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The formation of N-heterocycles with multiple substituents is important in organic synthesis. Herein, we report a novel method for the construction of functionalized dihydropyridinone rings through the annulation of an amide α-carbon with a tethered alkyne moiety. The reaction of the amide with the alkyne was achieved via O-silyl N,O-ketene acetal formation and silver-mediated addition. Furthermore, the developed method was applied for the total synthesis of phenanthroindolizidine and phenanthroquinolizidine alkaloids. By varying the coupling partners, a concise and collective total synthesis of these alkaloids was achieved.

The phenanthroindolizidine alkaloid (-)-tylophorine has been reported for its significant anticancer activity working through different biomechanistic pathways. The current study aimed to evaluate the anticancer activity of phenanthroindolizidine alkaloids isolated from Tylophora indica. Six phenanthroindolizidine alkaloid (compounds 1–6) in addition to septicine (7), chlorogenic acid (8), and chlorogenic acid methyl ester (9) were isolated from Tylophora indica using different chromatographic techniques including vacuum liquid chromatography (VLC) and preparative high performance liquid chromatography (HPLC). The isolated compounds structures' were determined using various spectro-analytical techniques, i.e., 1H-NMR, 13C-NMR, and mass spectrometry. The isolates' structural stereochemistry and structural geometries were determined with the help of chiroptical techniques together with comparisons with the available standard samples. The in vitro anti-proliferative activity on three different cell lines, MCF-7, HepG2, and HCT-116 were evaluated. Among all the isolated compounds, tylophorinidine (5) was the most active cytotoxic agent with the lowest IC50 values at 6.45, 4.77, and 20.08 μM against MCF-7, HepG2, and HCT-116 cell lines, respectively. The bioactivities were also validated by the in vitro kinase receptors inhibition assay. Compound (5) also exhibited the highest activity with lowest IC50 values (0.6 and 1.3 μM against the Aurora-A and Aurora-B enzymes, respectively), as compared with all the isolated alkaloidal products. The structure activity relationship on the molecular properties, molecular attributes, and bioactivity levels were analyzed, interrelated, and the molecular docking studies on two different receptors, Aurora-A and Aurora-B, were determined, which provided the confirmations of the bioactivity with receptor-ligand geometric disposition, energy requirements, lipophilicity, and detailed the binding pharmacophore involvements responsible for bioactivity elicitations. [ABSTRACT FROM AUTHOR]

The phenanthroindolizidine alkaloid (-)-tylophorine has been reported for its significant anticancer activity working through different biomechanistic pathways. The current study aimed to evaluate the anticancer activity of phenanthroindolizidine alkaloids isolated from Tylophora indica. Six phenanthroindolizidine alkaloid (compounds 1–6) in addition to septicine (7), chlorogenic acid (8), and chlorogenic acid methyl ester (9) were isolated from Tylophora indica using different chromatographic techniques including vacuum liquid chromatography (VLC) and preparative high performance liquid chromatography (HPLC). The isolated compounds structures’ were determined using various spectro-analytical techniques, i.e., 1H-NMR, 13C-NMR, and mass spectrometry. The isolates’ structural stereochemistry and structural geometries were determined with the help of chiroptical techniques together with comparisons with the available standard samples. The in vitro anti-proliferative activity on three different cell lines, MCF-7, HepG2, and HCT-116 were evaluated. Among all the isolated compounds, tylophorinidine (5) was the most active cytotoxic agent with the lowest IC50 values at 6.45, 4.77, and 20.08 μM against MCF-7, HepG2, and HCT-116 cell lines, respectively. The bioactivities were also validated by the in vitro kinase receptors inhibition assay. Compound (5) also exhibited the highest activity with lowest IC50 values (0.6 and 1.3 μM against the Aurora-A and Aurora-B enzymes, respectively), as compared with all the isolated alkaloidal products. The structure activity relationship on the molecular properties, molecular attributes, and bioactivity levels were analyzed, interrelated, and the molecular docking studies on two different receptors, Aurora-A and Aurora-B, were determined, which provided the confirmations of the bioactivity with receptor-ligand geometric disposition, energy requirements, lipophilicity, and detailed the binding pharmacophore involvements responsible for bioactivity elicitations.

