1-Methyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole-d3 is labelled 1-Methyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole (M330225) which is patented as a reagent to synthesize quinoxaline derivatives or heterocyclylamine derivatives as PI3 kinase inhibitors.