The synthesis of biologically active indolocarbazole natural products

Biotransformation Of l-Tryptophan To Produce Arcyriaflavin A With Pseudomonas putida KT2440

Natural products such as indolocarbazoles are a valuable source of highly bioactive compounds with numerous potential applications in the pharmaceutical industry. Arcyriaflavin A, isolated from marine invertebrates and slime molds, is one representative of this group and acts as a cyclin D1-cyclin-dependent kinase 4 inhibitor. To date, access to this compound has mostly relied on multi-step total synthesis. In this study, biosynthetic access to arcyriaflavin A was explored using recombinant Pseudomonas putida KT2440 based on a previously generated producer strain. We used a Design of Experiment approach to analyze four key parameters, which led to the optimization of the bioprocess. By engineering the formation of outer membrane vesicles and using an adsorbent in the culture broth, we succeeded to increase the yield of arcyriaflavin A in the cell-free supernatant, resulting in a nearly eight-fold increase in the overall production titers. Finally, we managed to scale up the bioprocess leading to a final yield of 4.7 mg arcyriaflavin A product isolated from 1 L of bacterial culture. Thus, this study showcases an integrative approach to improve biotransformation and moreover also provides starting points for further optimization of indolocarbazole production in P. putida.

Bisindolyl Maleimides and Indolylmaleimide Derivatives-A Review of Their Synthesis and Bioactivity

The evolution of bisindolyl maleimides and indolyl maleimide derivatives and their unique biological activities have stimulated great interest in medicinal chemistry programs. Bisindolylmaleimide (BIM)-type compounds arise from natural sources such as arcyriarubin and are biosynthetically related to indolocarbazoles. BIMs are commonly the immediate synthetic precursors of indolocarbazoles, lacking a central bond between the two aromatic units and making them more flexible and drug-like. Synthetic endeavours within this class of compounds are broad and have led to the development of both remarkably potent and selective protein kinase inhibitors. Clinical BIM examples include ruboxistaurin and enzastaurin, which are highly active inhibitors of protein kinase C-β. While BIMs are widely recognised as protein kinase inhibitors, other modes of activity have been reported, including the inhibition of calcium signalling and antimicrobial activity. Critically, structural differences can be used to exploit new bioactivity and therefore it is imperative to discover new chemical entities to address new targets. BIMs can be highly functionalised or chemically manipulated, which provides the opportunity to generate new derivatives with unique biological profiles. This review will collate new synthetic approaches to BIM-type compounds and their associated bioactivities with a focus on clinical applications.

Construction of heterocycle-fused tetrahydrocarbazoles through a formal [3 + 3]-annulation of 2-indolylmethanols with para-quinone methides

A metal-free approach for the synthesis of tetrahydroindolo[2,3-b]carbazoles has been developed through an acid-mediated one-pot [3 + 3]-annulation of 2-indolylmethanols and 3-indolyl-substituted para-quinone methides. This operationally simple protocol allowed us to prepare many unsymmetrical tetrahydroindolo[2,3-b]carbazoles in good to excellent yields with a broad substrate scope. This concept was also elaborated to the synthesis of tetrahydrothieno[2,3-b]carbazoles and tetrahydrothieno[3,2-b]carbazoles.

Discovery of unglycosylated indolocarbazoles as ROCK2 isoform-selective inhibitors for the treatment of breast cancer metastasis

Breast cancer metastasis is a major challenge in clinical therapy because of the absence of effective treatments. Rho-associated coiled-coil kinase (ROCK), which is essential for cell invasion and migration, has recently been suggested as a potential target for the treatment of cancer metastasis. Herein, we report the structure-activity relationships (SAR) of indolocarbazoles against ROCK2 and reveal the crucial role of the C-3 hydroxyl for ROCK2 inhibition. The most potent unglycosylated aglycone THK01 was demonstrated to bind to and stabilize ROCK2 with potent anti-metastatic effects in breast cancer in vitro and in vivo with no obvious toxicities. Further mechanistic studies revealed that the anti-metastatic effect of THK01 was closely related to the suppression of STAT3^Y705 activation. Moreover, THK01 exhibited excellent selectivity over the isoform protein ROCK1 (>100-fold). Taken together, with low toxicity, the ROCK2 inhibitor THK01 potently inhibited breast cancer metastasis through the ROCK2-STAT3 signaling pathway, which offers a new opportunity for the treatment of metastatic breast cancer.