Phenanthroindolizidines, such as antofine and tylophorine, are a family of natural alkaloids isolated from different species of Asclepiadaceas. They are characterized by interesting biological activities, such as pronounced cytotoxicity against different human cancerous cell lines, including multidrug-resistant examples. Nonetheless, these derivatives are associated with severe neurotoxicity and loss of in vivo activity due to the highly lipophilic nature of the alkaloids. Here, we describe the development of highly polar prodrugs of antofine and tylophorine as hypoxia-targeted prodrugs. The developed quaternary ammonium salts of phenanthroindolizidines showed high chemical and metabolic stability and are predicted to have no penetration through the blood–brain barrier. The designed prodrugs displayed decreased cytotoxicity when tested under normoxic conditions. However, their cytotoxic activity considerably increased when tested under hypoxic conditions.

Phenanthroindolizidine alkaloids that possess profound anti-proliferative activity and unique mode of action have recently attracted much attention as potential anti-cancer drug candidates. To intensively study the structure-activity-relationship, we designed, synthesized, and evaluated a series of derivatives of 6-desmethylantofine at C-6 position. Most of the derivatives exhibited potent anti-proliferative activity in BEL-7402 and HL60cells. Compound R-12 , the cyanomethyl ether of 6-desmethylantofine, exhibited significant anti-cancer activity and inhibited the proliferation of a panel of 30 cancer cell lines including 2 multi-drug-resistant cell lines with an average IC 50 value of 18.7 nM, which suggests that R-12 is a promising new anti-cancer agent. Our studies suggest that R-12 displayed potent inhibitory effect on cell growth and colony formation, which is associated with delaying S phase progression by inhibiting DNA synthesis in human hepatoma cancer BEL-7402, SMMC-7721 and ZIP-177 cells. [ABSTRACT FROM AUTHOR]

13a-(S)-3-pivaloyloxyl-6,7-dimethoxyphenanthro(9,10-b)-indolizidine (CAT3) is a novel oral anti-glioma pro-drug with a potent anti-tumor effect against temozolomide-resistant glioma. 13a(S)-3-hydroxyl-6,7-dimethoxyphenanthro(9,10-b)-indolizidine (PF403) is the active in vivo lipase degradation metabolite of CAT3. Both CAT3 and PF403 can penetrate the blood–brain barrier to cause an anti-glioma effect. However, PF403, which is produced in the gastrointestinal tract and plasma, causes significant gastrointestinal side effects, limiting the clinical application of CAT3. The objective of this paper was to propose a metabolism modification for CAT3 using a self-microemulsifying drug delivery system (SMEDDS), in order to reduce the generation of PF403 in the gastrointestinal tract and plasma, as well as increase the bioavailability of CAT3 in vivo and the amount of anti-tumor substances in the brain. Thus, a CAT3-loaded self-microemulsifying drug delivery system (CAT3-SMEDDS) was prepared, and its physicochemical characterization was systematically carried out. Next, the pharmacokinetic parameters of CAT3 and its metabolite in the rats’ plasma and brain were measured. Furthermore, the in vivo anti-glioma effects and safety of CAT3-SMEDDS were evaluated. Finally, Caco-2 cell uptake, MDCK monolayer cellular transfer, and the intestinal lymphatic transport mechanisms of SMEDDS were investigated in vitro and in vivo. Results show that CAT3-SMEDDS was able to form nanoemulsion droplets in artificial gastrointestinal fluid within 1 min, displaying an ideal particle size (15–30 nm), positive charge (5–9 mV), and controlled release behavior. CAT3-SMEDDS increased the membrane permeability of CAT3 by 3.9-fold and promoted intestinal lymphatic transport. Hence, the bioavailability of CAT3 was increased 79% and the level of its metabolite, PF403, was decreased to 49%. Moreover, the concentrations of CAT3 and PF403 were increased 2–6-fold and 1.3–7.2-fold, respectively, in the brain. Therefore, the anti-glioma effect in the orthotopic models was improved with CAT3-SMEDDS compared with CAT3 in 21 days. Additionally, CAT3-SMEDDS reduced the gastrointestinal side effects of CAT3, such as severe diarrhea, necrosis, and edema, and observed less inflammatory cell infiltration in the gastrointestinal tract, compared with the bare CAT3. Our work reveals that, through the metabolism modification effect, SMEDDS can improve the bioavailability of CAT3 and reduce the generation of PF403 in the gastrointestinal tract and plasma. Therefore, it has the potential to increase the anti-glioma effect and reduce the gastrointestinal side effects of CAT3 simultaneously.

