a [(35)S]GTPγS functional assay, with a Ke=0.18nM at the KOR and 273- and 16,700-fold selectivity for the KOR relative to the MOR and DOR, respectively. Calculated physiochemical properties for 3b suggest that it will cross the blood-brain barrier.

[Design, synthesis and anti-platelet aggregation activities of ligustrazine-tetrahydroisoquinoline derivatives]

Abstract: Fifteen novel ligustrazine-tetrahydroisoquinoline derivatives were designed and synthesized according to the association principle of pharmaceutical chemistry. The structures were identified by IR, NMR and ESI-MS. The inhibitory activities of platelet aggregation induced by ADP and AA have been measured by Bron method. Preliminary pharmacological results showed that compounds 7g, 7h and 7n had potent inhibitory activity against platelet aggregation induced by AA, and the compound 7o showed significant inhibitory activity against platelet aggregation induced by ADP.

Efficient asymmetric synthesis of 1-cyano-tetrahydroisoquinolines from lipase dual activity and opposite enantioselectivities in α-Aminonitrile resolution

Dual promiscuous racemization/amidation activities of lipases leading to efficient dynamic kinetic resolution protocols of racemic α-aminonitrile compounds are described. α-Amidonitrile products of high enantiomeric purity could be formed in high yields. Several lipases from different sources were shown to exhibit the dual catalytic activities, where opposite enantioselectivities could be recorded for certain substrates.

Stereoselective and regioselective intramolecular Friedel-Crafts reaction of aziridinium ions for synthesis of 4-substituted tetrahydroisoquinolines

Optically active 4-substituted tetrahydroisoquinolines were synthesized via intramolecular Friedel-Crafts (FC) reactions of aziridinium ions in a highly regio- and stereoselective manner. Control experiments suggest the formation and ring-opening of aziridinium ions as the key intermediates in the Lewis acid catalyzed FC reactions.

Asymmetric total synthesis of (-)-jorunnamycins A and C and (-)-jorumycin from L-tyrosine

Three renieramycin-type antitumor alkaloids, (-)-jorunnamycins A (1) and C (2) and (-)-jorumycin (3), have been synthesized by a new convergent approach, which features a highly regio- and stereoselective Pictet-Spengler cyclization to couple the isoquinoline and the trisubstituted phenylalaninol partners. This synthetic strategy opens an economical access to these important antitumor alkaloids with high yields: (-)-jorunnamycin A, as a common precursor to other renieramycin-type alkaloids and their analogues, is obtained with 18.1% overall yield from l-tyrosine.

Asymmetric cross-dehydrogenative coupling enabled by the design and application of chiral triazole-containing phosphoric acids

This report describes the development of an enantioselective C-N bond-forming reaction to produce 1,2,3,4-tetrahydroisoquinoline-derived cyclic aminals catalyzed by chiral phosphate anions. Central to the success of this goal was the design of a library of 3,3'-triazolyl BINOL-derived phosphoric acids capable of forming attractive hydrogen-bonding interactions with the peptide-like substrate. We envision this work will offer an alternative to the conventional strategy of increasing catalyst steric bulk to improve enantioselectivity with BINOL-derived phosphoric acids.

C-H bond functionalization via hydride transfer: formation of α-arylated piperidines and 1,2,3,4-tetrahydroisoquinolines via stereoselective intramolecular amination of benzylic C-H bonds

We here report a study of the intramolecular amination of sp(3) C-H bonds via the hydride transfer cyclization of N-tosylimines (HT-amination). In this transformation, 5-aryl aldehydes are subjected to N-toluenesulfonamide in the presence of BF(3)·OEt(2) to effect imine formation and HT-cyclization, leading to 2-arylpiperidines and 3-aryl-1,2,3,4-tetrahydroisoquinolines in a one-pot procedure. We examined the reactivity of a range of aldehyde substrates as a function of their conformational flexibility. Substrates of higher conformational rigidity were more reactive, giving higher yields of the desired products. However, a single substituent on the alkyl chain linking the N-tosylimine and the benzylic sp(3) C-H bonds was sufficient for HT-cyclization to occur. In addition, an examination of various arenes revealed that the electronic character of the hydridic C-H bonds dramatically affects the efficiency of the reaction. We also found that this transformation is highly stereoselective; 2-substituted aldehydes yield cis-2,5-disubstituted piperidines, while 3-substituted aldehydes afford trans-2,4-disubstituted piperidines. The stereoselectivity is a consequence of thermodynamic control. The pseudoallylic strain between the arene and tosyl group on the piperidine ring is proposed to rationalize the greater stability of the isomer with the aryl ring in the axial position. This preferential placement of the arene is proposed to affect the observed stereoselectivity.

