Design and synthesis of Rhodamine 110 derivative and Caspase-3 substrate for enzyme and cell-based fluorescent assay

N-Octyloxycarbonyl-R110 (1), with enhanced cell penetration and retention properties, was prepared from rhodamine 110. The tetrapeptide substrate N-Ac-DEVD-N′-octyloxycarbonyl-R110 (3) was prepared and shown to be efficiently cleaved by human recombinant caspase-3 and by apoptotic HL-60 cells. This substrate should prove useful in cell-based assays for apoptosis inducers and inhibitors.