**4. Conclusion**

The effects of several factors on the acylation reaction of rutin by hexadecanedioate acid were investigated. The reactions conducted at 80 ‐ 90°C showed high performances. The increase of rutin concentration from 65 mM to 196 mM led to the formation of mono ester (rutin 4‴‐ hexadecanedioate) and diester (dirutin 4‴, 4‴‐hexadecanedioate). The molar ratio diacid/ rutin (0.05 to 20) affects the selectivity of the reaction. In fact, in presence of excess of rutin both monoester and diester were synthesized. However, with diacid excess only the mono‐ ester was obtained. The results showed also that the water content of the media is a crucial factor. Drying the media by adding the molecular sieves in the outer loop of the reactor was the most efficient technique leading to water content lower than 200 ppm. In these condi‐ tions, the highest performances (conversion yield, initial rate) were reached at 90°C, 131 mM of rutin, 118 mM of acid, and 20 g/L of biocatalyst. At the equilibrium (50 hours), conversion yields of acid and rutin were respectively 73 and 74%, initial rate of monorutin ester formation was 2.20 mM/h and productivity was 1.44 g/(L/h). Depending on the water content and the diacid/rutin molar ratio, only mono‐ or both mono‐ and di‐rutin esters were synthesized. For water content higher than 800 ppm, only rutin 4‴‐hexadecanedioate was produced. At lower water content (<400 ppm), both rutin 4‴‐hexadecanedioate and dirutin 4‴, 4‴‐hexadecanedio‐ ate were observed. Higher values of diacid/rutin molar ratio favor the formation of monorutin ester.

Depending on the target application, the level of water content and molar ratio can be used to modulate the production of only mono‐ or both mono‐ and di‐ester. The acylation reaction took place only on the glycosidic part, which is the main quality to preserve or enhance the biologic activity of flavonoids. In a further study, physicochemical and biological activity of synthesized esters will be evaluated.
