Search

The O4-benzo[c]phenanthridine alkaloids exhibit potent antiproliferative activity against cancer cells, which is derived from their ability to inhibit of topoisomerase I and II. It has been reported that in the alkaloids a cationic quaternary ammonium atom, which results in resonance effects between ring A and B, is necessary for increased antiproliferative activity. These findings indicate the role of their substituents at ring A on inhibition of tumor cell proliferation. In the present study, we systematically assessed the cytotoxic activities of naturally occurring alkaloids and their derivatives containing various ring A substituents against two tumor cell lines, HCT-116 colon tumor cells and HL-60 promyelocytic leukemia cells. Among the cationic iminium alkaloids, which displayed more potent activity than the corresponding neutral derivatives, and the 7,8-oxygenated benzo[c]phenanthridine alkaloids, chelerythrine and NK109, exhibited stronger antiproliferative activity than the 8,9- and 9,10-oxygenated alkaloids. The activity of cationic iminium alkaloids could be correlated with the bond lengths of their ring A substituents and the electrostatic potentials of their ammonium molecules by DFT calculation., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Concise syntheses of 9-methoxyellipticine, 3,4-dihydroellipticine (µ-alkaloid D), 1,2,3,4-tetrahydroellipticine, 2-methyl-1,2,3,4-tetrahydroellipticine, olivacine, 3,4-dihydroolivacine, (±)-guatambuine, and (±)-janetine were developed starting from hexatriene intermediates readily obtained by Pd-catalyzed tandem cyclization/cross-coupling reaction of indolylborates. The route enables the facile construction of pyrido[4,3- b]carbazoles by Cu-catalyzed 6π-electrocyclization and subsequent transformation of the pyridocarbazole intermediates into pyrido[4,3- b]carbazole alkaloids. [ABSTRACT FROM AUTHOR]

In this study, we achieved the total synthesis of carbazole alkaloid mukoenine A through a seven-step sequence involving the construction of a carbazole framework using the electrocyclization of a 6π-electron system including an allene intermediate as the key step. Subsequently, the synthesis of pyrano[3,2- a ]carbazole alkaloid girinimbine was achieved by the construction of the pyran ring via selenoetherification of the o-allylic phenol moiety of mukoenine A. [Display omitted] • The total synthesis of mukoenine A has been accomplished via a seven-step sequence. • Girinimbine was synthesized by the construction of the pyran ring via mukoenine A. • The carbazole framework was constructed by the allene-mediated electrocyclization. [ABSTRACT FROM AUTHOR]

In this study, the total syntheses of 1,3,4-trisubstituted carbazole alkaloid clausamine E was accomplished via an eight-step sequence using construction of the 1,4-dioxygenated carbazole framework based on the cyclocarbonylation between 3-iodo-2-(prop-2-enyl)indole and CO (1 atm) in the presence of tributyl(vinyl)tin and a Pd catalyst. Image 1 • The total synthesis of clausamine E has been accomplished via an eight-step sequence. • Synthesis of 1,4-dioxygenated carbazoles by Pd-catalyzed cyclocarbonylation. • This method could be used as a versatile method to synthesize substituted carbazoles. [ABSTRACT FROM AUTHOR]

• The enantioselective total synthesis of (+)-asiaticumine A has been accomplished. • The construction of phenanthridine framework by MW-assisted electrocyclization. • The synthesis of 1,2-dihydroxyethyl moiety by Sharpless asymmetric dihydroxylation. • Its absolute configuration was determined to be S by Mosher's method. In this study, the first asymmetric enantioselective total syntheses of (+)-asiaticumine A (2) and its enantiomer were accomplished through a seven-step sequence using the bond formation between the C4a and N5 positions of the phenanthridine framework based on the microwave-assisted electrocyclization of cyclohexenylbenzaldoxime methyl ether as an aza 6π-hexatriene system followed by the Sharpless asymmetric dihydroxylation as the key step. In addition, the absolute configuration of natural (+)- 2 was determined to be S by Mosher's method. [ABSTRACT FROM AUTHOR]

Cu-catalyzed 6π-electrocyclization of triene-substrates of type (I) provides a facile access to pyrido[4,3-b]carbazoles, which represent advanced intermediates for the construction of various ellipticine and olivacine alkaloids. [ABSTRACT FROM AUTHOR]

The synthesis of alkaloid (I) is achieved in six steps in 60% overall yield from dihydroxymethylchromanone. [ABSTRACT FROM AUTHOR]