Synthesis and contractile activity of substituted 1,2,3,4-tetrahydroisoquinolines

A series of different 1-monosubstituted and 1,1-disubstituted 1,2,3,4-tetrahydro-isoquinolines was synthesized in high yields from different ketoamides. We have developed a convenient method for the synthesis of disubstituted derivatives by interaction of ketoamides with organomagnesium compounds, followed by cyclization in the presence of catalytic amounts of p-toluenesulfonic acid (PTSA). A number of substituents at the C-1 in the isoquinoline skeleton were introduced varying either carboxylic acid or organomagnesium compound. Some of the obtained 1,1-dialkyl-1,2,3,4-tetrahydro-isoquinolines possess contractile activity against guinea pig's gastric smooth muscle preparations.

[Design, synthesis, and PPARalpha/gamma agonistic activity of novel tetrahydroisoquinoline derivatives]

A series of tetrahydroisoquinoline derivatives were prepared and their peroxisome proliferator-activated receptor (PPAR) alpha/gamma agonistic activities were evaluated to obtain more potent PPAR agonist. All of them were new compounds, and their structures were confirmed by 1H NMR and HR-MS. Three compounds exhibited higher agonistic activities of PPARgamma than that of the comparison, six compounds exhibited higher agonistic activities of PPARalpha than that of the comparison, and compound 8a was discovered as a highly potent PPARalpha/gamma agonist that is much more active than that of WY14643 and rosiglitazone. The development of potent PPAR agonists may offer a new choice for the treatment of diabetes.

Radiosynthesis and in vivo evaluation of [(11)C]MC80 for P-glycoprotein imaging

P-glycoprotein (P-gp) is an ATP-dependent efflux pump protecting the body against xenobiotics. The in vitro characterized modulator 6,7-dimethoxy-2-(6-methoxy-naphthalen-2-ylmethyl)-1,2,3,4-tetrahydroisoquinoline (MC80) of the P-gp pump was labelled with (11)C and evaluated in vivo for its potential to image P-gp function and expression. Radiochemical pure (>98%) [(11)C]MC80 was obtained within 25 min starting from [(11)C]methyl iodide with radiochemical yield of 26%. Biodistribution studies in FVB mice demonstrated a high baseline brain uptake (7.66 + or - 1.38%ID/g at 1 min pi). Cerebral uptake was increased in mdr1a knock-out mice as well as after CsA pretreatment. Pre-administration of an excess of non-radioactive MC80 caused a reduced uptake in several target organs including brain, pancreas and intestines. The results indicate that [(11)C]MC80 kinetics are modulated by P-gp. Reversed phase-HPLC analysis of brain revealed an excellent metabolic profile (>90% intact [(11)C]MC80).

Diphosphine-catalyzed mixed double-Michael reaction: a unified synthesis of indolines, dihydropyrrolopyridines, benzimidazolines, tetrahydroquinolines, tetrahydroisoquinolines, dihydrobenzo-1,4-oxazines, and dihydrobenzo-3,1-oxazines

Seven different types of benzannulated N-heterocycles-indolines, dihydropyrrolopyridines, benzimidazolines, dihydrobenzo-3,1-oxazines, benzomorpholines, tetrahydroquinolines, and tetrahydroisoquinolines-can be obtained from simple dinucleophiles and electron-deficient acetylenes in one synthetic step. This powerful methodology was made possible through the use of diphenylphosphinopropane (DPPP) as the catalyst, with acetic acid and sodium acetate used as additives in some cases. The benzannulated N-heterocycles were isolated in excellent yields under mild metal-free conditions; they were purified without the need for aqueous workups.

Pictet-Spengler reactions for the synthesis of pharmaceutically relevant heterocycles

The synthesis of biologically active heterocyclic scaffolds is one of the significant challenges of modern synthetic chemistry. The Pictet-Spengler (PS) reaction, known for approximately a century, remains a particularly popular cyclization method. This review describes recent applications of the PS reaction in the total synthesis of alkaloids and biologically active analogs of tetrahydroisoquinoline and tetrahydro-β-carboline. The utility of PS cyclization in the synthesis of a range of heterocyclic scaffolds is also described.

