Recent advances of tryptanthrin and its derivatives as potential anticancer agents

Tryptanthrin is one of the well-known natural alkaloids with a broad spectrum of biological activities and can act as anti-inflammatory, anticancer, antibacterial, antifungal, antiviral, antitubercular, and other agents. Owing to its potent anticancer activity, tryptanthrin has been widely explored for the therapy of various cancers besides being effective against other diseases. Tryptanthrin with a pharmacological indoloquinazoline moiety can not only be modified by different functional groups to achieve various tryptanthrin derivatives, which may realize the improvement of anticancer activity, but also bind with different metal ions to obtain varied tryptanthrin metal complexes as potential anticancer agents, due to their higher anticancer activities in comparison with tryptanthrin (or its derivatives) and cisplatin. This review outlines the recent advances in the syntheses, structures, and anticancer activities of tryptanthrin derivatives and their metal complexes, trying to reveal their structure-activity relationships and to provide a helpful way for medicinal chemists in the development of new and effective tryptanthrin-based anticancer agents.

Total Synthesis of Calanthoside, a Potential Hair Growth Stimulant: A Facile Synthetic Approach via One-Pot S- and O-Glucosidic Bond Formation

The first total synthesis of calanthoside (1), which exhibits potent proliferative activity against human hair follicle dermal papilla cells, has been achieved in seven steps with an overall yield of 43% on a gram scale starting from anthranilic acid (11). The synthetic strategy features a one-pot process involving thioglucoside bond formation via nucleophilic substitution reaction and enol-glucosylation for building the S-,O-bisdesmoside structure of 1. Moreover, the one-pot reaction showed broad substrate adaptability to several sugar donors other than d-glucose, thus affording S,O-bisglycoside intermediates in ∼84% yield.

Indole Glycosides from Calanthe discolor with Proliferative Activity on Human Hair Follicle Dermal Papilla Cells

A methanol extract from the underground part of Calanthe discolor Lindl. (Orchidaceae) demonstrated significant proliferative activity on human hair follicle dermal papilla cells (HFDPC, % of control: 120.8 ± 0.2%) at 100 µg/mL against HFDPC. Through bioassay-guided separation of the extract, a new indole glycoside named 6'-O-β-D-apiofuranosylindican (1) was isolated along with six known compounds (2-7) including three indole glycosides. The stereostructure of 1 was elucidated based on its spectroscopic properties and chemical characteristics. Among the isolates, 1 (110.0 ± 1.0%), glucoindican (3, 123.9 ± 6.8%), and calanthoside (4, 158.6 ± 7.1%) showed significant proliferative activity at 100 µM. Furthermore, the active indole glycosides (1, 3, and 4) upregulated the expression of vascular endothelial growth factor (VEGF) and fibroblast growth factor-7 (FGF-7) mRNA and protein in HFDPC, which could be the mechanism of their proliferative activity.

CoCl2-promoted TEMPO oxidative homocoupling of indoles: access to tryptanthrin derivatives

The first example of one-step synthesis of tryptanthrin derivatives using indoles as the only substratesviadirect C–H transformation.

Novel FeII and CoII Complexes of Natural Product Tryptanthrin: Synthesis and Binding with G-Quadruplex DNA

Tryptanthrin is one of the most important members of indoloquinoline alkaloids. We obtained this alkaloid from Isatis. Two novel Fe^II and Co^II complexes of tryptanthrin were first synthesized. Single-crystal X-ray diffraction analyses show that these complexes display distorted four-coordinated tetrahedron geometry via two heterocyclic nitrogen and oxygen atoms from tryptanthrin ligand. Binding with G-quadruplex DNA properties revealed that both complexes were found to exhibit significant interaction with G-quadruplex DNA. This study may potentially serve as the basis of future rational design of metal-based drugs from natural products that target the G-quadruplex DNA.

Quercetin and Tryptanthrin: Two Broad Spectrum Anticancer Agents for Future Chemotherapeutic Interventions

The idea and practice of developing or identifying compounds capable of eliminating the transformed cells or cancer cells without being nontoxic to their normal counterparts deserves much importance. Since ages, plants have been considered and proven to be repertoires of chemicals possessing immense therapeutic potential. A proportion of these plant-derived compounds or phytochemicals were shown to be highly competent anticancer agents besides being effective against many other diseases. Representative compounds of different classes of phytochemicals are in clinical use against cancer. In this chapter, we discuss the anticancer potential of two compounds: quercetin, a flavonoid and tryptanthrin, an indoloquinazoline alkaloid, and the mechanisms behind their cytotoxic effects on cancers of different origin. The chapter also gives a brief mention of their properties that make them effective against cancer.

