Long-lived nuclear spin states in the solution NMR of four-spin systems

The existence of long-lived nuclear spin states in four-spin systems is explored by solution-state NMR experiments. Long-lived states are proved to exist in three different natural product molecules, each containing either a AA′BB′ or a AA′XX′ proton spin system. The measured state lifetimes are between four and eight times the spin-lattice relaxation time constants.