13a-(S)-3-pivaloyloxyl-6,7-dimethoxyphenanthro(9,10-b)-indolizidine (CAT3) is a novel oral anti-glioma pro-drug with a potent anti-tumor effect against temozolomide-resistant glioma in vivo. However, poor lipid solubility has limited the encapsulation efficacy during formulation development. Moreover, although the active metabolite of CAT3, 13a(S)-3-hydroxyl-6,7-dimethoxyphenanthro(9,10-b)-indolizidine (PF403), can penetrate the blood-brain barrier and approach the brain tissue with a 1000-fold higher anti-glioma activity than CAT3 in vitro, its bioavailability and Cmax were considerably low in plasma, limiting the anti-tumor efficacy. In this study, a novel oleic acid-CAT3 conjugate (OA-CAT3) was synthesized at the first time to increase the lipid solubility of CAT3. The OA-CAT3 loaded solid lipid nanoparticles (OA-CAT3-SLN) were constructed using an ultrasonic technique to enhance the bioavailability and Cmax of PF403 in plasma. Our results demonstrated that CAT3 was amorphous in the lipid core of OA-CAT3-SLN and the in vitro release was well controlled. Furthermore, the encapsulation efficacy and the zeta potential increased to 80.65 ± 6.79% and −26.7 ± 0.46 mV, respectively, compared to the normal CAT3 loaded SLN. As indicated by the high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS) quantitation, the monolayer cellular transepithelial transport rate of OA-CAT3-SLN improved by 2.42-fold relied on cholesterol compared to the CAT3 suspension. Hence, the in vitro cell viability of OA-CAT3-SLN in C6 glioma cells decreased to 29.77% ± 2.13% and 10.75% ± 3.12% at 48 and 72 h, respectively. Finally, compared to the CAT3 suspension, the in vivo pharmacokinetics in rats indicated that the plasma bioavailability and Cmax of PF403 as afforded by OA-CAT3-SLN increased by 1.7- and 5.5-fold, respectively. Overall, the results indicate that OA-CAT3-SLN could be an efficacious delivery system in the treatment of glioma.

In the course of synthesizing 3-demethyltylophorine (1) by Lewis acid catalyzed intramolecular Friedel-Crafts reaction starting from N-(3-hydroxy-2,6,7-trimethoxy-phenanthr-9-ylmethyl)-2-chloromethylpyrrolidine, two chlorinated phenanthrene derivatives N-(4,10-dichloro-3-hydroxy-2,6,7-trimethoxyphenanthr-9-ylmethyl)-2-chloromethylpyrrolidine (4) and N-(4-chloro-3-hydroxy-2,6,7-trimethoxyphenanthr-9-ylmethyl)-2-chloromethylpyrrolidine (5) were obtained. The structures of these compounds were determined by spectroscopic analysis.

Two new septicine-type alkaloids, fistulopsines A and B ( 1 and 2 ), together with four known phenanthroindolizidine alkaloids ((+)-septicine, (+)-tylophorine, (+)-tylocrebrine, and (–)-3,6-didemethylisotylocrebrine) and (+)-(6 S ,9 S )-vomifoliol, were isolated from the bark and leaves of Ficus fistulosa . The structures of these compounds were established by spectroscopic analysis. Fistulopsines A and B ( 1 and 2 ) showed in vitro growth inhibitory activities in HCT 116 and MCF7 cell lines with GI 50 ranging between 2–7 μM. Furthermore, both compounds 1 and 2 were found to predominantly arrest cells in G1 phase of the cell cycle without induction of apoptosis. HCT 116 cell cycle perturbation by both compounds was found to be transient (< 72 h). [ABSTRACT FROM AUTHOR]

