Synthesis of Xanthones: An Overview

Abstract

Among the known synthetic routes to obtain xanthones, the Grover, Shah, and Shah reaction, the cyclodehydration of 2, 2'-dihydroxybenzophenones and electrophilic cycloacylation of 2-aryloxybenzoic acids are the most popular methods. Due to important biological applications of xanthones, some synthetic strategies leading to more complex derivatives have been widely explored in the past years. Thus, the purpose of this review is to report some recent improvements of the classical synthetic methods as well as of some non-classical methods to obtain simple oxygenated xanthones. The strategies for introduction of substituents into the xanthonic nucleus are also summarized. Furthermore, different approaches used to synthesize complex structures, with an emphasis on the total synthesis of bioactive natural products, accomplished in the last twenty years, are also discussed. Besides the synthesis of xanthones, the reactivity of the xanthonic nucleus and its role as a key intermediate for the synthesis of other important classes of compounds are also highlighted.

Naturally Occurring Xanthones: Chemistry and Biology

“…Furthermore, in these cell cultures, compound (1) is selectively oxidized by a xanthone 6-hydroxylase to 1,3,5,6-tetrahydroxyxanthone [129]. Explored methods for synthesis of simple oxygenated xanthones have been documented by Sousa and Pinto [130].…”

A Physico-Biochemical Study on Potential Redox-Cyclers as Antimalarial and Antischistosomal Drugs

“…We now described a thorough physico-biochemical study of six compounds (Figure 6), which was conducted to gain a deeper understanding of the mechanism of action by which xanthone [16,63] and 1,4-naphthoquinone substrates could act as potential inhibitors of β-hematin crystallization through redox-cycling and exert antimalarial or antischistosomal activities. Plasmodium and Schistosoma parasites digest methemoglobin, resulting from endogenous oxidation of hemoglobin, as a source of essential nutrients (aminoacids) and detoxify the toxic free heme released during methemoglobin digestion via its biocrystallization into an insoluble and “inert” crystal called hemozoin (or malaria pigment or Schistosoma pigment, Figure 1).…”

Polyprenylated Phloroglucinols and Xanthones

“…Polyprenylated xanthones constitute a subclass of a larger class of compounds known as xanthones, all bearing a dibenzo-γ -pyrone scaffold [62]. Polyprenylated xanthones can further be divided, according to their oxidation degree, into mono-, di-, tri-, and so on, oxygenated compounds.…”

“…Polyprenylated xanthones can further be divided, according to their oxidation degree, into mono-, di-, tri-, and so on, oxygenated compounds. Recently, the classification, synthesis, and biological evaluation of simple xanthones have been reviewed extensively [62][63][64][65][66][67][68][69][70][71]. In this chapter we focus on the so-called caged Garcinia xanthones (CGXs), owing to their similarities (isolation, biosynthesis) to the aforementioned polyprenylated phloroglucinols.…”