[Bioactivity diversity and functional mechanism of tetrahydroisoquinoline alkaloids]

Tetrahydroisoquinoline alkaloids distributed widely in the nature and some have a broad application in clinic. More attention has been paid in recent years on this type of alkaloid, owing to the diverse range of biological activities exhibited by these alkaloids and the discovery of new functional mechanisms and molecular targets underlying these activities. This article summarized the recent advances in the biological activities and functional mechanism of tetrahydroisoquinoline, which included the activities such as antitumor, antibiotic, antivirus, anti-inflammatory, anticoagulation, bronchodilation, and the action on central nervous system, with the purpose of providing some ideas in the study of biological activity of this type of alkaloid and in the search for lead-compound and rational drug design.

Cross-cyclotrimerization with two nitriles as a synthetic pathway to unsymmetrically 3,3'-disubstituted bis(tetrahydroisoquinolines)

Microwave assisted CpCo(CO)(2) catalyzed cross-cyclotrimerizations of 1,7,9,15-hexadecatetrayne with two different nitriles to give unsymmetrically substituted bis(tetrahydroisoquinolines) was studied. The reaction proceeded with a range of alkyl and aryl nitriles with reasonable isolated yields.

Synthesis of 5,5-disubstituted butenolides based on a Pd-catalyzed gamma-arylation strategy

Methods for the construction of quaternary carbon centers are of great interest to synthetic chemists due to their presence in natural products. Development of the Pd-catalyzed arylation of butenolides with high selectivity for the gamma-position allows for a facile construction of quaternary centers. The preparation of a wide variety of gamma-aryl butenolides containing a number of functional groups is outlined. An application of this chemistry for a one-pot synthesis of a tricyclic tetrahydroisoquinolinone is demonstrated.

Chemistry of renieramycins. Part 8: synthesis and cytotoxicity evaluation of renieramycin M-jorunnamycin A analogues

Twenty-four ester analogues of renieramycin M (1m) were prepared from jorunnamycin A (3a), which was easily transformed from marine natural 1m in three steps. These analogues, along with 1m itself, cyanojorumycin (2b), and jorunnamycins A (3a) and C (3b), were evaluated in vitro for cytotoxicity by measuring IC(50) values through the 3-(4,5-dimethyltriazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay using human HCT116 colon carcinoma and MDA-MB-435 breast carcinoma cell lines. Nitrogen-containing heterocyclic ester derivatives 9a-f showed similar in vitro cytotoxicity to 1m, whereas the other derivatives were slightly less cytotoxic than 1m. 2'-Pyridinecarboxylic acid ester derivative (9c) exhibited a threefold increase in cytotoxicity relative to 1m.

Synthetic studies on Et-743. Assembly of the pentacyclic core and a formal total synthesis

A formal total synthesis of the potent anticancer agent Et-743 is described. The tetrahydroisoquinoline core is stereoselectively constructed using a novel radical cyclization of a glyoxalimine. Further elaboration of this core rapidly accessed the pentacyclic core of Et-743, but a mixture of regiosisomers was obtained in the key Pictet-Spengler ring closure. A known advanced intermediate in the synthesis of Et-743 was intercepted, constituting a formal synthesis of the molecule.

Design and Synthesis of Indole and Tetrahydroisoquinoline Hydantoin Derivatives as Human Chymase Inhibitors

The synthesis of new potential inhibitors of human chymase is described. Treatment of dihydroimidazo[1,5-a]indole and [1,5-b]isoquinoline-dione with thioaryl followed by oxidation gave the N-arylsulfonylmethyl of polycyclic hydantoin derivatives 3, 5 and 6.

Synthesis and cytotoxic evaluation of some cribrostatin-ecteinascidin analogues

Analogues of cribrostatin IV ( 1) and the potent antineoplastic agent ecteinascidin 743 ( 2) have been synthesized. The cytotoxic activity of these compounds ( 5, 14, 20) has been determined, and the cyanoamine-cribrostatin analogue ( 14) exhibits a 20-fold improvement with regard to the natural product 1.

