C199 is a PROTAC degrader targeting PRMT4 with a DC50 of 106 nM. It demonstrates high selectivity for PRMT4 compared to other protein arginine methyltransferases. C199 exhibits strong cellular degradation capacity and induces apoptosis in multiple myeloma cell lines. It efficiently eliminates PRMT4 protein through the VHL-proteasome pathway. C199 has a relatively long half-life and shows potent anti-multiple myeloma (MM) activity.