THE EFFECT OF CONFORMATION ON MEMBRANE-PERMEABILITY OF AN ACYLOXYALKOXY-LINKED CYCLIC PRODRUG OF A MODEL HEXAPEPTIDE

Purpose. To determine the different conformations of the acyloxyalkoxy -linked cyclic prodrug 1 of the model hexapeptide 2 in solution and to investigate the relationship between these solution conformations and the cellular permeability characteristics of this prodrug. Methods. T wo-dimensional Homonuclear Hartmann-Hahn spectroscopy, Rotating-Frame Overhouser effect spectroscopy, circular dichroism and molecular dynam ics simulations were used to find the solution conformers of cyclic pr odrug 1. Results. Our spectroscopic findings suggest that cyclic prodr ug I exhibits a major and a minor conformer in solution. The major con former appears to have a well-defined secondary structure, which invol ves a beta-turn and 4 --> I intramolecular hydrogen bond, creating a c ompact structure with a reduced average hydrodynamic radius compared t o the model hexapeptide 2. Conclusions. The increased ability of cycli c prodrug 1 to permeate membranes compared to the model hexapeptide 2 could be due to reduction in the average hydrodynamic radius of the mo lecule facilitating paracellular flux and/or the reduction in the hydr ogen bonding potential facilitating transcellular flux.