Solid state structure of coumarin anticoagulants: warfarin and sintrom. 13C CPMAS NMR and GIAO DFT calculations

Abstract 13 C CP MAS NMR spectra for warfarin and sintrom indicate that both coumarin anticoagulants are present in the solid phase as cyclic hemiketals. The differences Δ ′= δ solution − δ solid are of similar size for major and minor form present in solution, therefore no conclusion as to the configuration and conformation present in the solid state can be reached on that basis. The linear regressions of the experimental δ solid and the calculated carbon shieldings σ GIAO DFT were established, the correlation coefficients are higher than 0.99. Shielding constants of carbons C2, C3 and C4 are sensitive to the changes of configuration at C2; the results suggest that the RS structure is probable in the solid phase.