13C-NMR Studies of Marine Natural Products. A Further Investigation into the Spin-Lattice Relaxation Behavior of the Cembranoid Diterpene Sinularin

The 13C-nmr spin-lattice (T1) relaxation times for the cembranoid diterpene sinularin have been re-examined. Results of this study indicate that the solution conformation of the molecule, particularly in the region surrounding the δ-lactone is highly comparable to that observed in the crystal structure. This conclusion is in direct contrast to a previous study which invoked a different conformation for this region of the molecule to account for a disparity between the calculated and observed T1 relaxation times for the non-protonated carbons.