Small Molecule Inhibitors of Protein Kinase D: Early Development, Current Approaches, and Future Directions

Now entering its fourth decade, research on the biological function, small molecule inhibition, and disease relevance of the three known isoforms of protein kinase D, PKD1, PKD2, and PKD3, has entered a mature development stage. This mini-perspective focuses on the medicinal chemistry that provided a structurally diverse set of mainly active site inhibitors, which, for a brief time period, moved through preclinical development stages but have yet to be tested in clinical trials. In particular, between 2006 and 2012, a rapid expansion of synthetic efforts led to several moderately to highly PKD-selective chemotypes but did not yet achieve PKD subtype selectivity or resolve general toxicity and pharmacokinetic challenges. In addition to cancer, other unresolved medical needs in cardiovascular, inflammatory, and metabolic diseases would, however, benefit from a renewed focus on potent and selective PKD modulators.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Biomimetic Total Synthesis of the Spiroindimicin Family of Natural Products

A unified strategy for the biomimetic total synthesis of the spiroindimicin family of natural products was reported. Key transformations include a one-pot two-enzyme-catalyzed oxidative dimerization of L-tryptophan/5-chloro-L-tryptophan to afford the bis-indole precursors chromopyrrolic acid/5',5''-dichloro-chromopyrrolic acid, and regioselective C3'-C2'' and C3'-C4'' bond formation converting a common bis-indole skeleton to two skeletally different natural products, including (±)-spiroindimicins D and G with a [5,5] spiro-ring skeleton, and (±)-spiroindimicins A and H with a [5,6] spiro-ring skeleton, respectively.

Cytotoxic Indolocarbazoles From a Marine-Derived Streptomyces Sp. OUCMDZ-5380

Under the guidance of global natural product social molecular networking, three new indolocarbazoles named streptocarbazoles F–H (1-3), along with staurosporine (4) were isolated from the marine-derived Streptomyces sp. OUCMDZ-5380. Structures of streptocarbazoles F–H were, respectively, determined as N-demethyl-N-hexanoylstaurosporine (1), N-demethyl-N-(2-methyl-3-methoxypyridin-4-yl) staurosporine staurosporine (2), and 4-(N-demethylstaurosporine-N-yl)-1,2-dimethyl-3-methoxypyridinium (3) by spectroscopic analysis and electronic circular dichroism comparison with staurosporine. Compared with staurosporine (4), streptocarbazoles F–H (1-3) showed a selective antiproliferation of the acute myeloid leukemia cell line MV4-11 with the IC₅₀ values of 0.81, 0.55, and 1.88 μM, respectively.

Photochemical Synthesis of Indolocarbazoles through Tandem Indolization/Dimerization/Mannich Cyclization from Allenes

Indolocarbazole alkaloids and their derivatives were discovered to have potent protein kinase and topoisomerase I inhibitory activities. Disclosed herein is the photochemical synthesis of the indolocarbazole ring system from N-allenyl-2-iodoanilines. The tandem protocol included visible-light-mediated 5-exo-trig radical cyclization and subsequent radical dimerization, followed by acid-promoted deprotection and intramolecular Mannich cyclization. This strategy showed exceptional functional group tolerance and was successfully applied in the concise synthesis of natural products tjipanazoles B and D.

Self-Assembly of Naturally Small Molecules into Supramolecular Fibrillar Networks for Wound Healing

Self-assemblies of bioactively natural compounds into supramolecular hydrogels without structural modifications are of interest to improve their sustained releases and bioavailabilities in vivo. However, it is still a formidable challenge to dig out such a naturally small molecule with a meticulous structure which can be self-assembled to form a hydrogel for biomedical applications. Here, a new hydrogel consisting only of gallic acid (GA) via π-π stacking and hydrogen bond interactions, whereas none of GA analogues can form the similar supramolecular hydrogels, is reported. This interesting phenomenon is intriguing to further investigate the potential applications of GA hydrogels in wound healing. Notably, this GA hydrogel has rod-like structures with lengths varying from 10 to 100 µm. The biocompatibility and antibacterial tests prove that this well-assembled GA hydrogel has no cytotoxicity and excellent antibacterial activities against Escherichia coli and Staphylococcus aureus. Moreover, the GA hydrogel can significantly accelerate the process of wound healing with or without bacterial infections by mediation of inflammation signaling pathways. It is believed that the current study may shed a new light on the design of a supramolecular hydrogel based on self-assemblies of naturally small molecules to improve their bioavailabilities and diversify their uses in biomedical applications.

Sequential Metal Catalysis towards 7-Oxostaurosporine and Its Non-Natural Septanose Analogue

We report sequential metal catalysis towards indolocarbazole glycosides. The signature event is highlighted by i) Pd⁰ -catalyzed addition of indolocarbazole to alkoxyallene combined with ring-closing-metathesis; ii) Ru-catalyzed chemoselective olefin migration; iii) Pd^II -catalyzed oxidative cyclization to build the bicyclic core structure of the target compounds. This approach gave access to both natural pyranose- and non-natural septanose glycosides. A short formal synthesis of 7-oxostaurosporine was achieved via this strategy.

A simple and efficient copper-catalyzed three-component reaction to synthesize (Z)-1,2-dihydro-2-iminoquinolines

A operationally simple synthesis of (Z)-1,2-dihydro-2-iminoquinolines that proceeds under mild conditions is achieved by copper-catalyzed reaction of 1-(2-aminophenyl)ethan-1-ones, sulfonyl azides and terminal ynones. In particular, the reaction goes through a base-free CuAAC/ring-opening process to obtain the Z-configured products due to hydrogen bonding.