Hispidacine, an 8,4′-oxyneolignan featuring incorporation of an unusual 2-hydroxyethylamine moiety at C-7, and hispiloscine, a phenanthroindolizidine alkaloid, were isolated from the stem-bark and leaves of the Malaysian Ficus hispida Linn. Their structures were established by spectroscopic analysis. Hispidacine induced a moderate vasorelaxant activity in rat isolated aorta, while hispiloscine showed appreciable antiproliferative activities against MDA-MB-231, MCF-7, A549, HCT-116 and MRC-5 cell lines. [ABSTRACT FROM AUTHOR]

Abstract: New water soluble antofine C-13a analogues were designed, synthesized, and evaluated for antiproliferative activity against cancer cells. Particularly, (−)-(R)-13a-hydroxymethylantofine ((−)-(R)-4b) demonstrated notable growth inhibition against a panel of human cancer cell lines. This growth inhibition was associated with the arrest of the cell cycle in the G0/G1 phases and suppression of mTOR signaling in human lung A549 cancer cells. Compound (−)-(R)-4b also overcame paclitaxel-resistance in human lung cancer cells (A549-Pa) by suppressing P-glycoprotein expression. Furthermore, compound (−)-(R)-4b significantly inhibited the tumor growth of A549 and A549-Pa xenografts in a nude mouse model, which suggests it is a promising novel antitumor agent with sufficient aqueous solubility. [Copyright &y& Elsevier]

Abstract: A series of phenanthroindolizidine and phenanthroquinolizidine alkaloids and their 14-amino-derivatives (1–44) were prepared and systematically evaluated for their anti-tumor activities against A549 and HL60 cell lines. The bioassay results showed that most of these alkaloids possess good anti-tumor activities. Especially, compounds 15, 22, 28, 33–36, 40 and 42 displayed low nanomolar or subnanomolar levels of anti-tumor activity. The configuration of (13aS,14S)-14-hydroxyphenanthroindolizidines and (14aR,15R)-15-hydroxyphenanthroquinolizidines was confirmed to be optimal. 14-Amino-phenanthroindolizidines with increased polarity possess good anti-tumor activity, especially for compounds 26 and 28. Most of the phenanthroquinolizidine alkaloids exhibited higher anti-tumor activity than that of phenanthroindolizidine alkaloids. Our present study provides fundamental support for development and optimization of phenanthroindolizidine and phenanthroquinolizidine alkaloids as potential anti-tumor drugs. [Copyright &y& Elsevier]

Background: Phenanthroindolizidine alkaloids are a family of plant-derived compounds with significant antineoplastic activity. The specific biomolecular targets of these alkaloids have not yet been clearly identified. (+)-(13aS)-deoxytylophorinine is a new phenanthroindolizidine alkaloid originally extracted from the roots of Tylophora atrofolliculata and Tylophora ovata in our institute. (+)-(13aS)-deoxytylophorinine exerts both in vitro and in vivoanticancer activities. Methods: The in vivo anticancer effects and toxicity of this compound were investigated in mice, and interactions between this compound and double-helical DNA sequences were studied in detail with circular dichroic spectroscopy and fluorescence spectroscopy. Viscosity measurements were applied to check the interactive mode between this compound and DNA. Results: Potent anticancer effects were observed in vivo. Also, concentration-dependent interactions were observed and this compound seemed to interact in a sequence-specific manner with AT-repeated sequences of double-helical DNA. Such interactions were proved to be intercalating by viscosity measurements. Conclusions: Anticancer alkaloid (+)-(13aS)-deoxytylophorinine can have sequence-specific interactions with DNA in an intercalating manner. Copyright © 2011 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

In the course of synthesizing 3-demethyltylophorine (1) by Lewis acid catalyzed intramolecular Friedel-Crafts reaction starting from N-(3-hydroxy-2,6,7-trimethoxyphenanthr- 9-ylmethyl)-2-chloromethylpyrrolidine, two chlorinated phenanthrene derivatives N-(4,10-dichloro-3-hydroxy-2,6,7-trimethoxyphenanthr-9-ylmethyl)-2-chloromethylpyrrolidine (4) and N-(4-chloro-3-hydroxy-2,6,7-trimethoxyphenanthr-9-ylmethyl)-2-chloromethylpyrrolidine (5) were obtained. The structures of these compounds were determined by spectroscopic analysis. [ABSTRACT FROM AUTHOR]

