Synthesis of two pyranoquinolinones. What is the structure of cherimoline ?

Structural Simplification of Luotonin F: Discovery of Quinoline Derivatives as Novel Antifungal Agents for Plant Protection

Inspired by the natural quinoline alkaloid Luotonin F, a series of quinoline-3-hydrazide derivatives were designed and synthesized by structure simplification and evaluated for their fungicidal activities against plant phytopathogenic fungi. The bioassay results showed that these compounds exhibited broad-spectrum and highly efficient antifungal activities in vitro. Among them, compound W9 exhibited broad-spectrum inhibitory activities against R. solani, S. sclerotiorum, B. cinerea, F. graminearum, F. oxysporum, and P. capsici with EC50 values of 0.471, 0.752, 0.570, 0.329, 0.960, and 0.504 μg/mL, respectively. In particular, compound W9 was more effective against B. cinerea than the reference drugs Pyrimethanil (EC50 = 3.54 μg/mL) and Boscalid (EC50 = 1.37 μg/mL). Therefore, the preliminary mechanism of action of compound W9 on B. cinerea was explored. The results showed that it could affect the mycelial morphology, disrupt the integrity of the cell membrane, and increase the reactive oxygen species content. Furthermore, compound W9 exhibited excellent in vivo protection efficacy against B. cinerea compared to the reference drug Pyrimethanil. Thus, compound W9 is expected to be a novel broad-spectrum fungicidal candidate, exhibiting excellent fungicidal activities, which is worthy of further investigation.

Sequential condensation/biannulation reactions of β-(2-aminophenyl)-α,β-ynones with 1,3-dicarbonyls

A divergent domino condensation/biannulation reaction of β-(2-aminophenyl) α,β-ynones with 1,3-dicarbonyls to construct a polycyclic 4H-pyrano[3,4-c]quinoline core has been developed. The p-TsOH·H2O catalyzed reaction of β-(2-aminophenyl) α,β-ynones with β-ketoesters in ethanol proceeds with good to excellent yields to provide a simple and effective method for the synthesis of functionalized 4H-pyrano[3,4-c]quinolinones. Further elaboration of these latter derivatives with an excess of 20% NH4OH in EtOH at 50 °C helps achieve the synthesis of the perlodinine analogues benzo[c][2,7]naphthyridin-4(3H)-one derivatives in high yields. Moreover, the p-TsOH·H2O mediated reaction of β-(2-aminophenyl) α,β-ynones with β-di-ketones leads to the formation of a variety of structurally diverse 4H-pyrano[3,4-c]quinoline polycyclic ketals by the incorporation of an alcohol solvent molecule in a cascade fashion.

Confirmation of the Revised Structure of Samoquasine A and a Proposed Structural Revision of Cherimoline

The identity of the natural product samoquasine A has remained obscure since its isolation from custard apple seeds in 2000. One of the proposed structures, benzo[ f]phthalazin-4(3 H)-one, was prepared in two steps by regioselective ortho-lithiation/formylation of N, N-diisopropyl-2-naphthylamide, followed by cyclization with hydrazine, but was shown to be different from the natural product. Perlolidine, another candidate structure, was synthesized by a novel route involving a β-selective Heck reaction of butyl vinyl ether. Both perlolidine and samoquasine A are converted by trimethylsilyldiazomethane into the same N-methyl derivative. In addition, the ¹³C NMR spectra of perlolidine and another structurally mis-assigned natural product, cherimoline, are almost identical. Thus, both samoquasine A and cherimoline are actually perlolidine.

Iodination of carbohydrate-derived 1,2-oxazines to enantiopure 5-iodo-3,6-dihydro-2H-1,2-oxazines and subsequent palladium-catalyzed cross-coupling reactions

Iodination of carbohydrate-derived 3,6-dihydro-2H-1,2-oxazines of type 3 using iodine and pyridine in DMF furnished 5-iodo-substituted 1,2-oxazine derivatives 4 with high efficacy. The alkenyl iodide moiety of 1,2-oxazine derivatives syn-4 and anti-4 was subsequently exploited for the introduction of new functionalities at the C-5 position by applying palladium-catalyzed carbon–carbon bond-forming reactions such as Sonogashira, Heck, or Suzuki coupling reactions as well as a cyanation reaction. These cross-coupling reactions led to a series of 5-alkynyl-, 5-alkenyl-, 5-aryl- and 5-cyano-substituted 1,2-oxazine derivatives being of considerable interest for further synthetic elaborations. This was exemplarily demonstrated by the hydrogenation of syn-21 and anti-24 and by a click reaction of a 5-alkynyl-substituted precursor.

Heteroaromatic tosylates as electrophiles in regioselective Mizoroki-Heck-coupling reactions with electron-rich olefins

Heteroaromatic 2-pyridyl tosylates were successfully applied as electrophiles in palladium(0)-catalyzed Mizoroki-Heck-coupling reactions to electron-rich olefins with complete alpha-regioselectivity. This protocol represents a general strategy for the application of pyridyl tosylates and mesylates in the Mizoroki-Heck coupling. The catalytic system also proved adaptable to changes in the heteroaromatic core as well as large-scale applications. Finally, the synthetic utility of the functionalized alpha-heteroarylvinyl amides was established providing straightforward access to highly functionalized heteroaromatic compounds including chiral benzylic amide derivatives.

Solid-Phase Syntheses of Furopyridine and Furoquinoline Systems

[reaction: see text] Syntheses of 2-substituted furo[3,2-b]pyridines and furo[3,2-h]quinolines have been achieved for the first time in the solid-phase mode. The central enabling steps involved concomitant deprotection/cyclization promoted by the mild base K(2)CO(3). Reactions were monitored "in situ" in real time by a variety of spectroscopic techniques, which allowed full and accurate control of progress in these syntheses.