**2.3 Quinones**

Quinones are normally classed on the basis of their molecular structure, and accordingly, they are classified into three major groups: anthraquinones, benzoquinones, naphthoquinones. The three classes of quinones are aromatic ring based where anthraquinones, benzoquinones, and naphthoquinones have linear/angular anthracene ring, benzene ring, and naphthalenic ring, respectively [46]. Benzoquinones were isolated and had a substantial *in vitro* antimalarial action especially against strains of *P. falciparum* in a number of studies [47–49]. Recent studies on antimicrobial activity of quinones-rich *Aspidosperma nitidum* indicated strong *in vitro* antimalarial efficacy against W2 strain of *P. falciparum* and *P. berghei* in vivo respectively [50].

*Co-Crystallization of Plant-Derived Antimalarial Drugs: An Alternate Technique for Improved… DOI: http://dx.doi.org/10.5772/intechopen.106200*

#### **Figure 3.** *Some examples of the antimalarial quinones.*

Naphthoquinones such as atovaquone were identified and have shown antimalarial activity due to their quinonic nature [51, 52]. Plant-based quinones including 2-acetylnaphtho-[2,3b]-furan-4,9-dione and plumbagin high activity against *P. berghei* (IC50 = 0.002 μgml−1) and *P. falciparum* (IC50 = 0.05 μgml−1) respectively (**Figure 3**) [50, 53, 54].
