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New Synthetic Routes for the Valorization of Easily Accessible Bio-renewable Resources
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The olive tree (Olea europaea) is a natural source of a diversity of phenolic compounds, including secoiridoids. Oleuropein is the major secoiridoid found in olive tree and other plants from the Oleaceae family. It is found in olive fruit and small branches, although exists in higher amounts in olive leaves. Olive leaves are by-products from olive oil industries, and have no practical applications, being considered an easily accessible bio-renewable resource of oleuropein.
The molecular structure of oleuropein is divided in three subunits: hydroxytyrosol, glucose and monoterpene moieties. The glucose unit confers solubility in water, while hydroxytyrosol is responsible for most of its biological properties. However, the monoterpene moiety is more interesting in chemical reactivity point of view, having two asymmetric centers and seven potential reactive positions, available for synthetic modifications.
This work consisted on the extraction and isolation of oleuropein from olive leaves and the study of semi-synthetic transformations in order to obtain new derivatives, by removal of the glucose and hydroxytyrosol moieties, and modifications at monoterpene core, focusing on a complete study of the methanolysis reaction of oleuropein in acidic conditions. It was based on a screening of protic acids and acidic resins and a study of the temperature effect, with quantitative analysis by HPLC-UV, complemented by a mechanistic study of the reaction. A continuous flow approach was also performed, with positive results.
In one pot, the methanolysis reaction allowed several transformations on the molecular structure of oleuropein, with formation of a compound with reported antiviral activity and used as precursor on an anti-hypertensive drug synthesis, as well as compounds with potential to be used in the synthesis of derivatives with novel pharmaceutical properties and other additional interest.
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Oleuropein Olive leaves Biomass Methanolysis Catalysis