Abstract: Tylophorine, a representative phenanthroindolizidine alkaloid from Tylophora indica plants, exhibits anti-inflammatory and anti-cancerous growth activities. However, the underlying mechanisms of its anti-cancer activity have not been elucidated and its effects on cell cycle remain ambiguous. Here, we reveal by asynchronizing and synchronizing approaches that tylophorine not only retards the S-phase progression but also dominantly arrests the cells at G1 phase in HepG2, HONE-1, and NUGC-3 carcinoma cells. Moreover, tylophorine treatment results in down regulated cyclin A2 expression and overexpressed cyclin A2 rescues the G1 arrest by tylophorine. Thus, we are the first to report that the downregulated cyclin A2 plays a vital role in G1 arrest by tylophorine in carcinoma cells. [Copyright &y& Elsevier]

Abstract: A radical cascade involving 6-endo cyclization of aryl radicals generated from N-acryloyl-N-(1-methylethenyl)-9-bromophenanthren-10-ylmethylamines, followed by 5-endo-trig cyclization of the resulting α-amidoyl radicals afforded phenanthroindolizidines bearing a methyl substituent at the angular C13a position. 2,3,6-Trimethoxy derivative was synthesized by using this method, but its spectral data were not in accord with those of literature values reported for hypoestestatin 1. Further synthetic study toward hypoestestatin 1 is demonstrated. [Copyright &y& Elsevier]

Abstract: A cryptopleurine analogue, 7-methoxycryptopleurine, a phenanthroquinolizidine, was first found to exert potent anti-inflammatory activity in vitro and in vivo as well as have remarkable cytotoxic activity against cancer cells. The non-planar structure between the two major moieties, phenanthrene and indolizidine/quinolizidine, played a crucial role in the activity of phenanthroindolizidines or phenanthroquinolizidines in terms of cytotoxic effects on cancer cells and anti-inflammatory activity. We also showed that increase in planarity and rigidity of the indolizidine/quinolizidine moiety and change of the amine group into an amide by introducing a keto group to phenanthroindolizidines or phenanthroquinolizidines at the equivalent position 9 of tylophorine significantly reduced their activities. Moreover, in general, phenanthroquinolizidines are more potent than their respective phenanthroindolizines. [Copyright &y& Elsevier]

Abstract: Due to the profound cytotoxicities and interesting biochemical aspects, phenanthroindolizidine alkaloids have received an attention as potential therapeutic leads. To define the features of the molecule that are essential for cytotoxicity, we have synthesized and evaluated a series of phenanthroindolizidine alkaloid, antofine, analogues with different substituents on the phenanthrene ring. The systematic structure activity relationship studies elucidate the essential functional group requirement of phenanthrene ring, providing the basis for further development of phenanthroindolizidine alkaloids. [Copyright &y& Elsevier]

Phenanthroindolizidines, such as antofine and tylophorine, are a family of natural alkaloids isolated from different species of Asclepiadaceas. They are characterized by interesting biological activities, such as pronounced cytotoxicity against different human cancerous cell lines, including multidrug-resistant examples. Nonetheless, these derivatives are associated with severe neurotoxicity and loss of in vivo activity due to the highly lipophilic nature of the alkaloids. Here, we describe the development of highly polar prodrugs of antofine and tylophorine as hypoxia-targeted prodrugs. The developed quaternary ammonium salts of phenanthroindolizidines showed high chemical and metabolic stability and are predicted to have no penetration through the blood–brain barrier. The designed prodrugs displayed decreased cytotoxicity when tested under normoxic conditions. However, their cytotoxic activity considerably increased when tested under hypoxic conditions. [ABSTRACT FROM AUTHOR]

