Use of Two-Dimesnional NMR and Molecular Modelling for the Structure Determination of Novel Cyclophosphamide Derivatives: Diastereomers of 1-Aza-2-bis(2-chloroethyl)amino-3-oxa-2-oxo-2-phospha-7-thia-bicyclodecane and nonane

Article abstract of DOI:10.1002/mrc.1260301212

High-field NMR studies at 11.7 T of newly synthesized diastereomeric 1-aza-2-bis(2-chloroethyl)amino-3-oxa-2-oxo-2-phospha-7-thia-bicyclo<4.4.0>decanes (4, 5) and the corresponding <4.3.0>nonanes (6, 7) were carried out by employing a combination of one- and two-dimensional homo- and heteronuclear methods.Unambiguous 31P, 1H and 13C chemical shift assignments for these bicyclic derivatives of cyclophosphamide were obtained, and the spin-spin coupling involving 1H, 13C and 31P were analysed in detail to determine the stereochemistry.Particularly useful were 1H J-resolved experiments, which separated phosphorus-proton couplings from proton-proton couplings, and 1H-13C shift correlation experiments, which resolved the carbon-phosphorus couplings and provided information on the relative signs of J(P,H) and J(P,C).In addition, extensive molecular modelling calculations using various force-field (ALCHEMY, DISCOVER) and molecular orbital methods (MNDO, AM1, PM3) were carried out, and improved parameters for cyclophosphamides were developed for ALCHEMY.The diastereomeric pairs 4, 5 and 6, 7 differ in the axial vs. equatorial orientation of the sulphur substituent on the oxazaphosphorinane ring, which is itself exclusively in a chair conformation with axial P=O for all substances.Key words: Cyclophosphamides, 1H NMR, 13C NMR, 31P coupling constants, Molecular modelling