Phytosterol and alpha-lipoic acid conjugates: synthesis, free radical scavenging capacity and RP-LC-MS-APCI analysis

Plant sterols (PS) are bioactive compounds effective in reducing plasma cholesterol. Fatty acid esters of PS have improved solubility and blending properties when utilized in various food products. Naturally occurring α-lipoic acid (LA) and its reduced form dihydrolipoic acid (DHLA) are known for their antioxidant activity. In addition, they have shown an array of health benefi cial properties against obesity, diabetes, cancer, cardiovascular and infl ammatory diseases etc. Different LA conjugates have been reported to have increased bioactivity compared to the parent compounds. The objective of this study was to synthesize PS esters of LA (PSLA) and DHLA (PSDHLA) in order to increase their cholesterol lowering effect and reducing the risk of atherosclerosis with additional health benefi ts e.g. against oxidative stress. Synthesis of PSLA and PSDHLA was performed with a pure PS mixture of β-sitosterol, stigmasterol, campesterol and brassicasterol. The free radical scavenging capacity of the conjugates was assessed by the DPPH method. Remaining percentage of DPPH free radicals was measured at the steady state for different concentrations of PSLA and PSDHLA. High free radical scavenging capacity was observed for PSDHLA compared with PSLA. Effi cient concentration EC50 as a molar ratio for PSDHLA was 0.43. The derivatives were analyzed by RP-HPLC-MS-APCI. The order of the elution times of the compounds observed in HPLC-MS analysis was PS< PSDHLA< PSLA. Baseline separation was not achieved between campesterol and stigmasterol and their derivatives. These compounds could be identifi ed by their characteristic fragment ions from the mass spectral data.

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