Influence of the a-ring on the proton affinity and anticancer properties of the prodigiosins.

Prodigiosin (Prod, 1) is the parent member of a class of polypyrrole natural products that exhibit promising immunosuppressive and anticancer activities. They are known to act as H+/Cl- symporters possibly through electrostatic binding to Cl- that facilitates proton-coupled transmembrane transport of halides. This activity has been ascribed to their promotion of apoptosis by acidification of the intracellular pH (pHi).