Synthesis of cyclocholate-capped porphyrins

The syntheses of two types of semisynthetic receptor composed of porphyrins capped on one or both faces by a cyclic dilactone of cholic acid (a 7,24-cydo[2]cholate) are presented. The singly capped diarylporphyrin was made by macrolactonisation over a preformed porphyrin and also by porphyrin synthesis beneath a preformed cyclocholate cap. The doubly capped tetraarylporphyrin has been prepared by condensation of an aldehyde-functionalised cyclocholate with pyrrole under equilibrium conditions. A preparatively useful synthesis of 7,24-cyclo[2]cholates has been developed, and different conformations of protected and unprotected cyclocholates invoked to explain product distributions in porphyrin-cyclocholate synthesis. The ability of zinc porphyrins to bind basic species such as pyridine, hydrazine and DABCO has been used to support structural assignments and also to catalyse synthetically useful self-acylations and deacylations.