A synthesis of spiroindolo[2,1-b]quinazoline-6,2'-pyrido[2,1-b][1,3]oxazines from tryptanthrins and Huisgen zwitterions

Recent Strategies in the Nucleophilic Dearomatization of Pyridines, Quinolines, and Isoquinolines

Dearomatization reactions have become fundamental chemical transformations in organic synthesis since they allow for the generation of three-dimensional complexity from two-dimensional precursors, bridging arene feedstocks with alicyclic structures. When those processes are applied to pyridines, quinolines, and isoquinolines, partially or fully saturated nitrogen heterocycles are formed, which are among the most significant structural components of pharmaceuticals and natural products. The inherent challenge of those transformations lies in the low reactivity of heteroaromatic substrates, which makes the dearomatization process thermodynamically unfavorable. Usually, connecting the dearomatization event to the irreversible formation of a strong C-C, C-H, or C-heteroatom bond compensates the energy required to disrupt the aromaticity. This aromaticity breakup normally results in a 1,2- or 1,4-functionalization of the heterocycle. Moreover, the combination of these dearomatization processes with subsequent transformations in tandem or stepwise protocols allows for multiple heterocycle functionalizations, giving access to complex molecular skeletons. The aim of this review, which covers the period from 2016 to 2022, is to update the state of the art of nucleophilic dearomatizations of pyridines, quinolines, and isoquinolines, showing the extraordinary ability of the dearomative methodology in organic synthesis and indicating their limitations and future trends.

Synthesis and in vitro evaluation of antitumor activity of spiro[indolo[2,1-b]quinazoline-pyrano[2,3-d]pyrimidine] and spiro[indolo[2,1-b]quinazoline-pyrido[2,3-d]pyrimidine] derivatives by using 2D and 3D cell culture models

Cancer as one of the biggest human health problems remains unsolved. The identification of novel platforms with the highest efficacy and low toxicity is a big challenge among interested researchers. In this regard, we are interested to synthesis and evaluate antitumor activity of spiro[indolo[2,1-b]quinazoline-pyrano[2,3-d]pyrimidine] and spiro[indolo[2,1-b]quinazoline-pyrido[2,3-d]pyrimidine] derivatives. The spiro heterocycles were synthesized via four-component reaction of isatoic anhydride, isatins, malononitrile, and some CH-acids including barbituric acid/thiobarbituric acid and 4(6)-aminouracil in CH₂Cl₂ under reflux condition. The significant features of this process are short reaction time, easy purification without chromatographic process, and high yields which make it attractive. Next, we employed 2D and 3D cell culture models to evaluate biological activity of our compounds. Our results showed that among our seven products (4a-g), the compounds 4a and 4e are the best with 50% growth inhibitory concentration (IC₅₀) value lower than etoposide. Our results support this idea that the compounds 4a and 4e may be potential for drug designing in cancer therapy. However, more experiments will be required to find possible side effects of related compounds in vivo.