•The recent development of indole derivatives as antiviral agents was reviewed.•A comprehensive list of indole antiviral agents on market or in clinical trials was provided.•The future of indole-based antiviral agents was prospected.Indole represents one of the most important privileged scaffolds in drug discovery. Indole derivatives have the unique property of mimicking the structure of peptides and to bind reversibly to enzymes, which provide tremendous opportunities to discover novel drugs with different modes of action. There are seven indole-containing commercial drugs in the Top-200 Best Selling Drugs by US Retail Sales in 2012. There are also an amazing number of approved indole-containing drugs in the market as well as compounds currently going through different clinical phases or registration statuses. This review focused on the recent development of indole derivatives as antiviral agents with the following objectives: 1) To present one of the most comprehensive listings of indole antiviral agents, drugs on market or compounds in clinical trials; 2) To focus on recent developments of indole compounds (including natural products) and their antiviral activities, summarize the structure property, hoping to inspire new and even more creative approaches; 3) To offer perspectives on how indole scaffolds as a privileged structure might be exploited in the future.The recent developments of indole compounds for antiviral drug discovery were comprehensively reviewed.

•A series of novel indole-modified analogues of streptochlorin were synthesized.•Streptochlorin analogues were screened against seven phytopathogenic fungi.•Some compounds showed good antifungal activity in primary assays.•The SAR of the streptochlorin analogues were summarized.Streptochlorin, first isolated as a new antibiotic in 1988 from the lipophilic extracts of the mycelium of a Streptomyces sp, is an indole natural products with a variety of biological activities. Based on the methods developed for the synthesis of pimprinine in our laboratory, we have synthesized a series of indole-modified streptochlorin analogues and measured their activities against seven phytopathogenic fungi. Some of the analogues displayed good activity in the primary assays, and the seven compounds 10b, 10c, 11e, 13e, 21, 22c and 22e (shown in Figure 1) were identified as the most promising candidates for further study. Structural optimization is still ongoing with the aim of discovering synthetic analogues with improved antifungal activity.A series of novel streptochlorin analogues were designed and synthesized by modifying the indole moiety. Antifungal activity screening against seven phytopathogenic fungi led to the identification of seven compounds as the most promising candidate for further study.

4-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27, HPPD) is one of the most important targets for herbicide discovery. In the search for new HPPD inhibitors with novel scaffolds, triketone–quinoline hybrids were designed and subsequently optimized on the basis of the structure–activity relationship (SAR) studies. Most of the synthesized compounds displayed potent inhibition of Arabidopsis thaliana HPPD (AtHPPD), and some of them exhibited broad-spectrum and promising herbicidal activity at the rate of 150 g ai/ha by postemergence application. Most promisingly, compound III-l, 3-hydroxy-2-(2-methoxy-7-(methylthio)quinoline-3-carbonyl)cyclohex-2-enone (Ki = 0.009 μM, AtHPPD), had broader spectrum of weed control than mesotrione. Furthermore, compound III-l was much safer to maize at the rate of 150 g ai/ha than mesotrione, demonstrating its great potential as herbicide for weed control in maize fields. Therefore, triketone–quinoline hybrids may serve as new lead structures for novel herbicide discovery.

As an important fragment and synthetic intermediate, functionalized 6-arylsalicylate substructure widely exist in pharmacologically relevant natural products and bioactive compounds. In our recent works, we discovered two highly potent inhibitors for combating mutants of acetohydroxyacid synthase (AHAS), an important target for herbicide discovery. These two inhibitors contain 6-arylsalicylate skeleton. Previously, we have explored a new method to synthesize position-6 aryl substituted salicylic acid fragment. However, this method failed to synthesize 4-methyl-6-aryl salicylic acids. Herein, we developed a new efficient method for the synthesis of functionalized 4-methyl-6-bulkyarylsalicylates via a microwave-promoted Suzuki cross-coupling. This method has obvious advantages, such as a wide range of substrates, smooth and rapid reaction, moderate to excellent yields. Due to its superiority to the traditional available methods, this protocol could be utilized to synthesize pyrimidinyl(thio)salicylic acid and its derivatives.

On the basis of the principle of combination of active structural moieties, a modified and efficient synthetic method for three series of novel indole-based 1,3,4-oxadiazoles is described. Bioassays conducted at Syngenta showed that several of the synthesized compounds exhibit higher antifungal activity than pimprinine, the natural product which inspired this synthesis. Two main structural alterations were found to broaden the spectrum of biological activity in most cases. Compounds 3g, 6c, 6e, 6h, 9d, 9e, 9h and 9m (Fig. 1) were identified as the most active on the biological assays, and will be studied further.Graphical abstractWe efficiently synthesized three series of indole-based 1,3,4-oxadiazole derivatives, designed as analogues of the antifungal natural product pimprinine, and evaluated their antifungal activities.Highlights► Three series of novel analogues of natural product pimprinine were synthesized. ► Antifungal activity of fifty five analogues of pimprinine were screened. ► Some of the tested compounds showed good antifungal activity or broad spectrum. ► The structure–activity relationships of the pimprinine analogues were summarized.

Indoline-2,3-diones (isatins) and their derivatives are important heterocycles found in nature and present in numerous bioactive compounds. Very few examples related to the synthesis of 4-substituted-arylisatins have been reported before. Utilizing microwave irradiation, the synthesis of bulky 4-substituted-arylisatins via a Suzuki cross-coupling has been developed with a wide range of substrates. All the reactions proceeded smoothly and afforded moderate to excellent yields of products, which indicating that electronic effects and steric modifications have little effect on this reaction.