Efficient chiral 1H NMR analysis of indoloquinazoline alkaloids phaitanthrin A, cephalanthrin-A and their analogues with a chiral phosphoric acid.

A chiral phosphoric acid promoted enantioselective NMR recognition and determination of indoloquinazoline alkaloids phaitanthrin A, cephalanthrin-A and their analogues was described, which conveniently reveals their optical purities with high accuracy. Besides, pyrazine type tertiary alcohols, cyclic amino alcohols and diamines can also be well resolved under optimal conditions. Importantly, this methodology was further employed in the direct analysis of reaction mixtures of amino acid metal salt catalyzed asymmetric synthesis of phaitanthrin A, providing access to the optimized reaction conditions in high efficiency.