Synthesis of 4,5,6,7-tetrahydrothieno[3,2-c]pyridines and comparison with their isosteric 1,2,3,4-tetrahydroisoquinolines as inhibitors of phenylethanolamine N-methyltransferase

A series of substituted 4,5,6,7-tetrahydrothieno[3,2-c]pyridines (THTPs) was synthesized and evaluated for their human phenylethanolamine N-methyltransferase (hPNMT) inhibitory potency and affinity for the alpha(2)-adrenoceptor. The THTP nucleus was suggested as an isosteric replacement for the 1,2,3,4-tetrahydroisoquinoline (THIQ) ring system on the basis that 3-thienylmethylamine (18) was more potent as an inhibitor of hPNMT and more selective toward the alpha(2)-adrenoceptor than benzylamine (15). Although the isosterism was confirmed, with similar influence of functional groups and chirality in both systems on hPNMT inhibitory potency and selectivity, the THTP compounds proved, in general, to be less potent as inhibitors of hPNMT than their THIQ counterparts, with the drop in potency being primarily attributed to the electronic properties of the thiophene ring. A hypothesis for the reduced hPNMT inhibitory potency of these compounds has been formed on the basis of molecular modeling and docking studies using the X-ray crystal structures of hPNMT co-crystallized with THIQ-type inhibitors and S-adenosyl-L-homocysteine as a template.

Solid-Phase Synthesis and Insights into Structure−Activity Relationships of Safinamide Analogues as Potent and Selective Inhibitors of Type B Monoamine Oxidase

Safinamide, (S)-N2-{4-[(3-fluorobenzyl)oxy]benzyl}alaninamide methanesulfonate, which is in phase III clinical trials as an anti-Parkinson drug, and a library of alkanamidic analogues were prepared through an expeditious solid-phase synthesis and evaluated for their monoamine oxidase B (MAO-B) and monoamine oxidase A (MAO-A) inhibitory activity and selectivity. (S)-3-Chlorobenzyloxyalaninamide (8) and (S)-3-chlorobenzyloxyserinamide (13) derivatives proved to be more potent MAO-B inhibitors than safinamide (IC50 = 33 and 43 nM, respectively, vs 98 nM) but with a lower MAO-B selectivity (SI = 3455 and 1967, respectively, vs 5918). The highest MAO-B inhibitory potency (IC50 = 17 nM) and a good selectivity (SI = 2941) were displayed by (R)-21, a tetrahydroisoquinoline analogue of safinamide. Structure-affinity relationships and docking simulations pointed out strong negative steric effects of alpha-aminoamide side chains and para substituents of the benzyloxy groups and favorable hydrophobic interactions of meta substituents. The significantly diverse MAO-B affinities of a number of R and S alpha-aminoamide enantiomers, including the two rigid analogues (21) of safinamide, indicated likely enantioselective interactions at the enzymatic binding sites.

A new opioid designed multiple ligand derived from the micro opioid agonist endomorphin-2 and the delta opioid antagonist pharmacophore Dmt-Tic

Opioid compounds with mixed micro agonist/delta antagonist properties could be used as analgesics with low propensity to induce tolerance and dependence. Here we report the synthesis of a new designed multiple ligand deriving from the micro selective agonist endomorphin-2 and the delta selective antagonist pharmacophore Dmt-Tic. As predicted, the resulting bivalent ligand showed a micro agonist/delta antagonist profile deriving from the corresponding activities of each pharmacophore.

Dual serotonin transporter inhibitor/histamine H3 antagonists: development of rigidified H3 pharmacophores

A series of tetrahydroisoquinolines acting as dual serotonin transporter inhibitor/histamine H(3) antagonists is described. The introduction of polar aromatic spacers as part of the histamine H(3) pharmacophore was explored. A convergent synthesis of the final products allowing late stage introduction of the aromatic side chain was developed. In vitro and in vivo data are discussed.

Synthesis, resolution, stereochemistry, and molecular modeling of (R)- and (S)-2-acetyl-1-(4′-chlorophenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline AMPAR antagonists

Recently we identified (R,S)-2-acetyl-1-(4'-chlorophenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (6) as a potent non-competitive AMPA receptor antagonist able to prevent epileptic seizures. We report here the optimized synthesis of compound 6, its resolution by chiral preparative HPLC, and the absolute configuration of (R)-enantiomer established by X-ray diffractometry. The biological tests of the single enantiomers revealed that higher anticonvulsant and antagonistic effects reside in (R)-enantiomer as also suggested by molecular modeling studies.

