Enantioselective recognition of histidine and lysine esters by porphyrin chiral clefts and detection of amino acid conformations in the bound state

Resolution of the bisporphyrin Tröger's base analogue 1 affords homochiral clefts that tightly bind histidine esters in 80-86% e.e. and lysine benzyl ester in 48% e.e.; the histidine esters are bound in fixed conformations that can be readily detected by ¹H NMR spectroscopy as a result of the large dispersion of proton resonances by the ring currents of the two porphyrins.