Comprehensive bioanalytical multi-imaging by planar chromatography in situ combined with biological and biochemical assays highlights bioactive fatty acids in abelmosk

Abstract

The identification of the bioactivity of individual compounds in natural products is helpful to understand their therapeutic applications. Thus, a bioanalytical multi-imaging screening was developed and applied to 54 bark, leaf and seed extracts of Sri Lankan Abelmoschus moschatus (abelmosk) to find out the most bioactive individual compounds. The focus was laid on a comprehensive bioactivity profiling of its extracts. High-performance thin-layer chromatography (HPTLC) was hyphenated with seven effect-directed assays (EDA), i. e. biological (Gram-negative Aliivibrio fischeri and Gram-positive Bacillus subtilis), biochemical (α-glucosidase, β-glucosidase, acetylcholinesterase and tyrosinase) and chemical (2,2-diphenyl-1-picrylhydrazyl) assays. This multi-imaging was complemented by ultraviolet (UV), white light (Vis), fluorescence detection (FLD) and eight microchemical derivatizations. Heated electrospray ionization high-resolution mass spectrometry (HESI-HRMS) was used to characterize the most prominent multi-potent compound zone. It consisted of coeluting unsaturated fatty acids (linoleic acid and oleic acid), but also saturated fatty acids (palmitic acid and to a lower extent stearic acid, arachidic acid and behenic acid). For confirmation of the detected effects (antibacterial, free radical scavenger and inhibitor of α-glucosidase, β-glucosidase, acetylcholinesterase and tyrosinase), oleic acid was exemplarily analyzed by co-development and overlapped application (with sample). The proven effects underlined the beneficial health effects derived from unsaturated fatty acids like oleic acid. Exemplarily, the α-glucosidase and tyrosinase inhibition responses of the multi-potent compound zone were quantified equivalently in reference to oleic acid. The comparable results obtained by two independent enzymatic responses successfully proved the use of biochemical quantification by planar enzyme assays, and thus the new method based on HPTLC-UV/Vis/FLD-EDA-HESI-HRMS.

Keywords: Antibacterial; Bioprofiling; Enzyme inhibitor; HPTLC-UV/Vis/FLD-EDA-HESI-HRMS; Planar bioassay; Radical scavenger.