Solid-phase synthesis of tetrahydro-beta-carbolines and tetrahydroisoquinolines by stereoselective intramolecular N-carbamyliminium Pictet-Spengler reactions

A solid-phase method for the synthesis of tri-, tetra-, and pentacyclic compounds containing tetrahydro-beta-carboline, tetrahydroisoquinoline or analogous scaffolds is presented. The reaction proceeds with high stereoselectivity through an intermediate N-carbamyliminium ion that exclusively converts into Pictet-Spengler-type products with a variety of C-nucleophiles. Amino aldehydes masked with 3-Boc-(1,3)-oxazinane (Box) have been synthesized from amino acids, amino alcohols, or 2-nitro benzaldehydes. The amino moiety of these masked aldehydes has been converted into pentafluorophenyl carbamate to serve as a urea precursor. The building blocks were incorporated at the N-terminal of a resin-supported dipeptide through urea formation. Subsequent treatment with acid liberated the aldehyde quantitatively. A penultimate tryptophan residue gave rise, under the acetic conditions, to a spontaneous intramolecular Pictet-Spengler reaction with the liberated aldehyde. The reaction proceeded with a high degree of stereoselectivity affording tetrahydro-beta-carbolines with a de (de=diastereomeric excess) above 95 % and purity in the range of 90-99 %. This reaction has been extended to a range of other aromatic C-nucleophiles, including substituted indoles, benzenes, pyrene, furan, thiophenes, and benzothiophene with comparable stereoselectivity and purity. Prolonged exposure of the benzaldehyde-derived Pictet-Spengler products to strong acid and air lead to quantitative auto-oxidation which yielded compounds with a 3,4-dihydro-beta-carboline, a 3,4-dihydroisoquinoline, or a similar core structure.

Synthesis and inhibition of cancer cell proliferation of (1,3′)-bis-tetrahydroisoquinolines and piperazine systems

Some (1,3')-bis-tetrahydroisoquinolines were reported as scaffold intermediates for the synthesis of pentacyclic piperazine core alkaloids and their cytotoxicity against cancerous cell lines was evaluated. The NMR and X-ray structural assignments revealed an anti C3-C11 backbone stereochemistry of piperazine structures. Inhibition of cancer cell proliferation of (1,3')-bis-tetrahydroisoquinoline scaffolds and pentacyclic piperazine systems was assessed against three human cancer cell lines (K562 myelogenous leukemia, A549 lung carcinoma, MCF-7 breast adenocarcinoma) and both mouse tumor cell lines of blood (P388) and lymphocytic (L1210) leukemia with considerable activity against the latter. The cell cycle analysis was also studied by flow cytometry measurement on K562 cell line.

Pyrrolidino-tetrahydroisoquinolines as potent dual H3 antagonist and serotonin transporter inhibitors

A series of novel and potent pyrrolidino-tetrahydroisoquinolines with dual histamine H(3) antagonist/serotonin transporter inhibitor activity is described. A highly regio- and diastereoselective synthesis of the pyrrolidino-tetrahydroisoquinoline core involving acid mediated ring-closure of an acetophenone intermediate followed by reduction with NaCNBH(3) was developed. In vitro and in vivo data are discussed.

An Easy-To-Use, Regioselective, and Robust Bis(amidate) Titanium Hydroamination Precatalyst: Mechanistic and Synthetic Investigations toward the Preparation of Tetrahydroisoquinolines and Benzoquinolizine Alkaloids

Amidate-supported titanium amido complexes are efficient and regioselective precatalysts for intermolecular hydroamination of terminal alkynes with primary amines. The synthesis and characterization of the first bis(amidate)-supported titanium-imido complex is reported. Its role as the active catalytic species is suggested in the course of product distribution studies using deuterated substrates. The bis(amidate)-supported precatalysts exhibit good functional-group tolerance, even performing hydroaminations in the presence of ester and amide groups. This functional-group tolerance was exploited in the synthesis of a variety of 1-substituted tetrahydroisoquinoline alkaloids and a one-pot hydroaminative procedure for the high yielding preparation of the benzo[a]quinolizine skeleton.

Novel tetrahydroisoquinolines are histamine H3 antagonists and serotonin reuptake inhibitors

A series of novel 4-aryl-1,2,3,4-tetrahydroisoquinoline-based histamine H(3) ligands that also have serotonin reuptake transporter inhibitor activity is described. The synthesis, in vitro biological data, and select pharmacokinetic data for these novel compounds are discussed.

