Abstract

Quinones represent one of the most widespread groups of secondary metabolites in nature. These natural phenolic compounds occur in various families of plants, fungi, bacteria and insects, and play an important role as biologically active compounds in many biological electron-transfer processes, such as respiration and photosynthesis. Plant extracts containing naphthoquinones, an important subgroup of the quinones families, have been used for long time as traditional medicines and, presently, are being the focus of attention of researchers mostly because of their well-known and broad-range of biological activities (such as phytotoxic, insecticidal, antibacterial, fungicidal, anti-inflammatory, antiviral, and cytotoxic effects). In particular, the positive effect on human health of menadione (2-methyl-1,4- naphthoquinone or vitamin K3) has prompted its study by the pharmaceutical industry. Menadione is a fat-soluble vitamin that is used as an antihemorrhagic factor, a precursor of vitamin K that is transformed to menaquinone-4 and deposited in brain tissue, and a promising oncogenic agent against mammalian. The synthesis, purification and evaluation processes of menadione derivatives can be justified taking into account the potential positive pharmacologic effects of new compounds, when the incorporation of electronegative elements, such as halogens, nitro and sulfur groups substitutes, introduce new patterns of biological properties. Dichlone (2,3-dichloronaphthalene 1,4-dione) is a derivate that can be synthetized substituting the hydrogen atoms in positions on the 1-4 naphthoquinones, confers to its derivatives specific biological properties, including bactericidal activity, anticancer activity, and antimicrobial activity. The study related to the biological and other valuable effects of solid derivatives from 1-4 naphthoquinones requires their chemical synthesis and the recovery and/or purification according to the chemical structure of each derivative previously defined. Supercritical technology is an interesting alternative widely used to obtain natural extracts. Extractions using supercritical car- bon dioxide (scCO2) have some advantages over traditional extraction techniques, since they generate extracts free of toxic residues. Furthermore, carbon dioxide is cheap, inert, non-flammable and presents low critical temperature and pressure values, making attractive for extraction and fractionation of thermosensitive compounds. This contribution focuses on the description of the relationship between solubility behavior and chemical structure of quinone derivatives at different conditions of temperatures and pressure, and can be considered as a preliminary study to predict thermodynamics and biological aspect of new chemical derivatives.