Concise total syntheses of Marinoquinolines A–C

Three-Component Ring-Expansion Reaction of Indoles Leading to Synthesis of Pyrrolo[2,3-c]quinolines

Herein, we have developed an atom- and step-economic three-component cascade reaction that enables a modular platform for the synthesis of pyrrolo[2,3-c]quinoline compounds through ring-expansion/cyclization by way of novel N1-C2 cleavage of indoles. The metal-free catalytic system exhibits a broad functional group tolerance.

Environmentally friendly domino multicomponent strategy for the synthesis of pyrroloquinolinone hybrid heterocycles

An efficient and elegant assembly of pyrene/aryl fused pyrrolo[2,3-b]quinolinone and pyrrolizino[3,2-b]quinolinone hybrid heterocycles was achieved via a domino multicomponent reaction strategy using a solid state melt reaction (SSMR) condition. The 1,3-dipole component was generated in situ from N-methylgylcine/l-proline and isatin, while the Baylis-Hillman adduct prepared from pyrene-1-carbaldehyde and various benzaldehydes is used as the dipolarophile. The domino protocol comprises 1,3-dipolar cycloaddition and a consequent double annulation reaction process. The advantages of this cascade protocol include environmentally friendly conditions, the avoidance of toxic organic solvents, simple work-up and good to excellent product yields.

Bioactive natural products from Bacteroidetes

Covering: up to end of January 2022Bacteria representing the phylum Bacteroidetes produce a diverse range of natural products, including polyketides, peptides and lactams. Here, we discuss unique aspects of the bioactive compounds discovered thus far, and the corresponding biosynthetic pathways if known, providing a comprehensive overview of the Bacteroidetes as a natural product reservoir.

Mo-Catalyzed One-Pot Synthesis of N-Polyheterocycles from Nitroarenes and Glycols with Recycling of the Waste Reduction Byproduct. Substituent-Tuned Photophysical Properties

A catalytic domino reduction-imine formation-intramolecular cyclization-oxidation for the general synthesis of a wide variety of biologically relevant N-polyheterocycles, such as quinoxaline- and quinoline-fused derivatives, and phenanthridines, is reported. A simple, easily available, and environmentally friendly dioxomolybdenum(VI) complex has proven to be a highly efficient and versatile catalyst for transforming a broad range of starting nitroarenes involving several redox processes. Not only is this a sustainable, step-economical as well as air- and moisture-tolerant method, but also it is worth highlighting that the waste byproduct generated in the first step of the sequence is recycled and incorporated in the final target molecule, improving the overall synthetic efficiency. Moreover, selected indoloquinoxalines have been photophysically characterized in cyclohexane and toluene with exceptional fluorescence quantum yields above 0.7 for the alkyl derivatives.

Total synthesis of pyrrolo[2,3-c]quinoline alkaloid: trigonoine B

The first total synthesis of the pyrrolo[2,3-c]quinoline alkaloid trigonoine B (1) was accomplished via a six-step sequence involving the construction of an N-substituted 4-aminopyrrolo[2,3-c]quinoline framework via electrocyclization of 2-(pyrrol-3-yl)benzene containing a carbodiimide moiety as a 2-azahexatriene system. The employed six-step sequence afforded trigonoine B (1) in 9.2% overall yield. The described route could be employed for the preparation of various N-substituted 4-aminopyrroloquinolines with various biological activities.

Formation of 6-Azaindoles by Intramolecular Diels-Alder Reaction of Oxazoles and Total Synthesis of Marinoquinoline A

A new variant of the intramolecular Diels-Alder oxazole (IMDAO) cycloaddition that provides direct access to 6-azaindoles was developed. The IMDAO reaction was applied in a total synthesis of the aminophenylpyrrole-derived alkaloid marinoquinoline A, also featuring the use of a Curtius reaction for preparation of a 5-aminooxazole, a propargylic C,H-bond insertion, an in situ alkyne-allene isomerization, and a ruthenium-catalyzed cycloisomerization for benzene ring annulation to the 6-azaindole.

Regioselective ring expansion followed by H-shift of 3-ylidene oxindoles: a convenient synthesis of N-substituted/un-substituted pyrrolo[2,3-c] quinolines and marinoquinolines

Herein, we report a simple and metal-free protocol for the synthesis of 4-oxo-4,5-dihydro-3H-pyrrolo[2,3-c]quinolines. The present method under mild reaction conditions with wide functional group compatibility gives several unexplored N-substituted/unsubstituted 4-oxo-4,5-dihydro-3H-pyrrolo[2,3-c]quinolines and marinoquinolines in good to excellent yields. Mechanistic insights for the synthesis of N-substituted pyrroloquinolines reveal the ring expansion of 3-ylideneoxindoles and H-shift as the key steps.

Herein, we report a simple and metal-free protocol for the synthesis of 4-oxo-4,5-dihydro-3H-pyrrolo[2,3-c]quinolines.

Iridium-Catalyzed α-Selective Arylation of Styrenes by Dual C-H Functionalization

An Ir^I‐system modified with a ferrocene derived bisphosphine ligand promotes α‐selective arylation of styrenes by dual C−H functionalization. These studies offer a regioisomeric alternative to the Pd‐catalyzed Fujiwara–Moritani reaction.

Sequential hydroarylation/Prins cyclization: an efficient strategy for the synthesis of angularly fused tetrahydro-2H-pyrano[3,4-c]quinolines

Various aldehydes undergo a smooth cascade cyclization with N-(5-hydroxypent-2-yn-1-yl)-4-methyl-N-phenylbenzenesulfonamide in the presence of 10 mol% Ph₃PAuCl/AgSbF₆/In(OTf)₃ to furnish the corresponding tetrahydro-2H-pyrano[3,4-c]quinoline derivatives.

Arylsulfonylmethyl isocyanides: a novel paradigm in organic synthesis

p-Tosylmethyl isocyanide (TosMIC), an α-acidic isocyanide has emerged as a privileged reagent to access biologically relevant fused heterocycles and some natural products like (−)-ushikulide A, variolin B, porphobilinogen and mansouramycin B.

β-Selective C-H arylation of pyrroles leading to concise syntheses of lamellarins C and I

The first general β-selective C-H arylation of pyrroles has been developed by using a rhodium catalyst. This C-H arylation reaction, which is retrosynthetically straightforward but results in unusual regioselectivity, could result in de novo syntheses of pyrrole-derived natural products and pharmaceuticals. As such, we have successfully synthesized polycyclic marine pyrrole alkaloids, lamellarins C and I, by using this β-selective arylation of pyrroles with aryl iodides (C-H/C-I coupling) and a new double C-H/C-H coupling as key steps.

Marine natural products

This review covers the literature published in 2012 for marine natural products, with 1035 citations (673 for the period January to December 2012) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1241 for 2012), together with the relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Biomimetic synthesis and biological evaluation of Aplidiopsamine A

The first total synthesis of Aplidiopsamine A, a rare 3H-pyrrolo[2,3-c]quinoline alkaloid from the Aplidiopsis confluata, has been achieved following the proposed biosynthesis. This biomimetic synthesis requires only five steps and proceeds in 20.8% overall yield. Biological evaluation across large panels of discrete molecular targets identified that Aplidiopsamine A is a highly selective PDE4 inhibitor, a target for numerous CNS disorders.