Synthesis and Radioligand Binding Studies of Methoxylated 1,2,3,4-Tetrahydroisoquinolinium Derivatives as Ligands of the Apamin-Sensitive Ca2+-Activated K+ Channels

Several methoxylated 1,2,3,4-tetrahydroisoquinoliniums derived from N-methyl-laudanosine and N-methyl-noscapine were synthesized and evaluated for their affinity for apamin-sensitive binding sites. The quaternary ammonium derivatives have a higher affinity with regard to the tertiary amines. 6,7-Dimethoxy analogues possess a higher affinity than the 6,8- and 7,8-dimethoxy isomers. A 3,4-dimethoxybenzyl or a 2-naphthylmethyl moiety in C-1 position are more favorable than a 3,4-dimethoxyphenethyl group. Smaller groups such as propyl or isobutyl are unfavorable. In 6,7-dimethoxy analogues, increasing the size and lipophilicity with a naphthyl group in the C-1 position leads to a slight increase of affinity, while the same group in the 6,7,8-trimethoxy series is less favorable. The 6,7,8-trimethoxy derivative 3f is the first tertiary amine in the series to possess an affinity close to that of N-methyl-laudanosine and N-methyl-noscapine. Moreover, electrophysiological studies show that the most effective compound 4f blocks the apamin-sensitive afterhyperpolarization in rat dopaminergic neurons.

Novel potent anticonvulsant agent containing a tetrahydroisoquinoline skeleton

In our studies on the development of new anticonvulsants, we planned the synthesis of N-substituted 1,2,3,4-tetrahydroisoquinolines to explore the structure-activity relationships. All derivatives were evaluated against audiogenic seizures in DBA/2 mice, and the 1-(4'-bromophenyl)-6,7-dimethoxy-2-(piperidin-1-ylacetyl) derivative (26) showed the highest activity with a potency comparable to that of talampanel, the only noncompetitive alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) antagonist in clinical trials as an anticonvulsant agent. Electrophysiological experiments indicated that 26 acts as noncompetitive AMPA receptor modulator.

New opioid designed multiple ligand from Dmt-Tic and morphinan pharmacophores

Here, we report the synthesis of a designed multi-pharmacophore ligand derived from the linkage of a delta selective peptide antagonist (Dmt-Tic) and a mu/kappa morphinan agonist butorphan (MCL 101) through a two methylene spacer. The new compound MCL 450 maintains the same characteristics as those the two reference compounds. MCL 450 represents a useful starting point for the synthesis of other multiple opioid ligands endowed with analgesic properties with low tolerance and dependence.

Effect of lysine at C-terminus of the Dmt-Tic opioid pharmacophore

Substitution of Gly with side-chain-protected or unprotected Lys in lead compounds containing the opioid pharmacophore Dmt-Tic [H-Dmt-Tic-Gly-NH-CH(2)-Ph, mu agonist/delta antagonist; H-Dmt-Tic-Gly-NH-Ph, mu agonist/delta agonist; and H-Dmt-Tic-NH-CH(2)-Bid, delta agonist (Bid = 1H-benzimidazole-2-yl)] yielded a new series of compounds endowed with distinct pharmacological activities. Compounds (1-10) included high delta- (Ki(delta) = 0.068-0.64 nM) and mu-opioid affinities (Ki(mu) = 0.13-5.50 nM), with a bioactivity that ranged from mu-opioid agonism {10, H-Dmt-Tic-NH-CH[(CH2)4-NH2]-Bid (IC50 GPI = 39.7 nM)} to a selective mu-opioid antagonist [3, H-Dmt-Tic-Lys-NH-CH2-Ph (pA2(mu) = 7.96)] and a selective delta-opioid antagonist [5, H-Dmt-Tic-Lys(Ac)-NH-Ph (pA2(delta) = 12.0)]. The presence of a Lys linker provides new lead compounds in the formation of opioid peptidomimetics containing the Dmt-Tic pharmacophore with distinct agonist and/or antagonist properties.

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.

A convergent and enantioselective synthesis of (+)-amurensinine via selective C-H and C-C bond insertion reactions

A convergent and enantioselective synthesis of the natural product amurensinine is described. The synthetic strategy takes advantage of mild and selective C-H and C-C bond insertion reactions, in addition to the palladium-catalyzed aerobic oxidative kinetic resolution recently developed in these laboratories.

New 4-Spiroannulated Tetrahydroisoquinolines by a One-Pot Sequential Procedure. Isolation and Characterization of σ-Alkylpalladium Heck Intermediates

A simple and efficient entry to new tetrahydroisoquinolines 4-spiroannulated to a five-membered heterocyclic ring has been achieved starting from secondary N-allylamines and involving sequential 2-iodobenzylation/intramolecular Heck reaction/1,3-dipolar cycloaddition. A variety of Heck cyclization conditions were surveyed. When using Pd(PPh(3))(4) as catalyst, stable sigma-alkylpalladium iodide complexes were isolated and characterizated.