An Overview of Synthesis of Indole Alkaloids and Biological Activities of Secondary Metabolites Isolated from Hyrtios Species

Marine-Derived Lead Fascaplysin: Pharmacological Activity, Total Synthesis, and Structural Modification

Fascaplysin is a planar structure pentacyclic alkaloid isolated from sponges, which can effectively induce the apoptosis of cancer cells. In addition, fascaplysin has diverse biological activities, such as antibacterial, anti-tumor, anti-plasmodium, etc. Unfortunately, the planar structure of fascaplysin can be inserted into DNA and such interaction also limits the further application of fascaplysin, necessitating its structural modification. In this review, the biological activity, total synthesis and structural modification of fascaplysin will be summarized, which will provide useful information for pharmaceutical researchers interested in the exploration of marine alkaloids and for the betterment of fascaplysin in particular.

Regioselective Dichotomy in Ru(II)-Catalyzed C-H Annulation of Aryl Pyrazolidinones with 1,3-Diynes

Herein, we present a substrate-controlled regiodivergent strategy for the selective synthesis of C3 or C2-alkynylated indoles via ruthenium-catalyzed [3 + 2]-annulation of readily available pyrazolidinones and 1,3-diynes. Remarkably, C3-alkynylated indoles were obtained in good yields when 1,4-diarylbuta-1,3-diynes were employed as the coupling partners. On the other hand, dialkyl-1,3-diynes led to the selective formation of C2-alkynylated indoles. The key features of the strategy are the operationally simple conditions and external-oxidant-free, broad-scope, and substrate-switchable indole synthesis. Scale-up reactions and further transformations expanded the synthetic utility of the protocol.

Therapeutic potential of indole derivatives as anti-HIV agents: A mini-review

Acquired immunodeficiency syndrome (AIDS), caused by human immunodeficiency virus (HIV), is one of the leading causes of human deaths. The advent of different anti-HIV drugs over different disease progress has made AIDS/HIV from a deadly infection to chronic and manageable disease. However, the development of multidrug-resistant viruses, together with the severe side effects of anti-HIV agents, compromised their efficacy and limited the treatment options. Indoles, the most common frameworks in the bioactive molecules, represent attractive scaffolds for the design and development of novel drugs. Indole derivatives are potential inhibitors of HIV enzymes such as reverse transcriptase, integrase and protease, and some indole-based agents like Delavirdine have already been applied in clinics or under clinical evaluations for the treatment of AIDS/HIV, revealing that indole moiety is a useful template for the development of anti-HIV agents. This review focuses on the recent advancement of indole derivatives including indole alkaloids, hybrids, and dimers with anti-HIV potential, covering articles published between 2010 and 2020. The chemical structures, structure-activity relationship and mechanisms of action are also discussed.

Tryptophan derived natural marine alkaloids and synthetic derivatives as promising antimicrobial agents

Antimicrobial resistance has become a major threat to public health worldwide, as pathogenic microorganisms are finding ways to evade all known antimicrobials. Therefore, the demand for new and effective antimicrobial agents is also increasing. Natural products have always played an important role in drug discovery, either by themselves or as inspiration for synthetic compounds. The marine environment is a rich source of bioactive metabolites, and among them, tryptophan-derived alkaloids stand out for their abundance and by displaying a variety of biological activities, with antimicrobial properties being among the most significant. This review aims to reveal the potential of marine alkaloids derived from tryptophan as antimicrobial agents. Relevant examples of these compounds and their synthetic analogues reported in the last decades are presented and discussed in detail, with their mechanism of action and synthetic approaches whenever relevant. Several tryptophan-derived marine alkaloids have shown potent and promising antimicrobial activities, whether against bacteria, fungi, or virus. Synthetic approaches to many of the compounds have been developed and recent methodologies are proving to be efficient. Even though most of the studies regarding the antimicrobial activity are still preliminary, this class of compounds has proven to be worth of further investigation and may provide useful lead compounds for the development of antimicrobial agents. Overall, marine alkaloids derived from tryptophan are revealed as a valuable class of antimicrobials and molecular modifications in order to reduce the toxicity of these compounds and additional studies regarding their mechanism of action are interesting topics to explore in the future.

Natural indole-containing alkaloids and their antibacterial activities

As the growth in resistance to bacterial infection treatments poses a grave threat to global health in the 21st century, there is a constant need to explore novel antibacterial agents that have the ability to overcome drug resistance. Indole-containing alkaloids are widely distributed in nature, and a variety of indole-containing alkaloids have already been applied in clinical practice, proving that indole-containing alkaloids are fascinating and privileged scaffolds for the development of novel drugs. Moreover, indole-containing alkaloids could exert their antibacterial activity through the inhibition of efflux pumps, the biofilm, filamentous temperature-sensitive protein Z, and methicillin-resistant Staphylococcus aureus pyruvate kinase; so, indole-containing alkaloids constitute an important source of novel antibacterial agents. This review is an endeavor to highlight the advances in the development of indole-containing alkaloids with antibacterial potential, covering articles published in the recent 10 years.

Cytotoxic Scalarane Sesterterpenes from the Sponge Hyrtios erectus

Twelve new sesterterpenes along with eight known sesterterpenes were isolated from the marine sponge Hyrtios erectus collected off the coast of Chuuk Island, the Federated State of Micronesia. Based upon a combination of spectroscopic and computational analyses, these compounds were determined to be eight glycine-bearing scalaranes (1–8), a 3-keto scalarane (9), two oxidized-furan-bearing scalaranes (10 and 11), and a salmahyrtisane (12). Several of these compounds exhibited weak antiproliferation against diverse cancer cell lines as well as moderate anti-angiogenesis activities. The antiproliferative activity of new compound 4 was found to be associated with G0/G1 arrest in the cell cycle.