CONFORMATIONAL-ANALYSIS OF THE CIS-ISOMERS AND TRANSISOMERS OF FK506 BY NMR AND MOLECULAR-DYNAMICS

The potent immunosuppressant drug FK506 (2) has been examined by H-1- and C-13-NMR spectroscopy and NOE-restrained molecular dynamics to elucidate the conformation in solution. A combination of two- and three-dimensional NMR techniques was used to completely assign the H-1- and C-13-NMR chemical shifts of the two configurational isomers resulting from the cis-trans isomerization about the single amide bond. Hetero- and homonuclear coupling constants were measured to assign the diastereotopic methylene protons at C(16), C(18), and C(23). Intramolecular H-H distances were defined from NOESY spectra recorded at -30-degrees in CDCl3 and used as constraints in molecular-dynamics simulations. The conformational preferences of 2 in solution are discussed in light of the constitutional features recently proposed to be necessary for binding and activity.