13a-(S)-3-pivaloyloxyl-6,7-dimethoxyphenanthro(9,10-b)-indolizidine (CAT3) is a novel oral anti-glioma pro-drug with a potent anti-tumor effect against temozolomide-resistant glioma. 13a(S)-3-hydroxyl-6,7-dimethoxyphenanthro(9,10-b)-indolizidine (PF403) is the active in vivo lipase degradation metabolite of CAT3. Both CAT3 and PF403 can penetrate the blood–brain barrier to cause an anti-glioma effect. However, PF403, which is produced in the gastrointestinal tract and plasma, causes significant gastrointestinal side effects, limiting the clinical application of CAT3. The objective of this paper was to propose a metabolism modification for CAT3 using a self-microemulsifying drug delivery system (SMEDDS), in order to reduce the generation of PF403 in the gastrointestinal tract and plasma, as well as increase the bioavailability of CAT3 in vivo and the amount of anti-tumor substances in the brain. Thus, a CAT3-loaded self-microemulsifying drug delivery system (CAT3-SMEDDS) was prepared, and its physicochemical characterization was systematically carried out. Next, the pharmacokinetic parameters of CAT3 and its metabolite in the rats' plasma and brain were measured. Furthermore, the in vivo anti-glioma effects and safety of CAT3-SMEDDS were evaluated. Finally, Caco-2 cell uptake, MDCK monolayer cellular transfer, and the intestinal lymphatic transport mechanisms of SMEDDS were investigated in vitro and in vivo. Results show that CAT3-SMEDDS was able to form nanoemulsion droplets in artificial gastrointestinal fluid within 1 min, displaying an ideal particle size (15–30 nm), positive charge (5–9 mV), and controlled release behavior. CAT3-SMEDDS increased the membrane permeability of CAT3 by 3.9-fold and promoted intestinal lymphatic transport. Hence, the bioavailability of CAT3 was increased 79% and the level of its metabolite, PF403, was decreased to 49%. Moreover, the concentrations of CAT3 and PF403 were increased 2–6-fold and 1.3–7.2-fold, respectively, in the brain. Therefore, the anti-glioma effect in the orthotopic models was improved with CAT3-SMEDDS compared with CAT3 in 21 days. Additionally, CAT3-SMEDDS reduced the gastrointestinal side effects of CAT3, such as severe diarrhea, necrosis, and edema, and observed less inflammatory cell infiltration in the gastrointestinal tract, compared with the bare CAT3. Our work reveals that, through the metabolism modification effect, SMEDDS can improve the bioavailability of CAT3 and reduce the generation of PF403 in the gastrointestinal tract and plasma. Therefore, it has the potential to increase the anti-glioma effect and reduce the gastrointestinal side effects of CAT3 simultaneously. [ABSTRACT FROM AUTHOR]

13a-(S)-3-pivaloyloxyl-6,7-dimethoxyphenanthro(9,10-b)-indolizidine (CAT3) is a novel oral anti-glioma pro-drug with a potent anti-tumor effect against temozolomide-resistant glioma in vivo. However, poor lipid solubility has limited the encapsulation efficacy during formulation development. Moreover, although the active metabolite of CAT3, 13a(S)-3-hydroxyl-6,7-dimethoxyphenanthro(9,10-b)-indolizidine (PF403), can penetrate the blood-brain barrier and approach the brain tissue with a 1000-fold higher anti-glioma activity than CAT3 in vitro, its bioavailability and Cmax were considerably low in plasma, limiting the anti-tumor efficacy. In this study, a novel oleic acid-CAT3 conjugate (OA-CAT3) was synthesized at the first time to increase the lipid solubility of CAT3. The OA-CAT3 loaded solid lipid nanoparticles (OA-CAT3-SLN) were constructed using an ultrasonic technique to enhance the bioavailability and Cmax of PF403 in plasma. Our results demonstrated that CAT3 was amorphous in the lipid core of OA-CAT3-SLN and the in vitro release was well controlled. Furthermore, the encapsulation efficacy and the zeta potential increased to 80.65 ± 6.79% and −26.7 ± 0.46 mV, respectively, compared to the normal CAT3 loaded SLN. As indicated by the high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS) quantitation, the monolayer cellular transepithelial transport rate of OA-CAT3-SLN improved by 2.42-fold relied on cholesterol compared to the CAT3 suspension. Hence, the in vitro cell viability of OA-CAT3-SLN in C6 glioma cells decreased to 29.77% ± 2.13% and 10.75% ± 3.12% at 48 and 72 h, respectively. Finally, compared to the CAT3 suspension, the in vivo pharmacokinetics in rats indicated that the plasma bioavailability and Cmax of PF403 as afforded by OA-CAT3-SLN increased by 1.7- and 5.5-fold, respectively. Overall, the results indicate that OA-CAT3-SLN could be an efficacious delivery system in the treatment of glioma. [ABSTRACT FROM AUTHOR]