Synthesis and immunosuppressive activity of novel prodigiosin derivatives

Prodigiosins (Ps) represent a family of naturally occurring red pigments ch aracterized by a common pyrrolylpyrromethene skeleton. Some members of this family have been shown to possess interesting immunosuppressive properties exerted with a novel mechanism of action, different from that of currently used drugs. In fact, Ps inhibit phosphorylation and activation of JAK-3, a cytoplasmic tyrosine kinase associated with a cell surface receptor compon ent called common gamma-chain, which is exclusive of all IL-2 cytokine fami ly receptors. Blocking common gamma-chain transduction activity results in a potent and specific immunosuppressive activity. With respect to the inter esting and unexploited immunomodulating properties of this family of compou nds we initiated a medicinal chemistry program aimed at finding novel prodi giosin derivatives with improved immunosuppressive activity and lower toxic ity. Utilizing an unprecedented and flexible way of assembling the prodigio sin frame, a number of new derivatives have been prepared and tested leadin g to the choice of 4-benzyloxy-5-[(5-undecyl-2H-pyrrol-2-ylidene)methyl]-2, 2'-bi-1H-pyrrole (PNU-156804, 16) as a lead immunosuppressant.