Stephacidin B, the avrainvillamide dimer: a formidable synthetic challenge

A base-mediated synthesis of N-hydroxy- and N-alkoxyindoles from 2-nitrostyrenes

Sequential treatment of alkyl 2-(2-nitroaryl)-2-butenoates with potassium tert-butoxide and an electrophile, such as methyl iodide, benzyl bromide and allyl bromide, afforded N-alkoxyindoles. In related reactions, using sodium tert-pentoxide as the base with or without in situ addition of an electrophile afforded N-alkoxy- and N-hydroxyindoles, respectively. Electrophiles such as dimethylsulfate, p-tosyl chloride, and acetic anhydride afforded moderate yields of the respective N-methoxy-, N-tosyloxy, and N-acetoxyindoles, while methyl iodide, benzyl bromide, and 1-bromohexane failed to form alkylated products using sodium tert-pentoxide as the base.

Syntheses of New Multisubstituted 1-Acyloxyindole Compounds

The syntheses of novel 1-acyloxyindole compounds 1 and the investigations on reaction pathways are presented. Nitro ketoester substrate 2, obtained in a two-step synthetic process, underwent reduction, intramolecular addition, nucleophilic 1,5-addition, and acylation to afford 1-acyloxyindoles 1 in one pot. Based on the systematic studies, we established the optimized reaction conditions for 1 focusing on the final acylation step of the intermediate 1-hydroxyindole 8. With the optimized conditions, we succeeded in synthesizing 21 examples of new 1-acyloxyindole derivatives 1 in modest yields (Y = 24 − 35%). Among the 1-acyloxyindole compounds, 1-acetoxyindole compounds 1x were generally unstable, and their yields were relatively lower than the other 1-acyloxyindoles. We expect that a bulkier alkyl or aromatic group on R² could stabilize the 1-acyloxyindole compounds. Significantly, one-pot reactions of a four-step sequence successfully generated compounds 1 that are all new and might be difficult to be synthesized otherwise.

A combination of polarity reversal, Diels-Alder cycloaddition and skeletal remodeling to access pyridine-fused nitrones

An unprecedented cascade strategy consisting of polarity reversal, normal electron-demand Diels-Alder cycloaddition and skeletal remodeling was developed to construct novel pyridine-fused nitrones in up to 82% yield. The key to the success was the umpolung process, which transformed the electron-deficient 3-nitropyridinium ring into a reactive, π-extended cyclic nitroalkene, serving as a rarely reported hetero-diene to participate in normal Diels-Alder cycloadditions.

One-Pot Synthesis of Novel Multisubstituted 1-Alkoxyindoles

Studies on a one-pot synthesis of novel multisubstituted 1-alkoxyindoles 1 and their mechanistic investigations are presented. The synthesis of 1 was successfully achieved through consecutive four step reactions from substrates 2. The substrates 2, prepared through a two-step synthetic sequence, underwent three consecutive reactions of nitro reduction, intramolecular condensation, and nucleophilic 1,5-addition to provide the intermediates, 1-hydroxyindoles 8, which then were alkylated in situ with alkyl halide to afford the novel target products 1. We optimized the reaction conditions for 1 focusing on the alkylation step, along with the consideration of formation of intermediates 8. The optimized condition was SnCl₂·2H₂O (3.3 eq) and alcohols (R¹OH, 2.0 eq) for 1–2 h at 40 °C and then, base (10 eq) and alkyl halides (R²Y, 2.0 eq) for 1–4 h at 25–50 °C. Notably, all four step reactions were performed in one-pot to give 1 in good to modest yields. Furthermore, the mechanistic aspects were also discussed regarding the reaction pathways and the formation of side products. The significance lies in development of efficient one-pot reactions and in generation of new 1-alkoxyindoles.

A novel synthesis of N-hydroxy-3-aroylindoles and 3-aroylindoles

A straightforward indole synthesis via annulation of C-nitrosoaromatics with conjugated terminal alkynones was realised achieving a simple, highly regioselective, atom- and step economical access to 3-aroylindoles in moderate to good yields. Further functionalizations of indole scaffolds were investigated and an easy way to JWH-018, a synthetic cannabinoid, was achieved.

Notoamide-type alkaloid induced apoptosis and autophagyviaa P38/JNK signaling pathway in hepatocellular carcinoma cells

Eleven notoamides including four new congeners were isolated fromAspergillus ochraceus. Notoamide G inhibited the viability of hepatocellular carcinoma cell lines by regulation of apoptosis and autophagy through P38/JNK signaling pathway.

Penicimutamides D–E: two new prenylated indole alkaloids from a mutant of the marine-derived Penicillium purpurogenum G59

Two new prenylated indole alkaloids, penicimutamides D–E (1–2), were discovered via activating silent pathways in a marine-derived fungus.

Penicimutamides A–C: rare carbamate-containing alkaloids from a mutant of the marine-derived Penicillium purpurogenum G59

Three new and rare carbamate-containing penicimutamides A–C (1–3) were discovered via activating silent pathways in a marine-derived fungus.

The cascade radical cyclisation approach to prenylated alkaloids: synthesis of stephacidin A and notoamide B

A strategy for the synthesis of members of the prenylated indole alkaloid family is described, which involves a radical cascade process of an appropriately substituted diketopiperazine (DKP) core structure. Several approaches to the generation of the initial radical were explored, with the most successful involving treatment of a sulfenyl substituted DKP under classical reductive conditions by heating with Bu3SnH and a radical initiator. The required, fully substituted, radical precursor DKP structures were prepared using regio- and stereocontrolled enolate chemistry of simpler proline-tryptophan derived DKPs. The new approach allowed rapid access to a key polycyclic indoline structure, which was converted into either of the natural products stephacidin A or notoamide B.

Simple indole alkaloids and those with a nonrearranged monoterpenoid unit

This review covers the literature on simple indole alkaloids and those with a nonrearranged monoterpenoid unit. Newly isolated alkaloids, structure determinations, total syntheses and biological activities are included.

Cascade Reactions in Total Synthesis

The design and implementation of cascade reactions is a challenging facet of organic chemistry, yet one that can impart striking novelty, elegance, and efficiency to synthetic strategies. The application of cascade reactions to natural products synthesis represents a particularly demanding task, but the results can be both stunning and instructive. This Review highlights selected examples of cascade reactions in total synthesis, with particular emphasis on recent applications therein. The examples discussed herein illustrate the power of these processes in the construction of complex molecules and underscore their future potential in chemical synthesis.