The 0.42ppm peak shoulder in the high field region is the upfield shift peak of A_2-isoleucine shielded by the proximate A_(19)-tyrosyl in the three-dimensional structure and it disappears in the DOI spectrum.

• 高场区0.；42ppm的峰肩为A_2-异亮氨酸在三维结构中受邻近A_(19)-酪氨酸屏蔽影响的高场位移峰；该峰在DOI谱中消失。