Competition with covalently labelling indolinones (e.g. 2) not equipped with the JQ1ligand will occupy the DCAF11 binding site and, thereby, prevent BRD2 degradation such that higher BRD2 levels after pretreatment indicates more potent DCAF11labelling by the respective indolinone derivatives. A series of compounds consisting of 29 arylidene indolinone analogs 18-46 was obtained (for structures see Table ) and their activity was ranked by means of the qualitative ICW assay (Fig. ). As a general trend, variation of the substitution pattern in the phenyl ring of the benzylidene substituent is tolerated. However, more pronounced deviations from the phenyl ring to e.g. heterocycles in the 3-arylidene substituent lead to a decrease in activity (compare compound 2 with compounds 18-25). Introduction of different substituents into the indolinone core is tolerated as well. In particular, a Br at the 6-position (45), or functionalization of the indolinone N with a phenyl group (46) led to increased activity (Fig. , Table and Supplementary Fig. ). These results were confirmed by determination of the degradation activity of the corresponding bifunctional degraders 47 and 48 (derived from 45 and 46 respectively; Fig. and Supplementary Fig. ), and their degradation activities were also based on DCAF11 (Supplementary Fig. ).