Concise synthesis of 22-hydroxyacuminatine, cytotoxic camptothecinoid from Camptotheca acuminata, by pyridone benzannulation

Progress on the Synthesis of the Aromathecin Family of Compounds: An Overview

We present a systematic review of the methods developed for the synthesis of the aromathecin family of compounds (benz[6,7]indolizino[1,2-b]quinolin-11(13H)-ones) and their derivatives. These methods can be broadly classified into four categories based on the construction of pentacyclic structures: Category 1: by constructing a pyridone moiety (D-ring) on the pyrroloquinoline ring (A/B/C-ring), Category 2: by constructing a pyridine moiety (B-ring) on the pyrroloisoquinolone ring (C/D/E-ring), Category 3: by constructing an indolizidinone moiety (C/D-ring) in a tandem reaction, and Category 4: by constructing a pyrrolidine moiety (C-ring) on the isoquinolone ring (D/E-ring).

Synthesis of a 2(1H)-pyridone library via rhodium-catalyzed formation of isomunchones

Through the use of the dipolar cycloaddition of isomunchones with olefins the 2(1H)-pyridone ring system has been synthesized. (1) The use of different cyclization partners followed by diversification of the initial scaffold has provided libraries of 4-hydroxy-2(1H)-pyridones. There are no examples of this ring system in either PubChem or the MLSMR.

The structure-activity relationships of A-ring-substituted aromathecin topoisomerase I inhibitors strongly support a camptothecin-like binding mode

Aromathecins are inhibitors of human topoisomerase I (Top1). These compounds are composites of several heteroaromatic systems, namely the camptothecins and indenoisoquinolines, and they possess notable Top1 inhibition and cytotoxicity when substituted at position 14. The SAR of these compounds overlaps with indenoisoquinolines, suggesting that they may intercalate into the Top1-DNA complex similarly. Nonetheless, the proposed binding mode for aromathecins is purely hypothetical, as an X-ray structure is unavailable. In the present communication, we have synthesized eight novel series of A-ring-substituted (positions 1-3) aromathecins, through a simple, modular route, as part of a comprehensive SAR study. Certain groups (such as 2,3-ethylenedioxy) moderately improve Top1 inhibition, and, often, antiproliferative activity, whereas other groups (2,3-dimethoxy and 3-substituents) attenuate bioactivity. Strikingly, these trends are very similar to those previously observed for the A-ring of camptothecins, and this considerable SAR overlap lends further support (in the absence of crystallographic data) to the hypothesis that aromathecins bind in the Top1 cleavage complex as interfacial inhibitors in a 'camptothecin-like' pose.

Synthesis and biological evaluation of 14-(aminoalkyl-aminomethyl)aromathecins as topoisomerase I inhibitors: investigating the hypothesis of shared structure-activity relationships

The aromathecin topoisomerase I (top1) inhibitors offer promising scaffolds for the development of novel cancer chemotherapeutics. They are 'composites' of the camptothecin and indenoisoquinoline top1 inhibitors. Interestingly, some structure-activity relationship (SAR) overlap between the aromathecins and the indenoisoquinolines has been observed. For both classes, placement of certain polar groups in similar regions of the heteroaromatic system improves top1 inhibitory and antiproliferative activities. A series of water-soluble aromathecins substituted at position 14 with diaminoalkanes of various lengths has been prepared. These compounds all possess similar antiproliferative potency, but a general trend is observed: aromathecins with longer diaminoalkane substituents (>6 carbons) possess lower anti-top1 activity than their smaller counterparts (2-4 carbons), presumably as a result of unfavorable hydrophobic interactions. This trend is also noted with the indenoisoquinolines, revealing additional SAR overlap that supports the hypothesis that there is a 'universal' top1 inhibitor SAR.

Design, synthesis, and biological evaluation of 14-substituted aromathecins as topoisomerase I inhibitors

The aromathecin or "rosettacin" class of topoisomerase I (top1) inhibitors is effectively a "composite" of the natural products camptothecin and luotonin A and the synthetic indenoisoquinolines. The aromathecins have aroused considerable interest following the isolation and total synthesis of 22-hydroxyacuminatine, a rare cytotoxic natural product containing the 12 H-5,11a-diazadibenzo[ b, h]fluoren-11-one system. We have developed two novel syntheses of this system and prepared a series of 14-substituted aromathecins as novel antiproliferative topoisomerase I poisons. These inhibitors are proposed to act via an intercalation and "poisoning" mechanism identical to camptothecin and the indenoisoquinolines. Many of these compounds possess greater antiproliferative activity and anti-top1 activity than the parent unsubstituted compound (rosettacin) and previously synthesized aromathecins, as well as greater top1 inhibitory activity than 22-hydroxyacuminatine. In addition to potentially aiding solubility and localization to the DNA-enzyme complex, nitrogenous substituents located at the 14-position of the aromathecin system have been proposed to project into the major groove of the top1-DNA complex and hydrogen-bond to major-groove amino acids, thereby stabilizing the ternary complex.

Synthesis and bioevaluation of 22-hydroxyacuminatine analogs

A series of 22-hydroxyacuminatine analogs was prepared by using different Friedländer condensations. Several of the new compounds were tested for antiproliferative activity on cancer cell lines and for topoisomerase I inhibitory activity.

Short and efficient total synthesis of luotonin A and 22-hydroxyacuminatine using a common cascade strategy

Total syntheses of 22-hydroxyacuminatine and luotonin A were achieved in direct fashion and high overall yields (16% in eight steps and 47% in five steps, respectively). A mild cascade methodology was successfully applied in both syntheses as a common strategy. The new approach presents the advantages of short routes, high overall yields, use of stable intermediates, and ease of operations.

Novel, efficient total synthesis of natural 20(S)-camptothecin

Enantiopure 20(S)-camptothecin has been prepared from a known hydroxypyridone through a novel approach that involves a Claisen rearrangement, an asymmetric nucleophilic ethylation, a Heck coupling and a Friedländer condensation as the key transformations.