Study of Organic Radicals Generated upon Naphthoquinone-Hydantoins Reactions in Basic Aqueous Solution

Abstract

In this work, the synthesis of thiohydantoins from L-amino acids and isothiocyanates was studied, using a high purity method based on the Edman cycle. This process, expected to occur through Michael addition to a series of 1,4-naphthoquinone derivatives did not lead to the expected final product, rather leading to a colored mixture of compounds, where ESR spectra showed that some of them presented unpaired electrons, indicating that an electron transfer pathway was also involved in the reaction mixture. Detected organic radicals proved to be stable albeit the use of different experimental conditions. Voltammetric results indicate that the reactions lead to the formation of electroactive species, probably derived by homogeneous electron transfer between the reactive quinone moieties and the oxidizable urea functions within the hydantoin species.

The Relevance and Insights on 1,4-Naphthoquinones as Antimicrobial and Antitumoral Molecules: A Systematic Review

“…The hydroxyl-1,4 naphthoquinones such as juglone 2, lawsone 3, plumbagin 4, and lapachol 5 are natural NQs isolated from plants extensively used in traditional Indian medicine [15][16][17][18]. In the past decades, the substitution of diverse groups and modifications in the NQs ring have provided many derivatives with enhanced biological activity [19][20][21][22][23][24][25][26][27][28][29][30][31][32]. In this respect, lawsone derivatives, 3-(aminomethyl)-2-hydroxy-1,4-naphthoquinones 6, or amino naphthoquinone Mannich bases have been synthesized and evaluated as anticancer, antimalarial, antiviral, antifungal, and antibacterial molecules [19,20]; amino 7, and thioether 8 NQs (Figure 1), as well as the NQs with aromatic amines in carbon two or three, may tune their antifungal and antibacterial activity and anticancer activity, being the case for 2-acetyl-3-aminophenyl-1,4-naphthoquinones 9, which has been evaluated for in vitro antiproliferative activity against several types of human cancer cells with very promising results [21].…”

“…The indole quinone subunit is an important framework of the mitomycin family of antitumor agents [22][23][24][25]. Hence, efforts to develop methods to assemble polycyclic compounds containing pyrrole and quinone have been conducted by researchers [26,32]. Among them, pyrido [2,3-d]pyrimidine 12 and phenazine 13 ring systems (Figure 1) are principal skeletons among many pharmaceutical scaffolds with applications in synthetic and medicinal chemistry.…”