Cyanidin‐3‐glucoside lipophilic conjugates for topical application: Tuning the antimicrobial activities with fatty acid chain length

Background: Natural anthocyanins present a low solubility in lipophilic media, which compromises their effective application in lipophilic systems. In this work, cyanidin‐3‐O‐glucoside (Cy3glc) was esterified by the addition of fatty acids with increasing chain‐lengths and a structure-activity relationship was performed towards the description of the best analog for skin‐care applications. Methods: By enzymatic hemi‐synthesis, it was possible to obtain 5 structurally related derivatives of cyanidin‐3‐O‐glucoside with successive C2 increments in the aliphatic chain. The stability in hanks buffer and DMEM with or without FBS was followed by HPLC. The cytotoxicity against keratinocytes was evaluated by MTT assay. The antioxidant capacity was determined by using the fluorescent probe DCF‐DA. The effect on enzyme activity was evaluated towards tyrosinase, collagenase, and elastase enzymes by colorimetric assays. MIC and MBC values were obtained against reference strains and against multidrug‐resistant isolates. Results: In physiological conditions, cy3glc−fatty acid derivatives are more stable and may be converted to the native anthocyanin. The 5 conjugates showed lower antioxidant capacity and enzymatic inhibitory activities in comparison to the anthocyanin precursor. However, concerning the antibacterial activity, the insertion of a fatty acid chain sprouted the antibacterial activity, showing a clear biphasic effect and a more effective effect on Gram‐positive bacteria. Conclusions: Cy3glc‐C10 was the most effective compound considering the antimicrobial activity, although a general reduction was observed among the other activities evaluated. This work prompt further assays with a different panoply of derivatives ranging other features including saturation vs. unsaturation, even vs. odd carbon content and linear vs. branched.