Indole alkaloids from the roots of Isatis indigotica and their inhibitory effects on nitric oxide production

Three rare indole-2-S-glycosides, indole-3-acetonitrile-2-S-β-D-glucopyranoside (1), indole-3-acetonitrile-4-methoxy-2-S-β-D-glucopyranoside (2) and N-methoxy-indole-3-acetonitrile-2-S-β-D-glucopyranoside (3), together with 11 known indole alkaloids were isolated from the roots of Isatis indigotica Fort. (Cruciferae). The structures of 1-3 were elucidated on the basis of mass spectrometry and extensive 1D and 2D NMR spectroscopy. All of the isolated compounds were tested for inhibitory activity against LPS-induced nitric oxide production in RAW 264.7 macrophages. A plausible biosynthesis pathway of 1-3 is also proposed.

On the inhibition of 5-lipoxygenase product formation by tryptanthrin: mechanistic studies and efficacy in vivo

BACKGROUND AND PURPOSE

Leukotrienes (LTs) are pro-inflammatory mediators produced by 5-lipoxygenase (5-LO). Currently available 5-LO inhibitors either lack efficacy or are toxic and novel approaches are required to establish a successful anti-LT therapy. Here we provide a detailed evaluation of the effectiveness of the plant-derived alkaloid tryptanthrin as an inhibitor of LT biosynthesis.

EXPERIMENTAL APPROACH

We analysed LT formation and performed mechanistic studies in human neutrophils stimulated with pathophysiologically relevant stimuli (LPS and formyl peptide), as well as in cell-free assays (neutrophil homogenates or recombinant human 5-LO) and in human whole blood. The in vivo effectiveness of tryptanthrin was evaluated in the rat model of carrageenan-induced pleurisy.

KEY RESULTS

Tryptanthrin potently reduced LT-formation in human neutrophils (IC(50) = 0.6µM). However, tryptanthrin is not a redox-active compound and did not directly interfere with 5-LO activity in cell-free assays. Similarly, tryptanthrin did not inhibit the release of arachidonic acid, the activation of MAPKs, or the increase in [Ca(2+) ](i) , but it modified the subcellular localization of 5-LO. Moreover, tryptanthrin potently suppressed LT formation in human whole blood (IC(50) = 10µM) and reduced LTB(4) levels in the rat pleurisy model after a single oral dose of 10mg·kg(-1) .

CONCLUSIONS AND IMPLICATIONS

Our data reveal that tryptanthrin is a potent natural inhibitor of cellular LT biosynthesis with proven efficacy in whole blood and is effective in vivo after oral administration. Its unique pharmacological profile supports further analysis to exploit its pharmacological potential.

Isolation, structure elucidation, and synthesis of cytotoxic tryptanthrin analogues from Phaius mishmensis

Bioassay-guided chromatographic separation of the cytotoxic MeOH extract of Phaius mishmensis led to the isolation of two known and six new indoloquinazolinones, phaitanthrins A-E (1-5) and methylisatoid (6). The structures of the new compounds were elucidated by spectroscopic analysis. Phaitanthrin A (1) and tryptanthrin (7) showed moderate cytotoxicity against MCF-7, NCI-H460, and SF-268 cell lines. A series of ketone adducts of tryptanthrin were prepared and tested initially for anticancer activity in vitro against MCF-7, NCI-H460, and SF-268 human cancer cell lines. The 3-pentanone adduct 13 showed activity similar to tryptanthrin.

Astonishing diversity of natural surfactants: 6. Biologically active marine and terrestrial alkaloid glycosides

This review article presents 209 alkaloid glycosides isolated and identified from plants, microorganisms, and marine invertebrates that demonstrate different biological activities. They are of great interest, especially for the medicinal and/or pharmaceutical industries. These biologically active glycosides have good potential for future chemical preparation of compounds useful as antioxidants, anticancer, antimicrobial, and antibacterial agents. These glycosidic compounds have been subdivided into several groups, including: acridone; aporphine; benzoxazinoid; ergot; indole; enediyne alkaloidal antibiotics; glycosidic lupine alkaloids; piperidine, pyridine, pyrrolidine, and pyrrolizidine alkaloid glycosides; glycosidic quinoline and isoquinoline alkaloids; steroidal glycoalkaloids; and miscellaneous alkaloid glycosides.

Bioactive constituents of Chinese natural medicines. VII. Inhibitors of degranulation in RBL-2H3 cells and absolute stereostructures of three new diarylheptanoid glycosides from the bark of Myrica rubra

Three new diarylheptanoid glycosides, named (+)-S-myricanol 5-0-beta-D-glucopyranoside, myricanene A 5-O-alpha-L-arabinofuranosyl(1-->6)-beta-D-glucopyranoside, and myricanene B 5-0-alpha-L-arabinofuranosyl(1-->6)-beta-D-glucopyranoside, were isolated from the bark of Chinese Myrica rubra, together with twenty known compounds. The absolute stereostructures of the new diarylheptanoid glycosides were elucidated on the basis of chemical and physicochemical evidence, including the application of the modified Mosher's method. The inhibitory effects of isolated constituents on the release of beta-hexosaminidase from RBL-2H3 cells were examined, and several diarylheptanoids, myricanol, (+)-S-myricanol, myricanone, and myricanenes A and B, and a flavonol, myricetin, were found to show the inhibitory activity.