New methods for the synthesis of heterocyclic quinones (review)

Multigram scale synthesis of polycyclic lactones and evaluation of antitumor and other biological properties

An efficient four-step synthesis of tetracyclic lactones from 1,4-benzodioxine-2-carboxylic acid was developed. Ellipticine derivatives exhibit antitumor activity however only a few derivatives without carbazole subunit have been studied to date. Herein, several tetracyclic lactones were synthesized and biologically evaluated. Several compounds (2a, 3a, 4a and 5a) were found to be inhibitors of the Kras-Wnt pathway. The lactone 2a also exerted a potent inhibition of Tau protein translation and was shown to have capacity for CYP1A1-bioactivation. The results obtained are further evidence of the therapeutic potential of tetracyclic lactones related to ellipticine. Molecular modeling studies showed that compound 2a is inserted between helix α3 and α4 of the KRas protein making interactions with the hydrophobic residues Phe90, Glu91, Ile9364, Hie94, Leu133 and Tyr137and a hydrogen bond with residue Arg97.

Applications of Friedel-Crafts reactions in total synthesis of natural products

Over the years, Friedel-Crafts (FC) reactions have been acknowledged as the most useful and powerful synthetic tools for the construction of a special kind of carbon-carbon bond involving an aromatic moiety. Its stoichiometric and, more recently, its catalytic procedures have extensively been studied. This reaction in recent years has frequently been used as a key step (steps) in the total synthesis of natural products and targeted complex bioactive molecules. In this review, we try to underscore the applications of intermolecular and intramolecular FC reactions in the total syntheses of natural products and complex molecules, exhibiting diverse biological properties.

Total synthesis of ellipticine quinones, olivacine, and calothrixin B

A direct route to the synthesis of biologically active ellipticine quinones, olivacine, and calothrixin B is described. The prominent key steps involved are Friedel-Crafts hydroxyalkylation followed by oxidation and directed ortho-lithiation reactions of readily available indole-2-carboxylate esters with appropriately substituted pyridine and quinoline carboxaldehydes.

2,3-bis(2-pyridyl)-5,8-quinoxalinediones with metal chelating properties: synthesis and biological evaluation

The synthesis of 2,3-bis(2-pyridyl)-5,8-quinoxalinediones has been carried out in order to provide new antitumor drugs related to streptonigrin. Some derivatives have been found to possess significant cytotoxic properties and their mechanism of action has been studied. They were found to induce single-strand cleavage of covalently closed circular DNA (ccc-DNA). This biological activity requires an apparent in situ reduction (NADH activation) of the quinone to a hydroquinone or semiquinone radical, is facilitated by the presence of Cu(II), and involves activation of molecular oxygen to highly reactive radical species. Thus, although less active than the parent drugs, these molecules provide an attractive rationale for the observed cytotoxic and antitumor potency, as well as the cell-free single strand DNA cleavage efficacy of that family of drugs.