Detection and quantification of cyclo-dopa amides in Portulaca oleracea L. by HPLC-DAD and HPLC-ESI-MS/MS

Phytochemical Composition and Antioxidant Activity of Portulaca oleracea: Influence of the Steaming Cooking Process

“…Compounds 10 , 13 , 14 , 15 , 16 , 19 , 20, and 21 were characterized as cyclo-dopa amides, named oleraceins. In previous works, the presence of these phenolic alkaloids has been reported in Portulaca oleracea [ 19 , 36 , 37 ]. Compound 10 was identified as oleracein C, with [M-H] − at m/z 664 and fragment ions at m/z 502 ([M-Glc-H] − ; Glc = glucoside) and 340 ([M-Glc-Glc-H] − ) [ 19 ].…”

“…Compound 13 showed an [M-H] − ion at m/z 680. This compound has not been previously identified and, according to the study of the fragments, we propose a similar structure to oleracein J but without the ferulic acid group [M-C 10 H 8 O 3 -H] − [ 19 ], naming it as oleracein X, following the order of nomenclature of the compounds of this alkaloid family, whose structure was determined as 5-hydroxy-1-caffeic acyl-2,3dihydro-1 H -indole-2-carboxylic acid-6- O -diglucoside (C 30 H 35 NO 17 ) ( Figure 4 ). The fragment ions of oleracein X were m/z 518 (neutral loss of 163 Da corresponding to a caffeic acyl group ([M-C 9 H 6 O 3 -H] − )), m/z 356 (neutral loss of 325 Da belonging to two glucoside molecules ([M-C 12 H 20 O 10 -H] − )), m/z 246 (neutral loss of 435 Da corresponding to 325 Da and 110 Da from two glucoside (Glc) molecules and a 1,2-dihydroxybenzene molecule ([M-2Glc-C 6 H 5 O 2 -H] − )), and m/z 202 (neutral loss of 479 Da belonging to 435 Da of the loss explained previously and an additional loss of 44 Da from a carboxylic group ([M-2Glc-C 6 H 5 O 2 -CO 2 -H] − )).…”

“…It presented an [M-H] − ion at m/z 532 and the typical fragmentation of this alkaloid ( m/z 370, 326, 282) [ 10 ]. Compound 19 was characterized as another cyclo-dopa amide, specifically, oleracein N. It displayed an [M-H] − ion at m/z 840 and the fragment ions characteristics of this alkaloid ( m/z 694, 664, 518) [ 19 ]. Compound 20 was tentatively characterized as oleracein U, due to the [M + H] + ion at m/z 342 and base peak at m/z 147, previously reported in bibliography [ 13 ].…”

“…Compound 21 was identified as oleracein J. It showed [M-H] − ion at m/z 856 and the typical fragments ion of this cyclo-dopa amide ( m/z 694, 680, 356, and 246) [ 19 ]. In Figure 5 , all the oleraceins reported in scientific literature (oleracein A to oleracein W, including the new oleraceins X and Y) have been gathered, showing the chemical structures and molecular ions [M-H] − [ 12 , 19 , 38 , 39 , 40 ].…”

“…Compounds such as caffeic acid, ferulic acid, kaempferol, quercetin, and rutin have been previously identified [ 10 , 11 , 12 , 13 , 14 , 16 , 17 , 18 ]. This plant also shows a class of alkaloids, which are secondary metabolites, named cyclo-dopa amides, or oleraceins, are increasing the general interest [ 12 , 13 , 19 ]. These compounds show more or similar potent antioxidant characteristics than some natural antioxidants such as vitamin C and vitamin E [ 12 , 13 ].…”