Bioprofiling of Mexican Plectranthus amboinicus (Lour.) essential oil via planar chromatography–effect-directed analysis combined with direct analysis in real time high-resolution mass spectrometry

Aerial parts of Plectranthus amboinicus (Lour.) were collected in the Northern Mexico City for a comprehensive effect-directed profiling. Its hydrodistilled P. amboinicus essential oil (PAEO) was separated on HPTLC silica gel plates with n-hexane—ethyl acetate—ethanol, 95:3:2, followed by derivatization with the anisaldehyde–sulfuric acid reagent. The UV/Vis/FLD detection was expanded by a biological and biochemical detection. Eight different effect-directed assays were performed including the 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay as well as biochemical assays for inhibition of acetylcholinesterase, α- and β-glucosidases, α-amylase and tyrosinase as well as antimicrobial assays against Gram-negative Aliivibrio fischeri and Gram-positive Bacillus subtilis bacteria. The bioprofiling, subsequent direct analysis in real time mass spectrometry of the detected five bioactive compound zones and comparison with literature data resulted in the tentative assignment of caryophyllene oxide (hR_F 20), α-humulene (hR_F 26), carvacrol (hR_F 40), methyl carvacrol ether (hR_F 76) and caryophyllene (hR_F 84). The antimicrobial activity against Gram-negative bacteria of PAEO was elicited by a mixture of the multi-potent compounds, whereas α-humulene was strongly acting against Gram-positive bacteria. The antioxidant effect was related to carvacrol and the inhibitory effect over AChE, tyrosinase and glucosidases to α-humulene.