Analysis and purification of the diterpenes have been mainly carried out by HPLC (Gross et al., 1997, Hartman and Lago, 1973 and Kolling-Speer et al., 1999). The
most critical step of the whole process is the hydrolysis. The furan moiety of these diterpenes is labile, sensitive to acids, bases and oxidants, a problem associated with the heating procedure Selleck BMS-754807 commonly used to obtain the free diterpenes. Furthermore, kahweol is quite unstable in the free form, which highlights the importance of developing a more efficient and faster isolation method. Cafestol has been synthesised in many steps, being practically unfeasible (Corey, Wess, Xiang, & Singh, 1987). These difficulties have led to a restricted commercial availability of those furan diterpenes. In the field of organic chemistry, microwave irradiation proved to be a powerful method to enhance chemical processes. In many instances, the
use of sealed-vessel high-temperature microwave processing was able to dramatically reduce reaction times, consume less solvent, increase yields, reduce side reactions and improve reproducibility. Microwaves are known to be a more efficient heating method than traditional thermal processes. Reactions that require long reflux times can sometimes be carried out in a few hours or minutes in dedicated microwave irradiation equipment (Kappe, 2004). A significant number of reports have described microwave-assisted hydrolysis reactions and have shown them Atezolizumab order to be better than conventional heating (Cheng and Wu, 2011 and Richel et al., 2011). In the present study, a new method to obtain cafestol and kahweol was developed by a microwave-assisted protocol, through the methanolysis of the natural fatty acid furan diterpene derivatives present in green coffee oils (C. arabica). Methanol (HPLC grade), hexane and ethyl Rho acetate were purchased from Tedia (Rio de Janeiro, Brazil). Deionised water (Type I, 18 mΩ cm), filtered through a 0.45-μm pore size filter (Millipore, Bedford, MA) was used as an HPLC solvent. Potassium carbonate (K2CO3) was obtained
from Vetec (Duque de Caxias, Brazil). Brazilian commercial green coffee beans (C. arabica) were provided as a gift from Grão Mestre Café (Rio de Janeiro, Brazil). The beans were ground in a hammer mill grinder and sieved to obtain particles with diameters ranging from 0.297 to 0.59 mm. Thirty grams of the powder were transferred into a Soxhlet apparatus and extracted with 300 mL of hexane at 90 °C for about 16 h, in triplicate, according to the procedure developed by Araujo and Sandi (2006). The extract was filtered and the solvent removed using a rotary evaporator to yield 8.8% of oil. The procedure used to hydrolyse the diterpenes used 500 mg of green coffee oil which were treated with 3 mL of anhydrous methanol in the presence of 50 mg of K2CO3.