Cytotoxic bis-3,4-dihydro-beta-carbolines and bis-beta-carbolines

β-Carbolines as potential anticancer agents

β-Carbolines are indole alkaloids having a tricyclic pyrido[3,4-b]indole ring in their structure. Since the isolation of first β-carboline from Peganum harmala in 1841, the isolation and synthesis of various β-carboline derivatives surged in the following centuries. β-Carboline derivatives due to their widespread availability from natural sources, structural flexibility, quick reactivity and interaction with varied anticancer targets such as DNA (intercalation, groove binding, etc.), enzymes (GPX4, topoisomerases, kinases, etc.) and proteins (tubulin, ABCG2/BRCP1, etc.) have established themselves as promising lead compounds for the synthesis of various anticancer active agents. The current review covers the synthesis and isolation, anticancer activity, mechanism of action and SAR of various β-carboline containing molecules, its derivatives and congeners.

CuBr2-Catalyzed Mild Oxidation of 3,4-Dihydro-β-Carbolines and Application in Total Synthesis of 6-Hydroxymetatacarboline D

A green chemical method for the conversion of 3,4-dihydro-β-carbolines to β-carbolines has been developed using air as the oxidant. With 15 mol % CuBr₂ as the catalyst, 3,4-dihydro-β-carbolines could be efficiently oxidized to β-carbolines in dimethyl sulfoxide at room temperature in the presence of 1,8-diazabicyclo[5,4,0]undec-7-ene (or Et₃N). By applying this method, the first total synthesis of 6-hydroxymetatacarboline D was performed through 12 steps in 22% overall yield starting from l-5-hydroxy-tryptophan.

Design, synthesis and 3D-QSAR of beta-carboline derivatives as potent antitumor agents

In a continuing effort to develop novel beta-carbolines endowed with better pharmacological profiles, a series of beta-carboline derivatives were designed and synthesized based on the previously developed SARs. Cytotoxicities in vitro of these compounds against a panel of human tumor cell lines were also investigated. The results demonstrated that the N2-benzylated beta-carbolinium bromides 56-60 represented the most potent compounds with IC50 values lower than 10 microM. The application of 3D-QSAR to these compounds explored the structural basis for their biological activities. CoMFA (q2=0.513, r2=0.862) and CoMSIA (q2=0.503, r2=0.831) models were developed for a set of 47 beta-carbolines. The results indicated that the antitumor pharmacophore of these molecules were marked at position-1, -2, -3, -7 and -9 of beta-carboline ring.

Synthesis and in vitro cytotoxic evaluation of novel 3,4,5-trimethoxyphenyl substituted beta-carboline derivatives

To elucidate further our SARs' study on the chemistry and cytotoxic activity and probe the structural requirement for the potent antitumor activity of beta-carbolines, a series of novel 1,9-disubstituted and 1,3,9-trisubstituted beta-carboline derivatives were designed and synthesized from the starting material L-tryptophan and 3,4,5-trimethoxybenezaldehyde. Cytotoxic activities of these compounds in vitro were investigated, and the SARs associated with position-1, 3 and 9 substituents in beta-carbolines have also been discussed. It has been observed that these compounds only displayed moderate to weak cytotoxic activities. Interestingly, most of the investigated compounds displayed selectively cytotoxic activities to human BCG-823 cell lines with IC(50) value lower than 100 microM. In addition, the short alkyl substituents in position-9 increased the cytotoxic activities with the tendency of n-butyl > ethyl > methyl. These data confirmed that (1) an alkyl substituent at position-9 of beta-carboline nucleus plays an important role in determining their antitumor activities; (2) different beta-carbolines bearing various substituents in beta-carboline nucleus interacted selectively with specific targets leading to the difference of biochemical and pharmacological effects.