BASHD-J-resolved-COSY: a new method for measuring proton-proton spin coupling constants of multiplet signals.

An effective pulse sequence for measuring H-H coupling constants, named BASHD-J-resolved-COSY, has been developed. In the spin systems such as -CH(A)-CH(B)(CH(3))-CH(C)-, a methine proton H(B) splits into a multiplet owing to several vicinal couplings, resulting in attenuation of its cross-peak intensity. Therefore, the measurements of (3)J(H-H) with respect to H(B) are generally difficult in the E-COSY-type experiments. With the aim of accurate measurements of (3)J(H-H) in such a spin system, we have developed a new pulse sequence, which selectively decouples the secondary methyl group. The proposed pulse sequence provides the simplified cross-peak patterns, which are suitable for reliable measurements of (3)J(H-H) in a complicated natural product.