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-cyclo[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 ari 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 gs pyridine, hydrazine and DABCO has been used to support structural assignments and also to catalyse synthetically useful self-acylations and deacylations.